Wearable patterned nanocomposite circuits for temperature compensated strain sensing

Abstract

Various embodiments related to strain-sensitive nanocomposite circuits are disclosed. One example embodiment relates to a wearable sensor device comprising a flexible substrate and a nanocomposite compensation circuit. The nanocomposite compensation circuit can include two or more nanocomposite sensing elements integrated with material constituents of the flexible substrate. The nanocomposite compensation circuit can provide an output signal that is indicative of strain of a skin surface and compensated for ambient effects of an environment.

Description

PCT Application Attorney Docket No. 009062.8578. WO00 WEARABLE PATTERNED NANOCOMPOSITE CIRCUITS FOR TEMPERATURE COMPENSATED STRAIN SENSINGCROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent document claims priority to and benefits of U.S. Provisional Application 63 / 756,723, entitled “WEARABLE MATERIALS-BASED CIRCUITS FOR SENSING SKINSTRAINS WITHOUT AMBIENT EFFECTS,” and filed on February 10, 2025. The entire content of the above noted patent application is incorporated by reference as part of the disclosure of this patent document.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under N00014-20-1 -2329 and N00014-23-1-2647 awarded by the Office of Naval Research. The government has certain rights in this invention.TECHNICAL FIELD

[0003] Disclosed herein are systems, methods, and devices pertaining to wearable strainsensitive nanocomposite circuits.BACKGROUND

[0004] Human performance assessment of people of all ages, genders, and professions necessitates the measurement of physical movements and physiological parameters. Existing wearable skin-like and textile-based sensors for monitoring skin-strains, particularly those sensors based on piezoresistive nanocomposites, commonly employ resistive materials. However, when using these resistive materials in free living conditions, a common challenge among such sensors is that their sensing streams can be adversely affected by ambient environmental effects, such as temperature and humidity.BRIEF DESCRIPTION OF THE DRAWINGS

[0005] FIG. 1A shows a schematic of an example procedure of a fabrication method for producing a wearable sensor device, in accordance with the disclosed technology.

[0006] FIG. IB shows an image of an example wearable sensor device, in accordance with the disclosed technology.PCT Application Attorney Docket No. 009062.8578. WO00

[0007] FIG. 2 shows an image of an example fiber-integrated nanocomposite sensing element according to some embodiments of the disclosed technology.

[0008] FIG. 3 shows example strain sensing performance data of an example device based on the disclosed technology.

[0009] FIG. 4 shows an image of an example fiber-integrated nanocomposite sensing element according to some embodiments of the disclosed technology.

[0010] FIG. 5 shows a data plot of example electromechanical responses of some nanocomposite sensing elements based on the disclosed technology.

[0011] FIG. 6 shows an image of an example device according to an embodiment of the disclosed technology.

[0012] FIG. 7 shows an image of an example setup which was used in a study to characterize properties of a device based on the disclosed technology.

[0013] FIG. 8A shows an example electrical resistance time history of a device based on the disclosed technology.

[0014] FIG. 8B shows another example electrical resistance time history of a device based on the disclosed technology.

[0015] FIG. 9A shows an example circuit schematic of a Wheatstone bridge circuit that can be implemented in some example embodiments based on the disclosed technology.

[0016] FIG. 9B shows an example circuit schematic of a full bridge circuit that can be implemented in some example embodiments based on the disclosed technology.

[0017] FIG. 10 shows a schematic of an example wearable sensor device based on the disclosed technology.

[0018] FIG. 11 shows an image of an experimental setup which was used in a study, performed in accordance with disclosed techniques, to test an example device based on the disclosed technology.

[0019] FIG. 12 shows an example voltage output time history response of an example device based on the disclosed technology.

[0020] FIGS. 13A-13C show exemplary voltage output responses of a nanocomposite-based circuit based on the disclosed technology.

[0021] FIG. 14 shows an example force-strain cyclic mechanical response of a device based on the disclosed technology.

[0022] FIG. 15 shows an image of an example fiber-integrated nanocomposite device based on the disclosed technology.PCT Application Attorney Docket No. 009062.8578. WOOO

[0023] FIG. 16 shows a plot of example resistance versus time data obtained from a device based on the disclosed technology.

[0024] FIG. 17 shows a plot of example resistance versus time data obtained from an example fiber-integrated nanocomposite device based on the disclosed technology.

[0025] FIG. 18 shows a plot of example resistance versus time data obtained from a device based on the disclosed technology.

[0026] FIG. 19 shows an image of an example device and an experimental setup used in an example study, performed in accordance with disclosed techniques, to characterize the effects of temperature on the device.

[0027] FIG. 20 shows a plot of example resistance versus time data obtained from a device based on the disclosed technology.

[0028] FIG. 21 shows another plot of example resistance versus time data obtained from a device based on the disclosed technology.

[0029] FIG. 22 shows an example circuit schematic of a bridge circuit that can be implemented in various disclosed embodiments to provide temperature compensation.

[0030] FIG. 23 shows an image of an example device based on the disclosed technology and an experimental setup that can be implemented to characterize the device in accordance with some disclosed techniques.

[0031] FIG. 24 shows a schematic (left) of an example orthogonal configuration of nanocomposite sensing elements and an example breadboard circuit implementation of the orthogonal configuration, and a data plot (right) depicting temperature compensation performance that can be achieved using the orthogonal configuration.

[0032] FIG. 25 shows a schematic of an example longitudinal nanocomposite sensing element and an example breadboard circuit implementation of the longitudinal nanocomposite sensing element, and a data plot (right) depicting temperature compensation performance that can be achieved using the longitudinal nanocomposite sensing element.

[0033] FIG. 26 shows a flow chart of an example method according to an embodiment based on the disclosed technology.DETAILED DESCRIPTION

[0034] Human performance, in the context of one’s ability to physically perform a functional task with great efficiency, effectiveness, and precision, is critical for people of all ages, genders, and professions. Examples related to sports and the military are obvious, such as a golfer drivingPCT Application Attorney Docket No. 009062.8578. WOOO the ball downrange, a baseball pitcher throwing a curveball, and a marksman shooting at a distant target. While all athletes share the goal of maximizing their physical capabilities and improving the task outcome, human performance also extends to daily living, working, and personal wellness. A neurosurgeon needs to master fine motor movements to perform delicate surgeries, a patient undergoing physical therapy exercises to regain lost mobility, and an older adult aims to age healthily to independently perform mundane tasks. Although the desired outcomes are often well defined, the process for which one to achieve those objectives are not. What is needed is the ability to measure the physical and physiological processes of how these various functional tasks are executed, even though other psychological, environmental, and social aspects can also affect human performance. It is these movement-related sensing streams that contain rich information which can be extracted to augment behavior to enhance human performance, whether they are for improving athleticism, expediting recovery, or preventing injuries.

[0035] Noninvasive, multifunctional, wearable sensors, which can be mounted onto skin to measure physical, physiological, and biochemical parameters are being developed. The skin, being the largest organ in the human body, is not only a convenient surface for sensor attachment but is also the biochemical and mechanical interface between the person and environment where relevant sensing streams can be acquired. Often referred to as electronic skins (or e-skins), these wearable sensors mimic the properties of human skin and are designed to be soft, flexible, and conformable while densely packed with multi-modal sensing, signal conditioning, data processing, energy storage, and / or wireless communication functionalities. Such e-skins have been shown to measure various electrophysiological signals (e.g., electrocardiogram, electromyography, electroencephalogram), biochemical markers (e.g., glucose and pH), and biomechanical parameters (e.g., strain and pressure).

