WO2014209295A1

WO2014209295A1 - Device with programmable flexibility

Info

Publication number: WO2014209295A1
Application number: PCT/US2013/047781
Authority: WO
Inventors: Sung-Wei Chen; Christopher J. ROTHFUSS
Original assignee: Empire Technolgy Development Llc
Priority date: 2013-06-26
Filing date: 2013-06-26
Publication date: 2014-12-31

Abstract

Devices having programmable flexibility are disclosed, as well as methods for their preparation and operation. A device may include a plurality of flexible hollow tubes filled with a magnetorheological fluid, a plurality of permanent magnets affixed periodically inside each of the plurality of flexible hollow tubes, and a plurality of solenoids positioned and configured to produce a magnetic field that cancels at least a portion of a magnetic field produced by the plurality of permanent magnets to result in an applied magnetic field on the magnetorheological fluid. The magnetorheological fluid may be configured to flow when the applied magnetic field is lower than a threshold value and may become rigid when the applied magnetic field is higher than the threshold value.

Description

DEVICE WITH PROGRAMMABLE FLEXIBILITY

BACKGROUND

[0001] Miniaturization and increased processing power have led to great improvements in the portability of electronic devices. As a result, electronic devices have been reduced to pocket sizes or smaller without compromising on utility and performance. However, the usefulness of some miniaturized electronic devices may be limited by the display size of the device, which sometimes is desired to be larger than what can be fitted into a typical pocket for practical usage. Accordingly, flexible substrates and display devices may be desired for devices to be switchable between a larger or smaller form factor as needed. Further, it will be desirable for the substrate and devices to have programmable rigidity and flexibility to improve portability and usability of such devices.

SUMMARY

[0002] In an embodiment, a device having programmable flexibility may comprise a plurality of flexible hollow tubes filled with a magnetorheological fluid, a plurality of permanent magnets affixed periodically inside each of the plurality of flexible hollow tubes, and a plurality of solenoids positioned and configured to produce a magnetic field that cancels at least a portion of a magnetic field produced by the plurality of permanent magnets to result in an applied magnetic field on the magnetorheological fluid. The magnetorheological fluid may be configured to flow when the applied magnetic field is lower than a threshold value and become rigid when the applied magnetic field is higher than the threshold value.

[0003] In an embodiment, a method of making a device having programmable flexibility may comprise positioning a plurality of permanent magnets in a plurality of flexible hollow tubes filled with a magnetorheological fluid. The magnetorheological fluid may be configured to flow when an applied magnetic field is lower than a threshold value and become rigid when the applied magnetic field is higher than the threshold value. The method may further comprise positioning a plurality of solenoids on the plurality of flexible hollow tubes. The plurality of solenoids may be configured to produce a magnetic field that cancels at least a portion of a magnetic field produced by the plurality of permanent magnets to result in an applied magnetic field on the magnetorheological fluid. The method may further comprise integrating the plurality of flexible hollow tubes and the plurality of solenoids with a flexible substrate.

[0004] In an embodiment, a method of changing a shape of a device may comprise applying an effective amount of current across a plurality of solenoids. The device may comprise a plurality of flexible hollow tubes filled with a magnetorheological fluid and a plurality of permanent magnets affixed periodically inside each of the plurality of flexible hollow tubes. The plurality of solenoids may be positioned and configured to produce a magnetic field that cancels at least a portion of a magnetic field produced by the plurality of permanent magnets. The method may further comprise folding the device in a desired shape and stopping the current across the plurality of solenoids, whereby the device is fixed into the desired shape.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIGS. 1A, IB, and 1C depict a perspective top view of a device that may have a flexible substrate such that a plurality of flexible hollow tubes filled with an MR fluid are integrated with the flexible substrate, according to an embodiment.

[0006] FIG. 2 depicts a detailed view of an illustrative solenoid configuration according to an embodiment.

[0007] FIG. 3 depicts a graphical representation of a yield stress distribution within a MR fluid support tube according to an embodiment. [0008] FIG. 4 depicts a detailed cross-sectional view of an illustrative flexible hollow tube according to an embodiment.

[0009] FIG. 5 depicts a flow diagram for a method of making a device having programmable flexibility according to various embodiments.

[0010] FIG. 6 depicts a flow diagram for a method of operating a device having a programmable flexibility according to various embodiments.

[0011] FIG. 7 depicts a graphical representation of a second yield stress distribution within a MR fluid support tube according to an embodiment.

DETAILED DESCRIPTION

[0012] This disclosure is not limited to the particular systems, devices, and methods described, as these may vary. The terminology used in the description is for the purpose of describing the particular versions or embodiments only, and is not intended to limit the scope.

[0013] As used in this document, the singular forms "a," "an," and "the" include plural references unless the context clearly dictates otherwise. Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art. Nothing in this disclosure is to be construed as an admission that the embodiments described in this disclosure are not entitled to antedate such disclosure by virtue of prior invention. As used in this document, the term "comprising" means "including, but not limited to."

[0014] Described herein are devices having programmable flexibility, methods of making such devices, and methods of using such devices. Devices described herein may be rigid in a passive mode and become flexible on demand in an active mode, for example, by applying an electric current and/or a magnetic pulse. Such devices may be used in their rigid passive state, activated to be flexible, folded as desired in the active state, and made rigid again in the folded state for transportation and/or storage. In some embodiments, the devices may be reactivated to be flexible for unfolding and returned to the rigid passive state. In some embodiments, the devices may have a processor and a tangible, non-transitory, computer-readable memory. The memory may contain programming instructions that, when executed by the processor, cause the device to perform one or more operations according to the programming instructions. In some embodiments, the devices may incorporate sensors, such as motion sensors, strain sensors, and/or the like that are capable of sensing undesirable strain or stress placed on the device.

[0015] Specific examples of devices are not limited by this disclosure, and may include, for example, televisions, computer monitors, display monitors, billboard advertisements, cellular phones, feature phones, smartphones, pagers, personal digital assistants (PDA), cameras, tablets, phone-tablet hybrids ("phablets"), laptop computers, netbooks, ultrabooks, global positioning satellite (GPS) navigation devices, in-dash automotive components, media players, watches, handheld imaging devices, personal medical devices, electronic photo frames, security devices, keypads, and the like.

[0016] As used herein, the term "magnetorheological fluid" includes any fluids that, when subjected to a magnetic field, increase in viscosity and/or become magnetized. As used herein, the term "magnetorheological fluid" also encompasses ferrofluids. The magnetorheological fluid can have any number, type, size, and shape of particles dispersed herein, including magnetic particles, as described in greater detail herein.

[0017] FIGS. 1A and IB depict a perspective top view of a device, generally designated 100, that may have a flexible substrate such that a plurality of flexible hollow tubes 105 filled with a magnetorheological (MR) fluid are integrated with the flexible substrate, according to an embodiment. In some embodiments, the flexible substrate may be part of, for example, a flexible user interface, a flexible light emitting device, a flexible display device, a flexible portable electronic device, a flexible computer, a flexible communication device, a flexible battery, or any combination thereof. In some embodiments, the flexible substrate may be made from a flexible polymer, as described in greater detail herein.

[0018] In some embodiments, the device 100 may include the plurality of flexible hollow tubes 105, a plurality of permanent magnets 110 affixed periodically inside each of the plurality of flexible hollow tubes, and a plurality of solenoids 115 positioned and configured to produce a magnetic field that, when activated, cancels at least a portion of a magnetic field produced by the plurality of permanent magnets to result in an applied magnetic field on the MR fluid.

[0019] In various embodiments, the plurality of permanent magnets 110 may be fixed at intervals inside the plurality of flexible hollow tubes 105. In some embodiments, the distances between adjacent permanent magnets 110 may be substantially equal. In other embodiments, the distances between adjacent permanent magnets 110 may vary. In some embodiments, the plurality of permanent magnets 110 may be positioned relative to one or more fold lines 120. In some embodiments, the plurality of permanent magnets 110 may all face in the same direction in each flexible hollow tube 105. For example, all of the plurality of permanent magnets 110 may be arranged in a North-South configuration, where the north pole of a first permanent magnet faces the south pole of a second permanent magnet. In some embodiments, a first plurality of permanent magnets 110 in a first flexible hollow tube 105 may face a first direction, and a second plurality of permanent magnets in a second flexible hollow tube may face a second direction. Thus, the first plurality of permanent magnets 110 may be in a North-South direction and the second plurality of permanent magnets may be in a South-North direction. [0020] In some embodiments, the plurality of solenoids 115 may be positioned substantially surrounding the outside of the flexible hollow tubes 105. In some embodiments, such as depicted in FIG. 1A, the plurality of solenoids 115 may be positioned at a location that substantially corresponds to the location of the permanent magnets 110 inside the flexible hollow tubes. Thus, each permanent magnet 110 may have a corresponding solenoid 115 that substantially overlaps the permanent magnet. In other embodiments, such as the device 100 depicted in FIG. IB, the plurality of solenoids 115 may be positioned substantially around the outside of the flexible hollow tubes 105 between two of the permanent magnets. In particular embodiments, one or more or all of the solenoids 115 may be equidistant from the permanent magnets 110. In other particular embodiments, one or more or all of the solenoids 115 may be positioned at different intervals between the permanent magnets 110.

