Multi-axis differential strain sensor

Abstract

A flexible differential strain sensor, system, and method include 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 sensing element and the second sensing element include a conductive gel. The first sensing element is arranged to sense strain in the deformable substrate along the first axis. The second sensing element has 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. The second sensing element is arranged to cancel at least a portion of a stimulus along the first axis sensed by the first sensing element.

Description

[0001] Cross-references to related applications

[0002] This patent application claims the benefit of priority to U.S. Provisional Application Serial No. 63 / 038,547, filed June 12, 2020, which is incorporated herein by reference in its entirety. background

[0003] Strain sensors measure mechanical or other physical stimuli, such as strain on a substrate on which the strain sensor is placed. Deformations transmitted to the substrate of the strain sensor, such as tension, torsion, or deflection, can change some physical properties of the strain sensor. These changes in physical properties can be converted into strain and used to identify how the strain changes over time. Attached Figure Description

[0004] To facilitate the identification of any particular element or action in discussion, one or more of the highest significant digits in the figure references refer to the figure number in which the element was first introduced.

[0005] Figure 1 This is a block diagram of the flexible differential strain sensor in the example embodiment.

[0006] Figure 2 This is the topology of the flexible differential strain sensor in the example embodiment.

[0007] Figure 3 This is an electrical equivalent schematic diagram of the flexible differential strain sensor in the example embodiment.

[0008] Figure 4A and Figure 4B An abstract representation of the process by which a topology for a flexible differential strain sensor can be formed is shown in the example embodiment.

[0009] Figure 5 This is a block diagram of the flexible differential strain sensor in the example embodiment.

[0010] Figure 6 This is the topology of the three-dimensional flexible differential strain sensor in the example embodiment. Detailed description

[0011] For example, a flexible strain sensor has been disclosed in U.S. Patent Application Publication No. 2018 / 0247727 (“727 application”), published on August 30, 2018, which is incorporated herein by reference in its entirety. The 727 application discloses, for example, methods, apparatus, and exemplary embodiments for strain sensing using a deformable conductor (e.g., conductive gel) in Figures 7-10 and paragraphs

[0014] to

[0017] and

[0089] to

[0120] . As disclosed in the 727 application, the sensor system includes sensor elements that respond to stimuli by changing size (e.g., stretching). Examples disclosed in the 727 application, such as in paragraph

[00116] , may include a pattern of variable resistor meshes and / or unconnected or sparsely connected networks of variable resistors.

[0012] This paper discloses a flexible differential strain sensor that can be used to measure and distinguish stimuli occurring in two or more dimensions (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 specific axis of a substrate. Therefore, such a flexible differential strain sensor can provide relatively enhanced sensitivity to the nature of the strain on the substrate and / or the strain sensor.

[0013] Figure 1 This is a block diagram of a flexible differential strain sensor in an example embodiment. The flexible differential strain sensor 102 is configured to detect strain on a deformable substrate 104, and particularly strain along the X and Y axes of the deformable substrate 104. The deformable substrate 104 can be any object on or within which the conductive gel disclosed herein can be positioned and typically fixed. The deformable substrate 104 can be or may include natural and synthetic fibers, natural or synthetic rubber, elastomers, etc. Furthermore, in various alternative examples, the flexible differential strain sensor 102 can be implemented on a substrate designed to deform relatively little (if deformation is necessary), but allowing the flexible differential strain sensor 102 to detect potentially unwanted strain or deformation on the substrate. For example, the substrate can be metal, carbon fiber, etc., and the flexible differential strain sensor 102 can typically be used to identify strain on such structures. However, in various examples, the flexible differential strain sensor 102 is implemented with a deformable substrate 104, in which case the flexible differential strain sensor 102 with the deformable substrate 104 can be placed on and fixed to such a structure that can be deformed relatively little in order to determine the strain on such a structure.

[0014] For illustrative purposes, the deformable substrate 104 is effectively presented as a two-dimensional object, wherein strain is applied on one or both of the X and Y axes and detected by a component extending exactly along one of the X and Y axes. However, it should be recognized and understood that the component can be positioned at an angle to the X and Y axes, and conventional mathematical methods can be used to compensate for or otherwise account for angular differences relative to the X and Y axes. Furthermore, strain can be applied to the deformable substrate 104 on the Z axis, which is orthogonal to the X and Y axes, and the flexible differential strain sensor 102 can be sensitive to this strain. Moreover, as will be shown herein, the principles illustrated in the two-dimensional example can be applied to a three-dimensional example, where the strain sensor is positioned along the Z axis of the deformable substrate 104 and configured to directly sense the strain applied on the Z axis.

[0015] The flexible differential strain sensor 102 may include a first sensing element 106 having a first active portion 108 arranged to sense strain along the Y-axis (e.g., a first 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 cancelling portion 116, wherein a second terminal 118 provides an electrical output from the second sensing element 112. The second active portion 114 may be positioned on a deformable substrate 104 to sense strain along the X-axis (e.g., a second axis), and the cancelling portion 116 may be positioned on the deformable substrate 104 to logically or mathematically cancel the strain along the Y-axis detected by the first active portion 108 of the first sensing element 106. Thus, the first sensing element 106 may be sensitive to strain on the Y-axis but less sensitive or insensitive to strain on the X-axis. Conversely, the second sensing element 112 may be sensitive to strain applied on both the X-axis and Y-axis. In some examples, by arranging the offset portion 116 to be physically close to the first active portion 108, the offset portion 116 is subjected to the same or nearly the same strain along the Y-axis as the first active portion 108.

[0016] In various examples, both the first sensing element 106 and the second sensing element 112 are formed of conductive gel, as disclosed herein. The conductive gel can be positioned on or within the deformable substrate 104 by any suitable process, including printing, dispersing into filaments and voids of the deformable substrate 104, etc. The conductive gel can be implemented as one or more electrical traces configured to conduct current along the traces. The electrical properties of the conductive gel can change as the conductive gel stretches, contracts, or otherwise deforms (e.g., as strain is applied to the deformable substrate 104 and by extension). In various examples, the impedance (or more narrowly, resistance) of a given trace of the conductive gel can increase or decrease as the trace stretches, contracts, or otherwise deforms. This change in the resistance of the trace can correspond to the amount of strain applied to the deformable substrate 104 near the trace. Therefore, the first active portion 108, the second active portion 114, and the canceling portion 116 can be understood as specific portions of the conductive gel along a corresponding extended electrical trace along the X and Y axes of the deformable substrate 104. Although the impedance and / or other electrical properties of the conductive gel may change with deformation, it is significantly less brittle and less likely to break compared to conventional conductors used in electronic devices, and is significantly more elastic.