[0036] Measuring complex movements and physiological parameters for human performance assessment have been achieved using skin-strain measurements from thin film piezoresistive sensors. Besides nanocomposite elastomers, textile -based sensors have gained significant attention because of their acceptability for wearing. Motion Tape, which is a self-adhesive, elastic fabric with graphene nanosheet (GNS) thin films, has been demonstrated to accurately measure skin-strains across different locations on the body. In an example demonstration, its high sensitivity enabled Motion Tape to quantify muscle engagement, where skin-strain signal amplitudes were directly correlated with surface electromyography measurements at the same location. An advantage of these sensors is that the type of physical orPCT Application Attorney Docket No. 009062.8578. WOOO physiological signal acquired could be determined by where it is mounted on the body. An example is the monitoring of respiration rate using Motion Tape affixed onto the chest area.

[0037] A major challenge when using any type of piezoresistive nanocomposite wearable sensor is their intrinsic sensitivity to ambient conditions such as temperature and humidity, among others. A multitude of effects could simultaneously occur to increase or decrease the nanocomposite's electrical conductivity. How conductivity would change is inherently complex, since temperature changes could induce thermal expansion of the polymer matrix, alter electron tunneling behavior between fillers, and change filler conductivity, as well as charge transport properties.

[0038] Furthermore, most sensors are susceptible to ambient and environmental effects, and their measurements can change and drift according to these effects. Typically, other reference sensors are needed to compensate for this, which requires additional devices and circuitry be included in them, as well as additional electronics to collect data from these reference sensors at the same time.

[0039] Disclosed herein are various example embodiments related to wearable, strainsensitive piezoresistive nanocomposites. Some disclosed embodiments feature piezoresistive nanocomposites integrated with the individual fibers of a substrate (e.g., elastic fabric) to enable reliable strain sensing under various environmental conditions. Some embodiments of the disclosed technology can be used to provide a wearable sensor capable of measuring skin-strains that are correlated to motion, angles of rotation, movement, and muscle engagement. The sensor signals are not affected by changes in environmental conditions (e.g., humidity, body temperature, ambient temperature, and exposure to other liquids or effects) that may change the electrical resistance of the nanocomposites.

[0040] Among other features and benefits, the disclosed embodiments can be implemented to provide accurate skin-strain sensing and facilitate understanding of human functional movements. The disclosed embodiments are broadly applicable to many resistive nanocomposite sensors whose electrical properties are impacted by ambient conditions. Orthogonally patterned nanocomposite circuits based on the disclosed technology can help mitigate environmental noise signals to improve wearable sensor performance and stability within a compact form factor.

[0041] Some disclosed embodiments leverage the strain-sensitive properties of nanocomposites to provide a wearable, strain-sensitive device that can be used to provide sensor readings that are not affected by ambient effects. In some embodiments, this technical effect can be achieved by fabricating nanocomposites in different patterns and directions onto a substrate.PCT Application Attorney Docket No. 009062.8578. WO00 Some disclosed embodiments are fully integrated such that no additional circuits or reference sensors are needed and can include materials-based circuits created using printed functional materials.

[0042] Some disclosed embodiments relate to the deposition of strain-sensitive (e.g., piezoresistive nanocomposites) onto a substrate such as elastic fabric (e.g., kinesiology tape or K-Tape) or any other substrate.

[0043] Some disclosed embodiments utilize an elastic fabric that can be adhered anywhere on skin and on the body to measure skin-strains.

[0044] The disclosed embodiments can be fabricated using various deposition techniques. In some example embodiments, deposition can be performed by printing, spray-coating, or any other means of placing nanomaterial ink directly onto a substrate (e.g., fabric).

[0045] Some disclosed embodiments include nanocomposite sensors that can be formed in a unique geometry using techniques such as printing or stenciling. Some disclosed embodiments employ multiple, unique nanocomposite sensors in a pattern.

[0046] Some disclosed embodiments include nanocomposite sensors that are orthogonal to one another.

[0047] Some disclosed embodiments include nanocomposite sensors that are interconnected by conductive material printed directly onto a substrate (e.g., fabric) or physically connected by wires.

[0048] Some disclosed embodiments include nanocomposite sensors that form an electrical resistance bridge (e.g., half-bridge or full-bridge Wheatstone Bridge circuit).

[0049] Some disclosed embodiments include a materials-based circuit which, when adhered onto skin, can measure strains along its longitudinal direction, and the strain measurements will not be affected by ambient effects, such as temperature, humidity, etc.

[0050] Some disclosed embodiments can be used to provide strain measurements which are automatically compensated and unaffected by ambient conditions.

[0051] Some disclosed embodiments employ Motion Tape, which is a piezoresistive graphene nanosheet thin film integrated with an elastic fabric substrate that exhibits highly linear and repeatable strain sensing properties but also possesses temperature-dependent electrical characteristics.

[0052] In some disclosed embodiments, by designing and fabricating orthogonally oriented, fiber-integrated nanocomposites on the same substrate and then electrically connecting them toPCT Application Attorney Docket No. 009062.8578. WOOO yield a materials -based bridge circuit, reliable strain sensing during varying ambient temperatures can be achieved.

[0053] Some example embodiments relate to a method for patterning wearable piezoresistive nanocomposites so that strain measurements are automatically compensated and unaffected by ambient conditions such as temperature.

[0054] In some example embodiments, orthogonally oriented GNS thin films, which are electrically connected to yield a materials-based Wheatstone bridge circuit, can reliably measure strain despite varying ambient temperatures. GNS textile-based strain sensors are used as the foundation for which the patterned materials-based circuit is formed. In an example characterization performed in accordance with disclosed techniques, the nanocomposite's temperature-dependent electrical and electromechanical responses were characterized and it was demonstrated that the patterned nanocomposite's dynamic sensing behavior is stable despite varying ambient temperatures.

[0055] FIG. 1A shows an example procedure for preparing graphene nanosheet - ethyl cellulose (EC) (GNS-EC) solutions and fabricating a wearable sensor based on the disclosed technology. The procedure can include dispersing 30 mg / mE of GNS in a 2 wt.% EC solution dissolved in 200 proof ethyl alcohol. Adequate dispersion can be achieved and confirmed by visual observations after subjecting 20 mL of GNS-EC solution to 120 min of bath sonication, followed by 1 h of high-energy probe sonication, all at room temperature (~ 20 °C). The GNS-EC dispersion can then be heated at 40 °C and stirred at 400 rpm for ~ 30 min until it reaches the desired viscosity. The dispersion may be allowed to cool to room temperature and is herein referred to as GNS-EC ink. A wearable sensor can be fabricated by depositing GNS- ethyl cellulose (EC) ink onto elastic fabric substrates.

[0056] FIG. IB shows an image of an example wearable sensor based on the disclosed technology, such as that fabricated by the process shown in FIG. 1A, and how the example wearable sensor can be affixed onto skin. As shown in FIG. IB, electrical properties of the wearable sensor can be measured via multi-strand wires soldered to silver electrodes. Additionally, FIG. IB shows a GNS-EC fiber-integrated nanocomposite integrated with a fabric, K-tape substrate.

[0057] Some disclosed embodiments utilize Motion Tape, which is a wearable textile-based sensor, that derives its strain sensing properties from the GNS and EC fiber-integrated nanocomposite deposited onto commercially available kinesiology tape (K-Tape) (FIG. 1A and IB). In some disclosed sensors, the substrate (e.g., K-Tape) is orthotropic, where its longitudinalPCT Application Attorney Docket No. 009062.8578. WOOO spandex or elastane fibers endow it with low stiffness and high stretchability, while the transverse cotton fibers are stiffer but provide comfort, flexibility, and breathability. The unique orthotropic mechanical behavior of the substrate can be leveraged in some embodiments to provide a wearable strain sensor that is most sensitive along its longitudinal axis.

[0058] FIG. 2 shows an image of an example device comprising a longitudinal GNS-EC fiber-integrated nanocomposite sensing element. The longitudinal GNS-EC fiber-integrated nanocomposite sensing element can be integrated with various substrates, including fabric or textile substrates (e.g., K-tape, Motion Tape, etc.), in accordance with disclosed techniques.