[0021] In some embodiments, a MR fluid may be configured to flow when the applied magnetic field on the MR fluid is lower than a threshold value. In some embodiments, the MR fluid may become rigid when the applied magnetic field is higher than the threshold value. As a result, the device 100 may be folded and/or bent along the one or more fold lines 120 when the applied magnetic field is lower than the threshold value at the fold lines, and may be incapable of being folded and/or bent at the fold lines when the applied magnetic field is higher than the threshold value. Thus, when an electrical current is applied across the solenoids 115, the solenoids may generate a magnetic field that cancels the magnetic field of the permanent magnets 110 to result in the applied magnetic field that is below the threshold value, causing the MR fluid to flow so that the device can be folded and/or bent. Conversely, when the electrical current is removed from the solenoids 115, the magnetic field of the permanent magnets 110 may be restored, causing the MR fluid to become rigid so that the device 100 cannot be folded and/or bent. In some embodiments, the amount of current that is applied across the solenoids 115 may be varied to vary the rigidity of the MR fluid. Thus, for example, the amount of current may be increased and/or decreased across the solenoids 115 to adjust the magnetic field produced by the solenoids to cancel out the magnetic field produced by the permanent magnets 110. Accordingly, if the solenoids 115 are not producing a magnetic field that is strong enough to cancel out the magnetic field of the permanent magnets 110, the MR fluid may be too rigid to enable flexibility. Thus, by increasing the current, the magnetic field of the solenoids 115 can also be increased to a level that does cancel out the magnetic field of the permanent magnets 110 so that the MR fluid loses its rigidity.

[0022] In some embodiments, such as the device 100 shown in FIG. 1A, the permanent magnets 110 and/or the solenoids 115 may be positioned so that the fold lines 120 are between permanent magnets and/or the solenoids. Accordingly, the permanent magnets 110 and/or the solenoids 115 may be made of a flexible or a rigid material because they may not be folded. In other embodiments, such as the device 100 shown in FIG. IB, the permanent magnets 110 and/or the solenoids 115 may be positioned so that the fold lines 120 are substantially at the same location as the location of the permanent magnets 110 and/or the solenoids 115. Accordingly, the permanent magnets 110 and/or the solenoids 115 may be made of a flexible material capable of being folded 100. In some embodiments, the solenoids 115 may be located at substantially a midpoint distance between permanent magnets 110, which also corresponds to the fold line 120. These embodiments may provide a better reduction of a magnetorheological effect in an active state as they only affect selected sections of the device 100, and may therefore require less power to operate when compared to generating the magnetorheological effect throughout the entire device 100. Therefore, less power may be needed to generate an effective current in the solenoids 115 to produce a magnetic field that cancels out the magnetic field produced by the permanent magnets 110. In some embodiments, less programming may be necessary to effect folding of the device 100 because only a single current need be sent across the solenoids 115 as opposed to multiple currents in varying directions, as described in greater detail herein.

[0023] In various embodiments, such as the device 100 shown in FIG. 1C, an array of flexible hollow tubes 105 may occur in a plurality of directions. In some embodiments, the flexible hollow tubes 105 may be positioned in horizontal and vertical directions. In some embodiments, the flexible hollow tubes 105 may be positioned in diagonal directions. In some embodiments, the flexible hollow tubes 105 may be positioned substantially parallel and/or perpendicular with respect to each other. In some embodiments, the flexible hollow tubes 105 may be positioned with respect to the intended fold lines 120. In some embodiments, the flexible hollow tubes 105 may be positioned substantially perpendicular to the fold lines 120. In some embodiments, the flexible hollow tubes 105 may be positioned substantially parallel to the fold lines 120. As a result, the array of flexible hollow tubes 105 in multiple directions may allow for programmable rigidity and/or programmable flexibility in multiple directions. Thus, the device 100 may be folded and/or bent in multiple directions.

[0024] FIG. 2 depicts a detailed view of a solenoid configuration 215 according to an embodiment. FIG. 2 also illustrates a programmable flexibility of the device 100 according to an embodiment. This allows the device 100 (FIGS. 1A-1C) to be folded into any number of possible configurations by selectively changing the rigidity of the MR fluid in discrete regions.

[0025] In various embodiments, a current may be applied to a plurality of inner rows of solenoids B, C, as depicted by a first set of current flow arrows 220. In some embodiments, the first current 220 may cause the solenoids 215 in the inner rows B, C to produce a magnetic field that can counter the magnetic field produced by the permanent magnets 210, thereby reducing the magnetic flux density substantially around the permanent magnets 210 in the MR fluid. By reducing the magnetic flux density, the MR fluid may become flowable and the flexible hollow tubes 205 that support the MR fluid may therefore soften at the location of the reduced magnetic flux density. In some embodiments, a second current 225 having the same magnitude, but in a substantially opposite direction to the first current 220 may be applied to a plurality of outer rows A, D of solenoids 215. The second current 225 may produce an opposite effect of the first current 220, thereby strengthening the magnetic flux density substantially around the permanent magnets 210 in the MR fluid. By strengthening the magnetic flux density in the MR fluid, the MR fluid may become more rigid or remain rigid and hence stiffen or maintain rigidity of the flexible hollow tubes 205 that support the MR fluid at the location of the strengthened magnetic flux density. The result may be a localized weak section of the device substantially between the inner rows B, C that may act as a natural fold line along an axis 230 while localized sections of the device substantially surrounding the outer rows A, D remain rigid. After the device has been folded, the supply of first current 220 and second current 225 is ceased, which may allow the MR fluid within the tubes 205 to stiffen in a new folded configuration, which may effectively lock the device into the folded configuration.

[0026] FIG. 3 depicts a graphical representation of a yield stress distribution within a MR fluid support tube according to an embodiment. The support tube can be the flexible hollow tube as disclosed. A plateau on the graphical representation at approximately 125 kPa may indicate that the MR fluid has reached a magnetic saturation. However, those skilled in the art will recognize that other pressures may be indicative of magnetic saturation without departing from the scope of the present disclosure.

[0027] As depicted in FIG. 3, the midpoint passive yield stress is about 60% of the maximum value. In an some embodiments, passive yield stress may be maximized while active yield stress is minimized to provide the greatest range of flexibility control. Maximum passive yield stress may be achieved by ensuring that magnetic saturation is present throughout the MR fluid in order to provide the most rigidity for the device. This may be achieved by using more powerful magnets, reducing the spacing between the magnets, adjusting the properties of the MR fluid, and/or any combination thereof. Yield stress may be further enhanced above a passive level by flowing current through the solenoids in a direction that enhances the local field strength. Minimum active yield stress may be achieved by reducing or canceling the passive magnetic field such that the MR fluid viscosity is minimized. This may be achieved by applying more current to the appropriate solenoid(s), improving the solenoid geometry, adjusting the fluid properties to reduce the minimum viscosity, reduce the native yield stress of the tubing, and/or any combination thereof.

[0028] In various embodiments, the flexible hollow tube containing MR fluid in the rigid configuration may be modeled as a beam with two fixed supports under a uniform distributed load. The maximum stress at a point X within a round beam under the loading conditions may be described by Equation (1):

where σ is the stress in the beam, D is the diameter of the beam, L is the length of the beam and W is the distributed load on the beam. The load capacity of the beam may be determined by substituting the maximum allowable stress for the beam into Equation (1) and solving for the distributed load W. In some embodiments, Equation (1) may be useful in developing a general model for positioning of the hollow tube.

[0029] FIG. 4 depicts a detailed cross-sectional view of an illustrative flexible hollow tube 405 according to an embodiment. In some embodiments, the flexible hollow tube 405 may be filled with the MR fluid 410. In some embodiments, the MR fluid 410 may include a noncolloidal suspension of a plurality of magnetizable particles 415. In some embodiments, the flexible hollow tube 405 may further include the plurality of permanent magnets 425 at fixed locations therein. In some embodiments, one or more or all of the solenoids 420 may be positioned substantially surrounding an outside surface of the flexible hollow tube 405.