[0017] The two signals, Y1 at the first terminal 110 and X1 at the second terminal 118, can form an output vector from the flexible differential strain sensor 102 to recover and / or represent the strain field applied to the deformable substrate 104 and typically to the flexible differential strain sensor 102. The output vector can be processed in any suitable manner. For example, in some applications, the original signals X1 and Y1 can be processed by the signal processing unit 120 to determine and output the strain applied along the Y-axis as output signal Y2, and to determine and output the strain applied along the X-axis as output signal X2. The signal processing unit 120 may include an ohmmeter or other instrument for determining the impedance at terminals 110, 118, and a processor or other computational electronics that can convert impedance or impedance changes into strain on the flexible differential strain sensor 102 or otherwise correlate it with strain on the flexible differential strain sensor 102. For example, in an example implementation, a change of 0.03 ohms in impedance and / or resistance detected by signal processing unit 120 corresponds to a strain of one (1) millimeter on the conductive gel of flexible differential strain sensor 102 and on the trace formed by the conductive gel, as disclosed herein. In various examples, strain can be understood as a change in total length, although it should be recognized and understood that any feasible strain measure known in the art may be used additionally or alternatively.

[0018] Because Y1 is significantly sensitive to strain on the Y-axis due to the presence of the first active portion 108, but not a trace extending generally along the X-axis like the second active portion 114, the signal processing unit 120 can calculate the strain on the Y-axis by relating the impedance change of the first active portion 108 to the strain on the Y-axis, and output the resulting strain as Y2. In various examples, the signal processing unit 120 may simply buffer or transmit the signal Y1 as the output signal Y2 to provide an indication of the strain, and a remote processing unit, controller, or other electronic device may perform the operation of relating the impedance change to the strain on the flexible differential strain sensor 102.

[0019] Conversely, since the second sensing element 112 includes significant sensitivity to strain on both the X and Y axes, the signal processing unit 120 can generate an output signal X2 by subtracting the impedance change from the Y1 from the impedance change from X1. This output signal X2 indicates the strain applied along the X-axis of the second sensing element 112. Therefore, the signal processing unit 120 determines different sensitivities to impedance, which essentially cancels out the strain applied along the Y-axis to the first active portion 108 and the cancelling portion 116, making X2 primarily or entirely based on the impedance change along the second active portion 114. It should be recognized and understood that, for the purposes of this disclosure, although the first active portion 108 and the cancelling portion 116 can be placed very close to each other and formed by conductive gel traces having very similar properties, variations in the actual positioning of the conductive gel can cause a range of errors between the impedance changes of the first active portion 108 and the cancelling portion 116, which can propagate through differential calculations of the strain output at X2 on the X-axis. However, it should be recognized and understood that even if the output X2 does not completely eliminate the influence of strain on the Y-axis, this small error range can still produce a useful and accurate representation of strain on the X-axis. The same principle applies to the output Y2.

[0020] As described above, any processing of the output vector can be implemented in a manner tailored to the specific application. Typically, sensing elements can be arranged as a grid or array that can be partially and / or fully connected. These elements can generate an output vector of values ​​that can be analyzed to provide a representation of the strain field on the deformable substrate 104, measured individually or in combination with other sensors by the flexible differential strain sensor 102. The interpretation of the strain field can be application-based, and some examples of applications are described below.

[0021] In other embodiments, the flexible differential strain sensor 102 can be arranged in other configurations and use different numbers and / or types of sensing elements, active regions, and / or cancellation regions, etc. For example, sensing elements can be arranged in T-shapes, U-shapes, S-shapes, box shapes, etc. Different elements and / or regions can be arranged at angles other than right angles (e.g., acute and / or obtuse angles). Sensing elements can be incorporated into any arbitrary pattern, and signal processing can be adapted to different patterns. In some embodiments, signal processing can extract a composite signal indicating a stimulus in one dimension while canceling strain in one or more other dimensions and / or axes. These principles can be applied to the flexible differential strain sensor 102 having any number of elements, each element having any number of portions (active portions and / or cancellation portions), for any type of stimulus, such as motion, stress, strain, etc.

[0022] Figure 2 This is the topology of the flexible differential strain sensor 102 in the example embodiment. Specifically, this topology shows conductive gel traces 202. The traces 202 are generally positioned on the deformable substrate 104 (not shown) as illustrated to generate... Figure 1 The flexible differential strain sensor 102 is shown. The trace 202 includes Y-axis portions 204a, 204b, 204c, and 204d (these portions can be understood as the general Y-axis extensions of trace 202), and X-axis portions 206a, 206b, and 206c extending 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.

[0023] Trace 202 is coupled to or otherwise forms first node 208, second node 210, and third node 212. First node 208 and second node 210 typically describe the Y1 signal and are defined by portions 204a, 206a, and 204b. Second node 210 and third node 212 typically describe the X1 signal and are defined by portions 204b, 206b, 204d, 206c, and 204c. Therefore, it should be recognized that, in terms of the actual topology, both signals X1 and Y1 are at least partially affected by the Y-axis portion 204b of trace 202, and variations in impedance along the Y-axis portion 204b can cause variations in impedance to both X1 and Y1.

[0024] Figure 3This is an electrical equivalent schematic diagram of the flexible differential strain sensor 102 in an example embodiment. The electrical equivalent schematic diagram includes a first rheostat 302 corresponding to a first active portion 108, a second rheostat 304 corresponding to a second active portion 114, and a third rheostat 306 corresponding to a cancellation portion 116, all of which are located on the deformable substrate 104. The electrical equivalent schematic diagram also includes a first logic node 308 and a second logic node 310 across which a signal Y1 is generated; and a third logic node 312 and a fourth logic node 314 across which a signal X1 is generated. Although rheostats are discussed herein, it should be recognized and understood that rheostats provide variable impedance typically generated by deformation of trace 202, and not merely resistance in the narrow sense.

[0025] Note and emphasize, Figure 3 The electrical equivalent diagram is Figure 2 The product of the topological structure. Therefore, the first rheostat 302 illustrates the variable impedance generated by the deformation of the trace 202 along the Y-axis portions 204a, X-axis portions 206a, and Y-axis portions 204b. In an example where the X-axis portion 206a is very short (e.g., 100 micrometers or less), while the Y-axis portions 204a and 204b are each multiple millimeters or centimeters long, the first rheostat 302 can represent the change in impedance corresponding to those portions of the trace 202 (and, by association, the change in strain applied along the Y-axis). Similarly, the second rheostat 304 can correspond to the X-axis portions 206b and 206c, and the third rheostat 306 can correspond to the Y-axis portions 204b, 204c, and 204d. Furthermore, the first logical node 308 can correspond to the first node 208, the second logical node 310 and the third logical node 312 can correspond to the second node 210, and the fourth logical node 314 can correspond to the third node 212.

