Closely packed stretchable ultrasound array fabricated with surface charge engineering for contactless gesture and materials detection

Abstract

An apparatus including at least one ultrasound sensor is disclosed. The sensor is configured for contactless gesture recognition and material detection. The sensor includes a plurality of closely-packed transducer elements charged via surface charge engineering. The apparatus can further include a first electrode, and a second electrode, wherein the plurality of transducer elements are positioned between the first electrode and the second electrode. The apparatus can further include an input / output device and / or a central computer device configured to receive data collected by the sensor.

Description

CLOSELY PACKED STRETCHABLE ULTRASOUND ARRAY FABRICATEDWITH SURFACE CHARGE ENGINEERING FOR CONTACTLESS GESTURE AND MATERIALS DETECTIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This patent application is related to and claims the benefit of priority of U.S. Provisional Application 63 / 606,677, filed on December 6, 2023, the entire contents of which is incorporated by reference.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH DEVELOPMENT

[0002] This invention was made with government support under Grant Nos. EB030140 and EB031629 awarded by the National Institutes of Health. The Government has certain rights in the inventionFIELD

[0003] The present disclosure generally relates to an apparatus including at least one sensor configured for contactless gesture and / or material detection, and methods of making and using thereof.BACKGROUND

[0004] The rapid growth and commercialization of the immersive augmented and virtual reality (AR / VR) industry demands improvement in the natural and intuitive communications between humans and machines. Human-robot interaction (HRI) has also gained significant attention in recent years due to its potential applications in various fields, including gaming, healthcare, and emergency rescues, for example. As a primary mode to understand and mimic human-humaninteraction since the beginning of human cognition, hand gesture recognition (HGR) has been widely used for HRI because of its efficient communication in rugged environments that are difficult with verbal or facial expressions (e.g., construction sites and emergency rescues). Conventional methods for HGR typically rely on the use of visual or infrared cameras, electromyography (EMG) measurements, or stretchable strain sensors with resources-intensive machine learning algorithms to decipher the gestures. However, the accuracy of HGR has been hindered because of the limited visual image quality due to environmental interference, poor contact impedance, and low-quality data due to cross-talks in EMG and strain sensors. Additionally, performing HGR using imaging modalities demands sophisticated algorithms and expensive and bulky data acquisition systems, which may not be practical during daily operations.

[0005] Another significant limitation of current immersive HRI technology is its inability to deliver information regarding interacting materials, limiting it to only visual information. Material detection can add an extra communication channel between humans and machines, which may also aid the Artificial Intelligence (Al) algorithm to better understand interaction dynamics given the material's nature. However, incorporating an additional device for quantitative characterization increases the complexity of the system, and most advanced material characterization techniques are not feasible in practical implementation as HRI applications require contactless interaction.SUMMARY

[0006] We have determined that there is a demanding need to develop an alternative low-cost, easily deployable, multifunctional sensor configured for both contactless gesture recognition and material detection that overcomes the above detailed deficiencies. Recently, ultrasound-basedtechniques traditionally used for medical imaging have emerged as a promising alternative due to their ability to capture hand movements in 3D without physical contact and robustness to lighting conditions and occlusions. Ultrasound-based HGR involves the use of high-frequency sound waves to create a 3D image of a hand and track its movements. Furthermore, a wearable ultrasound array can analyze the surface geometry of the hand during gesture by using acoustic beamforming to steer and focus on a region of interest. However, an ultrasound array requires a pitch size to be comparable to or less than the wavelength in the acoustic medium to avoid grating lobes that result in a low signal-to-noise ratio (SNR) and poor image quality. Accordingly, we have determined that it is highly desirable to fabricate a densely packed wearable ultrasound array with the close placement of transducer elements.

[0007] Moreover, high-frequency ultrasound (>1 MHz) is essential to achieve low impedance at its resonant frequency, which requires a pitch of — 150-200 pm generally performed by human hand placement. Although dicing saws may be exploited for transducer placement, customized saw thickness is required to tailor the pitch or the operational frequency, increasing both startup and recursive costs to create challenges in future commercialization. Therefore, there is an urgent need for an alternative and effective method to fabricate a densely packed ultrasound array.