[0030] In various embodiments, the hollow tube 405 may be made from a flexible polymer. Specific examples of the flexible polymers may include polyethylene, polystyrene, polypropylene, polyimide, polythiophene, silicone, polydimethyl siloxane, polycarbonate, polyethylene terephthalate, polyethersulfone, polyethylene naphthalate, neoprene, nylon, latex, and/or the like. In some embodiments, the hollow tube 405 may be transparent. In other embodiments, the hollow tube 405 may be opaque. In yet other embodiments, the hollow tube 405 may be configured to transform from opaque to transparent and vice versa, depending on the application and/or one or more desired settings. This may be achieved, for example, by adding dye components or the like to the MR fluid to change the color of the MR fluid at the occurrence of particular circumstances, such as, for example, a change in electric field or a change in magnetic field. Specific examples of technologies that may use a hollow tube that is configured to change from opaque to transparent may include electronic ink ("e-Ink") displays, liquid crystal display technology, technologies that incorporate electrochromic materials, technologies that incorporate photochromies, technologies that incorporate photochromatics, technologies that incorporate thermotropics, and suspended particle display (SPD) technologies.

[0031] In various embodiments, the hollow tube 405 may have any cross- sectional shape, such as, for example, circular, rectangular, square, triangular, polygonal, T- shaped, I-shaped, or the like. In some embodiments, the hollow tube 405 may have substantially the same cross-sectional shape as other hollow tubes in the substrate. In other embodiments, the hollow tube 405 may have a different cross-sectional shape than one or more other hollow tubes in the substrate. In some embodiments, the size of the hollow tube 405 may depend on the application and/or one or more desired settings. Specific examples of maximum cross-sectional dimensions may include about 10 μιη, about 50 μιη, about 100 μιη, about 125 μιη, about 150 μιη, about 200 μιη, about 500 μιη, about 1 mm, or any value or range between any two of these values. In some embodiments, the hollow tube 405 may have any suitable length depending on the desired application of the device. Specific examples of a suitable length may include about 1 mm, about 2 mm, about 3 mm, about 5 mm, about 1 cm, about 5 cm, about 10 cm, about 50 cm, about 1 m, about 2 m, about 5 m, about 10 m, or any value or range between any two of these values. In some embodiments, the hollow tube 405 may be positioned in close contact with other hollow tubes so that the hollow tubes are tightly packed together. In other embodiments, the hollow tube 405 may be positioned a distance away from other hollow tubes. Specific examples of distances may include, for example, about 1 mm, about 5 mm, about 1 cm, about 5 cm, about 10 cm, about 50 cm, or any value or range between any two of these values.

[0032] In various embodiments, the MR fluid 410 may generally be selected from a class of fluids whose rheological properties change under the influence of a magnetic field. In some embodiments, the MR fluid 410 may include a carrier fluid such as a natural fatty oil, a mineral oil, a paraffin oil, a synthetic cycloparaffin oil, a synthetic paraffin oil, a hydraulic oil, a transformer oil containing chlorinated aromatic compounds, a synthetic hydrocarbon, water, a silicone oil, a silicone copolymer, an esterified fatty acid, a fluorinated silicone oil, a polyether, a fluorinated polyether, a polyether-polysiloxane copolymer, a polyphenylether, a polyester (such as a perfluorinated polyester, a dibasic acid ester, and a neopentylpolyol ester), a phosphate ester, a monobasic acid ester, a castor oil, a white oil, a halogenated organic liquid (such as a chlorinated hydrocarbon, a halogenated paraffin, a perfluorinated polyether, a halogenated hydrocarbon, and a fluorinated hydrocarbon), a diester, a polyoxyalkylene, a cyanoalkyl siloxane, a glycol, a glycol ester, a glycol ether, a synthetic hydrocarbon oil (including both unsaturated and saturated), or other suitable organic liquid. In a particular embodiment, the carrier fluid may include an oil derived from high molecular weight alpha olefins of about 8 to about 20 carbon atoms by acid catalyzed dimerization and by oligomerization using trialuminum alkyls as catalysts. In some embodiments, the viscosity of the carrier fluid may be about 1 mPa to about 1000 mPa, and more particularly about 3 mPa to about 800 mPa, as measured at 25° C.

[0033] In various embodiments, the carrier fluid may be non- volatile, non-polar, and may not include any significant amount of water. In some embodiments, the carrier fluid may not include any volatile solvents commonly used in lacquers or compositions that are coated onto a surface and then dried such as, for example, toluene, cyclohexanone, methyl ethyl ketone, methyl isobutyl ketone, and acetone to avoid evaporation or cross-reaction with the material of the hollow tube 405. In other embodiments, the carrier fluid may be water alone, or a water-based fluid having polar, water- miscible liquids such as, for example, methanol, ethanol, propanol, dimethyl sulfoxide, dimethyl formamide, ethylene carbonate, propylene carbonate, acetone, tetrahydrofuran, diethyl ether, or non-reactive combinations thereof. In some embodiments, the water-miscible liquids may be present in an amount of less than about 5 percent by weight of the MR fluid 410, the rest being water. In various embodiments, the carrier fluid may make up an amount of about 50 percent to about 95 percent by volume of the total MR fluid 410. In particular embodiments, the carrier fluid may be about 60 percent to about 85 percent by volume of the total MR fluid 410.

[0034] In some embodiments, the MR fluid 410 may have an acceptably low viscosity in the absence of a magnetic field but may display large increases in its dynamic yield stress and viscosity when it is subjected to a suitable magnetic field. Specific examples of a suitable magnetic field may include 1 Tesla, 1.5 Tesla, 2 Tesla, 3 Tesla, 5 Tesla, or any value or range between any two of these values. As the MR fluid 410 may contain a plurality of non-colloidal magnetizable particles 415 which are, for example, seven to eight times denser than the carrier fluid in which they are suspended, suitable dispersions of the particles 415 in the carrier fluid may be prepared so that the particles do not settle appreciably upon standing nor do they irreversibly coagulate to form aggregates. In some embodiments, the MR fluid 410 may include a solvent, including various organic liquids. In particular embodiments, one or more polar organic liquids may be used. In some embodiments, the solvent may have a relatively high boiling point so that the solvent does not evaporate when used. Specific examples of solvents may include carrier fluids known in the art such as ethylene glycol, ethylene glycol ethers, mineral oils, machine oils, silicone oils, and the like. In some embodiments, the MR fluid 410 may comprise about 1 weight percent to about 50 weight percent of the solvent, and more particularly about 4 weight percent to about 15 weight percent. In some embodiments, the solvent may be substantially free of water.

[0035] In some embodiments, the MR fluid 410 may also include one or more surfactants to prevent coagulation and settling of the magnetizable particles 415. Specific examples of surfactants may include, but are not limited to, oleic acid, tetramethylammonium hydroxide, citric acid, and soy lecithin. In some embodiments, the magnetizable particles 415 may be kept in suspension by dispersing a thixotropic agent in the MR fluid 410. Specific examples of a thixotropic agent include, but are not limited to, fumed silica, pyrogenic silica, silica gel, precipitated silica, titanium dioxide, iron oxides, and other polymer-modified metal oxides. The thixotropic agent may stabilize the MR fluid 410 by forming a network through hydrogen bonding. This network may break down under shear and may reform upon cessation of shear to keep the magnetizable particles 415 suspended while exhibiting low viscosity under shear. [0036] In various embodiments, the MR fluid 410 may also include one or more additives such as, for example, an anti-freezing agent, a corrosion inhibitor, a rust inhibiting agent, an anti-friction agent, a colorant, a desiccant, an alkalinizing agent, a carboxylate soap, an antioxidant, a lubricant, a viscosity modifier, a sulfur-containing compound, or any combination thereof. If present, the amount of these optional additives may be about 0.25 percent to about 10 percent by volume of the total volume of the MR fluid 410. In particular embodiments, the additives may make up about 0.5 percent to about 7.5 percent by volume of the MR fluid 410. Specific examples of the carboxylate soap may include, but are not limited to, lithium stearate, calcium stearate, aluminum stearate, ferrous oleate, ferrous stearate, zinc stearate, sodium stearate, strontium stearate, and mixtures thereof. Specific examples of sulfur-containing compounds may include, but are not limited to, thioesters such as tetrakis thioglycolate, tetrakis (3 -mercaptopropionyl) pentaerithritol, ethylene glycoldimercaptoacetate, 1,2,6-hexanetriol trithioglycolate, trimethylol ethane tri(3- mercaptopropionate), glycoldimercaptopropionate, bisthioglycolate, trimethylolethane trithioglycolate, trimethylolpropane tris(3-mercaptopropionate), thiols such as 1- dodecylthiol, 1-decanethiol, 1-methyl-l-decanethiol, 2-methyl-2-decanethiol, 1- hexadecylthiol, 2-propyl-2-decanethiol, 1-butylthiol, 2-hexadecylthiol, and/or the like. Specific examples of rust inhibiting agents may include, but are not limited to, sodium nitrite, sodium nitrate, sodium benzoate, borax, ethanolamine phosphate, and mixtures thereof. Specific examples of anti-freeze agents may include, but are not limited to, glycol compounds such as, for example, ethylene glycol and propylene glycol. Specific examples of anti-friction or lubricant agents may include, for example, graphite and molybdenum disulfide.

