Multi-axis differential strain sensor

Abstract

The flexible differential strain sensor, system, and method includes a deformable substrate having a first axis and a second axis different from the first axis, and a first sensing element and a second sensing element. The first and second sensing elements are composed of a conductive gel. The first sensing element is positioned to sense strain in the deformable substrate along the first axis. The second sensing element has a first portion positioned to sense strain in the deformable substrate along the first axis and a second portion positioned to sense strain in the deformable substrate along the second axis. The second sensing element is configured to cancel at least a portion of a stimulus sensed by the first sensing element along the first axis.

Description

[Background technology]

[0001] (CROSS-REFERENCE TO RELATED APPLICATIONS) This patent application claims the benefit of priority to U.S. Provisional Application No. 63 / 038,547, filed June 12, 2020, which is incorporated herein by reference in its entirety.

[0002] A strain sensor can measure a mechanical or other physical stimulus to the strain sensor, for example, through a substrate on which the strain sensor is disposed, thereby measuring strain on the substrate. The deformation of the substrate, such as stretching, twisting, bending, etc., that is translated into the strain sensor can cause a change in some physical property of the strain sensor. The change in the physical property can be converted into strain and used to determine changes in strain over time. [Brief explanation of the drawings]

[0003] To easily identify the discussion of any particular element or act, the most significant digit(s) in a reference number refers to the figure number in which that element is first introduced.

[0004] [Figure 1] FIG. 1 is a block diagram of a flexible differential strain sensor in an exemplary embodiment.

[0005] [Figure 2] 1 is a topology of a flexible differential strain sensor in an exemplary embodiment.

[0006] [Figure 3] FIG. 2 is an electrical equivalent circuit diagram of a flexible differential strain sensor in an exemplary embodiment.

[0007] [Figure 4A] 1 illustrates an abstract representation of a process by which a topology of a flexible differential strain sensor may be formed in an exemplary embodiment. [Figure 4B] 1 illustrates an abstract representation of a process by which a topology of a flexible differential strain sensor may be formed in an exemplary embodiment.

[0008] [Figure 5] FIG. 1 is a block diagram of a flexible differential strain sensor in an exemplary embodiment.

[0009] [Figure 6] 1 illustrates a topology of a three-dimensional flexible differential strain sensor in an exemplary embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] Flexible strain sensors are disclosed, for example, in U.S. Patent Application Publication No. 2018 / 0247727 (the "'727 Application"), published on August 30, 2018, and incorporated herein by reference in its entirety. The '727 Application discloses methods, apparatus, and exemplary embodiments for strain sensing comprising a deformable conductor, such as a conductive gel, for example, in Figures 7-10 and paragraphs

[0014] -

[0017] ,

[0089] -

[0120] , etc. As disclosed in the '727 Application, a sensor system includes a sensor element that responds to a stimulus by changing its dimensions, e.g., by strain. Examples disclosed in the '727 Application may include a variable resistive grid pattern and / or an unconnected or loosely connected variable resistive network, for example, in paragraph

[0116] .

[0011] Disclosed herein are flexible differential strain sensors that can be used to measure and distinguish between stimuli occurring in more than one dimension (e.g., along two different axes) by arranging sensor elements in a pattern. Examples disclosed herein can utilize differential signal processing to provide strain along a particular axis of a substrate. As a result, such flexible differential strain sensors can provide increased sensitivity relative to the nature of the strain on the substrate and / or on the strain sensor.

[0012] FIG. 1 is a block diagram of a flexible differential strain sensor in an exemplary embodiment. The flexible actuation strain sensor 102 is configured to detect strain on a deformable substrate 104, particularly along the X- and Y-axes of the deformable substrate 104. The deformable substrate 104 can be any object onto or within which the conductive gel disclosed herein can be disposed and generally affixed. The deformable substrate 104 can be or include natural and synthetic fibers, natural or synthetic rubber, elastomers, and the like. Furthermore, in various alternatives, the flexible differential strain sensor 102 can be implemented on a substrate intended to deform relatively small, yet still allow the flexible differential strain sensor 102 to detect potentially undesirable strains or deformations on the substrate. For example, the substrate can be metal, carbon fiber, or the like, and the flexible differential strain sensor 102 can generally be directed to identifying such structural strains. However, in various examples, the flexible differential strain sensor 102 is implemented using a deformable substrate 104, in which case the flexible differential strain sensor 102 with the deformable substrate 104 may be positioned and secured on such a relatively non-deformable structure to determine strain on such structure.

[0013] For purposes of explanation, the deformable substrate 104 is effectively presented as a two-dimensional object, with strains detected by components positioned along one or both of the X and Y axes and extending directly along one of the X and Y axes. However, it should be recognized and understood that components may be positioned at angles relative to the X and Y axes, and conventional mathematics may be utilized to compensate for or otherwise account for differences in angles relative to the X and Y axes. Additionally, strains may be applied to the deformable substrate 104 along a Z-axis, orthogonal to the X and Y axes, and the flexible differential strain sensors 102 may be sensitive to such strains. Furthermore, as illustrated herein, the principles illustrated in the two-dimensional examples may be applied to three-dimensional examples, with strain sensors positioned along the Z-axis of the deformable substrate 104 and configured to directly sense strains along the Z-axis.

[0014] The flexible differential strain sensor 102 may include a first sensing element 106 having a first active portion 108 positioned to sense strain along a first axis, e.g., a Y-axis. A first terminal 110 provides an electrical output from the first sensing element 106. A second sensing element 112 may have a second active portion 114 and a cancellation portion 116, and a second terminal 118 provides an electrical output from the second sensing element 112. The second active portion 114 may be positioned on the deformable substrate 104 to sense strain along an X-axis, e.g., a second axis, and the cancellation portion 116 may be positioned on the deformable substrate 104 to logically or mathematically cancel out the strain along the Y-axis detected by the first active portion 108 of the first sensing element 106. As a result, the first sensing element 106 may be sensitive to strain along the Y-axis but have little or no sensitivity to strain along the X-axis. In contrast, the second sensing element 112 may be sensitive to strain applied in both the X-axis and the Y-axis. In some examples, by placing the cancellation portion 116 in close physical proximity to the first active portion 108, the cancellation portion 116 experiences the same or approximately the same strain along the Y-axis as the first active portion 108.