[0059] FIG. 3 shows example strain sensing performance data of an example device based on the disclosed technology.

[0060] In an example demonstration, the device shown in FIG. 2 was subjected to tensile cyclic testing while its electrical resistance was simultaneously recorded. Cyclic load frame tensile tests to different peak strains were conducted to reveal the linear, repeatable, and stable strain sensing performance of the device as shown in FIG. 3. In another example characterization of the device, it was demonstrated that the electromechanical response of the device remains stable up to 200 cycles of loading while exhibiting strain sensitivities of 70 to 100 and an average linear coefficient of determination (R2) of 0.994.

[0061] FIG. 4 shows an image of an example device comprising transverse GNS-EC fiber-integrated nanocomposite sensing elements. As shown in FIG.4, the GNS-EC fiber-integrated nanocomposites are deposited horizontally along the K-Tape transverse axis.

[0062] FIG. 5 shows a data plot of example electromechanical responses of some nanocomposite sensing elements based on the disclosed technology.

[0063] To demonstrate how the orthotropic fabric construction enhances strain sensing along the longitudinal axis, load frame tests were conducted in an example demonstration using the GNS-EC fiber-integrated nanocomposites deposited horizontally along the K-Tape transverse axis (FIG.4). When strained in the longitudinal direction, the stiff transverse cotton fibers did not show significant Poisson's behavior with minor variations in GNS-EC electrical resistance response (FIG. 5). On the other hand, straining it in the transverse direction along the length of the nanocomposite yielded a significantly lower strain sensitivity versus standard Motion Tape (FIG. 5).

[0064] FIG. 6 shows a low-magnification microscope image of an example device according to an embodiment of the disclosed technology. Specifically, FIG. 6 shows a GNS-EC nanocomposite thin film deposited on K-tape (FIG. 6, right) and an adjacent area of the devicePCT Application Attorney Docket No. 009062.8578. WOOO with bare K-Tape (FIG. 6, left). As shown in FIG. 6, the GNS-EC nanocomposite is well-integrated with the individual textile fibers of the K-tape substrate, as opposed to forming a continuous film on the surface. In some disclosed embodiments, this technical feature enables the overall electromechanical properties of some GNS-EC nanocomposites to be strongly governed by the mechanical behavior of the fabric fibers of the substrate. In some disclosed embodiments, such features can be leveraged to provide a wearable sensor device that behaves approximately like a unidirectional strain sensor along its longitudinal axis.

[0065] FIG. 7 shows an image of an example setup to characterize temperature-dependent electrical properties during heating and cooling of a GNS-EC nanocomposite device based on the disclosed technology. In the example characterization, a thermocouple was mounted to the side of a beaker filled with water. It was hypothesized that the electrical and electromechanical properties of the device are sensitive to ambient temperature. Since the device is a wearable sensor, the range of temperature considered was akin to what a human would normally experience. Controlled testing was performed by affixing the device to the side of a beaker filled with water and gently heating it from room temperature or ~ 20 °C to 55 °C before cooling it again (FIG. 7).

[0066] FIG. 8A and FIG. 8B shows representative results of the device electrical resistance time histories during the heating and cooling cycles, respectively. The negative relationship between electrical resistance and temperature is consistent with other types of graphene and CNT nanocomposites studied elsewhere. The non-monotonic temperature-dependent electrical response can be a complex combination of filler, matrix, and filler / matrix interfacial thermally activated processes. Results of the example characterization show that some GNS-EC fiber-integrated nanocomposites exhibit temperature-dependent electrical resistance behavior.

[0067] Some disclosed embodiments relate to a patterned nanocomposite compensation circuit.

[0068] FIG. 9A shows an example circuit schematic of a Wheatstone bridge circuit that can be implemented in some example embodiments based on the disclosed technology.

[0069] FIG. 9B shows an example circuit schematic of a full bridge circuit that can be implemented in some example embodiments based on the disclosed technology.

[0070] Strain gages and resistive sensors are often interfaced with a Wheatstone bridge circuit (FIG. 9A) not only for acquiring voltage instead of resistance measurements but also for ambient effect compensation (e.g., temperature, humidity, or hydrostatic pressure). A disadvantage of using a classical Wheatstone bridge circuit is that it can be bulky, since itPCT Application Attorney Docket No. 009062.8578. WOOO requires discrete circuit elements mounted on a circuit board along with terminals for power and voltage measurements. Regardless, the compensation circuit is created by replacing the three fixed resistors in the quarter bridge (FIG. 9A) with one or three variable resistors to form a half or full bridge circuit (FIG. 9B), respectively. In all cases, when the bridge is powered with a supply voltage of V, across nodes 2 and 3 and all four resistive components (Ri, Rs, Rs, and R-i in Figure 9B) are of the same resistance, a 0 V output is achieved. When the bridge becomes imbalanced, Vois produced between nodes 1 and 4. The governing equation for the Wheatstone bridge circuit is:

[0071] By assuming that resistance change (AR) is always small so that second order factors are negligible, Equation 1 can be rewritten in terms of the resistance change for each resistor in the bridge circuit (i.e., ARi, AR2, ARs, and Zl / G):

[0072] In the full bridge circuit in FIG. 9B, Ri and Rs are subjected to both strain and ambient effects, whereas all other resistors only experience ambient effects, such as temperature changes. Both stress and temperature will induce strain (£) in the strain gage or Motion Tape alike, and its normalized change in resistance (ARn) can be calculated using:where Ro is the nominal or baseline resistance of the strain sensor and k is sensitivity. By expressing each resistive component in the full bridge using Equation 3 and substituting the expression into Equation 2, one gets:

[0073] Some disclosed embodiments include patterned nanocomposite compensation circuits. In one example embodiment, an orthogonally patterned nanocomposite based on the disclosed technology can achieve the same effectiveness as a Wheatstone bridge circuit compensating for temperature and ambient effects but without using discrete circuit elements. In some disclosed embodiments, both full bridge and half bridge implementations can be realized by depositing GNS-EC thin films in orthogonal orientations as illustrated in FIG. 9B and FIG. 10.PCT Application Attorney Docket No. 009062.8578. WO00

[0074] In some disclosed embodiments, each nanocomposite element serves as a variable resistor, with the longitudinal ones sensing strain and all of them experiencing the same ambient temperatures. In addition to compensating ambient effects, the orthogonal pattern can also account for Poisson's effect of the substrate (e.g. K-tape) when strain is applied along its longitudinal direction. The strains in the longitudinal (£i) and transverse (fj) nanocomposite elements can be expressed as:Si = sm+£T (5a)£t = ~V£rn +£T (5b) where £mis mechanical strain applied in the longitudinal axis, £r is strain due to thermal expansion or other ambient effects, and vis the substrate’s Poisson’s ratio. Equations 5a and 5b can be substituted into Equation 4, where variable resistors 1 and 3 are the longitudinal GNS-EC fiber-integrated nanocomposites, while 2 and 4 correspond to the transverse ones,where each subscript corresponds to the corresponding nanocomposite in the materials-based Wheatstone bridge circuit. Equation 6 can be further simplified to yield:

[0075] Equation 7 indicates that the effects of temperature and other ambient effects are eliminated (z.e., £1 is no longer present in the equation), and the resulting normalized voltage output is enhanced because of Poisson's effect too, with a slightly higher equivalent sensitivity of k(l + v) / 2.

