WO2025199188A1 - Knot-based strain sensor - Google Patents

Abstract

Disclosed herein is a sensor, comprising a cable structure having a plurality of cords stitched together in a crown sinnet configuration and at least one conductive element integrated into the cable structure to form a plurality of loops. At least two different loops of the plurality can contact each other in response to a geometric change in the cable structure, thereby changing a resistance of the conductive element. In some embodiments, the geometric change is caused by at least one of a: tension of the cable structure; compression of the cable structure; or bending of the cable structure.

Description

KNOT-BASED STRAIN SENSOR

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit under 35 U.S.C. §119 of U.S. Provisional Patent Application No. 63/567,115 filed on March 19, 2024, which is hereby incorporated by reference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH [0002] N/A

BACKGROUND

[0003] Wearable sensors have many applications, including health monitoring, sports performance monitoring, and human-machine interfacing. Across these possible applications, wearable strain sensors are used to measure and detect physical changes (e.g., human movement). Strain sensors can be used to measure dynamically changing textile strain during movement. Strain sensors are typically positioned over a joint where textile strain is most pronounced. In addition to monitoring human movement, strain sensors can be used to monitor the function of wearable devices, such as compression and loading garments, when sensors are secured to the garment fabric to measure fabric strains. Compression garments are used pervasively in medical applications to treat deep vein thrombosis, leg ulcers, lymphedema, or other venous and lymphatic disorders, or as a preventative measure for thrombosis (e.g., compression socks used during flight).

[0004] Ideal compression levels depend on the targeted condition, but over- or under-target pressures can minimize the effect of treatment or introduce negative effects. Quantitative feedback using garment-integrated sensors could help calibrate medical compression treatments. The ability to quantify compression may be beneficial in characterizing the effectiveness across levels of compression for specific applications. In wearable applications such as human movement monitoring or quantifying compression garments, including and integrating sensors into other textiles presents a number of different challenges. SUMMARY OF DISCLOSED EMBODIMENTS

[0005] Textile-based strain sensors include conductive yarns or fibers in stitch structures (e.g., embroidery, knits, or weaves), which can be used in smart textiles. While dependent on available conductive yarns and fibers, such strain sensors deploy simple fabrication methods, standard equipment, and commercially available components, making them both easy to reproduce and accessible to researchers and professionals in the smart textiles field. However, many existing textile resistance-based strain sensors exhibit limitations such as hysteresis and cycle fatigue, and their performance is often related to the mechanical properties of the garment on which they are placed. Thus, there is a need to explore different configurations of textile-based strain sensors to improve upon these limitations, while leveraging the many benefits of this sensor type. [0006] Disclosed herein is a strain sensors, including a type of textile-based strain sensor. The disclosed sensor includes a stand-alone cable structure, which makes the sensor less reliant on garment fabric properties, and enables it to be integrated in parallel or in series with the object or garment being measured. Additionally, the disclosed sensor structure is sensitive to both tension and compression (including bending), which differs from many existing tensile sensors, which primarily measure tensile strain. Benefits of the disclosed sensors include structural flexibility, suitable for wearable applications, and designs that are easy to integrate with other textiles in garments. The disclosed sensor type is also well- suited for use in highly-constrained environments, due to its ease of integration with textiles in existing garments, as well as its overall simplicity and unobtrusiveness.

[0007] According to one aspect of the disclosure, a sensor comprises a cable structure having a plurality of cords stitched together in a crown sinnet configuration and at least one conductive element integrated into the cable structure to form a plurality of loops. At least two different loops of the plurality can contact each other in response to a geometric change in the cable structure, thereby changing a resistance of the conductive element.

[0008] In some embodiments, the geometric change is caused by at least one of a: tension of the cable structure; compression of the cable structure; or bending of the cable structure. In some embodiments, the at least one conductive element includes at least a first conductive element and a second conductive element. In some embodiments, the at least one conductive element includes at least a first conductive element and a second conductive element and the first conductive element and second conductive element are coupled together. In some embodiments, the cable structure has an elongated shape, wherein the at least one conductive element extends along a length of the cable structure. In some embodiments, the plurality of cords includes polyvinyl chloride (PVC) plastic cords. In some embodiments, the at least one conductive element comprises a silver-coated polyamide continuous filament.