[0015] In various examples, the first sensing element 106 and the second sensing element 112 are each formed of a conductive gel as disclosed herein. The conductive gel may be disposed on or within the deformable substrate 104 through any suitable process, including printing, dispersing into filaments and voids of the deformable substrate 104, etc. The conductive gel may be implemented as one or more electrical traces configured to conduct electrical current along the traces. The electrical properties of the conductive gel may change as the conductive gel stretches, contracts, or otherwise deforms, e.g., as strain is applied to the deformable substrate 104 and thus the conductive gel. In various examples, the impedance (or, more narrowly, resistance) of a given trace of conductive gel may increase or decrease as the trace stretches, contracts, or otherwise deforms. Such a change in the resistance of the trace may correspond to the amount of strain applied on the deformable substrate 104 in the vicinity of the trace. As a result, the first active portion 108, the second active portion 114, and the compensation portion 116 may be understood to be particular portions of the conductive gel of the electrical trace that extend along one of the X and Y axes of the deformable substrate 104. The impedance and / or other electrical properties of the conductive gel may change as the conductive gel deforms, but the conductive gel may be significantly more brittle and fragile than traditional conductors used in electronic devices, and may be significantly more elastic.

[0016] The two signals, Y1 on the first terminal 110 and X1 on the second terminal 118, may form an output vector from the flexible differential strain sensor 102 to recover and / or represent the strain field commonly applied to the deformable substrate 104 and the flexible differential strain sensor 102. The output vector may be processed in any suitable manner. For example, in some applications, the raw signals X1 and Y1 may be processed by the signal processing unit 120 to determine and output the strain applied to the Y-axis as output signal Y2 and the strain applied to the X-axis as output signal X2. The signal processing unit 120 may include an ohmmeter or other device for determining the impedance at the terminals 110, 118, and a processor or other computing electronics that can convert or otherwise relate the impedance or change in impedance to strain in the flexible differential strain sensor 102. For example, in an exemplary embodiment, a 0.03 ohm change in impedance and / or resistance detected by the signal processing unit 120 is equivalent to a 1 millimeter strain of the conductive gel of the flexible differential strain sensor 102 and traces formed thereby, as disclosed herein. In various examples, strain may be understood to be a change in overall length, although it should be appreciated and understood that any viable metric for strain known in the art may additionally or alternatively be utilized.

[0017] Because Y1 has a first active portion 108 but does not have wiring that extends generally along the X-axis like the second active portion 114, and thus has greater sensitivity to strain in the Y-axis, the signal processing unit 120 may calculate the strain in the Y-axis by relating changes in impedance of the first active portion 108 to strain in the Y-axis and output the resulting strain as Y2. In various examples, the signal processing unit 120 may simply interfere with or pass signal Y1 through as output signal Y2 to provide an indication of strain, or a remote processing unit, controller, or other electronics may perform calculations that relate changes in impedance to strain on the flexible differential strain sensor 102.

[0018] In contrast, because the second sensing element 112 has significant sensitivity to strain in both the X-axis and the Y-axis, the signal processing unit 120 may generate an output signal X2 indicative of strain applied along the X-axis of the second sensing element 112 by subtracting the change in impedance from Y1 from the change in impedance from X1. As a result, the signal processing unit 120 determines a differential sensitivity to impedance that substantially cancels the strain applied to the first active portion 108 and the cancellation portion 116 along the Y-axis, leaving X2 primarily or entirely based on the change in impedance along the second active portion 114. For purposes of this disclosure, the first active portion 108 and the cancellation portion 116 may be formed of conductive gel traces located close to each other and of very similar properties, but it should be recognized and understood that variations in the actual location of the conductive gel may introduce some error between the change in impedance in the first active portion 108 and the cancellation portion 116 and propagate through the differential calculation of the strain on the X-axis output at X2. However, it should be appreciated and understood that even if the output X2 does not completely eliminate the effects of distortion on the Y axis, such small errors can still result in a useful and accurate representation of distortion on the X axis. The same principle applies to the output Y2.

[0019] As mentioned above, any processing of the output vector may be performed in a manner that may be customized for a particular application. Generally, the sensing elements may be arranged in a grid or array, which may be partially and / or fully connected. The elements may generate an output vector of values ​​that may be analyzed, alone or in combination with other sensors, to provide a representation of the strain field on the deformable substrate 104 measured by the flexible differential strain sensor 102. Interpretation of the strain field may be based on the application, some examples of which are described below.

[0020] In other embodiments, the flexible differential strain sensor 102 may be arranged in other configurations, using different numbers and / or types of sensing elements, active and / or cancellation regions, etc. For example, the sensing elements may be arranged in a T-shape, a U-shape, an S-shape, a box shape, etc. Different elements and / or regions may be arranged at angles other than right angles, such as acute and / or obtuse angles. The sensing elements may be arranged in any pattern, and the signal processing may be adjusted to accommodate different patterns. In some embodiments, the signal processing may extract a composite signal indicative of a stimulus in one dimension while canceling strain in one or more other dimensions and / or axes. These principles may be applied to flexible differential strain sensors 102 having any number of elements with any number of active and / or cancellation regions for any type of stimulus, such as motion, stress, strain, etc.

[0021] FIG. 2 is a topology of the flexible differential strain sensor 102 in an exemplary embodiment. In particular, the topology shows conductive gel electrical traces 202. The traces 202 may be positioned generally as shown on a deformable substrate 104 (not shown) to fabricate the flexible differential strain sensor 102 shown in FIG. 1. The traces 202 include Y-axis portions 204a, 204b, 204c, and 204d, which may be understood to be portions of the trace 202 extending generally along the Y-axis, and X-axis portions 206a, 206b, and 206c, which extend generally along the X-axis. The topology does not necessarily represent the relative lengths of the Y-axis portions 204a, 204b, 204c, and 204d and the X-axis portions 206a, 206b, and 206c.

[0022] Wire 202 is coupled to or otherwise formed with a first node 208, a second node 210, and a third node 212. First node 208 and second node 210 generally describe a Y1 signal defined by portions 204a, 206a, and 204b. Second node 210 and third node 212 generally describe an X1 signal defined by portions 204b, 206b, 204d, 206c, and 204c. Thus, from an actual topology perspective, it should be recognized that signals X1 and Y1 are at least partially affected by Y-axis portion 204b of wire 202, and that changes in impedance along Y-axis portion 204b can result in changes in impedance for both X1 and Y1.

[0023] 3 is an electrical equivalent schematic diagram of the flexible differential strain sensor 102 in an exemplary embodiment. The electrical equivalent circuit diagram includes a first varistor 302 corresponding to the first active portion 108, a second varistor 304 corresponding to the second active portion 114, and a third varistor 306 corresponding to the cancellation portion 116, all disposed on the deformable substrate 104. The electrical equivalent circuit diagram further includes a first logic node 308 and a second logic node 310 at which a signal Y1 is generated, and a third logic node 312 and a fourth logic node 314 at which a signal X1 is generated. While varistors are discussed herein, it should be recognized and understood that varistors generally provide a variable impedance generated by deformation of the wire 202, not just a resistance in the strict sense.

