Multi-axis differential strain sensor

Abstract

A flexible differential strain sensor, system, and method comprises 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 arranged to detect strain in the deformable substrate along the first axis. The second sensing element has a first portion arranged to detect strain in the deformable substrate along the first axis and a second portion arranged to detect strain in the deformable substrate along the second axis. The second sensing element is arranged to offset at least a portion of the stimulus detected by the first sensing element along the first axis.

Description

Background Technology

[0001] <Cross-reference to related applications>

[0002] This patent application claims the benefit of priority to U.S. provisional application serial number 63 / 038,547 filed on June 12, 2020, the entirety of which is incorporated herein by reference.

[0003] <Background Technology>

[0004] Strain sensors can measure mechanical or otherwise physical stimuli on the strain sensor, for example, through a substrate to which the strain sensor is applied, and thereby measure strain on the substrate. Deformations in the substrate that are converted into the strain sensor, such as stretching, twisting, and flexing, can cause changes in some physical properties of the strain sensor. Changes in physical properties can be converted into strain and can be used to identify changes in strain over time. Brief explanation of the drawing

[0005] To facilitate the identification of discussions regarding any specific element or action, the highest digit or numbers in the reference numbers refer to the drawing number where the element is first introduced. FIG. 1 is a block diagram of a flexible differential strain sensor in an exemplary embodiment. FIG. 2 is a topology of a flexible differential strain sensor in an exemplary embodiment. FIG. 3 is an electrical equivalent schematic diagram of a flexible differential strain sensor in an exemplary embodiment. FIGS. 4a and 4b illustrate an abstract representation of a process in which the topology of a flexible differential strain sensor can be formed in an exemplary embodiment. FIG. 5 is a block diagram of a flexible differential strain sensor in an exemplary embodiment. FIG. 6 is the topology of a three-dimensional flexible differential strain sensor in an exemplary embodiment. Specific details for implementing the invention

[0006] Flexible strain sensors are disclosed, for example, in U.S. Patent Application Publication No. 2018 / 0247727 ("'727 application"), published August 30, 2018, the entirety of which is incorporated herein by reference. The '727 application discloses methods, apparatuses, and exemplary embodiments for strain sensing having deformable conductors, such as conductive gels, for example, in FIGS. 7 through 10 and in paragraphs

[0014] through

[0017] and

[0089] through

[0120] . As disclosed in the '727 application, sensor systems include sensor elements that respond to stimuli by changing dimensions, for example, by stretching. In application '727, for example, in paragraph

[0116] , the examples disclosed may include variable resistor grid patterns and / or non-connected or sparsely connected variable resistor networks.

[0007] Flexible differential strain sensors are disclosed herein that can be used to measure stimuli occurring in two or more dimensions (e.g., along two different axes) by arranging sensor elements in patterns and to distinguish between them. Examples disclosed herein may utilize differential signal processing to provide strain along specific axes of a substrate. Consequently, these flexible differential strain sensors may provide relatively enhanced sensitivity to the nature of strain on the substrate and / or on the strain sensor.

[0008] FIG. 1 is a block diagram of a flexible differential strain sensor in an exemplary embodiment. The flexible differential 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) may be any object on which the conductive gel disclosed herein may be located on or within and generally fixed. The deformable substrate (104) may be natural and synthetic fibers, natural or synthetic rubber, elastomers, etc., or may comprise these. Additionally, in various alternative examples, the flexible differential strain sensor (102) may be implemented on a substrate intended to be relatively deformed, but allowing the flexible differential strain sensor (102) to detect potentially undesirable strain or deformation on the substrate. For example, the substrate may be a metal, carbon fiber, etc., and the flexible differential strain sensor (102) may generally be oriented to identify strain on these structures. However, in various examples, the flexible differential strain sensor (102) is implemented as a deformable substrate (104), and in this case, the flexible differential strain sensor (102) having the deformable substrate (104) may be applied to and fixed thereon on these relatively less deformable structures to determine strain on these structures.

[0009] For the purpose of illustration, a deformable substrate (104) is effectively presented as a two-dimensional object having strain applied on one or both of the X and Y axes and detected by components directly extending along one of the X and Y axes. However, it should be recognized and understood that components may be positioned at angles with respect to the X and Y axes, and that conventional mathematics may be used to compensate for or otherwise account for differences in angles with respect to the X and Y axes. Additionally, strain may be applied on the deformable substrate (104) on the Z-axis orthogonal to the X and Y axes, and a flexible differential strain sensor (102) may be sensitive to such strain. Furthermore, as illustrated herein, the principles illustrated in two-dimensional examples may be applied to three-dimensional examples having strain sensors positioned along the Z-axis of the deformable substrate (104) and configured to directly detect strain applied on the Z-axis.

[0010] A flexible differential strain sensor (102) may include a first sensing element (106) having a first active portion (108) arranged to detect strain along the Y-axis, for example, 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 counter-part (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 a deformable substrate (104) to detect strain along the X-axis, for example, a second axis, and the counter-part (116) may be positioned on the deformable substrate (104) to logically or mathematically counteract strain along the Y-axis detected by the first active portion (108) of the first sensing element (106). Consequently, the first sensing element (106) may be sensitive to strain on the Y-axis but may have little or no sensitivity to strain on the X-axis. In contrast, the second sensing element (112) may be sensitive to strain applied on both the X-axis and the Y-axis. In some examples, by arranging the offset portion (116) in physical proximity to the first active portion (108), the offset portion (116) experiences the same or nearly the same strain as the first active portion (108) along the Y-axis.