[0009] According to another aspect of the disclosure, a sensor comprises a cable structure having a plurality of cords stitched together in a crown sinnet configuration, wherein one of the plurality of cords is at least one conductive element with a plurality of loops, wherein at least two different loops of the plurality can contact each other in response to a geometric change in the cable structure, thereby changing a resistance of the conductive element. In some embodiments, the geometric change is caused by at least one of a: tension of the cable structure; compression of the cable structure; or bending of the cable structure. In some embodiments, the at least one conductive element includes at least a first conductive element and a second conductive element.

[0010] In some embodiments, the at least one conductive element includes at least a first conductive element and a second conductive element and a second one of the plurality of cords is the second conductive element. In some embodiments, the at least one conductive element includes at least a first conductive element and a second conductive element and the cable structure has an elongated shape, wherein the at least one conductive element extends along a length of the cable structure. In some embodiments, the sensor further comprises one or more threads integrated into the cable structure and configured to secure the cable structure to a textile.

[0011] According to another aspect of the disclosure, a sensor comprises a cable structure having a plurality of cords stitched together. In some embodiments, the sensor comprises at least one conductive element integrated into the cable structure to form a plurality of loops, wherein at least two different loops of the plurality can contact each other in response to a geometric change in the cable structure, thereby changing a resistance of the conductive element. In some embodiments, the sensor comprises one or more threads integrated into the cable structure and configured to secure the cable structure to a textile.

[0012] In some embodiments, the plurality of cords are stitched together in a crown sinnet configuration. In some embodiments, the geometric change is caused by at least one of a: tension of the cable structure; compression of the cable structure; or bending of the cable structure. In some embodiments, the at least one conductive element includes at least a first conductive element and a second conductive element. In some embodiments, the at least one conductive element includes at least a first conductive element and a second conductive element and the first conductive element and second conductive element are coupled together. In some embodiments, the one or more threads further comprise a first thread configured to form one or more stitches along the cable structure and the textile. In some embodiments, the one or more threads further comprise a first thread configured to form one or more stitches along the cable structure and the textile and there are two stitches.

DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0013] The manner and process of making and using the disclosed embodiments may be appreciated by reference to the figures of the accompanying drawings. It should be appreciated that the components and structures illustrated in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the concepts described herein. Like reference numerals designate corresponding parts throughout the different views. Furthermore, embodiments are illustrated by way of example and not limitation in the figures, in which:

[0014] FIG. 1 A is a perspective view of a strain sensor including a cable structure with an integrated conductive element;

[0015] FIG. 1 B is an enlarged view of a portion of the strain sensor of FIG. 1A, highlighting the conductive element;

[0016] FIG. 2 is a perspective view showing formation of a cable structure having a box knot configuration for use in a strain sensor; [0017] FIG. 3A is a side view showing an example of a strain sensor conductive element in a stretched state and a circuit diagram showing an equivalent resistive component for the stretched conductive element;

[0018] FIG. 3B is a side view showing an example of a strain sensor conductive element in an unstretched state and a circuit diagram showing equivalent resistive components for the unstretched conductive element;

[0019] FIG. 4A is a side view of a strain sensor integrated with a textile;

[0020] FIG. 4B is a top view of the sensor-textile integration of FIG. 4A;

[0021] FIG. 5 is a close-up image of strain sensor during fabrication having a conductive thread in a braided configuration;

[0022] FIG. 6 is a perspective view of a strain sensor and electronics integrated within a wearable garment; and

[0023] FIG. 7 is a set of graphs of AR/R-20 vs. strain (%).

DETAILED DESCRIPTION

[0024] FIGS. 1 A and 1 B show an example of a strain sensor 100 including a cable structure 110 and a conductive element 120 integrated therein. In the example shown, cable structure 110 can include four cords 112, 114, 116, 118 (e.g., flat cords) stitched together in crown sinnet configuration (such as a box knot configuration). Other number of cords and other stitching confirmations can be used. The conductive element 120 can be integrated within the cable structure 110 to form a plurality of loops, at least two different loops of the plurality can contact each other in response to a geometric change in the cable structure 110, thereby changing the resistance of the conductive element 120. The cable structure 110 can experience geometric changes through the contraction (i.e., compression) and expansion (i.e., stretching) of the structure or the cords 112, 114, 116, 118. Such geometric changes in the cable structure 110 can include tension of the cable structure 110, compression of the cable structure 110, and/or bending of the cable structure 110. The conductive element 120 is integrated into the cable structure 110 such that the geometric changes (i.e., when at least two different loops of conductive element 120 come into contact with each other or separate) alter the sensor resistance, allowing for the characterization of strain, compression, or bends using piezoresistive changes.