[0024] It is noted and emphasized that the electrical equivalent circuit diagram of Figure 3 is a product of the topologies of Figure 2. Thus, first varistor 302 accounts for the variable impedance caused by deformation of wire 202 along Y-axis portion 204a, X-axis portion 206a, and Y-axis portion 204b. In examples where X-axis portion 206a is very short, e.g., 100 micrometers or less, while Y-axis portions 204a and 204b are each a few millimeters or centimeters in length, first varistor 302 can represent the change in impedance, and therefore the strain applied along the Y-axis corresponding to those portions of wire 202. Similarly, second varistor 304 can correspond to X-axis portion 206b and X-axis portion 206c, while third varistor 306 can correspond to Y-axis portion 204b, Y-axis portion 204c, and Y-axis portion 204d. Furthermore, the first logical node 308 may correspond to the first node 208, the second logical node 310 and the third logical node 312 may correspond to the second node 210, and the fourth logical node 314 may correspond to the third node 212.

[0025] It should be appreciated and understood, however, that the principles of electrical equivalent circuit diagrams can be obtained with any suitable arrangement of electrical components and are not bound to any particular topology or to any particular electrical components. Accordingly, various examples of flexible differential strain sensors 102 are not necessarily implemented with conductive gel, to the extent that alternative components that change impedance as a function of local strain on the deformable substrate 104 and / or on the components themselves may be utilized. Similarly, flexible differential strain sensors 102 such as those shown in FIG. 1 may be implemented without variable impedance, so long as an alternative mechanism is feasible. However, implementation of flexible differential strain sensors 102 with conductive gel may offer advantages of electrical and mechanical simplicity, robustness, resilience, and cost, among other factors, compared to potential alternative components. Such advantages may be seen not only in the use of flexible differential strain sensors 102, but also in the manufacturing process for flexible differential strain sensors 102.

[0026] 4A and 4B illustrate an abstract representation of a process by which the topology of FIG. 2 of the flexible differential strain sensor 102 may be formed in an exemplary embodiment. In FIG. 4A, a grid of conductive gel is formed, including a portion 402 aligned with the Y-axis, a portion 404 aligned with the X-axis, along with nodes 208, 210, 212, and a fourth node 406. In FIG. 4B, certain portions 402, 404 of the grid are removed, for example, by cutting or otherwise severing them from the remainder of the conductive gel trace 202, as represented by the dashed lines. The remaining portions, i.e., the solid lines, correspond to the trace 202 and its various portions 204, 206 shown in the topology of FIG. 2. As a result, the fourth node 406 is also removed and rendered inoperable. While the grid structure of FIG. 4A is provided as an example, it should be recognized and understood that the grid may be scaled using more or fewer portions 402, 404 and more or fewer nodes.

[0027] Forming the initial grid in Figure 4A may have certain advantages over the process of simply directly generating the topology of Figure 2. In particular, the grid structure of Figure 4A allows for an initial configuration that can be easily adapted to any final desired topology by removing unnecessary portions. Furthermore, the initial grid may be implemented as an unconnected / sparsely connected grid pattern in which some vertices are ultimately associated with output nodes 208, 210, 212, 406, while other vertices 408 are not ultimately associated with output nodes 208, 210, 212, 406.

[0028] It is emphasized that while the initial grid of FIG. 4A is included as part of a process that may create the topology of FIG. 2 and doing so may provide certain advantages in adaptability of the manufacturing process to various use cases, the topology of FIG. 2 may be arrived at directly without utilizing an initial grid. In such a case, conductive gel may be applied to the topology without necessarily removing any portion of the conductive traces. While doing so may be less adaptable to different desired topologies, such a process may also be relatively quick to perform and result in less waste of conductive gel and other components.

[0029] 5 is a block diagram of a flexible differential strain sensor 502 in an exemplary embodiment. The flexible differential strain sensor 502 includes many of the same components as the flexible differential strain sensor 102. Thus, 502 may include a first sensing element 106 having a first active portion 108 positioned to sense strain along the Y-axis. A first terminal 110 provides an electrical output from the first sensing element 106. A second sensing element 112 may have a second active portion 114 and a cancellation portion 116, and a second terminal 118 provides an electrical output from the second sensing element 112. The second active portion 114 may be positioned on the deformable substrate 104 to sense strain along the X-axis, and the cancellation portion 116 may be positioned on the deformable substrate 104 to logically or mathematically cancel out strain along the Y-axis detected by the first active portion 108 of the first sensing element 106. As a result, the first sensing element 106 may be sensitive to strain on the Y-axis, but have little or no sensitivity to strain on the X-axis. In contrast, the second sensing element 112 may be sensitive to strain applied in both the X-axis and the Y-axis. Although the signal processing unit 120 is not shown, it should be appreciated and understood that such components may be included as part of the flexible differential strain sensor 502, as in the flexible differential strain sensor 102.

[0030] However, in contrast to flexible differential strain sensor 102, flexible differential strain sensor 502 generally forms a U-shape. As a result, first active portion 108 is spaced apart from cancellation portion 116. Flexible differential strain sensor 502 may therefore be relatively more sensitive than flexible differential strain sensor 102 to differential strain across the width of deformable substrate 104 along the X-axis, but relatively less sensitive to differential strain proximate first sensing element 106. It will be appreciated and understood that the principles discussed with respect to the relative differences between flexible differential strain sensor 102 and flexible differential strain sensor 502 may apply to any of a variety of alternative flexible differential strain sensors, such that various configurations may be implemented as desired.

[0031] 6 illustrates a topology of a three-dimensional flexible differential strain sensor 602 in an exemplary embodiment. The three-dimensional flexible differential strain sensor 602 is disposed on and within the deformable substrate 104 in all three axes, X, Y, and Z. Thus, in the illustrated example, the conductive gel trace 604 includes an upper major surface 606, a lower major surface 608, and a portion disposed through the deformable substrate 104 between the upper and lower major surfaces 606, 608. As illustrated, the trace 604 further includes nodes 610 at vertices 612; however, as disclosed herein, not all vertices 612 are nodes 610, but rather may be utilized as nodes 610 as desired.

[0032] It should be appreciated and understood that the topology is provided for illustrative purposes and that lengths may be exaggerated and not necessarily to scale. Thus, for example, if the deformable substrate 104 is a fabric, such as that used in a shirt, the lengths of the portions of the wires 604 along the X-axis and Y-axis may be a few millimeters or centimeters, while the length of the wires 604 along the Z-axis may be a few millimeters, e.g., 100 micrometers or less. Other examples of varying lengths are contemplated depending on the context in which the three-dimensional flexible differential strain sensor 602 is utilized.