[0026] However, it should be recognized and understood that the principle of the electrical equivalent diagram can be obtained through any suitable arrangement of electrical components and is not limited to any particular topology or any particular electrical component. Therefore, various examples of the flexible differential strain sensor 102 are not necessarily implemented using conductive gel; in this respect, alternative components can be utilized that change impedance according to local strain on the deformable substrate 104 and / or on the component itself. Similarly, as Figure 1The flexible differential strain sensor 102 shown can be implemented within the feasible range of alternative mechanisms without considering variable impedance. However, compared to potential alternative components, the implementation of the flexible differential strain sensor 102 with conductive gel offers advantages in terms of electrical and mechanical simplicity, robustness, resilience, and cost. These advantages can be seen in both the use of the flexible differential strain sensor 102 and in its manufacturing process.

[0027] Figure 4A and Figure 4B The example embodiment illustrates how it can be formed therefrom Figure 2 An abstract representation of the topological structure of the flexible differential strain sensor 102. Figure 4A In the process, a mesh of conductive gel is formed, including a portion 402 aligned with the Y-axis, a portion 404 aligned with the X-axis, and nodes 208, 210, 212, and a fourth node 406. Figure 4B In the diagram, certain portions 402, 404 of the mesh are removed, for example, by cutting or otherwise breaking them off from the remainder of the conductive gel trace 202, as shown by the dashed lines. The remaining portions (i.e., the solid lines) correspond to... Figure 2 The topology shows trace 202 and its constituent parts 204 and 206. Therefore, the fourth node 406 is also removed and is inoperable. Although provided as an example... Figure 4A The mesh structure is defined, but it should be recognized and understood that the mesh can be enlarged or shrunk, with more or fewer 402 and 404 sections and more or fewer nodes.

[0028] Compared to simply producing directly Figure 2 Compared to the process of forming topological structures, Figure 4A The initial grid in the model may have certain advantages. In particular, Figure 4A The mesh structure allows for an initial configuration that can be easily adapted to any desired final topology by removing unwanted parts. Furthermore, the initial mesh can be implemented as an unconnected / sparsely connected mesh pattern, where while some vertices eventually become associated with output nodes 208, 210, 212, and 406, other vertices 408 ultimately do not become associated with output nodes 208, 210, 212, and 406.

[0029] Although Figure 4A The initial mesh can be manufactured from it. Figure 2 The topology is incorporated as part of the process, and doing so can offer certain advantages in terms of the adaptability of the manufacturing process to various use cases. However, it is emphasized that it is possible to reach the topology directly without utilizing the initial mesh. Figure 2In this case, conductive gel can be applied to the topology without removing any portion of the conductive traces. While this may not be as adaptable to different desired topologies, such a process can be performed relatively quickly and results in less waste of conductive gel and other components.

[0030] Figure 5 This is a block diagram of a flexible differential strain sensor 502 in an example embodiment. The flexible differential strain sensor 502 includes many of the same components as those in the flexible differential strain sensor 102. Therefore, 502 may include a first sensing element 106 having a first active portion 108 arranged 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 canceling portion 116, wherein a second terminal 118 provides an electrical output from the second sensing element 112. The second active portion 114 may be positioned on a deformable substrate 104 to sense strain along the X-axis, and the canceling portion 116 may be positioned on the deformable substrate 104 to logically or mathematically cancel the strain along the Y-axis detected by the first active portion 108 of the first sensing element 106. Therefore, the first sensing element 106 may be sensitive to strain on the Y-axis but not very sensitive or insensitive to strain on the X-axis. Conversely, the second sensing element 112 may be sensitive to strain applied on both the X and Y axes. Although the signal processing unit 120 is not shown, it should be recognized and understood that such a component may be included as part of the flexible differential strain sensor 502, just as in the flexible differential strain sensor 102.

[0031] However, unlike the flexible differential strain sensor 102, the flexible differential strain sensor 502 is typically U-shaped. As a result, the first active portion 108 is spaced apart from the cancelling portion 116. Therefore, compared to the flexible differential strain sensor 102, the flexible differential strain sensor 502 can be relatively more sensitive to differential strain along the X-axis across the width of the deformable substrate 104, but relatively less sensitive to differential strain near the first sensing element 106. It should be recognized and understood that the principles discussed regarding the relative differences between the flexible differential strain sensor 102 and the flexible differential strain sensor 502 can be applied to any of the various alternative flexible differential strain sensors, and thus various configurations can be implemented as needed.

[0032] Figure 6This is the topology of the three-dimensional flexible differential strain sensor 602 in the example embodiment. The three-dimensional flexible differential strain sensor 602 is positioned on and within the deformable substrate 104 along all three axes (X-axis, Y-axis, and Z-axis). Therefore, in the illustrated example, the conductive gel trace 604 includes portions positioned on the top main surface 606, the bottom main surface 608, and a portion positioned to pass through the deformable substrate 104 between the top main surface 606 and the bottom main surface 608. As shown, the trace 604 also includes nodes 610 at vertices 612, although, as disclosed herein, not all vertices 612 are nodes 610, but are used as nodes 610 as needed.

[0033] The topology is provided for illustrative purposes, and it should be recognized and understood that lengths may be exaggerated and are not necessarily proportional. Thus, for example, when the deformable substrate 104 is a textile used, for example, in a shirt, the length of the portions of trace 604 along the X and Y axes may be multiple millimeters or multiple centimeters, while the length of trace 604 along the Z axis may be a fraction of a millimeter, such as one hundred (100) micrometers or less. Other examples of various lengths can be considered depending on the environment in which the three-dimensional flexible differential strain sensor 602 is used.

[0034] Furthermore, for clarity, the topology is provided in a simplified format, but it should be recognized and understood that it is similar to that regarding... Figure 4A and Figure 4B The described extended 3D mesh pattern can be used to increase the available portions of trace 604 and node 610. Figure 4A and Figure 4B Similar to the previous example, the extended mesh pattern allows for greater adaptability to the fabrication process of the three-dimensional flexible differential strain sensor 602 and / or allows for different fabrication methods. Figure 6 The cube shown has a 3D topology. Additional 3D topologies can also be achieved without the intermediate step of expanding the 3D mesh.

[0035] Based on the terminology presented regarding the flexible differential strain sensor 102, the portion of trace 604 extending along the Z-axis can be understood as forming a third sensing element 614, which includes at least one active portion and at least one canceling portion, for example, a third active portion and a second canceling portion. Assuming the illustrated topology of the three-dimensional flexible differential strain sensor 602 includes multiple portions of trace 604 along each axis, identifying each specific portion as an active or canceling portion may be subjective and tends to vary at any given time depending on the location on the deformable substrate 104 where strain evaluation is being performed. Therefore, the signal processing unit 120 can utilize any specific portion of trace 604 as an active or canceling portion as needed.