[0037] In various embodiments, the composition of the MR fluid 410 may vary within certain ranges. In some embodiments, the amount of the magnetizable particles 415 in the MR fluid 410 may be about 5 percent to about 80 percent by volume. In particular embodiments, the amount of the magnetizable particles 415 in the MR fluid 410 may be about 20 percent to about 60 percent by volume. In some embodiments, the amount of magnetizable particles 415 may be about 5 percent to about 50 percent by volume of the total volume of the MR fluid 410. Specific examples of an amount of magnetizable particles 415 may include about 5 percent to about 40 percent, 15 percent to about 40 percent, about 25 percent to about 40 percent, about 5 percent to about 30 percent, about 15 percent to about 30 percent, or any value or range between any two of these values, of the total volume of the MR fluid 410.

[0038] As understood by those skilled in the art, the weight percentage may vary for different magnetic materials. Expressed in terms of weight percent, in some embodiments, the amount of the magnetizable particles 415 in the MR fluid 410 may be about 0.1 weight percent to about 98 weight percent. In particular embodiments, the amount of the magnetizable particles 415 in the MR fluid 410 may be about 50 weight percent to about 95 weight percent. In particular embodiments, the amount of the magnetizable particles 415 in the MR fluid 410 may be about 50 weight percent to about 90 weight percent. In some embodiments, the amount of solids for the other materials may be about 0.1 weight percent to about 20 weight percent. In particular embodiments, the amount of solids for the other materials may be about 1 weight percent to about 12 weight percent. In some embodiments, additional solvents, if used, may make up less than about 20 weight percent of the MR fluid 410.

[0039] In various embodiments, the amount of magnetizable particles 415 in the MR fluid 410 may depend upon a desired magnetic activity and viscosity of the MR fluid. In some embodiments, the MR fluid 410 may have a magnetizable particles 415 to fluid ratio of about 1 :5 by volume. In particular embodiments, the ratio of magnetizable particles 415 to MR fluid 410 may be about 2:5 by volume. In other particular embodiments, the ratio may be a value of about 1:5 to about 2:5 by volume.

[0040] In various embodiments, the magnetizable particles 415 may be magnetic microparticles dispersed in the MR fluid 410. Any suitable dispersion may be used, including, for example, a homogenous dispersion of the particles 415 in the fluid 410. In some embodiments, the magnetizable particles 415 may include any number of suitable magnetizable material including various paramagnetic, superparamagnetic, ferromagnetic material, ferrimagnetic material, ferrite material, or a combination thereof. Specific examples of suitable magnetizable particles may include, but are not limited to, iron, iron alloys (such as those including aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese, and/or copper), iron oxides (including Fe2C>3, Fe₃0_4l as well as iron oxide compounds containing trace amounts of other elements), iron nitride, iron carbide, carbonyl iron, reduced carbonyl iron, potato iron, crushed iron, milled iron, melt-sprayed iron, nickel, cobalt, alnico, chromium dioxide, dysprosium gallium manganese arsenide, gadolinium, samarium-cobalt, neodymium, stainless steel, low carbon steel, and silicon steel. In some embodiments, the magnetizable particles 415 may include specific iron-cobalt and iron-nickel alloys. In some embodiments, the specific iron-cobalt alloys may have an iron to cobalt ratio of about 30:70 to about 95:5. In particular embodiments, the specific iron-cobalt alloy ratio may be about 50:50 to about 85: 15. In some embodiments, the iron-nickel alloys may have an iron to nickel ratio of about 90:10 to about 99:1. In particular embodiments, the specific iron- nickel alloy ratio may be about 94:6 to about 97:3. Without wishing to be bound by theory, small amounts of other elements, such as vanadium, chromium, and the like in the iron alloys may improve the ductility and mechanical properties of the alloys. The other elements may typically be present in an amount less than about 3.0 percent by weight. [0041] In various embodiments, the magnetizable particles 415 in the MR fluid 410 may be in the form of a metal powder which can be prepared by processes well known to those skilled in the art. Specific methods for the preparation of metal powders may include the reduction of metal oxides, grinding or attrition, electrolytic deposition, metal carbonyl decomposition, rapid solidification, or smelt processing.

[0042] In some embodiments, the magnetizable particles 415 may include an outer protective coating layer that is formed of any suitable material, including, but not limited to, a pure metal, a metal alloy, a ceramic, a glass, a polymer, a gelatine, or a combination thereof. In various embodiments, the magnetizable particles 415 may be coated with various polymer coatings, including various gelatines. As used herein, the term "gelatine" may include gelatine coacervates and gelatine-like complex coacervates. Combinations of gelatine with synthetic polyelectrolytes may be used as complex coacervates containing gelatine. Suitable synthetic polyelectrolytes may be those which are produced by the homo- or copolymerization of maleic acid, acrylic acid, methacrylic acid, acrylamide, and methacrylamide, for example. The term "gelatine" may also include a gelatine which is further cross-linked with customary hardeners, such as formaldehyde or glutaraldehyde, for example. In some embodiments, the polymer coating may include a synthetic polymer. Illustrative synthetic polymers may include, but are not limited to, polyesters, polyurethanes, particularly polyester urethanes and polyether urethanes, polycarbonates, polyester- polycarbonate copolymers, polyureas, melamine resins, polysiloxanes, fluoropolymers, and vinyl polymers. Illustrative vinyl polymers may include, but are not limited to, polyvinyl chloride, polyvinyl esters such as polyvinyl acetate, polystyrene, polyacrylic esters such as polymethyl methacrylate, polyethyl hexyl acrylate, polylauryl methacrylate, polystearyl methacrylate or polyethyl acrylate, and polyvinyl acetals such as polyvinyl butyral. Other illustrative synthetic polymers may include co- or terpolymers of different vinyl and vinylidene monomers, such a polystyrene-co-acrylonitrile, and copolymers of (meth)acrylic acid and (meth)acrylic esters.

[0043] In various embodiments, the magnetizable particles 415 may have any suitable size and shape. In some embodiments, the average longest dimension based on weight (weight average) of each magnetizable particle 415 may be about 0.1 μιη to about 500 μιη. In particular embodiments, the average longest dimension based on weight of each magnetizable particle 415 may be about 1 μιη to about 50 μιη. Specific examples of an average particle size may include about 1 μιη to about 500 μιη, about 1 μιη to about 250 μιη, about 1 μιη to about 100 μιη, about 10 μιη to about 500 μιη, about 10 μιη to about 250 μιη, about 10 μιη to about 100 μιη, or any range or value between any two of these ranges. In some embodiments, the shape of each magnetizable particle 415 may be irregular, rod-like, or acicular. In particular embodiments, the magnetizable particles 415 may be spherical or substantially spherical to achieve high degrees of filling. In some embodiments, the particle size may be selected so that a magnetizable particle 415 may include multiple magnetic domains. A magnetic domain is a region in which the magnetic fields of atoms are grouped together and aligned. In some embodiments, an average particle diameter size for a magnetizable particle 415 may generally be about 0.1 μιη to about 1000 μιη. In particular embodiments, the average particle diameter size may be about 0.1 μιη to about 500 μιη. In other particular embodiments, the average particle diameter size may be about 1.0 μιη to about 10 μιη.