[0033] Furthermore, while the topology is provided in a simplified format for purposes of clarity, it should be appreciated and understood that an expanded three-dimensional grid pattern similar to the grid pattern described with respect to Figures 4A and 4B may be utilized to increase the portion of available wiring 604 and nodes 610. With reference to Figures 4A and 4B, the expanded grid pattern may allow for relatively greater flexibility in the manufacturing process of the three-dimensional flexible differential strain sensor 602 and / or allow for three-dimensional topologies other than the cube shown in Figure 6. Additional three-dimensional topologies may likewise be implemented without the intermediate step of the expanded three-dimensional grid.

[0034] The portion of the wire 604 extending along the Z-axis may be understood to form a third sensing element 614 including at least one active portion and at least one cancellation portion, e.g., a third active portion and a second cancellation portion, based on the terminology presented with respect to the flexible differential strain sensor 102. Given that the illustrated topology of the three-dimensional flexible differential strain sensor 602 includes multiple portions of the wire 604 along each axis, the identification of each particular portion as an active portion or a cancellation portion is subjective and may change at any given time depending on the location on the deformable substrate 104 being evaluated for strain. Thus, the signal processing unit 120 may utilize any particular portion of the wire 604 as an active portion or a cancellation portion, as desired.

[0035] Similar to the two-dimensional flexible differential strain sensor 102, 502, the nodes 610 are coupled to the signal processing unit 120, and the variance in impedance across various sets of nodes 610 may be utilized as a vector to identify the three-dimensional strain disposed on the deformable substrate 104 and the three-dimensional flexible differential strain sensor 602 in general. In such an example, the resulting vector may include at least X1, Y1, and Z1, and may include more measurements along some or all of the axes based on which nodes 610 are utilized to form the vector. Additionally, the signal processing unit 120 may utilize parallel portions of the wires 604 to cancel out strain along parallel axes. Thus, to cancel out distortion along the Y-axis, signal processing unit 120 may, for example, subtract the impedance between two nodes 610 that include Y-axis portion 616a from the impedance between two nodes 610 that include Y-axis portion 616b, or subtract the impedance between two nodes 610 that include Y-axis portion 616c from the impedance between two nodes 610 that include Y-axis portion 616a, among various possible permutations.

[0036] In some embodiments, the flexible differential strain sensors 102, 502, 602 may be implemented as flexible and / or stretchable strain sensors using one or more deformable conductors for the sensing element, such as the deformable substrate and / or conductors disclosed in the '727 application. In some embodiments, the strain sensors 102, 502, 602 may be fabricated using any of the materials and / or manufacturing techniques described in U.S. Patent Application Publication No. 2020 / 0066628, published February 27, 2020, which is incorporated herein by reference in its entirety.

[0037] The strain sensors 102, 502, 602 may be used in a wide variety of applications using countless combinations of materials in accordance with the principles of the present disclosure. For example, flexible and / or stretchable strain sensors 102, 502, 602 may be applied to and / or integrated with articles of clothing, shoes, hats, backpacks or other bags, industrial textiles, upholstery, geotextiles, non-woven membranes, or any other manufactured article in which strain sensing may be useful.

[0038] In some exemplary embodiments, strain sensors 102, 502, 602 made of flexible and / or stretchable layers (e.g., various thermosetting films, sheets, etc., and / or thermoplastic polyurethane (TPU)) may be integrated into an article of clothing, such as a shirt or vest, to sense the breathing of a person wearing the article. The sensor may be positioned so that the horizontal (X-axis) portion of the sensor or gauge is over the rib cage and parallel to the horizon when the wearer is standing. The vertical (Y-axis) portion of the sensor may be aligned with the wearer's spine, i.e., perpendicular to the horizon when the wearer is standing. In such a configuration, the outputs from both the X-axis and Y-axis portions of the strain sensor 102, 502, 602 may provide a response to breathing by the wearer in various situations, where the vertical (Y-axis) portion may respond to bending of the wearer's back.

[0039] As disclosed herein, some of the inventive principles of the present disclosure relate to strain sensors 102, 502, 602 that can be sensitive to stimuli in two or more dimensions (e.g., along two different axes) in a manner that can distinguish between stimuli in the different dimensions. For example, a sensor may include two sensing elements, each of which may have an active portion positioned to sense stimuli along a different axis. One or both of the sensing elements may have a cancellation portion that can be configured to cancel the effect of stimuli along the axis of the other sensing element. Such an arrangement may be useful, for example, to cancel out unwanted noise from stimuli in a direction different from the direction being measured.

[0040] Such multi-axis strain sensors 102, 502, 602 can be used to distinguish between inputs in complex systems such as the human body. For example, such a multi-axis sensor system can be used to distinguish between changes in muscle dimension caused by gross motor activity, breathing, and muscle flexion. Furthermore, by way of example, a strain sensor 102, 502, 602 system can include garment-mounted sensing elements that stretch with rib cage expansion and can measure respiration using rib cage expansion. However, other movements, such as torso bending, can also stretch the sensor, leading to potential inaccuracies in respiration measurements. However, if a strain sensor 102, 502, 602 includes one sensing element positioned with its axis perpendicular to the spine and extending around a portion of the rib cage, and a second sensing element positioned with its axis extending parallel to the spine, the sensing system can detect torso bending through deformation of the second sensing element and use the information generated by the deformation of the second sensing element to distinguish between torso bending and respiration. The data generated by the strain sensors 102, 502, 602 ensures that respiration measurements are more accurate by determining what portion of the stretch of the first sensor is not due to respiration.

[0041] As a further example, multi-axial strain sensors 102, 502, 602 can be used to distinguish between different muscle recruitments in a given gross motor motion or between different directions of motion of a mechanical system. Another exemplary application of strain sensors 102, 502, 602 according to the present disclosure is in geotextiles for reinforcing embankments, levee structures, or other earthwork structures, where multi-axial sensors can distinguish between normal settlement and abnormal slumping or shifting that may indicate impending collapse. Other exemplary applications of multi-axial strain sensors 102, 502, 602 according to the present disclosure include, for example, sails for yachts, windsurfers, etc., kites, parachutes, etc. Additional examples include covers / cladding for machinery such as articulating joints, shape memory alloy actuators, etc. Still more examples include inflatable structures such as inflatable struts, tires, balloons, rafts, etc. Further examples include any structure, such as a chassis, frame, housing, etc., that can warp, bend, or otherwise deform in a manner that may be beneficial for sensing and / or measurement.

[0042] The details of the embodiments and exemplary implementations described herein are for illustrative purposes. The drawings are not necessarily drawn to scale. The principles of the present invention are not limited to these embodiments or details. Multiple inventive principles of this patent disclosure may have individual utility and benefits. However, combining the inventive principles described in this disclosure, including those parts incorporated by reference, may allow the individual parts to interact in novel ways to provide synergistic results.