[0011] 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 placed on or within the deformable substrate (104) through any suitable process, including printing, dispersion into the filaments and voids of the deformable substrate (104), etc. The conductive gel may be implemented as one or more electrical traces configured to conduct current along the traces. The electrical properties of the conductive gel may change as the conductive gel is stretched, contracted, or otherwise deformed, for example, on the deformable substrate (104) and as strain is imparted to the conductive gel by expansion. In various examples, the impedance (or more narrowly, resistance) of a given trace of the conductive gel may increase or decrease as the trace is stretched, contracted, or otherwise deformed. This change in the resistance of the trace may correspond to the amount of strain applied to the deformable substrate (104) adjacent to the trace. Consequently, the first active portion (108), the second active portion (114), and the offset portion (116) can be understood as specific portions of the conductive gel of the electrical traces extending along the X and Y axes of the deformable substrate (104), respectively. As the conductive gel is deformed, the impedance and / or other electrical properties of the conductive gel may change, but the conductive gel may be significantly less brittle, more prone to breakage, and significantly more resilient than conventional conductors used in electronic devices.

[0012] Two signals, Y1 on the first terminal (110) and X1 on the second terminal (118), can form an output vector from the flexible differential strain sensor (102) to restore and / or represent the strain field generally applied to the deformable substrate (104) and the flexible differential strain sensor (102). This output vector can be processed in any suitable manner. For example, in some applications, the raw signals X1 and Y1 can be processed by a signal processing unit (120) to determine and output the strain applied to the Y-axis as output signal Y2 and to determine and output 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 impedance at the terminals (110, 118) and a processor or other computing electronic device capable of converting the impedance or changes in impedance into strain on the flexible differential strain sensor (102) or otherwise associating them. For example, in an exemplary embodiment, a change of 0.03 ohms in impedance and / or resistance detected by the signal processing unit (120) is equivalent to a strain of 1 millimeter on the conductive gel of the flexible differential strain sensor (102) and the trace formed thereby, as disclosed herein. In various examples, strain may be understood as a change over the entire length, but it should be recognized and understood that any viable metric for strain known in the art may also or alternatively be used.

[0013] Since Y1 has a first active part (108) but generally has no trace extending along the X-axis, and thus has significant sensitivity to strain in the Y-axis, as the second active part (114) does, the signal processing unit (120) can calculate the strain in the Y-axis by relating a change in the impedance of the first active part (108) to strain in the Y-axis and outputting the resulting strain as Y2. In various examples, the signal processing unit (120) may simply buffer or pass the signal Y1 as the output signal Y2 to provide an indication of strain, and a remote processing unit, controller, or other electronic equipment may perform operations relating a change in impedance to strain in the flexible differential strain sensor (102).

[0014] In contrast, since the second sensing element (112) has significant sensitivity to strain on both the X-axis and the Y-axis, the signal processing unit (120) can generate an output signal X2 indicating 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. Consequently, the signal processing unit (120) determines a differential sensitivity to impedance that substantially offsets the strain applied to the first active part (108) and the offset part (116) along the Y-axis, leaving X2, based on the change in impedance along the second active part (114). For the purposes of this disclosure, the first active portion (108) and the offset portion (116) may be formed of conductive gel traces that are given very close to each other and have very similar properties, but it should be recognized and understood that variations in the actual positioning of the conductive gel may result in some margin of error between the change in impedance in the first active portion (108) and the offset portion (116), which may be propagated through differential calculation of strain on the X-axis output at X2. However, it should be recognized and understood that even if the output X2 does not completely exclude the influence of strain on the Y-axis, these small margins of error may nevertheless result in useful and accurate representations of strain on the X-axis. The same principles apply to the output of Y2.

[0015] As noted above, any processing of the output vector can be implemented in a manner that can be customized for a specific application. Generally, sensing elements may be arranged in grids or arrays that can be partially and / or fully connected. These elements, alone or in combination with other sensors, 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 by the flexible differential strain sensor (102). The analysis of this strain field may be based on an application, some examples of which are described below.

[0016] In other embodiments, the flexible differential strain sensor (102) may be arranged in different configurations and using different numbers and / or types of sensing elements, active and / or offset regions, etc. For example, the sensing elements may be arranged in a T-shape, U-shape, S-shape, 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 integrated in any pattern, and signal processing may be adjusted to accommodate different patterns. In some embodiments, signal processing may extract composite signals representing a stimulus in one dimension while offsetting strain in one or more different dimensions and / or axes. These principles may be applied to flexible differential strain sensors (102) having any number of elements, each element having any number of parts that are both active and / or offset for any type of stimulus, such as motion, stress, strain, etc.

[0017] FIG. 2 is a topology of a flexible differential strain sensor (102) in an exemplary embodiment. In particular, this topology illustrates a conductive gel electrical trace (202). The trace (202) can generally be positioned on a deformable substrate (104) (not shown) as illustrated in FIG. 1 to produce a flexible differential strain sensor (102). The trace (202) includes Y-axis portions (204a, 204b, 204c, 204d) which can be understood as portions of the trace (202) extending along the Y-axis, and X-axis portions (206a, 206b, 206c) which generally extend along the X-axis. This topology does not necessarily represent the relative lengths of the Y-axis portions (204a, 204b, 204c, 204d) and X-axis portions (206a, 206b, 206c).

[0018] The trace (202) is combined with or otherwise forms the first node (208), the second node (210), and the third node (212). The first node (208) and the second node (210) generally describe the Y1 signal defined by parts (204a, 206a, 204b). The second node (210) and the third node (212) generally describe the X1 signal defined by parts (204b, 206b, 204d, 206c, and 204c). Thus, from the perspective of actual topology, it should be recognized that signals X1 and Y1 are both at least partially affected by the Y-axis part (204b) of the trace (202), and that a change in impedance along the Y-axis part (204b) can result in a change in impedance for both X1 and Y1.