[0076] FIG. 10 shows an example wearable sensor device 1000 based on the disclosed technology. The wearable sensor device 1000 includes a flexible substrate 1002 (e.g., configured to interface with a skin surface exposed to an environment) and a patterned nanocomposite compensation circuit disposed on the flexible substrate 1002, in which a nanocomposite 1001 is patterned in accordance with disclosed techniques to form two orthogonally oriented GNS-EC fiber-integrated nanocomposite structures 1010, 1020, resulting in an equivalent half bridge circuit. For example, the nanocomposite 1001 can be patterned as two or more nanocomposite sensing elements integrated with material constituents of the flexible substrate 1002. As depicted in FIG. 10, the wearable sensor device 1000 includes a longitudinal nanocomposite 1020, referred to as the "active" arm of the bridge, and a transverse nanocomposite 1010, referredPCT Application Attorney Docket No. 009062.8578. WO00 to as the "passive" ami. The nominal resistance of each GNS-EC fiber-integrated nanocomposite structures 1010, 1020 can be fabricated to be approximately the same (e.g., ~ 1 kQ). The wearable sensor device 1000 also includes electrodes 1050 and a conductive trace 1060 that can be coupled to one or both of the longitudinal nanocomposite 1020 and transverse nanocomposite 1010. For example, the electrodes 1050 can be used to electrically couple one or both of the fiber-integrated nanocomposite structures 1010, 1020 to the conductive trace 1060 such that the device 1000 forms a complete sensor. The wearable sensor device 1000 includes measurement electrodes 1090 in electrical communication with at least some of the electrodes 1050 to allow an electrical output signal transduced by the electrodes 1050 to be readout. The conductive trace 1060 may couple the longitudinal nanocomposite 1020, transverse nanocomposite 1010, electrodes 1050, and measurement electrodes 1090. The electrical output signal can be compensated for one or more conditions in the environment based on sensed strain by at least one of the nanocomposite structures 1010, 1020. In an example readout procedure, the electrical output signal can be readout as a voltage or resistance measurement obtained using a measurement device (e.g., digital multimeter) electrically connected to selected measurement electrodes 1090.

[0077] In some embodiments of the device 1000, the fiber-integrated nanocomposite structures 1010, 1020 are structured to form a half-bridge circuit (e.g., half of the full bridge circuit shown in FIG. 9B). In some implementations, the device 1000 includes another halfbridge circuit formed using additional fiber-integrated nanocomposite structures that are substantially similar to the fiber-integrated nanocomposite structures 1010, 1020. Both halfbridge circuits may be electrically coupled to one another and the electrical output signal can be readout as a voltage (Vo) obtained by probing the measurement electrodes 1050 in accordance with the circuit diagram shown in FIG. 9B.

[0078] In some embodiments of the device 1000, the fiber-integrated nanocomposite structures 1010, 1020 are structured to form a half-bridge circuit (e.g., half of the full bridge circuit shown in FIG. 9B). In some implementations, the device 1000 includes two resistors that are connected in series (e.g., R1 and R2 in FIG. 9B; or R3 and R4 in FIG. 9B), where the resistance of those two resistors matches the resistances of the fiber-integrated nanocomposite structures 1010, 1020, respectively. The half-bridge circuit and the two resistors can be electrically coupled to one another and the electrical output signal can be readout as a voltage (Vo) obtained by probing the measurement electrodes 1050 in accordance with the circuit diagram shown in FIG. 9B.PCT Application Attorney Docket No. 009062.8578. WOOO

[0079] FIG. 11 shows an image of an experimental setup which was used in an example study to test a patterned Motion Tape device based on the disclosed technology. During the study, a nanocomposite bridge circuit based on the disclosed technology was connected to a bread board with a voltage source, two reference resistors selected to match the resistance of the GNS-EC fiber-integrated nanocomposites, and voltage output measurement terminals. Testing began with the baseline test, where the load frame strained the patterned Motion Tape by applying a cyclic sawtooth load pattern to a peak strain of 3%. Ambient temperature was kept constant during testing.

[0080] FIG. 12 shows an example plot of a representative voltage output time history response of the patterned device which was tested. FIG. 12 shows that its electromechanical response is stable and resembles the applied cyclic strain pattern. In FIG. 12, Vois the measured output voltage using the Wheatstone bridge setup (FIG. 9A). The electrical resistance of the GNS-EC fiber-integrated nanocomposite can be computed using Equation 1, given the resistances of the other three reference resistors in the circuit. The results of FIG. 12 are expected and comparable to those results of FIG. 3, thereby confirming strain sensing in a stable ambient environment.

[0081] The study continued by introducing temperature changes to the patterned Motion Tape materials-based circuit while simultaneously sensing applied strains. Starting at room temperature, a heat gun slowly warmed the entire test setup from ~ 20 °C to 55 °C, including the reference thermistor mounted adjacent to the patterned Motion Tape. Once temperature stabilized, the heat source was removed to allow the specimen to gradually cool (and decrease temperature) while tensile cyclic strains were applied. Measurements were acquired during the cooling phase, as opposed to during heating, because the rate of cooling was more consistent test after test versus trying to maintain a constant heating rate. Hot air blowing from the heat gun can also induce strains on the specimen, thus potentially affecting GNS-EC fiber-integrated nanocomposite electrical resistance behavior.

[0082] FIG. 13A shows a representative plot that overlays the recorded temperature and electrical resistance time histories during the cooling phase. The results in FIG. 13A confirm that, while the patterned Motion Tape device experienced a significant drop in temperature over the duration of testing, Voremained fairly stable because of temperature compensation enabled by the half bridge materials-based circuit. The tensile cyclic electromechanical response of the patterned Motion Tape is clearly resolved in FIG. 13A with minor fluctuations in baseline resistance or voltage. Equation 7 can be used to compute the strains, as measured by thePCT Application Attorney Docket No. 009062.8578. WOOO longitudinal GNS-EC fiber-integrated nanocomposite, given the applied source voltage, strain sensitivity, and Poisson’s ratio.

[0083] Additional tests were performed on the patterned Motion Tape device with the materials-based half bridge circuit disconnected. The transverse sensing element or passive arm was replaced with a discrete resistor of the same value to form a standard Wheatstone bridge circuit without any ambient effect compensation.

[0084] FIG. 13B shows that Vochanged dramatically with changing temperature. Vo, and equivalently the resistance of the active arm GNS-EC fiber-integrated nanocomposite, exhibits a low frequency increasing “drift” and is inversely proportional to the exponential decrease in temperature, which is consistent with findings previously shown in FIG. 8B. It is evident that, without compensation, Vodrifted significantly during changing temperature, even though the strain sensing waveforms could still be resolved from the results in FIG. 13B. The amplitude of the voltage drift was more than one order of magnitude greater than in the temperature compensated setup before (FIG. 13 A), which further highlighted the effectiveness of temperature compensation.

[0085] Another set of temperature-strain tests aimed to validate that the transverse GNS-EC nanocomposite element (passive arm) was minimally affected by applied strains along the longitudinal axis. During this set of tests, only the transverse nanocomposite was connected to the Wheatstone bridge circuit while the longitudinal element (active arm) was replaced with a fixed reference resistor, thereby also eliminating temperature compensation. The Votime history result, presented in FIG. 13C, is consistent with the observation that the horizontal fibers in the K-Tape substrate are significantly stiffer and, as a result, are minimally affected by transverse strains induced by Poisson's effect. The inversely proportional resistance drift associated with temperature changes is, however, significant and consistent with the test results in FIG. 13B and FIG. 8B.

[0086] FIG. 14 shows an example force-strain cyclic mechanical response of a patterned Motion Tape device employed in an example study performed in accordance with disclosed techniques. FIG. 14 plots the first 10 cycles of loading. It can be observed from FIG. 14 that there is clear hysteretic behavior, which is expected of textiles, and this mechanical behavior could contribute to slight nonlinearities in Motion Tape electromechanical response as was observed in FIG. 3 and FIG. 5. Additionally, its hysteretic response remained independent of time, and mechanical behavior remained consistent from cycle to cycle. This result further confirms that the drifts observed in FIG. 13B were not due to degrading mechanical propertiesPCT Application Attorney Docket No. 009062.8578. WOOO but rather because of primarily thermal effects. Overall, the results presented in FIG. 13 A, FIG.13B, and FIG. 13C confirm that the nanocomposite-based circuit successfully compensated for changing ambient temperature to output a voltage response that was directly proportional to the applied longitudinal strains.