[0044] In particular embodiments, the magnetizable particles 415 may be either monomodal or bimodal in a particulate distribution. The term "bimodal" may mean that the population of magnetizable particles 415 employed in the fluid 410 possesses two distinct maxima in their size or diameter. In some embodiments, the bimodal magnetizable particles 415 may be spherical or generally spherical. In bimodal compositions, the magnetizable particles 415 may be in two different size populations, one having a smaller diameter and another having a larger diameter. The particles in each of the populations may have a standard deviation no greater than two-thirds of the average diameter for the respective population. In some embodiments, the small magnetizable particles 415 may be at least 1 μιη in diameter so that they can be suspended and function as magnetorheological particles. In some embodiments, the practical upper limit on particle size may be about 100 μιη since particles of sizes greater than 100 μιη may usually not be spherical in configuration, but tend to be agglomerations of other shapes. However, for the practice of the embodiments disclosed herein, the mean diameter or most dominant sizes of the large particle group (for example, greater than 100 μιη) may be about 5 times to about 10 times the mean diameter or median particle size in the small particle group (for example, less than or equal to 100 μιη). The weight ratio of the two groups may be about 0.1 to about 0.9. The composition of the large and small particle groups may be the same or different.

[0045] In various embodiments, the magnetizable particles 415 may have a particle density that is substantially the same as the density of the MR fluid 410. In embodiments where the MR fluid 410 is a composite of fluids and other materials, including various rheology-modifying particulates, the density of MR fluid 410 is a composite density of the MR fluid and all of the other materials. In some embodiments, the magnetizable particles 415 may have a density that is substantially the same as the density of MR fluid 410 such that they may be dispersed within the fluid and have a substantially reduced tendency to settle. In embodiments where the density of the magnetizable particles 415 and the density of the MR fluid 410 are substantially equal, upon dispersion within the MR fluid 410, the magnetizable particles may have substantially no tendency to settle out of the MR fluid 410 and may form a stable or homogeneous suspension. In some embodiments, the magnetizable particles 415 may include a magnetizable shell over a hollow core, including spherical particles having a hollow core, such as, for example, having a spherical hollow core. In another embodiment, the magnetizable particles may include a magnetizable outer shell having a solid inner core of a glass, polymer material, ceramic material, or combination thereof, such as a core of a glass, polymer, or ceramic microsphere.

[0046] In various embodiments, the magnetizable particles 415 may be coated with the surfactant, as described in greater detail herein. In some embodiments, the surfactant may have a concentration of less than 0.1 percent by weight of the fully formulated MR fluid 410. As the concentration of surfactant increases, the yield stress decreases. While higher amounts of surfactant would be desirable, the amount of surfactant that may currently be used may be limited due to its interference with the function of the thixotropic agent.

[0047] In some embodiments, the behavior of the MR fluid 410 may be approximately modeled as a Bingham plastic governed by Equation (2):

τ = τ_γ(Η) + ηγ (2) where is τ the total shear stress within the MR fluid, η is the viscosity of the MR fluid, γ is the applied strain rate, and Ty(H) is the magnetic field-dependent critical shear stress, or yield stress, of the MR fluid. When no magnetic field is applied, the MR fluid 410 may behave in an approximately Newtonian fashion. However, applying a magnetic field, such as with one or more permanent magnets and/or one or more solenoids as described herein to the MR fluid 410 may cause the magnetizable particles 415 within the MR fluid 410 to magnetize and form chains parallel to the direction of the magnetic field. In this state, the MR fluid 410 may behave like an elastic solid so long as the stress within it is less than the yield stress. When the fluid stress surpasses the yield stress, the MR fluid 410 may begin to behave like a liquid again and may flow. This effect may also be reversible, and the MR fluid 410 may return to a quasi-Newtonian state when the magnetic field is removed. As the MR effect as described may be dependent upon the magnetic flux density within the MR fluid 410, the MR fluid 410 may therefore have tunable stiffness and viscosity.

[0048] In various embodiments, the MR fluid 410 may not require a strong magnetic field to achieve the rheological properties described herein. In some embodiments, a field strength at which an increase in the magnetic field within the fluid will no longer result in a change in rheological properties (a "magnetic saturation"), may be approximated by the product of a volume fraction of the magnetic particles (φ) in the fluid and a saturation polarization (Js) of that material. For example, an MR fluid 410 containing a volume fraction of 30 percent iron particles (Js = 2.1 Tesla) to 70 percent carrier fluid reaches a state of magnetic saturation with an applied field of approximately 0.63 Tesla. In some embodiments, the magnitude of the magnetic saturation of the MR fluid 410 may be sufficiently low such that saturation can be achieved in the proximity of the permanent magnets.

[0049] In various embodiments, the plurality of permanent magnets 425 may include one or more rare-earth materials, one or more ceramics, one or more ferromagnetic materials, and the like. Specific examples of rare-earth materials may include, for example, materials containing neodymium-iron-boron, neodymium, samarium-cobalt, yttrium-cobalt, and/or the like. Specific examples of ferromagnetic materials may include, for example, iron, low-carbon steel, various pure and impure iron oxides, iron silicide, nickel, cobalt, chromium (IV) oxide, permalloy, alnico, and the like. In some embodiments, the composition of each permanent magnet 425 may be appropriately chosen to provide a magnetic field strength sufficient to increase the viscosity of the MR fluid 410 so as to make the hollow tube 405 rigid. In some embodiments, the size of each permanent magnet 425 may be determined by factors such as, for example, the size of the hollow tube 405, the particular MR fluid 410 contained in the hollow tube, the composition of each permanent magnet, the desired flexibility and shape of the hollow tube in a folded state, the desired flexibility and shape of the hollow tube in an unfolded state, the number of permanent magnets that may be required, and/or the like.

[0050] In various embodiments, the plurality of permanent magnets 425 may be positioned and fixed inside each of the plurality of hollow tubes 405 filled with the MR fluid 410. In some embodiments, the plurality of permanent magnets 425 may be placed and affixed along the length of each of the plurality of hollow tubes 405 at equidistant intervals, as shown, for example, in FIGS. 1A-1C. In some embodiments, an axis Ai of each permanent magnet 425 may be aligned along an axis A₂ of the hollow tube 405 in which it is contained so as to produce a magnetic field along the axis of the hollow tube. In some embodiments, the plurality of permanent magnets 425 may be positioned with respect to each other such that the magnetic field created by each permanent magnet is uniform along the axis A₂ of the hollow tube 405.

[0051] In various embodiments, the strength of a magnetic field at a point along an axis of each permanent magnet 425 in a medium may be defined by Equation (3):

where L is the length of the magnet, R is the radius of the magnet, X is the distance between the point and the end of the magnet, BR is the remanence of the magnetic material, K_M is the relative permeability of the medium to the permeability of a vacuum, and Βχ is the magnetic flux density at point X. Without wishing to be bound by theory, when considering the simultaneous effects of several different sources of magnetic field at a point, the principle of magnetic superposition may be used to find an equivalent field strength. The principle of magnetic superposition states that the total magnetic field at a point is equal to the sum of the individual magnetic fields acting at that point. Accordingly, the magnetic field strength at an arbitrary point p on an axis between two identical permanent magnets 425 may be represented by Equation (4):

where X_pi is the distance from the end of one magnet to point p along the axis, X_P2 is the distance from the end of the other magnet to point p along the axis, and∑ B_p is the total magnetic flux density at point p.

[0052] In various embodiments, one or more or all of the solenoids 420 may be positioned to surround the outside surface of the hollow tube 405. In some embodiments, one or more or all of the solenoids 420 may be positioned substantially on top of each permanent magnet 425. In other embodiments, one or more or all of the solenoids 420 may be positioned between two permanent magnets 425.1n some embodiments, one or more or all of the solenoids 420 may be used to produce a magnetic field. In some embodiments, one or more or all of the solenoids 420 may be a length of electrically conductive wire wound into a helical coil. Examples of electrically conductive wire that may be used for solenoids include, but are not limited to, wires that contain one or more of silver, copper, gold, aluminum, calcium, tungsten, zinc, nickel, lithium, iron, platinum, carbon, and the like. In some embodiments, one or more or all of the solenoids may complete a plurality of turns around the hollow tube 405. Specific examples of the plurality of turns may include about 50 turns, about 100 turns, about 200 turns, about 500 turns, about 1000 turns, about 2000 turns, or any value or range between any two of these values. In some embodiments, one or more or all of the solenoids 420 may be densely packed. In particular embodiments, the densely-packed solenoid 420 may produce a magnetic field similar to that of a bar magnet when an electric current is passed through the solenoid. In some embodiments, one or more or all of the solenoids 420 may have a suitable loop radius. In particular embodiments, the loop radius of one or more or all of the solenoids 420 may substantially correspond to the radius of the hollow tube 405. Specific examples of loop radii may include about 1 mm, about 5 mm, about 1 cm, about 5 cm, about 10 cm, or any value or range between any two of these values.