[0019] FIG. 3 is an electrical equivalent schematic diagram of a flexible differential strain sensor (102) in an exemplary embodiment. This electrical equivalent schematic diagram includes a first varistor (302) corresponding to a first active portion (108), a second varistor (304) corresponding to a second active portion (114), and a third varistor (306) corresponding to a cancellation portion (116), all of which are located on a deformable substrate (104). This electrical equivalent schematic diagram further 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 varistors are discussed herein, it should be recognized and understood that varistors provide a variable impedance generally caused by deformation of the trace (202) rather than, in a narrow sense, merely resistance.

[0020] It is noted and emphasized that the electrical equivalent schematic of FIG. 3 is a product of the topology of FIG. 2. Accordingly, the first varistor (302) takes into account the variable impedance caused by the deformation of the trace (202) along the Y-axis portion (204a), the X-axis portion (206a), and the Y-axis portion (204b). In examples where the X-axis portion (206a) is very short, for example, 100 micrometers or less, while the Y-axis portion (204a) and the Y-axis portion (204b) are each several millimeters or centimeters long, the first varistor (302) can express a change in impedance and, by association, can express strain applied along the Y-axis corresponding to these portions of the trace (202). Similarly, the second varistor (304) may correspond to the X-axis portion (206b) and the X-axis portion (206c), while the third varistor (306) may correspond to the Y-axis portion (204b), the Y-axis portion (204c), and the Y-axis portion (204d). Additionally, the first logic node (308) may correspond to the first node (208), the second logic node (310) and the third logic node (312) may correspond to the second node (210), and the fourth logic node (314) may correspond to the third node (212).

[0021] However, it should be recognized and understood that the principles of the electrical equivalent schematic can be obtained by any suitable arrangement of electrical components and are not bound to any specific topology or any specific electrical components. Accordingly, various examples of the flexible differential strain sensor (102) are not necessarily implemented in a conductive gel to the extent that alternative components that change the impedance as a function of localized strain on the deformable substrate (104) and / or on the components themselves can be utilized. Similarly, the flexible differential strain sensor (102) as illustrated in FIG. 1 can be implemented regardless of variable impedance to the extent that alternative mechanisms are feasible. However, implementations of the flexible differential strain sensor (102) having a conductive gel can provide advantages of electrical and mechanical simplicity, robustness, flexibility, and cost, among other factors, compared to potential alternative components. These advantages can be seen in both the use of the flexible differential strain sensor (102) and the process of manufacturing the flexible differential strain sensor (102).

[0022] FIGS. 4a and 4b illustrate an abstract representation of a process in which the topology of FIG. 2 of a flexible differential strain sensor (102) in an exemplary embodiment can be formed. In FIG. 4a, a grid of conductive gel is formed, comprising parts (402) aligned with the Y-axis and parts (404) aligned with the X-axis, along with nodes (208, 210, 212) and a fourth node (406). In FIG. 4b, specific parts (402, 404) of the grid are removed, for example, by being cut or otherwise separated from the remainder of the conductive gel trace (202), as indicated by dashed lines. The remaining parts, i.e., solid lines, correspond to the trace (202) and its various parts (204, 206) exemplified in the topology of FIG. 2. Consequently, the fourth node (406) is also removed and ceases to operate. Although the grid structure of FIG. 4a is provided as an example, it should be recognized and understood that this grid can be expanded or contracted into more or fewer parts (402, 404) and more or fewer nodes.

[0023] The formation of the initial grid in FIG. 4a can bring certain advantages compared to a process that simply results in the topology of FIG. 2. In particular, the grid structure of FIG. 4a allows for an initial configuration that can be easily adapted to any final desired topology by removing unnecessary parts. Additionally, the initial grid can be implemented as a non-connected / sparsely connected grid pattern, where some vertices are ultimately associated with output nodes (208, 210, 212, 406), but other vertices (408) are not ultimately associated with output nodes (208, 210, 212, 406).

[0024] The initial grid of FIG. 4a is included as part of a process to which the topology of FIG. 2 can be achieved, and while doing so may provide specific advantages in the adaptability of the manufacturing process for various use cases, it is emphasized that the topology of FIG. 2 can be achieved directly without using the initial grid. In this case, the conductive gel can be applied to the topology without necessarily removing any part of the conductive trace. While doing so may make it less adaptable to different desired topologies, this process can also be performed relatively faster and result in less waste of the conductive gel and other components.

[0025] FIG. 5 is a block diagram of a flexible differential strain sensor (502) in an exemplary embodiment. This flexible differential strain sensor (502) includes many of the same components as the flexible differential strain sensor (102). Accordingly, 502 may include a first sensing element (106) having a first active portion (108) arranged to detect 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 counter-part (116), and a second terminal (118) provides an electrical output from the second sensing element (112). A second active portion (114) may be positioned on the deformable substrate (104) to detect strain along the X-axis, and a counteracting portion (116) may be positioned on the deformable substrate (104) to logically or mathematically counteract strain along the Y-axis detected by the first active portion (108) of the first sensing element (106). Consequently, the first sensing element (106) may be sensitive to strain along the Y-axis but may have little or no sensitivity to strain along the X-axis. In contrast, the second sensing element (112) may be sensitive to strain imparted on both the X-axis and the Y-axis. Although a signal processing unit (120) is not illustrated, it should be recognized and understood that such a component may be included as part of the flexible differential strain sensor (502), as in the flexible differential strain sensor (102).