[0087] FIG. 15 shows an image of an example fiber-integrated nanocomposite device based on the disclosed technology. The device of FIG. 15 comprises electrodes and a longitudinal GNS-EC fiber-integrated nanocomposite sensing element disposed on Motion Tape. The effects of moisture (e.g., sweat) on the electrical response of the device shown in FIG. 15 were investigated in an example demonstration by first employing the device using bare Motion Tape and later using Motion Tape with an integrated hydrophobic coating. The study included administering one drop of water on the nanocomposite sensing element every 10 minutes.

[0088] FIG. 16 shows a plot of example resistance versus time data obtained from the device in the example study. These results demonstrate that the effects of moisture on the device are insignificant, especially relative to the sensing response of the device.

[0089] FIG. 17 shows a plot of example resistance versus time data obtained from an example fiber-integrated nanocomposite device based on the disclosed technology. The device of FIG. 17 (inset) comprises electrodes and a GNS-EC fiber-integrated nanocomposite sensing element disposed on Motion Tape. The effects of moisture (e.g., sweat) on the electrical response of the device shown in FIG. 17 were investigated by first employing the device using bare Motion Tape and later using Motion Tape with an integrated hydrophobic coating. The study included administering one drop / spray of saline on the nanocomposite sensing element every minute. Results of the study are shown in FIG. 17.

[0090] FIG. 18 shows a plot of example resistance versus time data that was obtained from bare Motion Tape in another example study performed, in accordance with disclosed techniques, to investigate the effect of changes in ambient humidity on the electrical response of bare Motion Tape. The study involved placing bare Motion Tape in a chamber with a humidifier and turning on the humidifier for approximately 4 minutes. FIG. 18 shows the effect of changes in ambient humidity on the electrical resistance of Motion Tape.

[0091] FIG. 19 shows an image of an example device and an experimental setup used in an example study, performed in accordance with disclosed techniques, to characterize the effects of temperature on the device.

[0092] FIG. 20 and FIG. 21 show, respectively, a plot of example resistance versus time data obtained from the device during the study. During the study, the device was attached onto aPCT Application Attorney Docket No. 009062.8578. WOOO beaker filled with water (FIG. 19). Temperature tests were performed using a hotplate to heat the device and temperature was recorded using a thermocouple. Data was acquired from the device using digital multimeters.

[0093] FIG. 22 shows an example circuit schematic of a Wheatstone bridge circuit that can be implemented in various disclosed embodiments to provide a temperature compensation full bridge circuit.

[0094] FIG. 23 shows an image of an example device and an experimental setup used in an example study, performed in accordance with disclosed techniques, to investigate performance of example materials-based Motion Tape circuitry in providing temperature compensation. During the study, the device was attached onto a beaker filled with water (FIG. 23). Temperature compensation tests were performed using a hotplate to heat the device. As shown in FIG. 23, the device includes a longitudinal fiber-integrated nanocomposite sensing element and a transverse GNS-EC fiber-integrated nanocomposite sensing element, both disposed on Motion Tape. A Wheatstone half bridge circuit was formed using the orthogonal configuration of the longitudinal fiber-integrated nanocomposite sensing element and the transverse fiber-integrated nanocomposite sensing element.

[0095] FIG. 24 and FIG. 25 show example results obtained in the study. Specifically, FIG.24 (left) shows a schematic of the orthogonal configuration of the longitudinal fiber-integrated nanocomposite sensing element and the transverse fiber-integrated nanocomposite sensing element. FIG. 24 (left) also shows a breadboard circuit implementation of the orthogonal configuration of the longitudinal fiber-integrated nanocomposite sensing element and the transverse fiber-integrated nanocomposite sensing element. FIG. 25 (left) shows a schematic of a longitudinal fiber-integrated nanocomposite sensing element and a breadboard circuit implementation of the longitudinal fiber-integrated nanocomposite sensing element. Temperature compensation performance of the orthogonal configuration of the longitudinal fiber-integrated nanocomposite sensing element and the transverse fiber-integrated nanocomposite sensing element are shown in FIG. 24 (right). Temperature compensation performance of the longitudinal fiber-integrated nanocomposite sensing element are shown in FIG. 25 (right). The results shown in FIG. 24 and FIG. 25 demonstrate that embodiments of the disclosed technology can provide automatic temperature compensation to ambient effects.

[0096] Some disclosed embodiments can be fabricated in accordance with the following example techniques.PCT Application Attorney Docket No. 009062.8578. WO00

[0097] Graphene nanosheets can be synthesized using a water-assisted liquid-phase exfoliation (WALPE) process. Ethyl cellulose, 200 proof ethyl alcohol, and self-adhesive elastic fabric substrates, or kinesiology tape (K-Tape), can be purchased. A Voltera flexible conductive silver can be used to form electrodes at opposite ends of a nanocomposite, while a low-temperature solder wire can be deposited first and then used for soldering 30 American Wire Gauge (AWG) multi-strand wires (Digi-Key, Inc.) for ease of electrical measurements. Discrete circuit elements and electrical testing components can also be purchased.

[0098] In an example device fabrication process, GNS-EC ink was used as is to form a fiber-integrated nanocomposite coating on K-Tape. K-Tape was selected because of its strong and long-lasting adhesion on human skin, thereby making it an ideal platform for building noninvasive wearable sensors. A mask was prepared using Cricut to precisely cut out a rectangular opening of typically 20 x 10 mm2. The mask was then temporarily affixed onto the substrate by applying slight pressure and affixing it using Scotch masking tape, with the goal of minimizing any gaps between the mask and K-Tape. Drop casting with a pipette was employed to deposit ~ 0.5 mL of GNS-EC ink over the exposed section of the mask to form a rectangular layer of fiber-integrated nanocomposite coating on the K-Tape fabric. In total, drop casting was performed three consecutive times to form a uniform nanocomposite of ~ 5 to 15 pm thick that was well-integrated with the fabric fibers. In some implementations, additional drop casted layers can be deposited to fomr a thicker fiber-integrated nanocomposite, which can reduce Motion Tape nominal electrical resistance without impacting its strain sensing properties. The mask can be carefully peeled off and removed upon completion of drop casting.

[0099] Upon film drying after ~ 1 h in room temperature, the final step was to deposit conductive silver electrode pads at opposite ends of the rectangular GNS-EC fiber-integrated nanocomposite and then soldering 30 AWG multi-strand wires to the silver electrodes for ease of electrical measurements (FIG. IB). Depending on device requirements, either a single 20 x 10 mm2GNS-EC or two GNS-EC fiber-integrated nanocomposites (i.e., orthogonally oriented with respect to each other) may be deposited onto the substrate. The latter case with the two orthogonal nanocomposites can be used to form a patterned materials-based circuit based on the disclosed technology. The two GNS-EC fiber-integrated nanocomposites can be fabricated so that their nominal or unstrained electrical resistance values were as close to one another as possible (e.g., ~ 1 kQ).