[0043] Conductive compositions, such as conductive gels, included in the articles described herein can have a paste-like or gel-like consistency, which can be made by taking advantage of the structure that gallium oxide can impart to the composition when mixed into a eutectic gallium alloy, among other things. When mixed into a eutectic gallium alloy, gallium oxide can form microstructures or nanostructures, as further described herein, which can alter the bulk material properties of the eutectic gallium alloy.

[0044] As used herein, the term "eutectic" generally refers to a mixture of two or more phases of the composition having the lowest melting point, at which the phases simultaneously crystallize from a molten solution. The ratio of phases to obtain a eutectic is identified by the eutectic point on a phase diagram. One of the characteristics of a eutectic alloy is a sharp melting point.

[0045] The conductive composition can be characterized as a conductive shear-thinning gel composition. The conductive compositions described herein can also be characterized as compositions having the properties of a Bingham plastic. For example, the conductive composition can be a viscoplastic, i.e., rigid at low stress, capable of forming and maintaining three-dimensional features characterized by height and width, and flowing as a viscous fluid at high stress. Thus, for example, the conductive composition can have a viscosity ranging from about 10,000,000 cP to about 40,000,000 cP under low shear and about 150 to 180 cP under high shear. For example, under low shear conditions, the composition can have a viscosity of about 10,000,000 cP, about 15,000,000 cP, about 20,000,000 cP, about 25,000,000 cP, about 30,000,000 cP, about 45,000,000 cP, or about 40,000,000 cP. Under conditions of high shear, the composition has a viscosity of about 150 cP, about 155 cP, about 160 cP, 165 cP, about 170 cP, about 175 cP, or about 180 cP.

[0046] The conductive materials described herein have a conductivity of about 2×10 5 S / m~approx. 8×10 5 It may have any suitable conductivity, such as a conductivity of S / m.

[0047] The conductive compositions described herein can have any suitable melting point, such as a melting point of about -20°C to about 10°C, about -10°C to about 5°C, about -5°C to about 5°C, or about -5°C to about 0°C.

[0048] The conductive composition can comprise a mixture of a eutectic gallium alloy and gallium oxide, the mixture of eutectic gallium alloy and gallium oxide having a weight percentage (wt%) of eutectic gallium alloy between about 59.9% and about 99.9%, such as between about 67% and about 90%, and a wt% of gallium oxide between about 0.1% and about 2.0%, such as between about 0.2% and about 1%. For example, the conductive composition may be about 60%, about 61%, about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, about 100%, about 101%, about 102%, about 103%, about 104%, about 105%, about 106%, about 107%, about 108%, about 109%, about 110%, about 111%, about 112%, about 113%, about 114%, about 115%, about 116%, about 117%, about 118%, about 119%, about 120%, about 121%, about 122%, about 123%, about 124%, about 125%, about 126%, about 127%, about 128%, about 129%, about 130%, about 131%, about 132%, about 133%, about 134%, about 135%, about 136%, about 137%, about 138%, about 139%, about 140%, about 141%, about 142%, about 143%, about 144%, about 145%, about 146%, about 147%, about 148%, about 149%, about 1 The eutectic gallium alloy may have about 5%, about 96%, about 97%, about 98%, about 99%, or more, for example, about 99.9%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1.0%, about 1.1%, about 1.2%, about 1.3%, about 1.4%, about 1.5%, about 1.6%, about 1.7%, about 1.8%, about 1.9%, and about 2.0% gallium oxide.

[0049] Eutectic gallium alloys can include gallium-indium or gallium-indium-tin in any ratio of elements. For example, eutectic gallium alloys include gallium and indium. The conductive composition can have any suitable weight percent of gallium in the gallium-indium alloy, such as about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, about 60%, about 61%, about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, about 100%, about 101%, about 102%, about 103%, about 104%, about 105%, about 106%, about 107%, about 108%, about 109%, about 110%, about 111%, about 112%, about 113%, about 114%, about 115%, about 116%, about 117%, about 118%, about 119%, about 120%, about 12 about 40% to about 95%, such as about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, or about 95%.

[0050] The conductive composition can have a weight percent of indium in the gallium-indium alloy of about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, about 60%, about 61%, about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, about 100%, about 101%, about 102%, about 5% to about 60%, such as 4%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, or about 60%.

[0051] Eutectic gallium alloys can include gallium and tin. For example, the conductive composition can have a weight percent of tin in the alloy, which can be about 0.001%, about 0.005%, about 0.01%, about 0.05%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 1.5%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about From about 0.001% to about 50%, such as 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, or about 50%.

[0052] The conductive composition can include one or more microparticles or submicron-scale particles blended with a eutectic gallium alloy and gallium oxide. The particles can be coated with a eutectic gallium alloy or gallium, encapsulated with gallium oxide, or uncoated and suspended in the eutectic gallium alloy. The micro- or submicron-scale particles can range in size from nanometers to micrometers and be suspended in the gallium, gallium-indium alloy, or gallium-indium-tin alloy. The ratio of particles to alloy can be varied to change the flow characteristics of the conductive composition. Microstructures and nanostructures can be incorporated into the conductive composition by sonication or other suitable means. The conductive composition can include a colloidal suspension of microstructures and nanostructures in a eutectic gallium alloy / gallium oxide mixture.

[0053] The conductive composition may further include one or more microparticles or submicron-scale particles dispersed within the composition. This can be achieved by any suitable method, including suspending particles coated with eutectic gallium alloy or gallium, encapsulated with gallium oxide, or uncoated particles within the conductive composition, or particularly within a eutectic gallium alloy fluid. These particles range in size from nanometers to micrometers and can be suspended in gallium, gallium-indium alloy, or gallium-indium-tin alloy. The ratio of particles to alloy can be varied, particularly to change the fluid properties of at least one of the alloy and the conductive composition. Additionally, optional auxiliary materials can be added to the colloidal suspension or eutectic gallium alloy, particularly to enhance or modify its physical, electrical, or thermal properties. The distribution of microstructures and nanostructures within at least one of the eutectic gallium alloy and the conductive formulation can be achieved by any suitable method, including ultrasonication or other mechanical means, without the addition of particles. In certain embodiments, one or more microparticles or submicron particles are mixed with at least one of a eutectic gallium alloy and a conductive composition, wherein the wt% of the microparticles is between about 0.001% and about 40.0%, for example, about 0.001%, about 0.005%, about 0.01%, about 0.05%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 1.5%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, or about 10%. about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, or about 40%.