[0026] However, in contrast to the flexible differential strain sensor (102), the flexible differential strain sensor (502) generally forms a U-shape. As a result, the first active portion (108) is spaced apart from the offset portion (116). Consequently, the flexible differential strain sensor (502) may be relatively more sensitive to differential strain along the X-axis across the width of the deformable substrate (104) than the flexible differential strain sensor (102), but may be 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 as a result, various configurations can be implemented as desired.

[0027] FIG. 6 is the topology of a three-dimensional flexible differential strain sensor (602) in an exemplary embodiment. This three-dimensional flexible differential strain sensor (602) is positioned on and within a deformable substrate (104) in all three axes X, Y, and Z. Consequently, in the exemplary example, the conductive gel trace (604) includes portions positioned on the upper main surface (606), on the lower main surface (608), and through the deformable substrate (104) between the upper main surface (606) and the lower main surface (608). As illustrated, the trace (604) further includes nodes (610) at vertices (612), but not all vertices (612) are nodes (610) as disclosed herein, but rather are used as nodes (610) as desired.

[0028] It should be recognized and understood that such topologies are provided for illustrative purposes, and that these lengths may be exaggerated and do not necessarily need to be proportional. Thus, for example, if the deformable substrate (104) is a fabric used, for example, in a shirt, the lengths of the portions of the trace (604) along the X and Y axes may be several millimeters or centimeters, whereas the lengths of the trace (604) along the Z-axis may be fractions of a millimeter, for example, 100 micrometers or less. Other examples of various lengths are considered depending on the situations in which the three-dimensional flexible differential strain sensor (602) is used.

[0029] Additionally, while this topology is provided in a simplified format for the sake of clarity, it should be recognized and understood that an extended three-dimensional grid pattern similar to the grid pattern described in relation to FIGS. 4a and 4b may be used to increase the number of available traces (604) and nodes (610). As in FIGS. 4a and 4b, such an extended grid pattern may allow for relatively greater adaptability to the manufacturing process of the three-dimensional flexible differential strain sensor (602) and / or allow for three-dimensional topologies other than the cube exemplified in FIG. 6. Additional three-dimensional topologies may likewise be implemented without the intermediate step of the extended three-dimensional grid.

[0030] Parts of the trace (604) extending along the Z-axis may be understood to form a third sensing element (614) comprising at least one active part and at least one offset part, e.g., a third active part and a second offset part, based on the nomenclature presented for the flexible differential strain sensor (102). Given that the illustrated topology of the three-dimensional flexible differential strain sensor (602) includes multiple parts of the trace (604) along each axis, the identification of each specific part as an active part or an offset part may be subjective and may undergo change at any given time depending on the position on the deformable substrate (104) being evaluated for strain. Consequently, the signal processing unit (120) may use any specific part of the trace (604) as an active or offset part as desired.

[0031] As in the two-dimensional flexible differential strain sensors (102, 502), the nodes (610) can be coupled to the signal processing unit (120), and the dispersion in impedance across the nodes (610) of various pairs, which are used as vectors to identify the strain applied to the three-dimensional flexible differential strain sensor (602) and the deformable substrate (104) in three dimensions, is utilized. In this 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 used to form the vector. Additionally, the signal processing unit (120) may utilize parallel portions of the trace (604) to offset the strain along parallel axes. Accordingly, to offset strain along the Y-axis, the signal processing unit (120) may, among various possible permutations, subtract the impedance between two nodes (610) including the Y-axis portion (616a) from the impedance between two nodes (610) including the Y-axis portion (616b), or subtract the impedance between two nodes (610) including the Y-axis portion (616c) from the impedance between two nodes (610) including the Y-axis portion (616a).

[0032] In some embodiments, the flexible differential strain sensor (102, 502, 602) may be implemented as a flexible and / or extensible strain sensor using one or more deformable conductors for sensing elements such as the deformable substrates and / or conductors disclosed in application '727. In some embodiments, the 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.

[0033] Strain sensors (102, 502, 602) can be used in a wide variety of applications using countless combinations of materials according to the principles of the present disclosure. For example, flexible and / or extensible strain sensors (102, 502, 602) can be applied to and / or integrated into clothing, shoes, hats, backpacks or other bags, industrial fabrics, covers, geotextiles, non-woven membranes or any other manufactured article where strain sensing may be useful.

[0034] 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 TPU (thermoplastic polyurethane)) may be incorporated into clothing, such as a shirt or vest, to detect breathing by a person wearing the article. These sensors may be arranged so that the horizontal (X-axis) portion of the sensor or gauge is on the rib cage and parallel to the horizontal line when the wearer is standing. The vertical (Y-axis) portion of the sensor may be aligned with the wearer's spine, that is, perpendicular to the horizontal line when the wearer is standing. In this configuration, outputs from both the X-axis and Y-axis portions of the strain sensors (102, 502, 602) may provide a response to breathing by the wearer in various situations, provided that the vertical (Y-axis) portion can respond to bending of the wearer's back.

[0035] As disclosed herein, some of the inventive principles of the present disclosure relate to strain sensors (102, 502, 602) that may be sensitive to stimuli in two or more dimensions (e.g., along two different axes) in a manner that distinguishes between stimuli in different dimensions. For example, the sensor may include two sensing elements, each of which may have an active portion arranged to detect stimuli along different axes. One or both of these sensing elements may also have a counteracting portion arranged to counteract the effects of the stimuli along the axis of the other sensing element. Such an arrangement may be useful, for example, for counteracting unwanted artifacts of the stimuli in a direction different from that which is to be measured.