[0100] Performance of some disclosed embodiments was characterized in accordance with the following example techniques.PCT Application Attorney Docket No. 009062.8578. WO00

[0101] In an example study, cyclic electromechanical testing of some example embodiments was performed. Motion Tape specimens were subjected to uniaxial tensile cyclic strains using a Test Resources 100R electromechanical load frame as shown in FIG. 2. The electromechanical testing protocol was custom designed specifically for characterizing Motion Tape strain sensing properties, so it did not follow any American Society for Testing and Materials (ASTM) or International Organization for Standardization (ISO) protocol. The peak strains of the cyclic tests varied between 2% to 12%, but each test was executed at a constant loading rate of 0.1 % / s. Two-point probe electrical resistance measurements of Motion Tape response were acquired simultaneously during cyclic testing using a Keysight 34465A digital multimeter (DMM) sampling at ~ 1.5 Hz. For test cases involving using a Wheatstone bridge circuit, voltage output was also recorded using the Keysight 34465A DMM operated at the same sampling rate. An additional Keysight E3632A bench top power supply supplied 5 V to the nanocomposite circuit. All the resistance and voltage measurements were digitized and logged using Keysight BenchVue and time-synchronized with the load frame crosshead displacement and force measurements.

[0102] In another example study, the temperature -dependent electrical resistance properties of a GNS-EC fiber-integrated nanocomposite was studied using the test setup shown in FIG. 7 Motion Tape with a single GNS-EC thin film deposited parallel with the K-Tape longitudinal axis (i.e., stretchable direction) was used and affixed onto the side of a 150 mL Pyrex beaker. A reference Omega Type K thermocouple was also affixed adjacent to Motion Tape. The beaker was filled with 120 mL of distilled water and gently heated using a Coming digital stirring hot plate (FIG. 7). Testing entailed heating the room temperature water from ~ 20 °C to 55 °C, as well as allowing the heated water to cool back to room temperature. During each test (i.e., either the heating or cooling test), the electrical resistance time history, as well as the thermocouple voltage response, was each recorded using a Keysight 34465A DMM. Both DMMs were connected to the same personal computer so that time-synchronized measurements of electrical resistance and temperature could be acquired and stored using BenchVue. Both the heating and cooling tests were performed several times, as well as on different Motion Tape specimens.

[0103] In another example study performed to investigate temperature compensation, a disclosed nanocomposite materials-based circuit was simultaneously strained and subjected to temperature variations to validate its ability to reliably measure applied strains with minimal interference from the environment. Motion Tape specimens with two orthogonally oriented GNS-EC fiber-integrated nanocomposites on each K-Tape substrate to form a half bridge circuitPCT Application Attorney Docket No. 009062.8578. WO00 were utilized. The test began with mounting the patterned materials-based circuit, along its longitudinal axis, on a Test Resources 100R load frame. In addition, a thermistor was attached onto a bare section of the K-tape substrate to measure its temperature throughout the tests. The nanocomposite half bridge circuit was connected to a breadboard, where a Keysight E3632A bench top power supply provided 5 V to the circuit. The voltage outputs of the half bridge circuit and the thermistor were acquired using separate Keysight 34465A DMMs and the time-synchronized data logged using BenchVue. Then, a heat gun, positioned ~ 50 cm away from the mounted specimen, blew hot air to gradually heat the specimen from room temperature to ~ 55 °C. Once temperature had stabilized, the heat source was removed to allow the specimen to cool back down to room temperature of ~ 25 °C, while the Test Resources 100R load frame executed up to 20 cycles of tensile loads to 3% peak strain. The test was stopped when the measured temperature of the specimen stabilized or was ~ 25 °C or at room temperature.

[0104] The present patent document discloses various example embodiments related to integrated nanocomposite sensing elements, including a method of patterning and creating orthogonally oriented piezoresistive fiber-integrated nanocomposites that are electrically connected to form a bridge circuit capable of providing temperature-compensated strain sensing. Some disclosed embodiments relate to a patterned Motion Tape materials-based circuit which can automatically compensate for its temperature-dependent properties, while producing a stable strain sensing response, when the circuit is simultaneously subjected to both temperature changes and tensile cyclic strains.

[0105] Various disclosed techniques are broadly applicable to any resistive nanocomposite sensor whose electrical resistance could be affected by ambient environmental effects, such as temperature and humidity.

[0106] Some disclosed embodiments utilize Motion Tape. Because Motion Tape and other nanocomposites are designed to be worn on the body, temperature variations resulting from different activity levels or environmental conditions are likely and expected. Some disclosed embodiments include wearable sensing devices which leverage orthogonally patterned materials-based circuits that can mitigate environmental noise signals to improve sensing performance, all within a compact form factor by incorporating nanocomposites on the same substrate.

[0107] FIG. 26 shows a flow chart of an example method 2600 according to an embodiment of the disclosed technology. At step 2610, the method 2600 includes obtaining an output signal, indicative of strain of a skin surface exposed to an environment, fromPCT Application Attorney Docket No. 009062.8578. WO00 a patterned nanocomposite compensation circuit disposed on a flexible substrate configured to interface with the skin surface in the environment. In some implementations, the patterned nanocomposite compensation circuit comprises two or more nanocomposite sensing elements integrated with material constituents of the flexible substrate. In some implementations, the output signal is compensated for one or more conditions in the environment based on a first strain sensed using a first of the two or more nanocomposite sensing elements and a second strain sensed by a second of the two or more nanocomposite sensing elements.Examples / Solutions

[0108] The disclosed embodiments support inter alia the following exemplary technical solutions.

[0109] In some embodiments in accordance with the present technology (example Al), a wearable device for sensing skin-strains includes an elastic substrate; piezoresistive nanocomposite sensors disposed on the elastic substrate in a predetermined pattern; conductive material, disposed on the elastic substrate or physically connected to the elastic substrate by wires, configured to interconnect the piezoresistive nanocomposite sensors to each other; and circuitry configured to obtain strain measurements using the piezoresistive nanocomposite sensors when the wearable device is in contact with skin.

[0110] Example A2 includes the wearable device of example Al or any of examples A1-A5, wherein the strain measurements are obtained from the skin of a subject, and wherein the strain measurements are correlated to motion, angles of rotation, movement, and muscle engagement of the subject.

[0111] Example A3 includes the wearable device of example Al or any of examples A1-A5, wherein the circuitry includes a Wheatstone bridge circuit.

[0112] Example A4 includes the wearable device of example Al or any of examples A1-A5, wherein the predetermined pattern comprises piezoresistive nanocomposite sensors that are orthogonal to each other.

[0113] Example A5 includes the wearable device of example A 1 or any of examples A 1 - A4, wherein the circuitry is further configured to modify the strain measurements to compensate for environmental conditions around the wearable sensing device.

[0114] In some embodiments in accordance with the present technology (example A6), a method of patterning wearable piezoresistive nanocomposites includes the wearable device of any of examples A1-A5.PCT Application Attorney Docket No. 009062.8578. WO00

[0115] In some embodiments in accordance with the present technology (example Bl), a wearable sensor device includes flexible substrate configured to interface with a skin surface exposed to an environment; and a patterned nanocomposite compensation circuit disposed on the flexible substrate, the patterned nanocomposite compensation circuit configured to provide an output signal that is indicative of strain of the skin surface and compensated for one or more conditions in the environment, the patterned nanocomposite compensation circuit comprising: two or more nanocomposite sensing elements integrated with material constituents of the flexible substrate, electrodes disposed at opposing ends of each of the two or more nanocomposite sensing elements, measurement electrodes in electrical communication with at least some of the electrodes to allow the output signal to be readout, and electrically conductive circuitry configured to electrically couple the two or more nanocomposite sensing elements, the electrodes, and the measurement electrodes, wherein the output signal is compensated for the one or more conditions in the environment based on sensed strain by at least one of the two or more nanocomposite sensing elements.

[0116] Example B2 includes the wearable sensor device of example Bl or any of examples B1-B17, wherein the two or more nanocomposite sensing elements comprise: a first nanocomposite sensing element disposed along a first direction of the flexible substrate and configured to sense a first strain indicative of mechanical strain applied along the first direction, and a second nanocomposite sensing element disposed along a second direction of the flexible substrate that is different from the first direction and configured to sense a second strain caused by at least one of a thermal expansion of the flexible substrate and the one or more conditions in the environment.