[0053] In various embodiments, one or more or all of the solenoids 420 may be configured to nullify the magnetic field produced by one or more of the permanent magnets 425. In some embodiments, one or more or all of the solenoids 420 may be activated to produce a magnetic field that nullifies the magnetic field produced by one or more of the permanent magnets 425, and/or be deactivated to stop producing a magnetic field, thereby preventing nullification of the magnetic field produced by one or more of the permanent magnets. For example, one or more or all of the solenoids 420 may be configured to produce a magnetic field that is equal in magnitude and opposite in direction to the magnetic field produced by one or more of the permanent magnets 425. In some embodiments, one or more or all of the solenoids 420 may be activated and/or deactivated individually. In other embodiments, one or more or all of the solenoids 420 may be activated and/or deactivated in one or more groups up to and including all of the solenoids. In some embodiments, one or more or all of the solenoids 420 may be activated and/or deactivated by varying the electric current flowing through the solenoid, as described in greater detail herein. In some embodiments, when the solenoids 420 are deactivated (in an OFF state), the permanent magnets 425 may provide a sufficient magnetic field to increase the viscosity of the MR fluid 410, thereby making the hollow tube 405 rigid. In some embodiments, when the solenoids 420 are activated (in an ON state), the solenoids may nullify the magnetic field produced by the permanent magnets 425 to reduce the viscosity of the MR fluid 410, thereby making the hollow tube 405 flexible.

[0054] In various embodiments, the strength of the magnetic field at a point X along the axis of an activated solenoid 420 may be described by Equation (5): K^₀NIa²

^Bx = 3 (5)

2 {X² + a² ) 2 where /Jo is the magnetic permeability of a vacuum (4π x 10^"7 Tm/A), X is the distance from the center of the solenoid to the point along the solenoid axis, N is the number of coils in the solenoid, / is the current flowing through the solenoid and a is the radius of each coil. In some embodiments, the magnetic field produced by one or more or all of the solenoids 420 may be greatest at the center of the solenoid. As a distance X between a point under consideration and the center of the solenoid 420 increases, the strength of the magnetic field may decrease. For example, at a distance of one coil-radius from the center of the solenoid 420, the strength of the produced magnetic field may be less than half of the field strength at the center. Therefore, in order to achieve a specified magnetic field at a point which is a significant distance from the center of the solenoid 420, the solenoid must produce a magnetic field which is much larger than the desired field at that point.

[0055] In various embodiments, one or more power supplies may be used to provide an electrical current across one or more or all of the solenoids 420. The power supply is not limited by this disclosure and may include any device that is capable of generating energy, storing energy, and/or providing energy to one or more or all of the solenoids 420 and/or other components of the device 100 (FIGS. 1A-1C), whether or not specifically enumerated herein. In some embodiments, the power supply may be configured to increase and/or decrease the amount of electrical current across one or more or all of the solenoids 420. Specific examples of a current that may be produced may include about 1 amp, about 1.5 amps, about 2 amps, about 3 amps, about 5 amps, about 10 amps, about 20 amps, or any value or range between any two of these values. In an illustrative embodiment, the power supply may be a flexible lithium battery. [0056] In various embodiments, one or more or all of the solenoids 420 may be associated with one or more heat-dissipating components. Illustrative heat-dissipating components may include, for example, heat sinks, heat exchangers, and/or the like. The one or more heat-dissipating components may keep one or more or all of the solenoids 420 within a preferred heat range, prevent the heat given off from one or more or all of the solenoids from disrupting and/or destroying other components of the device 100 (FIGS. 1A-1C), and/or the like.

[0057] FIG. 5 depicts a flow diagram for a method of making a device having programmable flexibility, according to various embodiments. The processes described herein are merely exemplary; additional or fewer operations or alternative processes may be used without departing from the scope of this disclosure.

[0058] In various embodiments, a plurality of permanent magnets may be positioned 505 in a plurality of hollow tubes. In some embodiments, the plurality of permanent magnets may be positioned 505 by affixing the plurality of permanent magnets periodically inside each of the plurality of hollow tubes. In some embodiments, the permanent magnets may be affixed at various intervals within each hollow tube. In some embodiments, the permanent magnets may be positioned 505 to produce a magnetic field along an axis of the plurality of hollow tubes. Specific examples of the axis may include a horizontal axis and a vertical axis. In some embodiments, the plurality of permanent magnets may be positioned 505 in an attracting position. In some embodiments, the plurality of permanent magnets may be positioned 505 by inserting each magnet into the hollow tube at a specific location and affixing the permanent magnet to the inside of the hollow tube. Affixing may occur by any method now known or later developed, including, using an adhesive, welding, heat forming, molding, and/or the like. The number of hollow tubes and the number of permanent magnets positioned 505 therein is not limited by this disclosure, and may include any number of permanent magnets and any number of hollow tubes.

[0059] In various embodiments, the hollow tubes may be filled 510 with a MR fluid. In some embodiments, the remaining space in each hollow tube after the permanent magnets are positioned 505 may be completely filled 510 with the MR fluid. In other embodiments, the remaining space in each hollow tube after the permanent magnets are positioned 505 may be partially filled 510 with MR fluid.

[0060] In various embodiments, a plurality of solenoids may be positioned 515 on the hollow tubes. In some embodiments, the plurality of solenoids may be positioned 515 on an outside surface of the hollow tubes. In some embodiments, the plurality of solenoids may be positioned 515 at substantially the same location as each permanent magnet, as described in greater detail herein. In other embodiments, the plurality of solenoids may be positioned 515 substantially between each permanent magnet, as previously described herein. In some embodiments, the plurality of solenoids may be positioned 515 and configured to cancel at least a portion of the magnetic field produced by the plurality of permanent magnets. In particular embodiments, the plurality of solenoids may be positioned 515 and configured to produce a magnetic field that is equal in magnitude and opposite in direction to the magnetic field produced by the plurality of permanent magnets when an effective amount of electric current flows through the plurality of solenoids.

[0061] In various embodiments, the plurality of hollow tubes may be integrated 520 with a substrate. In some embodiments, the substrate may be a flexible substrate. In some embodiments, the plurality of hollow tubes may be integrated 520 with the flexible substrate by encapsulating the plurality of hollow tubes and the plurality of solenoids into a flexible polymer substrate. In other embodiments, the plurality of hollow tubes may be integrated 520 with the flexible substrate by attaching the plurality of flexible hollow tubes and the plurality of solenoids to a surface of the flexible substrate. The flexible substrate may be a flexible polymer substrate. Specific examples of the flexible polymer substrate may include a flexible polymer, a flexible user interface, a flexible light emitting device, a flexible display device, and a flexible battery. In some embodiments, the plurality of flexible hollow tubes may be tightly packed and may act as the flexible polymer substrate. For example, the plurality of flexible hollow tubes may be composed of a material and may be positioned and affixed together in such a manner that they act as the flexible polymer substrate without the need for additional materials.

[0062] FIG. 6 depicts a flow diagram for a method of changing a shape of a device, according to various embodiments. The processes described herein are merely exemplary; additional or fewer operations or alternative processes may be used without departing from the scope of this disclosure.

[0063] In various embodiments, a current may be applied 605 across a plurality of solenoids. In some embodiments, an electrical current that is effective in causing a magnetic field to be produced from the solenoids may be applied 605. In some embodiments, the amount of current to be applied 605 may be increased and/or decreased affect the rigidity of the MR fluid, as described in greater detail herein. In some embodiments, the effective amount of electrical current may be applied 605 to a subset of the plurality of solenoids. In particular embodiments, the subset of the plurality of solenoids may be determined by a desired shape of the device. For example, if a device is to be folded in half, only a first portion of the solenoids may have an effective amount of electrical current applied 605 to them. If the device is to be folded in thirds, a second portion of the solenoids may have an effective amount of electrical current applied 605 to them. In some embodiments, the determination of the subset of solenoids to receive an effective amount of electrical current may be selected through the use of any user interface components, including, but not limited to, switches, buttons, toggles, touchscreen commands, voice commands, and the like. In some embodiments, the subset of the plurality of solenoids may be determined by a software program. As previously described herein, the plurality of solenoids may be positioned on an outside surface of a plurality of hollow tubes filled with the MR fluid and a plurality of permanent magnets. The plurality of solenoids may be positioned so that when the electrical current is applied across the plurality of solenoids, a magnetic field is produced that cancels at least a portion of a magnetic field produced by the plurality of permanent magnets. In some embodiments, the magnetic field produced by the solenoids may be equal in magnitude and opposite in direction to the magnetic field produced by the plurality of permanent magnets.