[0036] These multi-axis strain sensors (102, 502, 602) can be used to distinguish between inputs in complex systems such as the human body. For example, this multi-axis sensor system can be used to distinguish between total movement, respiration, and changes in muscle dimensions caused by muscle flexion. Additionally, as an example, the strain sensor (102, 502, 602) system may include a sensing element attached to clothing that can use rib cage extension to measure respiration when the rib cage extension is extended. However, other movements, such as bending of the torso, can also cause the sensor to be extended, leading to potential inaccuracies in respiration measurement. However, if the strain sensor (102, 502, 602) includes one sensing element arranged such that its axis extends perpendicular to the spine and around part of the rib cage, and a second sensing element arranged such that its axis extends parallel to the spine, the sensing system can detect bending of the torso through deformation of the second sensing element and can use the information generated by the deformation of the second sensing element to distinguish between bending of the torso and breathing. The data generated by the strain sensor (102, 502, 602) can determine which part of the extension of the first sensor is not due to breathing, thus ensuring that breathing measurements are more accurate.

[0037] As an additional example, multi-axis strain sensors (102, 502, 602) may be used to distinguish between the recruitment of different muscles in a given total motion, or between different directional movements of a mechanical system. Other exemplary applications of the strain sensors (102, 502, 602) according to the present disclosure are in geotextiles for reinforcing berms, levies, or other earthwork structures, in which the multi-axis sensors can distinguish between normal settling and abnormal slumping or shifting that may indicate imminent collapse. Other exemplary applications of the multi-axis strain sensors (102, 502, 602) according to the present disclosure include, for example, sails for sailboats, windsurfers, kites, parachutes, etc. Additional examples include covering / cladding for machines such as articulated joints, shape memory alloy actuators, etc. Further examples include inflatable structures such as inflatable braces, tires, balloons, rubber boats, etc. Additional examples include any structures such as chassis, frames, housings, etc. that can be bent, curved, or otherwise deformed in a manner that may be beneficial for sensing and / or measurement.

[0038] The embodiments and exemplary implementation details described herein are for illustrative purposes only. The drawings are not necessarily drawn to scale. The principles of the invention are not limited to these embodiments or details. Many of the inventive principles of this disclosure may have individual utility and advantages. However, when combined, the inventive principles described herein, including the parts referred to by reference, may enable individual elements to interact in novel ways to provide synergistic results.

[0039] Electrically conductive compositions, such as conductive gels, included in the articles described herein may have a paste-like or gel-like viscosity that can be produced, for example, by utilizing the structure that gallium oxide can impart to the composition when gallium oxide is mixed into a eutectic gallium alloy. When mixed into a eutectic gallium alloy, gallium oxide may form micro or nano-structures as further described herein, and these structures may alter the bulk material properties of the eutectic gallium alloy.

[0040] 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 crystallize simultaneously from a molten solution at this temperature. The ratio of phases to obtain eutectic is identified by the eutectic point on the phase diagram. One of the characteristics of eutectic alloys is their sharp melting point.

[0041] Electrically conductive compositions can be characterized as conductive shear thinning gel compositions. The electrically conductive compositions described herein can also be characterized as compositions having the properties of Bingham plastics. For example, electrically conductive compositions can be viscoelastics, so they are rigid and can form and maintain three-dimensional features characterized by height and width at low stresses but flowing like viscous fluids at high stresses. Thus, for example, electrically conductive compositions can have a viscosity in the range of about 10,000,000 cP to about 40,000,000 cP under low shear and about 150 to 180 at high shear. For example, under low shear conditions, this 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, this 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.

[0042] The electrically conductive compositions described herein are about 2 x 10 5 S / m to about 8 x 10 5 It can have any suitable conductivity, such as the conductivity of S / m.

[0043] The electrically conductive compositions described herein may 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.

[0044] These electrically conductive compositions may comprise a mixture of a eutectic gallium alloy and a gallium oxide, wherein the mixture of the eutectic gallium alloy and the gallium oxide has a weight percentage (wt %) of about 59.9% to about 99.9% of the eutectic gallium alloy, such as about 67% to about 90%, and a wt %) of about 0.1% to about 2.0% of the gallium oxide, such as about 0.2% to about 1%. For example, these electrically conductive compositions include about 99.9% eutectic gallium alloy, 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%, 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%, and about 70%. It can have 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% or more of gallium oxide.

[0045] Eutectic gallium alloys may contain gallium-indium or gallium-indium-tin in any proportion of the elements. For example, eutectic gallium alloys contain gallium and indium. These electrically conductive compositions are, 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%, Any suitable percentage of gallium by weight in a gallium-indium alloy of about 40% to about 95% can be present, such as 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%.

[0046] These electrically conductive compositions are 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 The gallium-indium alloy may have a percentage of indium by weight of about 5% to about 60%, such as 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%.

[0047] These eutectic gallium alloys may contain gallium and tin. For example, these electrically conductive compositions are 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 The alloy may have a percentage of tin by weight ranging from about 0.001% to about 50%, such as 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%.

[0048] These electrically conductive compositions may comprise one or more micro-particles or sub-micron-scale particles blended with a eutectic gallium alloy and gallium oxide. These particles may be suspended within a eutectic gallium alloy that is coated in gallium or gallium and encapsulated in gallium oxide, or a eutectic gallium alloy that is not coated in the aforementioned manner. These micro- or sub-micron-scale particles may have a size in the nanometer to micrometer range and may be suspended in gallium, a gallium-indium alloy, or a gallium-indium-tin alloy. The particle-to-alloy ratio may be varied and may alter the flow properties of the electrically conductive composition. These micro and nano-structures may be blended within the electrically conductive composition via sonication or other suitable means. These electrically conductive compositions may comprise a colloidal suspension of micro and nano-structures within a eutectic gallium alloy / gallium oxide mixture.