[0117] Example B3 includes the wearable sensor device of example B2 or any of examples B1-B17, wherein the output signal is based on the first strain and the second strain.

[0118] Example B4 includes the wearable sensor device of example B2 or any of examples B1-B17, wherein the first direction and the second direction are orthogonal.

[0119] Example B5 includes the wearable sensor device of example Bl or any of examples B1-B17, wherein the two or more nanocomposite sensing elements are piezoresistive.

[0120] Example B6 includes the wearable sensor device of example B 1 or any of examples Bl -B 17, wherein a first strain applied along a first direction of the flexible substrate is sensed as a change in an electrical resistance of a first of the two or more nanocomposite sensing elements, wherein a second strain caused by thermal expansion of the flexible substrate or the one or more conditions in the environment is sensed as a change in an electrical resistance of a second of thePCT Application Attorney Docket No. 009062.8578. WO00 two or more nanocomposite sensing elements, wherein the output signal is based on the first strain and the second strain.

[0121] Example B7 includes the wearable sensor device of example Bl or any of examples B1-B17, wherein the patterned nanocomposite compensation circuit is configured in a bridge circuit topology.

[0122] Example B8 includes the wearable sensor device of example B7 or any of examples B1-B17, wherein the bridge circuit topology corresponds to a Wheatstone bridge circuit topology.

[0123] Example B9 includes the wearable sensor device of example Bl or any of examples B1-B17, wherein each of the two or more nanocomposite sensing elements comprises a graphene nanosheet (GNS)- ethyl cellulose (EC) thin film.

[0124] Example BIO includes the wearable sensor device of example B 1 or any of examples B1-B17, wherein a strain sensitivity of the wearable sensor device is based on an orientation of the two or more nanocomposite sensing elements with respect to the flexible substrate.

[0125] Example B 11 includes the wearable sensor device of example B 1 or any of examples B1-B17, wherein the flexible substrate comprises a fabric material, wherein the material constituents of the flexible substrate correspond to fibers of the fabric material.

[0126] Example B 12 includes the wearable sensor device of example B 1 or any of examples B1-B17, wherein some or all of the two or more nanocomposite sensing elements have a substantially similar nominal or unstrained electrical resistance.

[0127] Example B 13 includes the wearable sensor device of example B 1 or any of examples B1-B17, wherein the flexible substrate comprises kinesiology tape.

[0128] Example B 14 includes the wearable sensor device of example B 1 or any of examples Bl -Bl 7, wherein the wearable sensor device is patterned by deposition of a graphene nanosheet (GNS)- ethyl cellulose (EC) thin film onto the flexible substrate.

[0129] Example B 15 includes the wearable sensor device of example B 1 or any of examples Bl -Bl 7, wherein the flexible substrate is orthotropic.

[0130] Example B16 includes the wearable sensor device of example B15 or any of examples B 1-B 17, wherein the flexible substrate comprises a first stiffness along a longitudinal direction of the flexible substrate, wherein the flexible substrate comprises a second stiffness along a transverse direction of the flexible substrate, wherein the first stiffness is lower than the second stiffness.PCT Application Attorney Docket No. 009062.8578. WOOO

[0131] Example B 17 includes the wearable sensor device of example B 1 or any of examples Bl -Bl 6, wherein the one or more conditions relate to one or more of: humidity in the environment, a temperature in the environment, a body temperature of a wearer, or an exposure of the wearable sensor device to a liquid.

[0132] In some embodiments in accordance with the present technology (example Bl 8), a method for sensing skin strain using a wearable sensor device according to any one of the examples of B 1 -B 17.

[0133] In some embodiments in accordance with the present technology (example Bl 9), a method includes: obtaining an output signal, indicative of strain of a skin surface exposed to an environment, from a patterned nanocomposite compensation circuit disposed on a flexible substrate configured to interface with the skin surface in the environment, the patterned nanocomposite compensation circuit comprising two or more nanocomposite sensing elements integrated with material constituents of the flexible substrate, wherein the output signal is compensated for one or more conditions in the environment based on a first strain sensed using a first of the two or more nanocomposite sensing elements and a second strain sensed by a second of the two or more nanocomposite sensing elements.

[0134] Example B20 includes the method of example B19 or any of examples B19-B31, wherein the first strain is caused by a mechanical strain of the flexible substrate, wherein the second strain is caused by the one or more conditions in the environment.

[0135] Example B21 includes the method of example B19 or any of examples B19-B31, wherein the patterned nanocomposite compensation circuit comprises: electrodes disposed at opposing ends of each of the two or more nanocomposite sensing elements, measurement electrodes in electrical communication with at least some of the electrodes to allow the output signal to be readout, and electrically conductive circuitry configured to electrically couple the two or more nanocomposite sensing elements, the electrodes, and the measurement electrodes.

[0136] Example B22 includes the method of example B19 or any of examples B19-B31, wherein the first of the two or more nanocomposite sensing elements is disposed along a longitudinal direction of the flexible substrate, wherein the second of the two or more nanocomposite sensing elements is disposed along a transverse direction of the flexible substrate.

[0137] Example B23 includes the method of example B19 or any of examples B19-B31, wherein the two or more nanocomposite sensing elements are piezoresistive.PCT Application Attorney Docket No. 009062.8578. WO00

[0138] Example B24 includes the method of example B19 or any of examples B19-B31, wherein the patterned nanocomposite compensation circuit is configured in a bridge circuit topology.

[0139] Example B25 includes the method of example B19 or any of examples B19-B31, wherein each of the two or more nanocomposite sensing elements comprises a graphene nanosheet (GNS)- ethyl cellulose (EC) thin film.

[0140] Example B26 includes the method of example B19 or any of examples B19-B31, wherein the flexible substrate comprises a fabric material, wherein the material constituents of the flexible substrate correspond to fibers of the fabric material.

[0141] Example B27 includes the method of example B19 or any of examples B19-B31, wherein some or all of the two or more nanocomposite sensing elements have a substantially similar nominal or unstrained electrical resistance.

[0142] Example B28 includes the method of example B19 or any of examples B19-B31, wherein the flexible substrate comprises kinesiology tape.

[0143] Example B29 includes the method of example B19 or any of examples B19-B31, wherein the flexible substrate is orthotropic.

[0144] Example B30 includes the method of example B19 or any of examples B19-B31, wherein the flexible substrate comprises a first stiffness along a longitudinal direction of the flexible substrate, wherein the flexible substrate comprises a second stiffness along a transverse direction of the flexible substrate, wherein the first stiffness is lower than the second stiffness.

[0145] Example B31 includes the method of example B19 or any of examples B19-B30, wherein the one or more conditions relate to one or more of: humidity in the environment, a temperature in the environment, a body temperature of a wearer, or an exposure of the wearable sensor device to a liquid.Conclusion

[0146] Implementations of the subject matter and the functional operations described in this patent document can be implemented in various systems, digital electronic circuitry, or in computer software, firmware, or hardware, including the structures disclosed in this specification and their structural equivalents, or in combinations of one or more of them. Implementations of the subject matter described in this specification can be implemented as one or more computer program products, i.e., one or more modules of computer program instructions encoded on a tangible and non-transitory computer readable medium for execution by, or to control the operation of, data processing apparatus. The computer readable medium can be a machine-PCT Application Attorney Docket No. 009062.8578. WOOO readable storage device, a machine-readable storage substrate, a memory device, a composition of matter effecting a machine-readable propagated signal, or a combination of one or more of them. The term “data processing unit” or “data processing apparatus” encompasses all apparatus, devices, and machines for processing data, including by way of example a programmable processor, a computer, or multiple processors or computers. The apparatus can include, in addition to hardware, code that creates an execution environment for the computer program in question, e.g., code that constitutes processor firmware, a protocol stack, a database management system, an operating system, or a combination of one or more of them.