[0008] This disclosure relates to a stretchable ultrasound sensor with a plurality (e.g., an array) of closely packed transducer elements that leverages surface charge engineering between the transducer elements and nearby films. The sensor can decipher material characteristics and hand gestures based on non-contact triboelectrification. For example, the sensor can interpret gestures such as a punch, waving hand, etc., and can further estimate the triboelectricity of a material by evaluating the time constant of exponentially decaying impedance during an electrostatic induction phase, independent of force or pressure applied. The multimodal decoupling withcontactless ultrasound transducer elements in triboelectric material characteristics and gesture recognition can pave the way for next-generation human robot interactions.

[0009] In an exemplary embodiment, an apparatus comprises at least one ultrasound sensor, including a plurality of transducer elements, wherein the plurality of transducer elements are surface charged, and wherein the transducer elements are closely packed such that each of the transducer elements is spaced 50 pm or less from immediately adjacent transducer elements of the plurality of transducer elements, a first electrode, and a second electrode, wherein the plurality of transducer elements are positioned between the first electrode and the second electrode. The apparatus further includes an input / output device configured to receive data from the at least one ultrasound sensor, wherein the data comprises gesture recognition data and / or material detection data.

[0010] In some embodiments, the gesture recognition data comprises measured changes in capacitance and / or impedance collected by the at least one ultrasound sensor.

[0011] In some embodiments, the gesture recognition data further comprises measured changes in a time decay constant collected by the at least one ultrasound sensor.

[0012] In some embodiments, the material detection data comprises measured changes in a realtime decay constant given by wherein T is a time decay constant of a materialto be detected, A is a projected surface area of the material to be detected, W is a height of the potential barrier of the material to be detected, k is a Boltzmann factor, T is a temperature of the material to be detected, and S’ is a material-specific constant.

[0013] In some embodiments, the apparatus further includes a central computer device configured to receive data from the at least one ultrasound sensor and / or the input / output device.

[0014] In some embodiments, the plurality of transducer elements are arranged in a two- dimensional array.

[0015] In some embodiments, the plurality of transducer elements include 1 -3 lead zirconate titanate.

[0016] In some embodiments, the first electrode comprises a first conductive metal on a first substrate, and the second electrode comprises a second conductive metal on a second substrate.

[0017] In some embodiments, the at least one ultrasound sensor further includes a first contact layer positioned between the first electrode and the plurality of transducer elements; and a second contact layer positioned between the second electrode and the plurality of transducer elements.

[0018] In some embodiments, the at least one ultrasound sensor is embedded within an elastomeric material.

[0019] In some embodiments, the at least one ultrasound sensor is configured for contactless gesture recognition.

[0020] In some embodiments, the at least one ultrasound sensor is configured for gesture recognition within 10 cm.

[0021] In an exemplary embodiment, a method of collecting gesture recognition data and / or material detection data comprises providing an apparatus including at least one ultrasound sensor, comprising a plurality of transducer elements, wherein the transducer elements are closely packed such that each of the transducer elements is spaced 50 pm or less from immediately adjacent transducer elements of the plurality of transducer elements, and wherein the plurality of transducer elements are surface charged, a first electrode, and a second electrode, wherein the plurality of transducer elements are positioned between the first electrode and thesecond electrode. The metho further comprises collecting the gesture recognition data and / or the material detection data via the ultrasound sensor; and transmitting the collected gesture recognition data and / or the material detection data to an input / output device for evaluation of the collected gesture recognition data and / or the material detection data.

[0022] In some embodiments, collecting the gesture recognition data comprises measuring changes in capacitance and / or impedance via the at least one ultrasound sensor.

[0023] In some embodiments, collecting the gesture recognition data further comprises measuring changes in a time decay constant via the at least one ultrasound sensor.

[0024] In some embodiments, collected the material detection data comprises measuring changes in an areal-time decay constant given by wherein T is a time decay constant ofa material to be detected, A is a projected surface area of the material to be detected, W is a height of the potential barrier of the material to be detected, A: is a Boltzmann factor, T is a temperature of the material to be detected, and S is a material-specific constant.

[0025] In some embodiments, the method further comprises transmitting the collected gesture recognition data and / or the material detection data to a central computer device for evaluation of the collected gesture recognition data and / or the material detection data.

[0026] In some embodiments, collecting the gesture recognition data and / or the material detection data via the ultrasound sensor is completed without any imaging techniques.