[0054] The one or more micron or submicron particles can be made of any suitable material, including soda glass, silica, borosilicate glass, quartz, copper oxide, silver-coated copper, non-oxide copper, tungsten, supersaturated tin granules, glass, graphite, silver-coated copper, such as silver-coated copper spheres and silver-coated copper flakes, copper flakes, or copper spheres, or combinations thereof, or any other material that can be wetted by at least one of the eutectic gallium alloy and the conductive composition. The one or more microparticles or submicron-scale particles can have any suitable shape, including spheroids, rods, tubes, flakes, plates, cubes, prisms, pyramids, cages, and dendrimer shapes. The one or more microparticles or submicron-scale particles may be of any suitable size, including a size range of about 0.5 microns to about 60 microns, such as about 0.5 microns, about 0.6 microns, about 0.7 microns, about 0.8 microns, about 0.9 microns, about 1 micron, about 1.5 microns, about 2 microns, about 3 microns, about 4 microns, about 5 microns, about 6 microns, about 7 microns, about 8 microns, about 9 microns, about 10 microns, about 11 microns, about 12 microns, about 13 microns, about 14 microns, about 15 microns, about 16 microns, about 17 microns, about 18 microns, about 19 microns, about 20 microns, about 21 microns, about 22 microns, about 23 microns, about 24 microns, The thickness can be about 25 microns, about 26 microns, about 27 microns, about 28 microns, about 29 microns, about 30 microns, about 31 microns, about 32 microns, about 33 microns, about 34 microns, about 35 microns, about 36 microns, about 37 microns, about 38 microns, about 39 microns, about 40 microns, about 41 microns, about 42 microns, about 43 microns, about 44 microns, about 45 microns, about 46 microns, about 47 microns, about 48 microns, about 49 microns, about 50 microns, about 51 microns, about 52 microns, about 53 microns, about 54 microns, about 55 microns, about 56 microns, about 57 microns, about 58 microns, about 59 microns, or about 60 microns.

[0055] The conductive compositions described herein can be made by any suitable method, including mixing a surface oxide formed on the surface of a eutectic gallium alloy into the bulk of the eutectic gallium alloy by shear mixing of the surface oxide / alloy interface. Shear mixing of such compositions can form a conductive shear-thinning gel composition by inducing cross-sectional microstructures in the surface oxide. A colloidal suspension of the microstructures can be formed within the eutectic gallium alloy / gallium oxide mixture, for example, as gallium oxide particles and / or sheets.

[0056] The surface oxide can be mixed in any suitable ratio, such as a ratio between about 59.9% (by weight) and about 99.9% eutectic gallium alloy and about 0.1% (by weight) and about 2.0% gallium oxide. For example, the weight percentage of the gallium alloy mixed with gallium oxide may be about 60%, 61%, about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, The eutectic gallium alloy may be about 95%, about 96%, about 97%, about 98%, about 99%, or more (e.g., about 99.9%) eutectic gallium alloy, while the weight percentage of gallium oxide is about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1.0%, about 1.1%, about 1.2%, about 1.3%, about 1.4%, about 1.5%, about 1.6%, about 1.7%, about 1.8%, about 1.9%, and about 2.0% gallium oxide. In embodiments, the eutectic gallium alloy may include gallium-indium or gallium-indium-tin in any ratio of the listed elements. For example, the eutectic gallium alloy may include gallium and indium.

[0057] The weight percentage of gallium in the gallium-indium alloy is about 40% to about 95%, for example, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, about 60%, about 61%, about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, about 100%, about 101%, about 102%, about 103%, about 104%, about 105%, about 106%, about 107%, about 108%, about 109%, about 110%, about 111%, about 112%, about 113%, about 114%, about 115%, about 116%, about 117%, about 118%, about 119%, about 120%, about 121%, about 122%, about 123%, about 124%, about 125%, about 126%, about 127%, about 128%, about 129 %, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, or about 95%.

[0058] Alternatively or additionally, the weight percentage of indium in the gallium-indium alloy is about 5% to about 60%, for example, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, It can be about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, or about 60%.

[0059] The eutectic gallium alloy can include gallium, indium, and tin. The weight percentage of tin in the gallium-indium-tin alloy can be about 0.001% to about 50%, for example, about 0.001%, about 0.005%, about 0.01%, about 0.05%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 1.5%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about It can be 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, or about 50%.

[0060] The weight percentage of gallium in the gallium-indium-tin alloy is about 40% to about 95%, for example, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, about 60%, about 61%, about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99%, about 100%, about 101%, about 102%, about 103%, about 104%, about 105%, about 106%, about 107%, about 108%, about 109%, about 110%, about 111%, about 112%, about 113%, about 114%, about 115%, about 116%, about 117%, about 118%, about 119%, about 120%, about 121%, about 122%, about 123%, about 124%, about 125%, about 126%, about 127%, about 128%, about 1 It can be 4%, about 65%, about 66%, about 67%, about 68%, about 69%, about 70%, about 71%, about 72%, about 73%, about 74%, about 75%, about 76%, about 77%, about 78%, about 79%, about 80%, about 81%, about 82%, about 83%, about 84%, about 85%, about 86%, about 87%, about 88%, about 89%, about 90%, about 91%, about 92%, about 93%, about 94%, or about 95%.

[0061] Alternatively or additionally, the weight percentage of indium in the gallium-indium-tin alloy is about 5% to about 60%, for example, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%. , about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, or about 60%.