[0147] A computer program (also known as a program, software, software application, script, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file in a file system. A program can be stored in a portion of a file that holds other programs or data (e.g., one or more scripts stored in a markup language document), in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers that are located at one site or distributed across multiple sites and interconnected by a communication network.

[0148] The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

[0149] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read only memory or a random access memory or both. The essential elements of a computer are a processor for performing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto optical disks, or optical disks. However, a computer need not have suchPCT Application Attorney Docket No. 009062.8578. WOOO devices. Computer readable media suitable for storing computer program instructions and data include all forms of nonvolatile memory, media and memory devices, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices. The processor and the memory can be supplemented by, or incorporated in, special purpose logic circuitry.

[0150] While this patent document contains many specifics, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in this patent document in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a subcombination or variation of a subcombination.

[0151] Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, the separation of various system components in the embodiments described in this patent document should not be understood as requiring such separation in all embodiments.

[0152] Only a few implementations and examples are described and other implementations, enhancements and variations can be made based on what is described and illustrated in this patent document.

Claims

1. PCT Application Attorney Docket No. 009062.8578. WOOO CLAIMSWhat is claimed is:

1. A wearable sensor device, comprising:a flexible substrate configured to interface with a skin surface exposed to an environment; anda patterned nanocomposite compensation circuit disposed on the flexible substrate, the patterned nanocomposite compensation circuit configured to provide an output signal that is indicative of strain of the skin surface and compensated for one or more conditions in the environment, the patterned nanocomposite compensation circuit comprising:two or more nanocomposite sensing elements integrated with material constituents of the flexible substrate,electrodes disposed at opposing ends of each of the two or more nanocomposite sensing elements,measurement electrodes in electrical communication with at least some of the electrodes to allow the output signal to be readout, andelectrically conductive circuitry configured to electrically couple the two or more nanocomposite sensing elements, the electrodes, and the measurement electrodes, wherein the output signal is compensated for the one or more conditions in the environment based on sensed strain by at least one of the two or more nanocomposite sensing elements.

2. The wearable sensor device of claim 1 , wherein the two or more nanocomposite sensing elements comprise:a first nanocomposite sensing element disposed along a first direction of the flexible substrate and configured to sense a first strain indicative of mechanical strain applied along the first direction, anda second nanocomposite sensing element disposed along a second direction of the flexible substrate that is different from the first direction and configured to sense a second strain caused by at least one of a thermal expansion of the flexible substrate and the one or more conditions in the environment.

3. The wearable sensor device of claim 2, wherein the output signal is based on the first strain and the second strain.PCT Application Attorney Docket No. 009062.8578. WOOO 4. The wearable sensor device of claim 2, wherein the first direction and the second direction are orthogonal.

5. The wearable sensor device of claim 1, wherein the two or more nanocomposite sensing elements are piezoresistive.

6. The wearable sensor device of claim 1 , wherein a first strain applied along a first direction of the flexible substrate is sensed as a change in an electrical resistance of a first of the two or more nanocomposite sensing elements, wherein a second strain caused by thermal expansion of the flexible substrate or the one or more conditions in the environment is sensed as a change in an electrical resistance of a second of the two or more nanocomposite sensing elements, wherein the output signal is based on the first strain and the second strain.

7. The wearable sensor device of claim 1, wherein the patterned nanocomposite compensation circuit is configured in a bridge circuit topology.

8. The wearable sensor device of claim 7, wherein the bridge circuit topology corresponds to a Wheatstone bridge circuit topology.

9. The wearable sensor device of claim 1 , wherein each of the two or more nanocomposite sensing elements comprises a graphene nanosheet (GNS)- ethyl cellulose (EC) thin film.

10. The wearable sensor device of claim 1, wherein a strain sensitivity of the wearable sensor device is based on an orientation of the two or more nanocomposite sensing elements with respect to the flexible substrate.

11. The wearable sensor device of claim 1, wherein the flexible substrate comprises a fabric material, wherein the material constituents of the flexible substrate correspond to fibers of the fabric material.

12. The wearable sensor device of claim 1, wherein some or all of the two or more nanocomposite sensing elements have a substantially similar nominal or unstrained electrical resistance.

13. The wearable sensor device of claim 1, wherein the flexible substrate comprises kinesiology tape.PCT Application Attorney Docket No. 009062.8578. WOOO 14. The wearable sensor device of claim 1, wherein the wearable sensor device is paterned by deposition of a graphene nanosheet (GNS)- ethyl cellulose (EC) thin film onto the flexible substrate.

15. The wearable sensor device of claim 1, wherein the flexible substrate is orthotropic.

16. The wearable sensor device of claim 15, wherein the flexible substrate comprises a first stiffness along a longitudinal direction of the flexible substrate, wherein the flexible substrate comprises a second stiffness along a transverse direction of the flexible substrate, wherein the first stiffness is lower than the second stiffness.

17. The wearable sensor device of claim 1 , wherein the one or more conditions relate to one or more of: humidity in the environment, a temperature in the environment, a body temperature of a wearer, or an exposure of the wearable sensor device to a liquid.

18. A method for sensing skin strain using a wearable sensor device according to any one of claims 1-17.

19. A method, comprising:obtaining an output signal, indicative of strain of a skin surface exposed to an environment, from a patterned nanocomposite compensation circuit disposed on a flexible substrate configured to interface with the skin surface in the environment, the patterned nanocomposite compensation circuit comprising two or more nanocomposite sensing elements integrated with material constituents of the flexible substrate,wherein the output signal is compensated for one or more conditions in the environment based on a first strain sensed using a first of the two or more nanocomposite sensing elements and a second strain sensed by a second of the two or more nanocomposite sensing elements.

20. The method of claim 19, wherein the first strain is caused by a mechanical strain of the flexible substrate, wherein the second strain is caused by the one or more conditions in the environment.PCT Application Attorney Docket No. 009062.8578. WOOO 21. The method of claim 19, wherein the patterned nanocomposite compensation circuit comprises:electrodes disposed at opposing ends of each of the two or more nanocomposite sensing elements,measurement electrodes in electrical communication with at least some of the electrodes to allow the output signal to be readout, andelectrically conductive circuitry configured to electrically couple the two or more nanocomposite sensing elements, the electrodes, and the measurement electrodes.

22. The method of claim 19, wherein the first of the two or more nanocomposite sensing elements is disposed along a longitudinal direction of the flexible substrate, wherein the second of the two or more nanocomposite sensing elements is disposed along a transverse direction of the flexible substrate.

23. The method of claim 19, wherein the two or more nanocomposite sensing elements are piezoresistive.

24. The method of claim 19, wherein the patterned nanocomposite compensation circuit is configured in a bridge circuit topology.

25. The method of claim 19, wherein each of the two or more nanocomposite sensing elements comprises a graphene nanosheet (GNS)- ethyl cellulose (EC) thin film.

26. The method of claim 19, wherein the flexible substrate comprises a fabric material, wherein the material constituents of the flexible substrate correspond to fibers of the fabric material.

27. The method of claim 19, wherein some or all of the two or more nanocomposite sensing elements have a substantially similar nominal or unstrained electrical resistance.

28. The method of claim 19, wherein the flexible substrate comprises kinesiology tape.

29. The method of claim 19, wherein the flexible substrate is orthotropic.

30. The method of claim 19, wherein the flexible substrate comprises a first stiffness along a longitudinal direction of the flexible substrate, wherein the flexible substrate comprises aPCT Application Attorney Docket No. 009062.8578. WOOO second stiffness along a transverse direction of the flexible substrate, wherein the first stiffness is lower than the second stiffness.

31. The method of claim 19, wherein the one or more conditions relate to one or more of: humidity in the environment, a temperature in the environment, a body temperature of a wearer, or an exposure of the wearable sensor device to a liquid.

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