[0064] In various embodiments, the device may be folded 610. In some embodiments, the device may be folded 610 into a desired shape. In some embodiments, the desired shape may be selected via the use of any user interface components, including, but not limited to, switches, buttons, toggles, touchscreen commands, voice commands, and the like. In other embodiments, the desired shape may be selected via the use of a software application. In some embodiments, the desired shape may be dependent upon the positioning of the hollow tubes, the solenoids, and/or other components. In some embodiments, the device may be folded 610 by bending the device across an axis. In some embodiments, the axis may be determined by the location of the solenoids to which a current is applied 605.

[0065] In various embodiments, the current may be removed 615 from the solenoids. In some embodiments, by removing 615 the current from the solenoids, the device may become rigid in the folded position, as described in greater detail herein. In some embodiments, removing 615 the current from the solenoids may be completed via any number of switches, buttons, toggles, touchscreen commands, voice commands, and the like that are configured to send a signal to the power source to cut the electrical current to the solenoids. In some embodiments, one or more sensors may be employed, where the sensors determine whether the device has been folded 610, and if it has been folded, the sensors send a signal to the power source to remove 615 the current from the solenoids.

EXAMPLES

Example 1 : Device Construction

[0066] A flexible tablet computing device having a flexible display substrate will allow for the computing device to be folded in half when not in use so as to allow for greater portability and to fit into most pockets. The flexible display will include a plurality of flexible tubes that are made up of a transparent polymer and are tightly packed together to form a substrate. Each tube will have two rare-earth magnets made of a neodymium-iron- boron, and grade N42 mixture that exhibits a remanence of 1.03-1.3 Tesla. The rare-earth magnets will be cylindrical shaped with a radius of 3.175 mm, a thickness of 6.35 mm, and a distribution of 1.03 cm, where the distribution corresponds to the separation of magnets from each other along the axis. Each rare-earth magnet will be positioned exactly 15 mm from either side of the center of the substrate within each flexible tube. The rare-earth magnets will be magnetized along the axis of the tubes and will be secured in an attracting orientation, so that the north pole of one magnet is facing toward the south pole of another magnet. A plurality of solenoids having a loop radius of 3.97 mm and 200 turns will be placed around the outside surface of each tube equidistant from each pair of rare-earth magnets, so that the solenoids are all in a line down the center of the substrate, which is also the location of the fold axis for the flexible tablet computing device. The solenoids will be made of a transparent metallic composition capable of conducting electricity. A MR fluid having a volume fraction of 30 percent carbonyl iron particles with a saturation polarization of 2.1 Tesla, a particle diameter of 7-9 μιη and a purity of approximately 99.5 percent iron, to 70 percent of a carrier fluid comprising silicon oil will be dispersed inside the flexible tubes. The MR fluid will have an applied field of approximately 0.63 Tesla exerted by the rare-earth magnets before activation of the solenoids. A flexible lithium battery will act as a power source for the solenoids, as well as other components of the flexible tablet computing device. The battery will be capable of providing an electric current of 2 amperes across the solenoids to achieve optimum yield stress, as shown by the graphical representation in FIG. 7. The yield stress depicted in FIG. 7 refers to the yield stress of the MR fluid only, and does not factor in the yield stress of the tubes.

[0067] In a passive state, each tube will be magnetically saturated for most of its length. The passive yield stress at the midpoint of each tube will be approximately 119 kilopascals for the MR fluid alone. By applying the current to the solenoid, the field can be completely nullified within the solenoid, leading to a low yield stress so that the tablet can be folded.

Example 2: Device Usage

[0068] A user will use a foldable tablet computing device having a display substrate that is capable of being folded into fourths for maximum portability. To be folded into fourths, the tablet will contain two fold axes that are perpendicular to each other, with each fold axis bisecting the tablet in both a vertical and a horizontal direction. To properly fold, the tablet will have a display substrate that is made up of a plurality of flexible tubes arranged in a grid pattern and containing a plurality of permanent magnets and MR fluid therein. Each flexible tube will also incorporate a plurality of solenoids surrounding the outside of the tube and positioned in substantially the same location as each permanent magnet. In an inactivated state, the magnetic field from the plurality of permanent magnets will cause the MR fluid to become rigid so that the device cannot be bent. In an active state, the magnetic field from the solenoids will cancel out the magnetic force from the permanent magnets, thereby causing the MR fluid to flow so that the device can be bent. [0069] The user will be able to fold the tablet by pressing a button located on an external surface of the tablet device. The button can be pressed once if the user desires to only fold the tablet along a first axis. If the user desires to fold the tablet along both axes, the button can be pressed twice. The button will send a signal to the battery to provide a current across all or a portion of the solenoids, depending on how many times the button has been depressed. As a result, the solenoids will activate, thus putting the tablet in an activated state. The magnetic force from the solenoids will cancel out the magnetic force from the permanent magnets, thereby allowing the user to fold the tablet. Once the user has folded the tablet, he/she will press the button one more time to send a signal to the battery to cease transmission of the electric current across the solenoids and lock the tablet in a folded state. Once the user is ready to unfold the tablet, he/she presses the button, unfolds the tablet, and presses the button again to lock it into an unfolded state. The tablet will be configured to be turned on and used only when it is in the unfolded state, and may not be used when in the folded state.

Example 3 : Use with a Strain Sensor

[0070] A user will use a tablet computer that is capable of being folded at specific crease locations. The tablet will have a display substrate that is made up of a plurality of flexible tubes arranged in a grid pattern and containing a plurality of permanent magnets and MR fluid therein. Each flexible tube will also incorporate a plurality of solenoids surrounding the outside of the tube and positioned in substantially the same location as each permanent magnet. In an inactivated state, the magnetic field from the plurality of permanent magnets will cause the MR fluid to become rigid so that the device cannot be bent. In an active state, the magnetic field from the solenoids will cancel out the magnetic force from the permanent magnets, thereby causing the MR fluid to flow so that the device can be bent. [0071] The tablet will also incorporate a strain sensor that is configured to sense strain in the areas on the display substrate where the tablet is designed to be folded, as well as the areas that are not designed to be folded. The strain sensor will also be functionally connected to a computing device that controls the active and inactive states.

[0072] Similar to Example 2 depicted herein, the user will be able to fold the tablet by pressing a button located on an external surface of the tablet device. The button will also be connected to the computing device, which will then direct the battery to provide a current across all or a portion of the solenoids, based on the program instructions included in a memory connected to the computing device. As a result, the solenoids will activate, thus putting the tablet in an activated state. The magnetic force from the solenoids will cancel out the magnetic force from the permanent magnets, thereby allowing the user to fold the tablet. Once the user has folded the tablet, he/she will press the button one more time to send a signal to the computing device, which will direct the battery to cease transmission of the electric current across the solenoids and lock the tablet in a folded state. Once the user is ready to unfold the tablet, he/she presses the button, unfolds the tablet, and presses the button again to lock it into an unfolded state. The tablet will be configured to be turned on and used only when it is in the unfolded state, and may not be used when in the folded state.

[0073] If the tablet experiences torsional strain, such as, for example, when the user attempts to fold or unfold the tablet without pressing the button first, when the tablet is accidentally twisted, and when the user attempts to fold or unfold the tablet in a location where it is not intended to be folded, the strain sensor will send a signal to the computing device, which will then complete a number of additional tasks, such as directing the battery to increase the current so that the tablet becomes more rigid, directing the tablet to display a warning message, and directing the tablet to emit an audible tone. [0074] In the above detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be used, and other changes may be made, without departing from the spirit or scope of the subject matter presented herein. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein.

[0075] The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and apparatuses within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds, compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.

[0076] With respect to the use of substantially any plural and/or singular terms herein, those having skill in the art can translate from the plural to the singular and/or from the singular to the plural as is appropriate to the context and/or application. The various singular/plural permutations may be expressly set forth herein for sake of clarity. [0077] It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims (for example, bodies of the appended claims) are generally intended as "open" terms (for example, the term "including" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," et cetera). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (for example, "a" and/or "an" should be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (for example, the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations). Furthermore, in those instances where a convention analogous to "at least one of A, B, and C, et cetera" is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (for example, " a system having at least one of A, B, and C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, et cetera). In those instances where a convention analogous to "at least one of A, B, or C, et cetera" is used, in general such a construction is intended in the sense one having skill in the art would understand the convention (for example, " a system having at least one of A, B, or C" would include but not be limited to systems that have A alone, B alone, C alone, A and B together, A and C together, B and C together, and/or A, B, and C together, et cetera). It will be further understood by those within the art that virtually any disjunctive word and/or phrase presenting two or more alternative terms, whether in the description, claims, or drawings, should be understood to contemplate the possibilities of including one of the terms, either of the terms, or both terms. For example, the phrase "A or B" will be understood to include the possibilities of "A" or "B" or "A and B."