[0025] The cable structure 110 includes a plurality of cords 112, 114, 116, 118 that extend generally along the length (e.g., in the direction of the x axis) of the cable structure 110. Each cord 112, 114, 116, 118 loops back and forth along the axis perpendicular to the length (e.g., in the direction of the y axis and z axis). Thus, a first cord 112 and a second cord 114 extend along a side of the cable structure 110 substantially facing the x-y plane, while a third cord 116 and a fourth cord 118 extend along another adjacent side of the cable structure 110 substantially facing the x-z plane. The plurality of cords 112, 114, 116, 118 extend generally along their respective directions to form a crown sinnet configuration (the formation of which will be discussed further in conjunction with FIG. 2).

[0026] The conductive element 120 extends generally along the length (e.g., in the direction of the x axis) of the cable structure 110 and substantially parallel to the first cord 112 and the second cord 114 substantially along the x-y plane. The conductive element 120 extends substantially along the x-y plane between the first cord 112 and the second cord 114 forming loops in the cable structure 110. FIG. 1 B is an enlarged view of a portion 106 of strain sensor 100. For ease of reference, a line 122 is added to illustrate the loops of the conductive element 120 through the cable structure 110. The loops of the conductive element 120 are generally in line (i.e. , substantially following) the third cord 116 and fourth cord 118 as the cords 116, 118 extend along the side of the cable structure 110.

[0027] The conductive element 120 can be disposed on a side of the third cord 116, such that it does not come into contact with the fourth cord 118. Disclosed herein are three ways for the conductive element 120 to extend along the cable structure 110. First, the conductive element 120 follows the edge of the third cord116, and exits the sensor 100 at either end. Second, the conductive element 120 follows the edge of the third cord 116, loops around the end of the sensor 100 to then follows the edge of fourth cord 118 and exists the sensor 100 on the same end that it entered. In this configuration, the portions of conductive element 120 following the third cord 116 should not come into contact with the portions following the fourth cord 118. [0028] Third, two independent conductive elements are included in the cable structure 110, forming two independent sensors within the single box knot cable structure 110. In this configuration, there may be one conductive element that is more sensitive to bending in a certain direction, compared to the conductive element on the other side of box knot cable structure. For example, one conductive element could follow the edge of the third cord 116, and one could follow the edge of fourth cord 118. Each enters the box knot cable structure 110 on one end and exits on the other end. In this configuration, the conductive element following the third cord 116 should preferably not come into contact with the conductive element following the fourth cord 118. In general, the conductive elements included on each side should avoid contacting each other (to maintain the sensor loop mechanism), but there could be unforeseen interest in manipulating the loop structures and contacts across the sensor. Thus, while three configurations are discussed herein, others may be possible

[0029] In some embodiments, there may be more than one conductive element. In some embodiments, the at least one conductive elements includes a first conductive element and a second conductive element. The two or more conductive material strands may intersect to enable additional arrangements of the loops (i.e., the resistors or delta shapes that will be discussed further in conjunction with FIGS. 3A-3D). The first conductive element and the second conductive element may be coupled together. For example, the conductive elements may be braided, twisted, or otherwise woven together. When there are more than one conductive element (i.e., arranged in a 2-ply, or 3-ply, or a braided configuration), the “plying” configuration enables the conductive elements to act as one single conductor.

[0030] In some embodiments, there may be a second conductive element on an opposing side of the cable structure. In such an embodiment, the first conductive element and the second conductive element may not come into contact with one another. In some embodiments, the conductive element can extend along a portion of the cable structure.

[0031] In some embodiments, there may be no separate conductive element and one or more of the cords 112, 114, 116, 118 in the cable structure 110 is the conductive element. Any of the plurality of cords 112, 114, 116, 118 may be the conductive element. In some embodiments, there may be a second conductive element, for example a second one of the plurality of cords 112, 114, 116, 118, included in the cable structure. In an embodiment where two of the plurality of cords 112, 114, 116, 118 are conductive elements, the two cords may be two thin flat cords running in parallel. In some embodiments, the cable structure 110 has an elongated shape and the at least one conductive element 120 extends along a length (e.g., in the direction of the x axis) of the cable structure 110.

[0032] The cords 112, 114, 116, 118 may comprise a polyvinyl chloride (PVC) plastic cords (e.g., lacing) or other flexible materials. In some embodiments, the cords 112, 114, 116, 118 may comprise conductive textiles (e.g. , ribbons, ropes, or flat textiles) or conductive plastics (e.g., conductive polypropylene or conductive polyethylene). The cord may be about 2.3 mm (+/- 2 mm) in width. The cord may be a commercial off-the-shelf PVC plastic lacing (with no conductive properties). The cord may be a 2.3 mm-width flat lacing composed of PVC plastic.