[0062] One or more microparticles or submicron-scale particles can be mixed with the eutectic gallium alloy and gallium oxide. For example, one or more microparticles or submicron particles can be mixed in the mixture. The wt% of the microparticles in the composition can be about 0.001% to about 40.0%, for example, about 0.001%, about 0.005%, about 0.01%, about 0.05%, about 0.1%, about 0.2%, about 0.3%, about 0.4%, about 0.5%, about 0.6%, about 0.7%, about 0.8%, about 0.9%, about 1%, about 1.5%, about 2%, about 3%, about 4%, about 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 12%, about 13%, about 14%, about 15%, about 16%, about 17%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, about 40%, about 41%, about 42%, about 43%, about 44%, about 45%, about 46%, about 47%, about 48%, about 49%, about 50%, about 51%, about 52%, about 53%, about 54%, about 55%, about 56%, about 57%, about 58%, about 59%, about 60%, about 61%, about 62%, about 63%, about 64%, about 65%, about 66%, about 67%, about 68%, about 18%, about 19%, about 20%, about 21%, about 22%, about 23%, about 24%, about 25%, about 26%, about 27%, about 28%, about 29%, about 30%, about 31%, about 32%, about 33%, about 34%, about 35%, about 36%, about 37%, about 38%, about 39%, or about 40%. In embodiments, the particles can be soda glass, silica, borosilicate glass, quartz, copper oxide, silver-coated copper, non-copper oxide, tungsten, supersaturated tin granules, glass, graphite, silver-coated copper such as silver-coated copper spheres and silver-coated copper flakes, copper flakes or copper spheres, or combinations thereof, or any other material that can be wetted by gallium. In some embodiments, the one or more microparticles or submicron-scale particles are in the shape of a spheroid, a rod, a tube, a flake, a plate, a cube, a prism, a pyramid, a cage, and a dendrimer.In certain embodiments, the one or more microparticles or submicron-scale particles are in the size range of about 0.5 microns to about 60 microns, about 0.5 microns, about 0.6 microns, about 0.7 microns, about 0.8 microns, about 0.9 microns, about 1 micron, about 1.5 microns, about 2 microns, about 3 microns, about 4 microns, about 5 microns, about 6 microns, about 7 microns, about 8 microns, about 9 microns, about 10 microns, about 11 microns, about 12 microns, about 13 microns, about 14 microns, about 15 microns, about 16 microns, about 17 microns, about 18 microns, about 19 microns, about 20 microns, about 21 microns, about 22 microns, about 23 microns, about 24 microns, about 25 microns, about 26 microns, about 27 microns, about 28 microns, about 29 microns, about 30 microns, about 31 microns, about 32 microns, about 33 microns, about 34 microns, about 35 microns, about 36 microns, about 37 microns, about 38 microns, about 39 microns, about 40 microns, about 41 microns, about 42 microns, about 43 microns, about 44 microns, about 45 microns, about 46 microns, about 47 microns, about 48 microns, about 49 microns, about 50 microns, about 51 microns, about 52 microns, about 53 microns, about 54 microns, about 55 microns, about 56 microns, about 57 microns, about 58 microns, about 59 microns, about 60 microns, about 61 microns, about 62 micro about 25 microns, about 26 microns, about 27 microns, about 28 microns, about 29 microns, about 30 microns, about 31 microns, about 32 microns, about 33 microns, about 34 microns, about 35 microns, about 36 microns, about 37 microns, about 38 microns, about 39 microns, about 40 microns, about 41 microns, about 42 microns, about 43 microns, about 44 microns, about 45 microns, about 46 microns, about 47 microns, about 48 microns, about 49 microns, about 50 microns, about 51 microns, about 52 microns, about 53 microns, about 54 microns, about 55 microns, about 56 microns, about 57 microns, about 58 microns, about 59 microns, or about 60 microns.

[0063] Example

[0064] Example 1 is a flexible differential strain sensor comprising: a deformable substrate having a first axis and a second axis different from the first axis; a first sensing element comprising a conductive gel arranged to sense strain in the deformable substrate along the first axis; and a second sensing element comprising a conductive gel having a first portion arranged to sense strain in the deformable substrate along the first axis and a second portion arranged to sense strain in the deformable substrate along the second axis, wherein the second sensing element is arranged to cancel at least a portion of a stimulus sensed by the first sensing element along the first axis.

[0065] In Example 2, the subject matter of Example 1 includes wherein an electrical impedance of the conductive gel of the first and second sensing elements changes in response to a change in strain on the deformable substrate, and the first and second sensing elements are configured to sense the strain based at least in part on the change in impedance.

[0066] In Example 3, the subject matter of Example 2 includes a signal processing unit operatively coupled to the first sensing element and the second sensing element and configured to determine strain along the first axis by subtracting a change in impedance from the second sensing element from a change in impedance from the first sensing element.

[0067] In Example 4, the subject matter of Example 3 includes the signal processing unit further configured to determine strain along a second axis based on a change in impedance from the first sensing element.

[0068] In Example 5, the subject matter of Example 4 includes wherein the signal processing unit is further configured to output vectors indicative of distortion along the first axis and along the second axis.

[0069] In Example 6, the subject matter of Example 5 includes the vector indicating a rate of change of strain on the deformable substrate relative to an initial strain.

[0070] In Example 7, the subject matter of Example 6 includes the rate of change of the strain corresponding to the rate of change of the deformation of the deformable substrate.

[0071] In Example 8, the subject matter of Examples 2-7 includes the first axis being orthogonal to the second axis, the deformable substrate further having a third axis orthogonal to the first and second axes, and further comprising a third sensing element comprising a conductive gel positioned to sense strain in the deformable substrate along at least the third axis.

[0072] In Example 9, the subject matter of Examples 1-8 includes the first sensing portion including a first active portion, the second sensing portion including a second active portion and a cancellation portion, and the first active portion, the second active portion, and the cancellation portion each including a variable impedance based at least in part on a strain applied to the respective first active portion, second active portion, and cancellation portion.

[0073] In Example 10, the subject matter of Examples 1-9 includes, wherein the deformable substrate is configured to be attached to a structure to determine a strain on the structure.

[0074] Example 11 describes a method of making a flexible differential strain sensor, comprising: obtaining a deformable substrate having a first axis and a second axis different from the first axis; disposing on the deformable substrate a first sensing element including a conductive gel for sensing strain in the deformable substrate along the first axis; and disposing on the deformable substrate a second sensing element including the conductive gel having a first portion for sensing strain in the deformable substrate along the first axis and a second portion disposed for sensing strain in the deformable substrate along the second axis, wherein the second sensing element is disposed to cancel at least a portion of a stimulus sensed by the first sensing element along the first axis.

[0075] In Example 12, the subject matter of Example 11 includes wherein an electrical impedance of the conductive gel of the first and second sensing elements changes in response to a change in strain on the deformable substrate, and the first and second sensing elements are configured to sense the strain based at least in part on the change in impedance.

[0076] In Example 13, the subject matter of Example 12 further includes operably coupling a signal processing unit to the first sensing element and the second sensing element, wherein the signal processing unit is configured to determine the strain along the first axis by subtracting a change in impedance from the second sensing element from a change in impedance from the first sensing element.

[0077] In Example 14, the subject matter of Example 13 includes the signal processing unit further configured to determine strain along the second axis based on a change in impedance from the first sensing element.

[0078] In Example 15, the subject matter of Example 14 includes, wherein the signal processing unit is further configured to output vectors indicative of distortion along the first axis and along the second axis.

[0079] In Example 16, the subject matter of Example 15 includes the vector indicating a rate of change of strain on the deformable substrate relative to an initial strain.

[0080] In Example 17, the subject matter of Example 16 includes wherein the rate of change of the strain corresponds to the rate of change of the deformation of the deformable substrate.

[0081] In Example 18, the subject matter of Examples 12-17 includes, wherein the first axis is orthogonal to the second axis, and the deformable substrate further has a third axis orthogonal to the first and second axes, and further including disposing a third sensing element on the deformable substrate, the third sensing element including a conductive gel, to sense strain in the deformable substrate along at least the third axis.

[0082] In Example 19, the subject matter of Examples 11-18 includes, wherein the first sensing portion includes a first active portion, the second sensing portion includes a second active portion and a cancellation portion, and wherein the first active portion, the second active portion, and the cancellation portion each include a variable impedance based at least in part on a strain applied to the respective first active portion, second active portion, and cancellation portion.