[0049] These electrically conductive compositions may further comprise one or more micro-particles or sub-micron-scale particles dispersed within the composition. This can be achieved in any suitable manner, comprising suspending particles—coated in a eutectic gallium alloy or gallium, encapsulated in a gallium oxide, or uncoated in the aforementioned manner—in the electrically conductive composition, or specifically, in a eutectic gallium alloy fluid. These particles may have a size in the nanometer to micrometer range and may be suspended in gallium, a gallium-indium alloy, or a gallium-indium-tin alloy. Among other things, the particle-to-alloy ratio may be varied to alter the fluid properties of at least one of the alloy and the electrically conductive compositions. Additionally, among other things, any auxiliary material is added to the colloidal suspension or the eutectic gallium alloy to enhance or modify its physical, electrical, or thermal properties. The distribution of micro and nano-structures within at least one of the eutectic gallium alloy and the electrically conductive compositions may be achieved through any suitable means, including sonication or other mechanical means, without the addition of particles. In certain embodiments, one or more of these micro-particles or sub-micron particles comprise about 0.001% to about 40.0% of micro-particles, e.g., 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.At least 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%, or about 40 wt% of eutectic gallium alloys and electrically conductive compositions It is blended with one.

[0050] One or more of these micro- or sub-micron particles may be made of any suitable material comprising silver-coated copper, copper flakes, or copper spheres, or a combination thereof, such as soda glass, silica, borosilicate glass, quartz, copper oxide, silver-coated copper, non-oxide copper, tungsten, supersaturated tin granules, glass, graphite, silver-coated copper spheres, and silver-coated copper flakes, or any other material that can be wetted by at least one of eutectic gallium alloys and electrically conductive compositions. One or more of these micro-particles or sub-micron scale particles may have any suitable shape, including shapes of ellipsoids, rods, tubes, flakes, plates, cubes, prismatic, pyramidal, cages, and dendrimers. One or more of these micro-particles or sub-micron scale particles are, 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, approx. 2 microns, approx. 3 microns, approx. 4 microns, approx. 5 microns, approx. 6 microns, approx. 7 microns, approx. 8 microns, approx. 9 microns, approx. 10 microns, approx. 11 microns, approx. 12 microns, approx. 13 microns, approx. 14 microns, approx. 15 microns, approx. 16 microns, approx. 17 microns, approx. 18 microns, approx. 19 microns, approx. 20 microns, approx. 21 microns, approx. 22 microns, approx. 23 microns, approx. 24 microns, approx. 25 microns, approx. 26 microns, approx. 27 microns, approx. 28 microns, approx. 29 microns, approx. 30 microns, approx. 31 microns, approx. 32 microns, approx. 33 microns, approx. 34 microns, approx. 35 microns, approx. 36 microns, approx. 37 It may have any suitable size, including a size range of about 0.5 microns to about 60 microns, such as 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.

[0051] The electrically conductive compositions described herein may be prepared by any suitable method comprising the step of blending surface oxides formed on the surface of a eutectic gallium alloy by shear mixing of the surface oxide / alloy interface into the bulk of the eutectic gallium alloy. Shear mixing of these compositions may induce cross-linked microstructures in the surface oxides; thereby forming a conductive shear thinning gel composition. A colloidal suspension of microstructures may be formed in the eutectic gallium alloy / gallium oxide mixture, for example, as gallium oxide particles and / or sheets.

[0052] These surface oxides can be blended in any suitable ratio, such as in a ratio of about 59.9% (by weight) to about 99.9% eutectic gallium alloy to about 0.1% (by weight) to about 2.0% gallium oxide. For example, the percentage by weight of the gallium alloy blended with gallium oxide is approximately 60%, 61%, approximately 62%, approximately 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%, approximately 95%, approximately 96%, approximately While the eutectic gallium alloy is 97%, about 98%, about 99%, or about 99.9% or higher, 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 the examples, these eutectic gallium alloys may contain gallium-indium or gallium-indium-tin in any proportion of the listed elements. For example, eutectic gallium alloys may contain gallium and indium.

[0053] The weight percentage of gallium in the gallium-indium alloy is 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%, 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 It may be approximately 40% to approximately 95%, such as 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%.

[0054] Alternatively or also, the weight percentage of indium in the gallium-indium alloy is 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 It may be about 5% to about 60%, such as 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%.

[0055] Eutectic gallium alloys may include gallium, indium, and tin. The weight percentage of tin in the gallium-indium-tin alloy is approximately 0.001%, approximately 0.005%, approximately 0.01%, approximately 0.05%, 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%, approximately 1.5%, approximately 2%, approximately 3%, approximately 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 It may be approximately 0.001% to approximately 50%, such as 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%.

[0056] The weight percentage of gallium in the gallium-indium-tin alloy is 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%, 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 It may be approximately 40% to approximately 95%, such as 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%.

[0057] Alternatively or also, the weight percentage of indium in the gallium-indium-tin alloy is 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 It may be about 5% to about 60%, such as 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%.