[0036] Similar to the two-dimensional flexible differential strain sensors 102 and 502, nodes 610 can be coupled to the signal processing unit 120, and the impedance variation across each pair of nodes 610 is used as a vector to identify the three-dimensional strain applied to the deformable substrate 104 and typically to the three-dimensional flexible differential strain sensor 602. In such an example, the resulting vector may include at least X1, Y1, and Z1, and may include more measurements along some or all axes depending on which nodes 610 are used to form the vector. Furthermore, the signal processing unit 120 may utilize the parallel portions of the trace 604 to cancel out strain along the parallel axes. Thus, to cancel out strain along the Y-axis, the signal processing unit 120 may, for example, subtract the impedance between two nodes 610 including Y-axis portion 616a from the impedance between the two nodes 610 including Y-axis portion 616b, or subtract the impedance between two nodes 610 including Y-axis portion 616c from the impedance between the two nodes 610 including Y-axis portion 616a, and so on.

[0037] In some embodiments, the flexible differential strain sensors 102, 502, 602 may be implemented as flexible and / or tensile strain sensors using one or more deformable conductors (e.g., deformable substrates and / or conductors disclosed in '727 application) for the sensing element. In some embodiments, strain sensors 102, 502, 602 may be manufactured 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.

[0038] Based on the principles of this disclosure, strain sensors 102, 502, and 602 can be used in a variety of applications using various combinations of materials. For example, flexible and / or stretchable strain sensors 102, 502, and 602 can be applied to and / or integrated into clothing, footwear, hats, backpacks or other bags, industrial textiles, upholstery, geotextiles, nonwoven films, or any other manufactured article in which strain sensing may be useful.

[0039] In some example 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)) can be integrated into clothing articles such as shirts or vests to sense the breathing of a person wearing the article. The sensors can be arranged such that the horizontal (X-axis) portion of the sensor or meter is on the chest cavity and, if the wearer is standing, parallel to the horizon. The vertical (Y-axis) portion of the sensor can be aligned with the wearer's spine, i.e., if the wearer is standing, the vertical (Y-axis) portion is perpendicular to the horizon. In such a configuration, in various cases, if the vertical (Y-axis) portion can respond to the flexion of the wearer's back, the outputs from the X-axis and Y-axis portions of strain sensors 102, 502, 602 can provide a response to the wearer's breathing.

[0040] As disclosed herein, some inventive principles relate to strain sensors 102, 502, 602, which are sensitive to stimuli in two or more dimensions (e.g., along two different axes) in a manner that can distinguish stimuli in different dimensions. For example, the sensor may include two sensing elements, each having an active portion arranged to sense stimuli along different axes. One or both sensing elements may also have a cancellation portion that can be arranged to cancel the effect of stimuli along the axis of the other sensing element. For example, such an arrangement can be used to cancel unwanted stimulus artifacts in directions different from the direction being measured.

[0041] Such multiaxial strain sensors 102, 502, and 602 can be used to distinguish inputs in complex systems such as the human body. For example, such a multiaxial sensor system can be used to distinguish between gross motor movement, respiration, and changes in muscle size caused by muscle flexion and extension. Furthermore, as an example, the strain sensor system 102, 502, and 602 may include a sensing element fixed to clothing that stretches with chest expansion, which can utilize chest expansion to measure respiration. However, other movements, such as torso bending, can also cause sensor stretching, leading to potential inaccuracies in respiration measurements. However, if the strain sensor 102, 502, and 602 includes a sensing element and a second sensing element, the first sensing element being arranged such that its axis is perpendicular to the spine and extends around a portion of the chest cavity, and the second sensing element being arranged such that its axis extends parallel to the spine, then the sensing system can detect torso bending by the deformation of the second sensing element, and can use the information generated by the deformation of the second sensing element to distinguish between torso bending and respiration. The data generated by strain sensors 102, 502, and 602 can determine which part of the stretch in the first sensor is not attributable to breathing, thus ensuring more accurate breathing measurements.

[0042] As another example, multiaxial strain sensors 102, 502, and 602 can be used to distinguish the recruitment of different muscles in a given gross motion, or different directional movements of a mechanical system. Another example application of strain sensors 102, 502, and 602 according to this disclosure is in geotextiles used to reinforce embankments, dams, or other earthwork structures, where the multiaxial sensors can distinguish between normal settlement and anomalous collapse or displacement, which can indicate an impending collapse. Other example applications of multiaxial strain sensors 102, 502, and 602 according to this disclosure include sails (e.g., sails for sailboats, windsurfing boards, etc.), kites, parachutes, and so on. Additional examples include coverings / claddings for machinery such as articulated joints and shape memory alloy actuators. Even more examples include inflatable structures such as inflatable struts, tires, balloons, rubber boats, etc. Further examples include any structures, such as chassis, frames, shells, etc., that can warp, bend, or otherwise deform in a manner conducive to sensing and / or measurement.

[0043] The embodiments and exemplary implementation details described herein are for illustrative purposes. The accompanying drawings are not necessarily shown to scale. The principles of the invention are not limited to these embodiments or details. The various inventive principles disclosed in this patent may have individual uses and benefits. However, when combined, the inventive principles described in this disclosure, including portions incorporated by reference, can enable individual elements to interact in new ways to provide synergistic results.

[0044] The conductive compositions (e.g., conductive gels) contained in the articles described herein may, for example, have a paste or gel consistency, which can be achieved by utilizing the structure that gallium oxide can impart to the composition when it is incorporated into a eutectic gallium alloy. When incorporated 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.

[0045] As used herein, the term "eutectic" generally refers to a mixture of two or more phases of a composition having the lowest melting point, wherein these phases simultaneously crystallize from the molten solution at that temperature. The ratio of the phases that yield the eutectic is determined by the eutectic point on the phase diagram. One characteristic of eutectic alloys is that they have a distinct melting point.

[0046] Conductive compositions can be characterized as conductive shear-thinning gel compositions. The conductive compositions described herein can also be characterized as compositions exhibiting Bingham plastic properties. For example, conductive compositions can be viscoplastic, such that they are rigid under low stress and capable of forming and maintaining three-dimensional features characterized by height and width, but flow as a viscous fluid under high stress. Thus, for example, conductive compositions have a viscosity of about 10,000,000 cP to about 40,000,000 cP under low shear and a viscosity of about 150 to 180 under high shear. For example, under low shear conditions, the composition has 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 high shear conditions, 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.

[0047] The conductive compositions described herein can have any suitable conductivity, for example from about 2 x 10⁻⁶. 5 S / m to approximately 8x10 5 Conductivity in S / m.

[0048] The conductive compositions described herein may have any suitable melting point, such as from about -20°C to about 10°C, from about -10°C to about 5°C, from about -5°C to about 5°C, or from about -5°C to about 0°C.