[0083] In Example 20, the subject matter of Examples 11-19 includes, wherein the deformable substrate is configured to be attached to a structure to determine strain on the structure.

[0084] Example 21 is at least one machine-readable medium comprising instructions that, when executed by a processing circuit, cause the processing circuit to perform the operations of any of Examples 1-20.

[0085] Example 22 is an apparatus including means for carrying out any one of Examples 1 to 20.

[0086] The twenty-third embodiment is a system for implementing any one of the first to twentieth embodiments.

[0087] Example 24 is a method using any one of Examples 1 to 20.

[0088] Some portions of this specification are presented in terms of algorithms or symbolic representations of operations on data stored as bits or binary digital signals in a machine memory (e.g., computer memory). These algorithms or symbolic representations are examples of techniques used by those skilled in the data processing arts to convey the substance of their work to others skilled in the art. An "algorithm," as used herein, is a self-consistent sequence of operations or similar processes leading to a desired result. In this context, algorithms and operations involve physical manipulations of physical quantities. Typically, though not necessarily, such quantities may take the form of electrical, magnetic, or optical signals capable of being stored, accessed, transferred, combined, compared, and otherwise manipulated by a machine. It is sometimes convenient, primarily for reasons of common usage, to refer to such signals using terms such as "data," "content," "bits," "values," "elements," "symbols," "characters," "terms," ​​"digits," "numbers," etc. However, these terms are merely convenient labels and should be associated with the appropriate physical quantities.

[0089] Unless otherwise noted, descriptions herein using terms such as "processing," "computing," "calculating," "determining," "presenting," "displaying," etc. may refer to machine (e.g., computer) actions or processes that manipulate or transform data represented as physical (e.g., electronic, magnetic, or optical) quantities in one or more memories (e.g., volatile memory, non-volatile memory, or any suitable combination thereof), registers, or other mechanical components that receive, store, transmit, or display information. Furthermore, unless otherwise noted, the terms "a" or "an" are used herein, as is common in patent documents, to include one or more instances. Finally, the term "or" as used herein refers to a non-exclusive "or" unless otherwise noted.

Claims

1. a deformable substrate having a first axis and a second axis different from the first axis; a first sensing element comprising a conductive gel positioned to sense strain in the deformable substrate along the first axis; a second sensing element comprising a conductive gel having a first portion positioned to sense strain in the deformable substrate along the first axis and a second portion positioned to sense strain in the deformable substrate along the second axis; the second sensing element is positioned such that the first portion of the second sensing element is proximate to the first sensing element to cancel at least a portion of the strain sensed by the first sensing element along the first axis.

2. 10. The flexible strain sensor of claim 1, wherein an electrical impedance of the conductive gel of the first and second sensing elements changes in response to a change in strain on the deformable substrate, and the first and second sensing elements are configured to sense the strain based at least in part on the change in impedance.

3. 3. The flexible strain sensor of claim 2, further comprising a signal processing unit operatively coupled to the first sensing element and the second sensing element and configured to determine the strain along the first axis by subtracting a change in impedance from the first sensing element from a change in impedance from the second sensing element.

4. The flexible strain sensor of claim 3 , wherein the signal processing unit is further configured to determine the strain along the second axis based on a change in impedance from the first sensing element.

5. The flexible strain sensor of claim 4 , wherein the signal processing unit is further configured to output a vector indicative of the strain along the first axis and along the second axis.

6. The flexible strain sensor of claim 5 , wherein the vector indicates a rate of change of strain on the deformable substrate relative to an initial strain.

7. The flexible strain sensor of claim 6 , wherein the rate of change of the strain corresponds to the rate of change of the deformation of the deformable substrate.

8. the first axis is orthogonal to the second axis, and the deformable substrate further has a third axis orthogonal to the first and second axes; The flexible strain sensor of claim 2 , further comprising a third sensing element comprising a conductive gel positioned to sense strain in the deformable substrate along at least the third axis.

9. the first sensing element includes a variable impedance based at least in part on a strain applied to the first sensing element; the second portion of the second sensing element includes a variable impedance based at least in part on a strain applied to the second portion of the second sensing element; The flexible strain sensor of claim 1 , wherein the first portion of the second sensing element comprises a variable impedance based at least in part on a strain applied to the first portion of the second sensing element.

10. The flexible strain sensor of claim 1 , wherein the deformable substrate is configured to be attached to a structure to determine strain on the structure.

11. obtaining a deformable substrate having a first axis and a second axis different from the first axis; disposing a first sensing element on the deformable substrate, the first sensing element including a conductive gel for sensing strain in the deformable substrate along the first axis; disposing a second sensing element on the deformable substrate, the second sensing element comprising a conductive gel having a first portion for sensing strain in the deformable substrate along the first axis and a second portion disposed for sensing strain in the deformable substrate along the second axis; 1. A method of making a flexible strain sensor, wherein the second sensing element is positioned such that the first portion of the second sensing element is proximate to the first sensing element to cancel at least a portion of the strain sensed by the first sensing element along the first axis.

12. 12. The method of claim 11, wherein an electrical impedance of the conductive gel of the first and second sensing elements changes in response to a change in strain on the deformable substrate, and the first and second sensing elements are configured to sense the strain based at least in part on the change in impedance.

13. 13. The method of claim 12, further comprising operably coupling a signal processing unit to the first sensing element and the second sensing element, the signal processing unit configured to determine the strain along the first axis by subtracting a change in impedance from the first sensing element from a change in impedance from the second sensing element.

14. The method of claim 13 , wherein the signal processing unit is further configured to determine the strain along the second axis based on a change in impedance from the first sensing element.

15. The method of claim 14 , wherein the signal processing unit is further configured to output vectors indicative of the distortion along the first axis and along the second axis.

16. The method of claim 15 , wherein the vector represents a rate of change of strain on the deformable substrate relative to an initial strain.

17. The method of claim 16 , wherein the rate of change of the strain corresponds to the rate of change of the deformation of the deformable substrate.

18. the first axis is orthogonal to the second axis, and the deformable substrate further has a third axis orthogonal to the first and second axes; 13. The method of claim 12, further comprising disposing a third sensing element comprising a conductive gel on the deformable substrate to sense strain in the deformable substrate along at least the third axis.

19. the first sensing element includes a variable impedance based at least in part on a strain applied to the first sensing element; the second portion of the second sensing element includes a variable impedance based at least in part on a strain applied to the second portion of the second sensing element; The method of claim 11 , wherein the first portion of the second sensing element includes a variable impedance based at least in part on a strain applied to the first portion of the second sensing element.

20. The method of claim 11 , wherein the deformable substrate is configured to be attached to a structure to determine strain on the structure.

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