[0033] The conductive element 120 may have some detectable resistance per unit of length, for example a resistance of about 200 Ohms/m (+/-10 Ohms/m). In some embodiments, the conductive element 120 is a thread, yarn, fiber, other silver coated fibers, a stainless steel thread, a conductive carbon fibers, or threads with conductive cores. The conductive element 120 may comprise a silver-coated polyamide continuous filament with a resistance of about 200 Ohms/m (+/- 10 Ohms/m). The conductive element 120 may be a commercial-off-the-shelf silver- coated polyamide continuous filament with a resistance of about 200 Ohms/m (+/- 10 Ohms/m). In some embodiments, the sensors can be formed using Silver- Tech+ Conductive Thread (AMANN Group, Bonnigheim, Germany), which is a silver-coated polyamide continuous filament thread with a resistance of less than or equal to 200 O/m. These threads can be used singularly as a single thread or several threads can be used in a 3-ply braided configuration.

[0034] FIG. 2 is a perspective view of a cable structure 200 that can be provided within a strain sensor. For example, cable structure 200 may be similar to or the same as the cable structure 110 of FIGS. 1A and 1 B. Cable structure 200 has a box knot configuration. FIG. 2 illustrates how to form the box knot configuration (which may be referred to herein as a crown sinnet or a four-strand crown sinnet) with a plurality of cords 202, 204, 206, 208. The plurality of cords 202, 204, 206, 208 extend generally along the length (e.g., in the direction of the x axis) of the cable structure 200. Each cord 202, 204, 206, 208 loops back and forth along the axis perpendicular to the length (e.g., in the direction of the y axis and z axis).

[0035] To form a first box (which may be referred to herein as a first crown), lay a first cord 202 generally parallel to a third cord 206 substantially along the z-y plane, with a second cord 204 generally parallel to a fourth cord 208 substantially along the x-y plane. Lay the second cord 204 tightly over the end of the first cord 202 and stick the fourth cord 208 through the bight left by the first cord 202. Lay the third cord 206 over the end of the second cord 204 and stick the third cord 206 through the bight left by the fourth cord 208. Draw all of the cords 202, 204, 206, 208 tight. The box knot configuration is built up of successive boxes, like the one just described. In an embodiment where a conductive element is included and is separate from the plurality of cords 202, 204, 206, 208, the first box knot forms the “sensor base.”

[0036] The length of a strain sensor employing the cable structure 200 can vary based on the number of stitches or the stitch density, due to the tightness in the box stitches formed during fabrication. The sensor length may be selected based on the anticipated application of the sensor. The sensor length can be adjusted for practical reasons. Further, the length of the conductive element can be adjusted to change the baseline resistance of the sensor.

[0037] In some embodiments, the cable structure can include 23 stitches, resulting in a strain sensor length of about 82 mm (+/- 2 mm) to about 89 mm (+/- 2 mm). The 82 mm to 89 mm length can be selected to ensure that the strain sensor has appropriate attachment points on the textile. For example, a strain sensor with a length of 82 mm to 89 mm may be appropriate to determine a strain generalized across a portion of a lower leg. In some embodiments, stitch density in the disclosed strain sensor ranges from about 2.7 stitches (+/- 1 stitch) to about 2.9 stitches (+/- 1 stitch) per cm (i.e. , 6.9 to 7.4 stitches per inch).

[0038] The cords of the sensor may be woven to form other configurations, including, other types of sinnets with varying numbers of strands, etc. The conductive element may be included in other configurations, including for example, 1-ply, 3-ply, or braided strands. Disclosed strain sensor designs can accommodate a wide range of materials to support its use in different applications and/or environments. Several sensor properties can be customized to change sensor performance including: sensor total length (i.e., number of box knot stiches); tightness or density of box knot stitches; flat cord material properties; conductive material properties; total length of conductive material; and conductive material configuration, e.g., 1 -ply, 3-ply, braided strands, etc.

[0039] FIGS. 3A and 3B show a strain sensor conductive element in stretched and unstretched states, respectively, along with equivalent resistive components. FIG. 3A shows a conductive element 300 in a stretched state and an equivalent resistive component 310. The stretched state means the loops 306a, 306b, 306c of the conductive element 300 do not contact one another. A first loop 306a, a second loop 306b, and a third loop 306c extend along the conductive element 300.