[0058] One or more micro-particles or sub-micron scale particles can be blended with eutectic gallium alloy and gallium oxide. For example, one or more of these micro-particles or sub-micron particles are in the composition in an amount of about 0.001% to about 40.0% of the micro-particles, 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 It can be blended with a mixture in wt % of 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 the embodiments, these particles may be made of any suitable material comprising silver-coated copper, copper flakes, or copper spheres, or a combination thereof, such as soda glass, silica, borosilicate glass, quartz, copper oxide, silver-coated copper, non-oxide copper, tungsten, supersaturated tin granules, glass, graphite, silver-coated copper spheres, and silver-coated copper flakes, or any other material that can be wetted by gallium. In some embodiments, one or more of these micro-particles or sub-micron scale particles are in the shape of ellipsoids, rods, tubes, flakes, plates, cubes, prismatic, pyramidal, cages, and dendrimers. In certain embodiments, one or more of these micro-particles or sub-micron scale particles are about 0.5 microns, about 0.6 microns, about 0.7 microns, about 0.8 microns, approx. 0.9 microns, approx. 1 micron, approx. 1.5 microns, approx. 2 microns, approx. 3 microns, approx. 4 microns, approx. 5 microns, approx. 6 microns, approx. 7 microns, approx. 8 microns, approx. 9 microns, approx. 10 microns, approx. 11 microns, approx. 12 microns, approx. 13 microns, approx. 14 microns, approx. 15 microns, approx. 16 microns, approx. 17 microns, approx. 18 microns, approx. 19 microns, approx. 20 microns, approx. 21 microns, approx. 22 microns, approx. 23 microns, approx. 24 microns, approx. 25 microns, approx. 26 microns, approx. 27 microns, approx. 28 microns, approx. 29 microns, approx. 30 microns, approx. 31 microns, approx. 32 microns, approx. 33 microns, approx. Any suitable size including a size range of about 0.5 microns to about 60 microns, such as 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.

[0059] Examples

[0060] 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 detect strain in the deformable substrate along the first axis; a second sensing element comprising a conductive gel having a first portion arranged to detect strain in the deformable substrate along the first axis and a second portion arranged to detect strain in the deformable substrate along the second axis; and the second sensing element is arranged to offset at least a portion of the stimulus detected by the first sensing element along the first axis.

[0061] In Example 2, the subject of Example 1 includes that the electrical impedance of the conductive gel of the first and second sensing elements changes in response to a change in strain on a deformable substrate, and that the first and second sensing elements are configured to sense strain based, at least partially, on the change in impedance.

[0062] In Example 3, the subject of Example 2 includes a signal processing unit configured to determine strain along a first axis by operatively coupling to a first sensing element and a second sensing element and by subtracting a change in impedance from the second sensing element from a change in impedance from the first sensing element.

[0063] In Example 4, the subject of Example 3 includes the signal processing unit being further configured to determine strain along a second axis based on a change in impedance from a first sensing element.

[0064] In Example 5, the subject of Example 4 includes the signal processing unit being additionally configured to output a vector indicating strain along the first axis and along the second axis.

[0065] In Example 6, the subject of Example 5 includes the vector representing the percentage change in strain on the deformable substrate relative to the initial strain.

[0066] In Example 7, the subject of Example 6 includes that a percentage change in strain corresponds to a percentage change in deformation of the deformable substrate.

[0067] In Example 8, the subject of Examples 2 through 7 comprises a first axis orthogonal to a second axis, and the deformable substrate further comprises a third sensing element comprising a conductive gel arranged to detect strain in the deformable substrate along at least the third axis.

[0068] In Example 9, the subject of Examples 1 through 8 comprises a first sensing portion including a first active portion, a second sensing portion including a second active portion and a counter-offering portion, and each of the first active portion, the second active portion, and the counter-offering portion includes a variable impedance based at least partially on a strain applied to each of the first active portion, the second active portion, and the counter-offering portion.

[0069] In Example 10, the subject of Examples 1 through 9 includes a deformable substrate being attached to a structure and configured to determine strain on the structure.

[0070] Example 11 is a method for manufacturing a flexible differential strain sensor, comprising the steps of: obtaining a deformable substrate having a first axis and a second axis different from the first axis; arranging a first sensing element, comprising a conductive gel, on the deformable substrate for sensing strain in the deformable substrate along the first axis; arranging a 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 arranged to sense strain in the deformable substrate along the second axis; wherein the second sensing element is arranged to offset at least a portion of the stimulus detected by the first sensing element along the first axis.

[0071] In Example 12, the subject of Example 11 includes that the electrical impedance of the conductive gel of the first and second sensing elements changes in response to a change in strain on a deformable substrate, and that the first and second sensing elements are configured to sense strain based, at least partially, on the change in impedance.

[0072] In Example 13, the subject of Example 12 includes the step of operatively coupling a signal processing unit to a first sensing element and a second sensing element, wherein the signal processing unit is configured to determine strain along a first axis by subtracting a change in impedance from the second sensing element from a change in impedance from the first sensing element.

[0073] In Example 14, the subject of Example 13 includes the signal processing unit being further configured to determine strain along a second axis based on a change in impedance from a first sensing element.

[0074] In Example 15, the subject of Example 14 includes the signal processing unit being additionally configured to output a vector indicating strain along the first axis and along the second axis.

[0075] In Example 16, the subject of Example 15 includes the vector representing the percentage change in strain on the deformable substrate relative to the initial strain.

[0076] In Example 17, the subject of Example 16 includes that a percentage change in strain corresponds to a percentage change in deformation of the deformable substrate.

[0077] In Example 18, the subject of Examples 12 to 17 comprises the step of arranging a third sensing element on a deformable substrate, 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 comprises a conductive gel that senses strain in the deformable substrate along at least the third axis.