[0049] The conductive composition may comprise a mixture of a eutectic gallium alloy and gallium oxide, wherein the eutectic gallium alloy in the mixture has a weight percentage (wt%) between about 59.9% and about 99.9% (e.g., between about 67% and about 90%), and the gallium oxide in the mixture has a weight percentage (wt%) between about 0.1% and about 2.0% (e.g., between about 0.2% and about 1%). For example, the conductive composition may have a weight percentage of 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%, and about [missing information]. 93%, about 94%, about 95%, about 96%, about 97%, about 98%, about 99% or greater, such as about 99.9% eutectic gallium alloys, and 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.

[0050] Eutectic gallium alloys can include gallium-indium or gallium-indium-tin in any elemental ratio. For example, eutectic gallium alloys include gallium and indium. The conductive composition in the gallium-indium alloy can have any suitable weight percentage of gallium, which is between about 40% and 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%, approximately 64%, approximately 65%, approximately 66%, approximately 67%, approximately 68%, approximately 69%, approximately 70%, approximately 71%, approximately 72%, approximately 73%, approximately 74%, approximately 75%, approximately 76%, approximately 77%, approximately 78%, approximately 79%, approximately 80%, approximately 81%, approximately 82%, approximately 83%, approximately 84%, approximately 85%, approximately 86%, approximately 87%, approximately 88%, approximately 89%, approximately 90%, approximately 91%, approximately 92%, approximately 93%, approximately 94%, or approximately 95%.

[0051] The conductive composition in the gallium-indium alloy may contain a certain weight percentage of indium, which is between about 5% and 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%, and about 28%. Approximately 29%, approximately 30%, approximately 31%, approximately 32%, approximately 33%, approximately 34%, approximately 35%, approximately 36%, approximately 37%, approximately 38%, approximately 39%, approximately 40%, approximately 41%, approximately 42%, approximately 43%, approximately 44%, approximately 45%, approximately 46%, approximately 47%, approximately 48%, approximately 49%, approximately 50%, approximately 51%, approximately 52%, approximately 53%, approximately 54%, approximately 55%, approximately 56%, approximately 57%, approximately 58%, approximately 59%, or approximately 60%.

[0052] Eutectic gallium alloys may include gallium and tin. For example, the conductive composition may contain a weight percentage of tin in the alloy, ranging from about 0.001% to about 50%, such as 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 5%, about 6%, about 7%, about 8%, about 9%, about 10%, about 11%, about 1%, etc. 2%, approximately 13%, approximately 14%, approximately 15%, approximately 16%, approximately 17%, approximately 18%, approximately 19%, approximately 20%, approximately 21%, approximately 22%, approximately 23%, approximately 24%, approximately 25%, approximately 26%, approximately 27%, approximately 28%, approximately 29%, approximately 30%, approximately 31%, approximately 32%, approximately 33%, approximately 34%, approximately 35%, approximately 36%, approximately 37%, approximately 38%, approximately 39%, approximately 40%, approximately 41%, approximately 42%, approximately 43%, approximately 44%, approximately 45%, approximately 46%, approximately 47%, approximately 48%, approximately 49%, or approximately 50%.

[0053] The conductive composition may comprise one or more microparticles or submicron-sized particles mixed with a eutectic gallium alloy and gallium oxide. The particles may be suspended within the eutectic gallium alloy, or coated in the eutectic gallium alloy or gallium and encapsulated in gallium oxide, or not coated in the aforementioned manner. The size of the micron-sized or submicron-sized particles can range from nanometers to micrometers, and they may be suspended in gallium, gallium-indium alloy, or gallium-indium-tin alloy. The particle-to-alloy ratio may be varied, and this may alter the flow properties of the conductive composition. Microstructures and nanostructures may be mixed within the conductive composition by ultrasonication or other suitable means. The conductive composition may include colloidal suspensions of microstructures and nanostructures in the eutectic gallium alloy / gallium oxide mixture.

[0054] The conductive composition may also include one or more microparticles or submicron-sized particles dispersed within the composition. This can be achieved in any suitable manner, including by suspending the particles within the conductive composition, or specifically within a eutectic gallium alloy fluid, wherein the particles are either coated in the eutectic gallium alloy or gallium and encapsulated in gallium oxide, or are not coated in the aforementioned manner. The size of these particles can range from nanometers to micrometers and can be suspended in gallium, gallium-indium alloy, or gallium-indium-tin alloy. The particle-to-alloy ratio can be varied to alter the fluid properties of at least one of the alloy and the conductive composition, etc. Furthermore, any auxiliary materials can be added to the colloidal suspension or the eutectic gallium alloy 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 composition can be achieved by any suitable means, including ultrasonic treatment or other mechanical means, without the addition of particles. In some 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%, approximately 5%, approximately 6%, approximately 7%, approximately 8%, approximately 9%, approximately 10%, approximately 11%, approximately 12%, approximately 13%, approximately 14%, approximately 15%, approximately 16%, approximately 17%, approximately 18%, approximately 19%, approximately 20%, approximately 21%, approximately 22%, approximately 23%, approximately 24%, approximately 25%, approximately 26%, approximately 27%, approximately 28%, approximately 29%, approximately 30%, approximately 31%, approximately 32%, approximately 33%, approximately 34%, approximately 35%, approximately 36%, approximately 37%, approximately 38%, approximately 39%, or approximately 40%.

[0055] The one or more micron or submicron particles may be made of any suitable material, including soda glass, silica, borosilicate glass, quartz, copper oxide, silver-plated copper, non-oxidized copper, tungsten, supersaturated tin particles, glass, graphite, silver-plated copper (e.g., silver-plated copper spheres and silver-plated copper sheets), copper sheets or copper spheres or combinations thereof, or any other material that can be wetted by at least one of eutectic gallium alloys and conductive compositions. The one or more micro or submicron particles may have any suitable shape, including spherical, rod-shaped, tubular, sheet-like, plate-like, cubic, prismatic, pyramidal, cage-like, and dendritic macromolecular shapes. The one or more microparticles or submicron particles may have any suitable size, including a size range from about 0.5 micrometers to about 60 micrometers, such as about 0.5 micrometers, about 0.6 micrometers, about 0.7 micrometers, about 0.8 micrometers, about 0.9 micrometers, about 1 micrometer, about 1.5 micrometers, about 2 micrometers, about 3 micrometers, about 4 micrometers, about 5 micrometers, about 6 micrometers, about 7 micrometers, about 8 micrometers, about 9 micrometers, about 10 micrometers, about 11 micrometers, about 12 micrometers, about 13 micrometers, about 14 micrometers, about 15 micrometers, about 16 micrometers, about 17 micrometers, about 18 micrometers, about 19 micrometers, about 20 micrometers, about 21 micrometers, about 22 micrometers, and about 23 micrometers. Approximately 24 micrometers, approximately 25 micrometers, approximately 26 micrometers, approximately 27 micrometers, approximately 28 micrometers, approximately 29 micrometers, approximately 30 micrometers, approximately 31 micrometers, approximately 32 micrometers, approximately 33 micrometers, approximately 34 micrometers, approximately 35 micrometers, approximately 36 micrometers, approximately 37 micrometers, approximately 38 micrometers, approximately 39 micrometers, approximately 40 micrometers, approximately 41 micrometers, approximately 42 micrometers, approximately 43 micrometers, approximately 44 micrometers, approximately 45 micrometers, approximately 46 micrometers, approximately 47 micrometers, approximately 48 micrometers, approximately 49 micrometers, approximately 50 micrometers, approximately 51 micrometers, approximately 52 micrometers, approximately 53 micrometers, approximately 54 micrometers, approximately 55 micrometers, approximately 56 micrometers, approximately 57 micrometers, approximately 58 micrometers, approximately 59 micrometers, or approximately 60 micrometers.