[0040] FIG. 3B shows a conductive element 330 in an unstretched state and equivalent resistive components 340. The unstretched state means the loops 336a, 336b, 336c of the conductive element 330 make contact with one another. A first loop 336a, a second loop 336b, and a third loop 336c extend along the conductive element 330 The first loop 336a forms a first contact point 338a and a second contact point 338b with the second loop 336b. The second loop 336b forms a third contact point 338c and a fourth contact point 338d with the third loop 336c. The third loop 336c forms a fifth contact point 338e. The first contact point 338a corresponds to a first circle 342a, the second contact point 338b corresponds to a second circle 342b, the third contact point 338c corresponds to a third circle 342c, the fourth contact point 338d corresponds to a fourth contact point 342d, and the fifth contact point 338e corresponds to a fifth contact point 342e.

[0041] The unstretched configuration disclosed in FIGS. 3B forms a complex arrangement of resistors in delta shapes, which can be transformed to calculate total resistance using delta-wye resistor transformations. When stretched, as disclosed in FIGS. 3A, the contacts creating the delta shapes are disconnected, creating a single length of conductive material with a defined resistance value. There exist many other possible configurations of the conductive element between the stretched and unstretched states, with some contacts remaining and others disconnected.

[0042] FIGS. 4A and 4B show a strain sensor 400, with a side view shown in FIG. 4A and a top view shown in FIG. 4B. The sensor 400 of FIGS. 4A and 4B includes a cable structure 402 and a conductive element 450 integrated into the cable structure 402. Further, two attachment points are formed by non-conductive threads 460, 470 integrated into the cable structure and configured to secure the cable structure 402 to a textile 480.

[0043] The cable structure 402 includes a plurality of cords 410, 420, 430, 440 stitched together that extend generally along the length (e.g., in the direction of the x axis) of the cable structure 402. Each cord 410, 420, 430 440 loops back and forth along the axis perpendicular to the length (e.g., in the direction of the y axis and z axis). Thus, a first cord 410 and a second cord 420 extend along one side of the cable structure 402 substantially facing the x-y plane, while a third cord 430 and a fourth cord 440 extend along another adjacent side of the cable structure 402 substantially facing the x-z plane. The plurality of cords 410, 420, 430, 440 extend generally along their respective directions to form a box knot configuration.

[0044] FIGS. 4A and 4B show an attachment of 3.5 stitches, disposed between the first attachment point formed by a first thread 460 and the second attachment point formed by a second thread 470 that secure the sensor 400 to the textile 480. In FIG. 4A, the first cord 410 extends substantially along the z axis and the x axis to form a first stitch 1 , a second stitch 2, a third stitch 3 between the first attachment point formed by thread 460 and the second attachment point formed by thread 470. Further, the first cord 410 extends to form a fourth stitch 4 adjacent to the second attachment point formed by thread 470. The second cord 420 extends substantially along the z axis and the x axis to form a first half stitch 1.5, a second half stitch 2.5, a third half stitch 3.5 between the first attachment point formed by thread 460 and the second attachment point formed by thread 470.

[0045] In FIG. 4B, the fourth cord 440 extends substantially along the y axis and the x axis to form a first stitch 1 , a second stitch 2, a third stitch 3 between the first attachment point formed by thread 460 and the second attachment point formed by thread 470. Further, the fourth cord 440 extends to form a fourth stitch 4 adjacent to the second attachment point formed by thread 470. The third cord 430 extends substantially along the y axis and the x axis to form a first half stitch 1 .5, a second half stitch 2.5, a third half stitch 3.5 between the first attachment point formed by thread 460 and the second attachment point formed by thread 470. Thus, by viewing the sensor 400 from the side view (FIG. 4A) or the top view (FIG. 4B) there are 3.5 stitches disposed between the two attachment points formed by threads 460, 470.

[0046] The conductive element 450 extends generally along the length (e.g., in the direction of the x axis) of the cable structure 402 and parallel to the first cord 410 and the second cord 420 substantially along the x-y plane. The conductive element 450 extends substantially along the x-y plane between the first cord 410 and the second cord 420 forming loops in the cable structure.