[0078] In Example 19, the subject of Examples 11 through 18 comprises a first sensing portion including a first active portion and a second sensing portion including a second active portion and a counter-offering portion, wherein each of the first active portion, the second active portion, and the counter-offering portion includes a variable impedance based at least partially on a strain applied to each of the first active portion, the second active portion, and the counter-offering portion.

[0079] In Example 20, the subject of Examples 11 to 19 includes a deformable substrate being attached to a structure and configured to determine strain on the structure.

[0080] Example 21 is at least one machine-readable medium comprising instructions that, when executed by a processing circuit, cause the processing circuit to perform operations implementing any of Examples 1 to 20.

[0081] Example 22 is a device comprising means for implementing any of Examples 1 to 20.

[0082] Example 23 is a system that implements any of Examples 1 through 20.

[0083] Example 24 is a method of using any of Examples 1 through 20.

[0084] Some parts of this specification are presented in terms of algorithms or symbolic representations of operations on data stored as bits or binary digital signals within machine memory (e.g., computer memory). These algorithms or symbolic representations are examples of techniques used by those skilled in the art of data processing to convey the nature of their operations to other skilled in the art. As used herein, "algorithm" is a self-consistent sequence of operations or similar processing leading to a desired result. In this context, algorithms and operations involve the 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. For general reasons, it is sometimes convenient to refer to these signals using words such as "data," "content," "bits," "values," "elements," "symbols," "characters," "terms," ​​"numbers," and "numerals." However, these words are merely convenient labels and must be associated with appropriate physical quantities.

[0085] Unless specifically stated otherwise, discussions in this specification using words such as “processing,” “computing,” “calculating,” “determining,” “presenting,” “displaying,” etc., may refer to actions or processes of a machine (e.g., a computer) that manipulate or transform data represented as 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. Additionally, unless specifically stated otherwise, the terms “a” or “an” are used in this specification to include one or more instances, as is common in patent literature. Finally, as used in this specification, the conjunction “or” refers to a non-exclusive “or” unless specifically stated otherwise.

Claims

Claim 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 a conductive gel arranged to detect strain in the deformable substrate along the first axis; a second sensing element comprising a conductive gel having a first portion arranged to detect strain in the deformable substrate along the first axis and a second portion arranged to detect strain in the deformable substrate along the second axis; wherein the second sensing element is arranged to offset at least a portion of the stimulus detected by the first sensing element along the first axis. Claim 2 A flexible differential strain sensor according to claim 1, wherein the 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 detect the strain based, at least partially, on the change in impedance. Claim 3 A flexible differential strain sensor according to claim 2, further comprising a signal processing unit operatively coupled to the first sensing element and the second sensing element, 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. Claim 4 In paragraph 3, the flexible differential strain sensor is further configured such that the signal processing unit determines strain along the second axis based on a change in impedance from the first sensing element. Claim 5 In claim 4, the flexible differential strain sensor is further configured such that the signal processing unit outputs a vector indicating the strain along the first axis and along the second axis. Claim 6 In claim 5, the vector is a flexible differential strain sensor indicating a percentage change in strain on the deformable substrate relative to the initial strain. Claim 7 In claim 6, the percentage change in strain corresponds to a percentage change in deformation of the deformable substrate, a flexible differential strain sensor. Claim 8 A flexible differential strain sensor according to claim 2, 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 comprises a third sensing element comprising a conductive gel arranged to detect strain in the deformable substrate along at least the third axis. Claim 9 A flexible differential strain sensor according to claim 1, wherein the first sensing portion comprises a first active portion, the second sensing portion comprises a second active portion and a offset portion, and each of the first active portion, the second active portion, and the offset portion comprises a variable impedance based at least partially on a strain applied on each of the first active portion, the second active portion, and the offset portion. Claim 10 A flexible differential strain sensor according to claim 1, wherein the deformable substrate is attached to a structure and configured to determine strain on the structure. Claim 11 A method for 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 on the deformable substrate, comprising a conductive gel, for detecting strain on the deformable substrate along the first axis; and arranging a second sensing element on the deformable substrate, comprising a conductive gel, having a first portion for detecting strain on the deformable substrate along the first axis and a second portion arranged to detect strain on the deformable substrate along the second axis; wherein the second sensing element is arranged to offset at least a portion of the stimulus detected by the first sensing element along the first axis. Claim 12 A method according to claim 11, wherein the 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 partially, on the change in impedance. Claim 13 A method according to claim 12, further comprising the step of operatively coupling a signal processing unit to the first sensing element and to 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. Claim 14 In paragraph 13, the signal processing unit is further configured to determine strain along the second axis based on a change in impedance from the first sensing element. Claim 15 In paragraph 14, the method further configured such that the signal processing unit outputs a vector indicating the strain along the first axis and along the second axis. Claim 16 In paragraph 15, the vector is a method of indicating a percentage change in strain on the deformable substrate relative to the initial strain. Claim 17 In paragraph 16, the percentage change in the strain corresponds to the percentage change in the deformation of the deformable substrate. Claim 18 A method according to claim 12, comprising the step of arranging a third sensing element on a deformable substrate, 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 comprising a conductive gel that senses strain in the deformable substrate along at least the third axis. Claim 19 A method according to claim 11, wherein the first sensing portion comprises a first active portion, the second sensing portion comprises a second active portion and a counter-offering portion, and each of the first active portion, the second active portion, and the counter-offering portion comprises a variable impedance based at least partially on a strain applied to each of the first active portion, the second active portion, and the counter-offering portion. Claim 20 In claim 11, the method wherein the deformable substrate is attached to a structure and configured to determine strain on the structure.

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