[0056] The conductive compositions described herein can be prepared by any suitable method, including methods that incorporate surface oxides formed on the surface of a eutectic gallium alloy into the bulk of the eutectic gallium alloy through shear mixing at the surface oxide / alloy interface. Shear mixing of such compositions can induce cross-linked microstructures in the surface oxides, thereby forming a conductive shear-diluted gel composition. Colloidal suspensions of microstructures can be formed within eutectic gallium alloy / gallium oxide mixtures (e.g., gallium oxide particles and / or sheets).

[0057] The surface oxide can be mixed in any suitable ratio, for example, between about 59.9% (by weight) and about 99.9% eutectic gallium alloy and between about 0.1% (by weight) and about 2.0% gallium oxide. For example, the weight percentages of the gallium alloy mixed with gallium oxide are 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 9%, and so on. The eutectic gallium alloy comprises 3%, approximately 94%, approximately 95%, approximately 96%, approximately 97%, approximately 98%, approximately 99%, or greater, such as approximately 99.9%, of gallium oxide in weight percentages of approximately 0.1%, approximately 0.2%, approximately 0.3%, approximately 0.4%, approximately 0.5%, approximately 0.6%, approximately 0.7%, approximately 0.8%, approximately 0.9%, approximately 1.0%, approximately 1.1%, approximately 1.2%, approximately 1.3%, approximately 1.4%, approximately 1.5%, approximately 1.6%, approximately 1.7%, approximately 1.8%, approximately 1.9%, and approximately 2.0%. In embodiments, the eutectic gallium alloy may include gallium-indium or gallium-indium-tin in any proportion of the mentioned elements. For example, the eutectic gallium alloy may comprise gallium and indium.

[0058] The weight percentage of gallium in gallium-indium alloys can range from approximately 40% to approximately 95%, for example, approximately 40%, approximately 41%, approximately 42%, approximately 43%, approximately 44%, approximately 45%, approximately 46%, approximately 47%, approximately 48%, approximately 49%, approximately 50%, approximately 51%, approximately 52%, approximately 53%, approximately 54%, approximately 55%, approximately 56%, approximately 57%, approximately 58%, approximately 59%, approximately 60%, approximately 61%, approximately 62%, approximately 63%, and approximately 64%. Approximately 65%, approximately 66%, approximately 67%, approximately 68%, approximately 69%, approximately 70%, approximately 71%, approximately 72%, approximately 73%, approximately 74%, approximately 75%, approximately 76%, approximately 77%, approximately 78%, approximately 79%, approximately 80%, approximately 81%, approximately 82%, approximately 83%, approximately 84%, approximately 85%, approximately 86%, approximately 87%, approximately 88%, approximately 89%, approximately 90%, approximately 91%, approximately 92%, approximately 93%, approximately 94%, or approximately 95%.

[0059] Alternatively or additionally, the weight percentage of indium in the gallium-indium alloy can be between about 5% and 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%, or about 29%. Approximately 30%, approximately 31%, approximately 32%, approximately 33%, approximately 34%, approximately 35%, approximately 36%, approximately 37%, approximately 38%, approximately 39%, approximately 40%, approximately 41%, approximately 42%, approximately 43%, approximately 44%, approximately 45%, approximately 46%, approximately 47%, approximately 48%, approximately 49%, approximately 50%, approximately 51%, approximately 52%, approximately 53%, approximately 54%, approximately 55%, approximately 56%, approximately 57%, approximately 58%, approximately 59%, or approximately 60%.

[0060] Eutectic gallium alloys can include gallium, indium, and tin. The weight percentage of tin in gallium-indium-tin alloys can range from 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 14%. %, approximately 15%, approximately 16%, approximately 17%, approximately 18%, approximately 19%, approximately 20%, approximately 21%, approximately 22%, approximately 23%, approximately 24%, approximately 25%, approximately 26%, approximately 27%, approximately 28%, approximately 29%, approximately 30%, approximately 31%, approximately 32%, approximately 33%, approximately 34%, approximately 35%, approximately 36%, approximately 37%, approximately 38%, approximately 39%, approximately 40%, approximately 41%, approximately 42%, approximately 43%, approximately 44%, approximately 45%, approximately 46%, approximately 47%, approximately 48%, approximately 49%, or approximately 50%.

[0061] The weight percentage of gallium in gallium-indium-tin alloys can range from approximately 40% to approximately 95%, for example, approximately 40%, approximately 41%, approximately 42%, approximately 43%, approximately 44%, approximately 45%, approximately 46%, approximately 47%, approximately 48%, approximately 49%, approximately 50%, approximately 51%, approximately 52%, approximately 53%, approximately 54%, approximately 55%, approximately 56%, approximately 57%, approximately 58%, approximately 59%, approximately 60%, approximately 61%, approximately 62%, approximately 63%, and approximately 64%. Approximately 65%, approximately 66%, approximately 67%, approximately 68%, approximately 69%, approximately 70%, approximately 71%, approximately 72%, approximately 73%, approximately 74%, approximately 75%, approximately 76%, approximately 77%, approximately 78%, approximately 79%, approximately 80%, approximately 81%, approximately 82%, approximately 83%, approximately 84%, approximately 85%, approximately 86%, approximately 87%, approximately 88%, approximately 89%, approximately 90%, approximately 91%, approximately 92%, approximately 93%, approximately 94%, or approximately 95%.

[0062] Alternatively or additionally, the weight percentage of indium in the gallium indium tin alloy can be between about 5% and 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%. %, approximately 30%, approximately 31%, approximately 32%, approximately 33%, approximately 34%, approximately 35%, approximately 36%, approximately 37%, approximately 38%, approximately 39%, approximately 40%, approximately 41%, approximately 42%, approximately 43%, approximately 44%, approximately 45%, approximately 46%, approximately 47%, approximately 48%, approximately 49%, approximately 50%, approximately 51%, approximately 52%, approximately 53%, approximately 54%, approximately 55%, approximately 56%, approximately 57%, approximately 58%, approximately 59%, or approximately 60%.