[0047] The cable structure 402 is secured to the textile 480 at the attachment points by two threads 460, 470. The threads 460, 470 extend generally along the width (e.g., in the direction of the y axis) of the cable structure 402 and form one or more stitches along the box knot configuration of the cable structure 402 and the textile 480. One stitch refers to the interval between these repeating loops of the threads 460, 470 in the box knot configuration of the sensor 400. The first thread 460 extends substantially along the x-y plane to form a first loop 462 and a second loop 464, weaving through the cords 410, 420, 430, 440. The second thread 470 extends substantially along the x-y plane to form a first loop 472 and a second loop 474, weaving through the cords 410, 420, 430, 440. The attaching stitches (i.e., loops 462, 464, 472, 474) are symmetrical up and down the sensor 400 (i.e., first loop 462 and second loop 464, first loop 472 and second loop 474), both are present to ensure a robust attachment as the textile 480 undergoes geometric changes (i.e., stretches).

[0048] The threads 460, 470 extend through the cable structure 402 so as to avoid contact with the conductive element 450. The threads 460, 470 are carefully woven through, to ensure they do not ensnare the conductive element 450 and cause the conductive element 450 to deviate from the loop structure or obstruct the conductive element 450 from other conductive contact points. If the conductive element 450 were to be snagged, or otherwise fixed, it could unexpectedly interfere with the expected motion, resistance wise. As shown in FIG. 4B, the conductive element 450 extend substantially parallel along the x-y plane on one side of the third cord 430, while the threads 460, 470 extend substantially along the x-y plane on an opposing side of the third cord 430. The separation of the attachment point elements (i.e. , threads 460, 470) from the conductive thread elements (i.e., conductive element 450) by third cord 430 is notably useful in minimizing interference.

[0049] The threads 460, 470 secure the cable structure 402 to the textile 480 through the use of a needle and thread. One round of stitching (i.e., one stitch up and one stitch down) is depicted in FIGS. 4A-4B, forming the first loop 462, 472 and second loop 464, 474. “Stitches” in reference to the threads 460, 470 is referring to the thread connecting the sensor 400 to the textile 480, while earlier “stitches” referred to the number of stacked crowns (i.e., boxes) in the cable structure. Accordingly, these attachment points may be referred to as “attachment stitching,” as opposed to the loops “stitches” of the box knot configuration itself. Thus, two stitches are shown in FIGS. 4A-4B, forming the attachment points. [0050] In some embodiments, three rounds of stitching may be called for to ensure a strong attachment and, thus, more or less loops may be used. Further, each stitch may be tightened to ensure a strong attachment of the cable structure to the textile. Furthermore, this stitching can be done by navigating the needle through the lacing of the cable structure and conductive element. Threads 460, 470 should include stronger thread material, to ensure a secure attachment and that the strain measured is of the fabric’s, not the threads 460, 470 of the attachment system. In some embodiments, the threads 460, 470 may comprise a polyester thread, a nonconductive, inelastic thread, nylon, or any other embroidery thread, sewing thread, or other similar fibers.

[0051] The cable structure 402 may be attached to the textile 480 in a way that does not damage the textile, ensures accurate transfer of strain from the base textile to the sensor 400, and does not interfere with function of the sensor 400. The sensor 400 can be attached to the textile 480 at the two terminal ends of the sensor 400, or at intervals throughout the length of the sensor 400, as disclosed in FIGS. 4A-4B. The textile 480 may be situated on one side of the sensor 400 or the sensor 400 may loop around the textile 480. The sensor 400 may be attached on both sides of the sensor. The sensor 400 may be attached more than twice, depending on the length of the sensor 400. Several attachments may be included to ensure the sensor 400 does not buckle in some settings (for example, if the textile is stretchy and usually shrunken). Thus, generally, for longer sensors 400 there may be more attachment points.

[0052] FIG. 5 is a close-up image of a side view of a strain sensor 500 including a cable structure 510 and a needle 520 inserting a conductive element 530 inserted into the cable structure 510. The needle 520 disclosed in FIG. 5 is used for fabrication only and is removed from the sensor after fabrication is completed. Further, the needle 520 may be used to integrate the resulting sensor 500 into fabric, such as the configuration outlined in FIGS. 4A-4B.

[0053] FIG. 6 shows an example of a wearable sensor 600 including a strain sensor 610, which may be similar to or the same as sensor 100 in FIG. 1 , and electronics 630, 640, 650 integrated into a wearable garment 620 (i.e., a clothing item). Disposed adjacent to the sensor 610 is hardware 630 that includes one or more light emitting diode (LED) indicators 640, which is connected to the sensor 610 through wired connections 650. The sensor 610 is disposed in a fabric sleeve on the wearable garment 620. If human contact with the conductive materials, such as the conductive element 120 in FIG. 1 , is a concern for a given application the sensor 610 can be covered by a fabric sleeve.