[0078] In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.

[0079] As will be understood by one skilled in the art, for any and all purposes, such as in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and a combination of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, et cetera As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, et cetera As will also be understood by one skilled in the art all language such as "up to," "at least," and the like include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member. Thus, for example, a group having 1-3 cells refers to groups having 1, 2, or 3 cells. Similarly, a group having 1-5 cells refers to groups having 1, 2, 3, 4, or 5 cells, and so forth.

[0080] Various of the above-disclosed and other features and functions, or alternatives thereof, may be combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art, each of which is also intended to be encompassed by the disclosed embodiments.

Claims

CLAIMS What is claimed is:

1. A device having programmable flexibility, the device comprising: a plurality of flexible hollow tubes filled with a magnetorheological fluid; a plurality of permanent magnets affixed periodically inside each of the plurality of flexible hollow tubes; and

a plurality of solenoids positioned and configured to produce a magnetic field that cancels at least a portion of a magnetic field produced by the plurality of permanent magnets to result in an applied magnetic field on the magnetorheological fluid,

wherein the magnetorheological fluid is configured to flow when the applied magnetic field is lower than a threshold value and become rigid when the applied magnetic field is higher than the threshold value.

2. The device of claim 1, further comprising a flexible substrate, wherein the plurality of flexible hollow tubes are integrated with the flexible substrate.

3. The device of claim 2, wherein the flexible substrate is a flexible polymer, a flexible user interface, a flexible light-emitting device, a flexible display device, a flexible portable electronic device, a flexible computer device, a flexible communication device, or a flexible battery.

4. The device of claim 1, wherein the plurality of flexible hollow tubes comprise a flexible polymer.

5. The device of claim 1, wherein the magnetorheological fluid comprises silicon oils, hydrocarbon oils, or mineral oils.

6. The device of claim 1, wherein the magnetorheological fluid comprises magnetic microparticles having an average diameter of about 0.1 μιη to about 50 μιη.

7. The device of claim 1, wherein the magnetorheological fluid comprises magnetic microparticles comprising carbonyl iron, powder iron, iron-cobalt, dysprosium, magnetite, gallium manganese arsenide, gadolinium, cobalt, nickel, samarium-cobalt, neodymium, alnico, or combinations thereof.

8. The device of claim 1, wherein the magnetorheological fluid comprises magnetic microparticles and a carrier fluid in a ratio of about 1:5 by volume to about 2:5 by volume.

9. The device of claim 1, wherein the plurality of permanent magnets comprise rare-earth magnets.

10. The device of claim 1, wherein the plurality of permanent magnets comprise samarium-cobalt, neodymium, neodymium-iron-boron, yttrium-cobalt, or combinations thereof.

11. The device of claim 1, wherein the plurality of permanent magnets are positioned to produce a magnetic field along an axis of the plurality of flexible hollow tubes.

12. The device of claim 1, wherein the plurality of solenoids are positioned over the plurality of permanent magnets and are configured to produce a magnetic field equal in magnitude and opposite in direction to the magnetic field produced by the plurality of permanent magnets when an effective amount of electric current flows through the plurality of solenoids.

13. The device of claim 1, wherein the plurality of solenoids are positioned over the magnetorheological fluid and are configured to produce a magnetic field equal in magnitude and opposite in direction to the magnetic field produced by the plurality of permanent magnets when an effective amount of electric current flows through the plurality of solenoids.

14. The device of claim 1, further comprising at least one power supply for powering the plurality of solenoids.

15. The device of claim 1, wherein the device is rigid when no current flows through the plurality of solenoids and the device is flexible when an effective amount of electric current flows through at least a subset of the plurality of solenoids.

16. The device of claim 1, further comprising one or more heat-dissipating components associated with the plurality of solenoids.

17. A method of making a device having programmable flexibility, the method comprising: positioning a plurality of permanent magnets in a plurality of flexible hollow tubes filled with a magnetorheological fluid, wherein the magnetorheological fluid is configured to flow when an applied magnetic field is lower than a threshold value and become rigid when the applied magnetic field is higher than the threshold value; positioning a plurality of solenoids on the plurality of flexible hollow tubes wherein the plurality of solenoids are configured to produce a magnetic field that cancels at least a portion of a magnetic field produced by the plurality of permanent magnets to result in the applied magnetic field on the magnetorheological fluid; and integrating the plurality of flexible hollow tubes and the plurality of solenoids with a flexible substrate.

18. The method of claim 17, wherein positioning the plurality of permanent magnets comprises affixing the plurality of permanent magnets periodically inside each of the plurality of flexible hollow tubes to produce the magnetic field along an axis of the plurality of flexible hollow tubes.

19. The method of claim 17, wherein positioning the plurality of permanent magnets comprises affixing the plurality of permanent magnets in an attracting position.

20. The method of claim 17, wherein positioning the plurality of solenoids comprises positioning the plurality of solenoids on a portion of the plurality of flexible hollow tubes having the plurality of permanent magnets wherein the plurality of solenoids are configured to produce a magnetic field equal in magnitude and opposite in direction to the magnetic field produced by the plurality of permanent magnets when an effective amount of electric current flows through the plurality of solenoids.

21. The method of claim 17, wherein positioning the plurality of solenoids comprises positing the plurality of solenoids on a portion of the plurality of flexible hollow tubes having the magnetorheological fluid wherein the plurality of solenoids are configured to produce a magnetic field equal in magnitude and opposite in direction to the magnetic field produced by the plurality of permanent magnets when an effective amount of electric current flows through the plurality of solenoids.

22. The method of claim 17, wherein the integrating comprises encapsulating the plurality of flexible hollow tubes and the plurality of solenoids into a flexible polymer substrate.

23. The method of claim 17, wherein the integrating comprises attaching the plurality of flexible hollow tubes and the plurality of solenoids to a surface of a flexible polymer substrate.

24. The method of claim 17, wherein the flexible substrate is a flexible polymer, a flexible user interface, a flexible light-emitting device, a flexible display device, or a flexible battery.

25. The method of claim 17, wherein the plurality of flexible hollow tubes comprise a flexible polymer.

26. The method of claim 17, wherein the magnetorheological fluid comprises silicon oils, hydrocarbon oils, or mineral oils.

27. The method of claim 17, wherein the magnetorheological fluid comprises magnetic microparticles having an average diameter of about 0.1 μιη to about 10 μιη.

28. The method of claim 17, wherein the magnetorheological fluid comprises microparticles comprising carbonyl iron, powder iron, iron-cobalt, or combinations thereof.

29. The method of claim 17, wherein the magnetorheological fluid comprises magnetic microparticles and a carrier fluid in a ratio of about 1:5 by volume to about 2:5 by volume.

30. The method of claim 17, wherein the plurality of permanent magnets comprise rare-earth magnets.

31. The method of claim 17, wherein the plurality of permanent magnets comprise samarium-cobalt, neodymium, neodymium-iron-boron, yttrium-cobalt, or combinations thereof.

32. A method of changing a shape of a device, the method comprising: applying an effective amount of current across a plurality of solenoids, wherein the device comprises a plurality of flexible hollow tubes filled with a magnetorheological fluid, a plurality of permanent magnets affixed periodically inside each of the plurality of flexible hollow tubes, and a plurality of solenoids positioned and configured to produce a magnetic field that cancels at least a portion of a magnetic field produced by the plurality of permanent magnets;

folding the device in a desired shape; and

stopping the current across the plurality of solenoids, whereby the device is fixed in to the desired shape.

33. The method of claim 32, wherein the plurality of solenoids are positioned over the plurality of permanent magnets and configured to produce a magnetic field equal in magnitude and opposite in direction to the magnetic field produced by the plurality of permanent magnets when an effective amount of electric current flows through the plurality of solenoids.

34. The method of claim 32, wherein the plurality of solenoids are positioned over the magnetorheological fluid and configured to produce a magnetic field equal in magnitude and opposite in direction to the magnetic field produced by the plurality of permanent magnets when an effective amount of electric current flows through the plurality of solenoids.

35. The method of claim 32, wherein an effective amount of current is applied to a subset of the plurality of solenoids.

36. The method of claim 35, wherein the subset of the plurality of solenoids is determined by the desired shape of the device.

37. The method of claim 35, wherein the effective amount of current and the subset of the plurality of solenoids are determined by a software.

38. The method of claim 32, wherein folding comprises bending the device across an axis.