[0063] One or more microparticles or submicron particles can be mixed with eutectic gallium alloys and gallium oxide. For example, one or more microparticles or submicron particles can be mixed with a mixture wherein the wt% of the microparticles in the composition is between about 0.001% and about 40.0%, such as 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%, or about 5%. Approximately 6%, approximately 7%, approximately 8%, approximately 9%, approximately 10%, approximately 11%, approximately 12%, approximately 13%, approximately 14%, approximately 15%, approximately 16%, approximately 17%, approximately 18%, approximately 19%, approximately 20%, approximately 21%, approximately 22%, approximately 23%, approximately 24%, approximately 25%, approximately 26%, approximately 27%, approximately 28%, approximately 29%, approximately 30%, approximately 31%, approximately 32%, approximately 33%, approximately 34%, approximately 35%, approximately 36%, approximately 37%, approximately 38%, approximately 39%, or approximately 40%. In embodiments, the particles may be soda glass, silica, borosilicate glass, quartz, copper oxide, silver-plated copper, non-oxidized copper, tungsten, supersaturated tin particles, glass, graphite, silver-plated copper (e.g., silver-plated copper balls and silver-plated copper sheets), copper sheets or copper balls or combinations thereof, or any other material that can be wetted by gallium. In some embodiments, one or more microparticles or submicron-sized particles are in the form of spherical, rod-shaped, tubular, sheet-like, plate-like, cubic, prismatic, pyramidal, cage-like, and dendritic macromolecular shapes. In some embodiments, the size of one or more microparticles or submicron-sized particles ranges from about 0.5 micrometers to about 60 micrometers, for example, about 0.5 micrometers, about 0.6 micrometers, about 0.7 micrometers, about 0.8 micrometers, about 0.9 micrometers, about 1 micrometer, about 1.5 micrometers, about 2 micrometers, about 3 micrometers, about 4 micrometers, about 5 micrometers, about 6 micrometers, about 7 micrometers, about 8 micrometers, about 9 micrometers, about 10 micrometers, about 11 micrometers, about 12 micrometers, about 13 micrometers, about 14 micrometers, about 15 micrometers, about 16 micrometers, about 17 micrometers, about 18 micrometers, about 19 micrometers, about 20 micrometers, about 21 micrometers, about 22 micrometers, about 23 micrometers, about 2... 4 micrometers, approximately 25 micrometers, approximately 26 micrometers, approximately 27 micrometers, approximately 28 micrometers, approximately 29 micrometers, approximately 30 micrometers, approximately 31 micrometers, approximately 32 micrometers, approximately 33 micrometers, approximately 34 micrometers, approximately 35 micrometers, approximately 36 micrometers, approximately 37 micrometers, approximately 38 micrometers, approximately 39 micrometers, approximately 40 micrometers, approximately 41 micrometers, approximately 42 micrometers, approximately 43 micrometers, approximately 44 micrometers, approximately 45 micrometers, approximately 46 micrometers, approximately 47 micrometers, approximately 48 micrometers, approximately 49 micrometers, approximately 50 micrometers, approximately 51 micrometers, approximately 52 micrometers, approximately 53 micrometers, approximately 54 micrometers, approximately 55 micrometers, approximately 56 micrometers, approximately 57 micrometers, approximately 58 micrometers, approximately 59 micrometers, or approximately 60 micrometers.

[0064] Example

[0065] 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 conductive gel arranged to sense strain in the deformable substrate along the first axis; and a second sensing element comprising conductive gel having a first portion and a second portion, the first portion being arranged to sense strain in the deformable substrate along the first axis and the second portion being arranged to sense strain in the deformable substrate along the second axis; wherein the second sensing element is arranged to counteract at least a portion of the stimulus along the first axis sensed by the first sensing element.

[0066] In Example 2, the subject of Example 1 includes a conductive gel whose impedance changes in response to a change in strain on a deformable substrate, wherein the first and second sensing elements are configured to sense strain at least in part based on the change in impedance.

[0067] In Example 3, the subject of Example 2 includes a signal processing unit operatively coupled to a first sensing element and a second sensing element, the signal processing unit being configured to determine strain along a second axis by subtracting the impedance change from the first sensing element from the impedance change from the second sensing element.

[0068] In Example 4, the subject of Example 3 includes that the signal processing unit is further configured to determine strain along the first axis based on impedance changes from the first sensing element.

[0069] In Example 5, the subject of Example 4 includes a signal processing unit that is further configured to output a vector indicating strain along the first axis and along the second axis.

[0070] In Example 6, the subject of Example 5 includes a vector indicating the percentage change of strain on a deformable substrate relative to the initial strain.

[0071] In Example 7, the subject of Example 6 includes a situation where the percentage change in strain corresponds to the percentage change in the deformation of the deformable substrate.

[0072] In Example 8, the subject matter of Examples 2-7 includes a first axis orthogonal to a second axis, and the deformable substrate also has a third axis orthogonal to the first and second axes, and the subject matter further includes a third sensing element comprising a conductive gel, the third sensing element being arranged to sense strain in the deformable substrate at least along the third axis.

[0073] In Example 9, the subject matter of Examples 1-8 includes a first sensing portion comprising a first active portion, a second sensing portion comprising a second active portion and a canceling portion, and each of the first active portion, the second active portion and the canceling portion comprising a variable impedance at least in part based on strain applied to the respective first active portion, the second active portion and the canceling portion.

[0074] In Example 10, the subject matter of Examples 1-9 includes a deformable substrate configured to be attached to a structure to determine strain on the structure.

[0075] Example 11 is a method of manufacturing a flexible differential strain sensor, the method comprising: obtaining a deformable substrate having a first axis and a second axis different from the first axis; disposing a first sensing element comprising a conductive gel on the deformable substrate to sense strain in the deformable substrate along the first axis; disposing a second sensing element comprising a conductive gel on the deformable substrate, the second sensing element having a first portion and a second portion, the first portion sensing strain in the deformable substrate along the first axis, the second portion sensing strain in the deformable substrate along the second axis; wherein the second sensing element is arranged to counteract at least a portion of the stimulus along the first axis sensed by the first sensing element.

[0076] In Example 12, the subject of Example 11 includes a conductive gel whose impedance changes in response to a change in strain on a deformable substrate, wherein the first and second sensing elements are configured to sense strain at least in part based on the change in impedance.

[0077] In Example 13, the subject of Example 12 includes operatively coupling a signal processing unit to a first sensing element and a second sensing element, the signal processing unit being configured to determine strain along a second axis by subtracting an impedance change from an impedance change from a first sensing element from an impedance change from a second sensing element.

[0078] In Example 14, the subject of Example 13 includes a signal processing unit further configured to determine strain along a first axis based on impedance changes from a first sensing element.

[0079] In Example 15, the subject of Example 14 includes a signal processing unit that is further configured to output a vector indicating strain along a first axis and along a second axis.

[0080] In Example 16, the subject of Example 15 includes a vector indicating the percentage change in strain on a deformable substrate relative to an initial strain.