[0054] The conductive element exits each end of the sensor 610 and can be integrated with read-out electronics 630. The conductive element exiting the sensor can be secured or stitched into the surrounding suit fabric, interfacing with a metal snap connector and insulated copper wires. The read-out electronics 630 can include commercial off-the-shelf electronics, or custom electronics, configured to measure the resistance of the sensor. Custom read out electronics may include one or more of: one or more light pipes; one or more light emitting diodes (LEDs); one or more on/off switches; one or more push buttons; one or more custom boards; one or more secure digital (SD) cards; one or more micro USB connectors; one or more batteries; one or more battery holders; one or more wires; and an enclosure.

[0055] The read-out electronics can read out a current or voltage via the conductive element and further processing can be used to detect the geometric changes of the cable structure of the strain sensor 610. The raw data collected by the strain sensor 610 is converted to units of resistance using a voltage divider. Dynamic resistance changes are visible in the time-series resistance data, which may be used for human movement monitoring applications. The resistance data may be converted to units of strain using a pre-defined calibration curve relating strain to resistance. Similarly, resistance or strain may be converted to fabric tension or compression loads using a pre-defined calibration curve.

[0056] FIG. 7 is a set of graphs 700, 710, 720 of AR/R.20 vs. strain (%). A first graph 700 discloses AR/R-20 702 vs. strain (%) 704 for sensor samples tested with a maximum test strain of 10%. A second graph 710 discloses AR/R-20 712 vs. strain (%) 714 for sensor samples tested with a maximum test strain of 20%. A third graph 720 discloses AR/R-20 722 vs. strain (%) 724 for sensor samples tested with a maximum test strain of 30%.

[0057] The graphs 700, 710, 720 disclose strain-resistance relationship of the disclosed strain sensor, including six sensor samples. These graphs 700, 710, 720 illustrate a clear relationship between sensor mechanical changes and resistance output. Three test profiles were completed on each sensor sample, and each test profile included a different maximum test strain, including: graph 710 disclosing a strain of 10%, graph 710 disclosing a strain of 20%, and graph 720 disclosing a strain of 30%.

[0058] The testing range included compression (-) and tension (+) states in the sensor, which enabled the characterization of resistance changes across these relevant geometric changes. Each test profile included ten consecutive cycles (with mean shown), with increasing strain applied at a constant rate of extension from the starting length (-40%) to the maximum test strain, followed by a symmetric decrease in strain in a sawtooth pattern. Resistance is normalized to the approximately baseline resistance at -20% strain. Variation across samples is observed, which is likely due to the limitations of manual fabrication methods, which could be automated in future. Hysteresis and time-dependent characteristics are apparent, and may be appropriate targets for improved sensor materials.

[0059] Disclosed herein is a textile-based strain sensor, which utilizes conductive yarns or fibers in stitch structures (e.g., embroidery, knits, or weaves). Benefits of the disclosed sensor include structural flexibility, suitable for wearable applications, and designs that are easy to integrate with other textiles in wearable garments. The disclosed sensor utilizes available conductive yarns and fibers, simple fabrication methods, standard equipment, and commercially available components, making it both easy to reproduce and accessible to researchers and professionals in the smart textiles field. The sensor can be mounted on top of a textile, but does not have to be mounted to a textile to function properly. Alternatively, the sensor can be integrated in the textile itself. The disclosed sensor is well-suited for use in highly-constrained environments, due to its ease of integration with textiles in existing garments, as well as its overall simplicity and unobtrusiveness.

[0060] Various embodiments of the concepts, systems, devices, structures and techniques sought to be protected are described herein with reference to the related drawings. Alternative embodiments can be devised without departing from the scope of the concepts, systems, devices, structures and techniques described herein. It is noted that various connections and positional relationships (e.g., over, below, adjacent, etc.) are set forth between elements in the following description and in the drawings. These connections and/or positional relationships, unless specified otherwise, can be direct or indirect, and the described concepts, systems, devices, structures and techniques are not intended to be limiting in this respect. Accordingly, a coupling of entities can refer to either a direct or an indirect coupling, and a positional relationship between entities can be a direct or indirect positional relationship.

[0061] As an example of an indirect positional relationship, references in the present description to forming layer "A" over layer "B" include situations in which one or more intermediate layers (e.g., layer "C") is between layer "A" and layer "B" as long as the relevant characteristics and functionalities of layer "A" and layer "B" are not substantially changed by the intermediate layer(s).The following definitions and abbreviations are to be used for the interpretation of the claims and the specification. As used herein, the terms "comprises," "comprising,” “includes," "including," "has," "having," "contains" or "containing," or any other variation thereof, are intended to cover a non-exclusive inclusion. For example, a composition, a mixture, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but can include other elements not expressly listed or inherent to such composition, mixture, process, method, article, or apparatus.

[0062] The terms "one or more" and "one or more" are understood to include any integer number greater than or equal to one, i.e. one, two, three, four, etc. The terms "a plurality" are understood to include any integer number greater than or equal to two, i.e. two, three, four, five, etc. The term "connection" can include an indirect "connection" and a direct "connection".

[0063] References in the specification to "one embodiment, "an embodiment," "an example embodiment," etc., indicate that the embodiment described can include a particular feature, structure, or characteristic, but every embodiment can include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0064] Use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0065] It is to be understood that the disclosed subject matter is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The disclosed subject matter is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. As such, those skilled in the art will appreciate that the conception, upon which this disclosure is based, may readily be utilized as a basis for the designing of other structures, methods, and systems for carrying out the several purposes of the disclosed subject matter. Therefore, the claims should be regarded as including such equivalent constructions insofar as they do not depart from the spirit and scope of the disclosed subject matter.

[0066] Although the disclosed subject matter has been described and illustrated in the foregoing illustrative embodiments, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the details of implementation of the disclosed subject matter may be made without departing from the spirit and scope of the disclosed subject matter.

Claims

CLAIMS What is claimed is:

1 . A sensor, comprising: a cable structure having a plurality of cords stitched together in a crown sinnet configuration; and at least one conductive element integrated into the cable structure to form a plurality of loops, wherein at least two different loops of the plurality can contact each other in response to a geometric change in the cable structure, thereby changing a resistance of the conductive element.

2. The sensor of claim 1 , wherein the geometric change is caused by at least one of a: tension of the cable structure; compression of the cable structure; or bending of the cable structure.

3. The sensor of claim 1 , wherein the at least one conductive element includes at least a first conductive element and a second conductive element.

4. The sensor of claim 3, wherein the first conductive element and second conductive element are coupled together.

5. The sensor of claim 1 , wherein the cable structure has an elongated shape, wherein the at least one conductive element extends along a length of the cable structure.

6. The sensor of claim 1 , wherein the plurality of cords includes polyvinyl chloride (PVC) plastic cords.

7. The sensor of claim 1 , wherein the at least one conductive element comprises a silver-coated polyamide continuous filament.

8. A sensor, comprising: a cable structure having a plurality of cords stitched together in a crown sinnet configuration, wherein one of the plurality of cords is at least one conductive element with a plurality of loops, wherein at least two different loops of the plurality can contact each other in response to a geometric change in the cable structure, thereby changing a resistance of the conductive element.

9. The sensor of claim 8, wherein the geometric change is caused by at least one of a: tension of the cable structure; compression of the cable structure; or bending of the cable structure.

10. The sensor of claim 8, wherein the at least one conductive element includes at least a first conductive element and a second conductive element.

11. The sensor of claim 10, wherein a second one of the plurality of cords is the second conductive element.

12. The sensor of claim 10, wherein the cable structure has an elongated shape, wherein the at least one conductive element extends along a length of the cable structure.

13. The sensor of claim 8, further comprising one or more threads integrated into the cable structure and configured to secure the cable structure to a textile.

14. A sensor, comprising: a cable structure having a plurality of cords stitched together; at least one conductive element integrated into the cable structure to form a plurality of loops, wherein at least two different loops of the plurality can contact each other in response to a geometric change in the cable structure, thereby changing a resistance of the conductive element; and one or more threads integrated into the cable structure and configured to secure the cable structure to a textile.

15. The sensor of claim 14, wherein the plurality of cords are stitched together in a crown sinnet configuration.

16. The sensor of claim 14, wherein the geometric change is caused by at least one of a: tension of the cable structure; compression of the cable structure; or bending of the cable structure.

17. The sensor of claim 14, wherein the at least one conductive element includes at least a first conductive element and a second conductive element.

18. The sensor of claim 17, wherein the first conductive element and second conductive element are coupled together.

19. The sensor of claim 14, wherein the one or more threads further comprise a first thread configured to form one or more stitches along the cable structure and the textile.

20. The sensor of claim 19, further comprising two stitches.