[0081] In Example 17, the subject of Example 16 includes a situation where the percentage change in strain corresponds to the percentage change in the deformation of the deformable substrate.

[0082] In Example 18, the subject matter of Examples 12-17 includes a first axis orthogonal to a second axis, and the deformable substrate also has a third axis orthogonal to the first and second axes, and the method further includes: arranging a third sensing element comprising a conductive gel on the deformable substrate to sense strain in the deformable substrate at least along the third axis.

[0083] In Example 19, the subject matter of Examples 11-18 includes a first sensing portion comprising a first active portion, a second sensing portion comprising a second active portion and a canceling portion, and wherein each of the first active portion, the second active portion and the canceling portion comprises a variable impedance at least in part based on strain applied to the respective first active portion, second active portion and canceling portion.

[0084] In Example 20, the subject matter of Examples 11-19 includes a deformable substrate configured to be attached to a structure to determine strain on the structure.

[0085] Example 21 is at least one machine-readable medium including instructions that, when executed by processing circuitry, cause the processing circuitry to perform operations to implement any one of Examples 1-20.

[0086] Example 22 is an apparatus that includes means for implementing any one of Examples 1-20.

[0087] Example 23 is a system for implementing any one of Examples 1-20.

[0088] Example 24 is a method that uses any one of Examples 1-20.

[0089] Some portions of this specification are presented based on algorithms or symbolic representations of operations on data stored in machine memory (e.g., computer memory) as bit or binary digital signals. These algorithms or symbolic representations are technical examples used by those skilled in the art of data processing to convey the essence of their work to others skilled in the art. As used herein, an "algorithm" is a self-consistent sequence of operations or similar processing that leads to a desired result. In this context, algorithms and operations involve physical manipulation of physical quantities. Typically, but not necessarily, these quantities may take the form of electrical, magnetic, or optical signals that can be stored, accessed, transmitted, combined, compared, or otherwise manipulated by a machine. Primarily for common use, it is sometimes convenient to use terms such as "data," "content," "bit," "value," "element," "symbol," "character," "term," "number," or "digit" to refer to such signals. However, these terms are merely convenient labels and are associated with appropriate physical quantities.

[0090] Unless otherwise specified, discussions using terms such as “processing,” “calculating,” “measuring,” “determining,” “presenting,” and “displaying” herein may refer to the actions or processes of a machine (e.g., a computer) that manipulate or transform data representing physical (e.g., electronic, magnetic, or optical) quantities within one or more memories (e.g., volatile memory, non-volatile memory, or any suitable combination thereof), registers, or other machine components that receive, store, transmit, or display information. Furthermore, unless otherwise specified, as is common in patent literature, the terms “a” or “an” are used herein to include one or more instances. Finally, as used herein, unless otherwise specified, the conjunction “or” refers to a non-exclusive “or.”

Claims

1. 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 an electrically conductive gel, the first sensing element arranged to sense strain in the deformable substrate along the first axis; a second sensing element comprising an electrically conductive gel, the second sensing element 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 along the first axis sensed by the first sensing element; wherein the electrically conductive gel of the first sensing element and the second sensing element changes in electrical impedance in response to changes in strain on the deformable substrate, and wherein the first sensing element and the second sensing element are configured to sense strain based at least in part on changes in impedance; and a signal processing unit operably coupled to the first sensing element and the second sensing element, the signal processing unit configured to determine strain along the second axis by subtracting changes in impedance from the second sensing element from changes in impedance from the first sensing element; wherein the signal processing unit is further configured to determine strain along the first axis based on changes in impedance from the first sensing element; wherein the signal processing unit is further configured to output a vector indicative of strain along the first axis and along the second axis.

2. The flexible differential strain sensor of claim 1, wherein, The vector is indicative of a percentage change in strain on the deformable substrate relative to an initial strain.

3. The flexible differential strain sensor of claim 2, wherein, The percentage change in strain corresponds to a percentage change in deformation of the deformable substrate.

4. The flexible differential strain sensor of claim 1, wherein, The first axis is orthogonal to the second axis, and the deformable substrate further has a third axis orthogonal to the first axis and the second axis, and the flexible differential strain sensor further comprises: a third sensing element comprising an electrically conductive gel, the third sensing element arranged to sense strain in the deformable substrate along at least the third axis.

5. The flexible differential strain sensor of claim 1, wherein, The first sensing portion comprises a first active portion, wherein the second sensing portion comprises a second active portion and a cancellation portion, and wherein each of the first active portion, the second active portion, and the cancellation portion comprises a variable impedance based at least in part on strain applied on the respective first active portion, second active portion, and cancellation portion.

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

7. A method of manufacturing a flexible differential strain sensor, comprising: obtaining a deformable substrate having a first axis and a second axis different from the first axis; arranging a first sensing element comprising an electrically conductive gel on the deformable substrate, the first sensing element for sensing strain in the deformable substrate along the first axis; arranging a second sensing element comprising an electrically conductive gel on the deformable substrate, the second sensing element having a first portion for sensing strain in the deformable substrate along the first axis and a second portion for sensing strain in the deformable substrate along the second axis; wherein the second sensing element is arranged to cancel at least a portion of the stimulus sensed by the first sensing element along the first axis; wherein an electrical impedance of the electrically conductive gel of the first sensing element and the second sensing element changes in response to changes in strain on the deformable substrate, and wherein the first sensing element and the second sensing element are configured to sense strain based at least in part on changes in impedance; and operably coupling a signal processing unit to the first sensing element and the second sensing element, the signal processing unit configured to determine strain along the second axis by subtracting changes in impedance from the second sensing element from changes in impedance from the first sensing element; wherein the signal processing unit is further configured to determine strain along the first axis based on changes in impedance from the first sensing element; wherein the signal processing unit is further configured to output a vector indicative of strain along the first axis and along the second axis.

8. The method of claim 7, wherein, the vector is indicative of a percentage change in strain on the deformable substrate relative to an initial strain.

9. The method of claim 8, wherein, the percentage change in strain corresponds to a percentage change in deformation of the deformable substrate.

10. The method of claim 7, wherein, the first axis is orthogonal to the second axis, and the deformable substrate further has a third axis orthogonal to the first axis and the second axis, and the method further comprises: arranging a third sensing element comprising an electrically conductive gel on the deformable substrate, the third sensing element for sensing strain in the deformable substrate along at least the third axis.

11. The method of claim 7, wherein, the first sensing portion comprises a first active portion, wherein the second sensing portion comprises a second active portion and a cancellation portion, and wherein each of the first active portion, the second active portion, and the cancellation portion comprises a variable impedance based at least in part on strain applied on the respective first active portion, second active portion, and cancellation portion.

12. The method of claim 7, wherein, the deformable substrate is configured to be attached to a structure to determine strain on the structure.

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