[0027] In some embodiments, the at least one ultrasound sensor is configured for contactless gesture recognition.

[0028] In some embodiments, the at least one ultrasound sensor is configured for gesture recognition within 10 cm.BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other objects, aspects, features, advantages, and possible applications of embodiments of the present innovation will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings. Like reference numbers used in the drawings may identify like components.

[0030] FIG. 1 is a schematic illustration and exploded view of an exemplary apparatus and its components.

[0031] FIG. 2 is a schematic illustration showing an exemplary method of making an exemplary transducer elements.

[0032] FIG. 3 is a schematic illustration showing an exemplary method of making an exemplary embodiment of an apparatus.

[0033] FIG. 4A is a schematic block diagram illustrating an exemplary embodiment of a system for transmitting sensor data collected by a sensor.

[0034] FIG. 4B is a schematic block diagram illustrating an exemplary embodiment of a system for transmitting sensor data collected by more than one sensor.

[0035] FIG. 5 is a schematic block diagram of an exemplary embodiment of an apparatus utilizing a plurality of sensors for providing data to at least one input / output device for collection and evaluation of the sensor data. The collected sensor data can be evaluated by the input / output device or a central computer device that can be communicatively connected to the input / output device.

[0036] FIG. 6 is a flow chart illustrating an exemplary embodiment of a system for transmitting data collected by the sensor.

[0037] FIG. 7 shows optical images of a closely packed ultrasound array of transducer elements using 12 pm (left) polyimide (PI) and 30 pm (right) PI for surface charge engineering.

[0038] FIG. 8 is a schematic illustration showing an exemplary triboelectric nanogenerator measurement setup for surface electrification between 1-3 PZT composite and hair.

[0039] FIG. 9 is a graph demonstrating the triboelectric characterization of a human hair sample and PZT, showing charge retention up to 2 nC.

[0040] FIG. 10 is a graph demonstrating the triboelectric characterization of a human hair sample and PZT, showing peak output voltage around 20 V.

[0041] FIG. 11 is a graph demonstrating the triboelectric characterization of PI with different thicknesses relative to PZT, indicating decreased charge retention as the PI thickness increases.

[0042] FIG. 12 is a graph demonstrating the triboelectric characterization of PI with different thicknesses relative to PZT, indicating decreased peak voltage as the PI thickness increases.

[0043] FIG. 13 is an image of an exemplary PZT element holding the 12 pm-think PI film against gravity with the electrostatic force.

[0044] FIG. 14 shows optical images demonstrating the attachment of the PI film with various thicknesses on the PZT transducer element.

[0045] FIG. 15 is a graph showing an impedance and phase angle spectrum of a 1-3 PZT composite with a thickness of 420 pm (resonant and anti-resonant frequencies marked with shaded circles).

[0046] FIG. 16 is a graph showing an impedance and phase angle spectrum of the 1-3 PZT composite with a thickness of 200 pm.

[0047] FIG. 17 is a graph showing time and frequency domain characterizations with a bandwidth of 57.1% and a spatial time pulse of 1.5 ps.

[0048] FIG. 18 is a graph showing time and frequency domain characterizations of the 1-3 PZT composite with a thickness of 200 pm.

[0049] FIG. 19A shows a map demonstrating invariance in the impedance or current density during motion of the object.

[0050] Fig 19B shows a map demonstrating Invariance in the impedance or current density during motion of the.

[0051] FIG. 20 is a graph showing triboelectric characterization between the skin and Ecoflex showing charge retention.

[0052] FIG. 21 shows a potential distribution map obtained from a COMSOL simulation for contactless triboelectrification between an object and transducer.

[0053] FIG. 22 shows a displacement current norm map obtained from a COMSOL simulation for contactless triboelectrification between an object and transducer.

[0054] FIG. 23 is a graph showing the dependency of capacitance on the distance between an object and transducer.

[0055] FIG. 24 is an illustration of a cross-section view of an exemplary transducer element.

[0056] FIG. 25 is an image demonstrating invariance of triboelectricity during the change of the orientation or curvature (negative or positive) of the hand.

[0057] FIG. 26 is a schematic illustration showing maximum principal strain distribution in Cu interconnects during bending.

[0058] FIG. 27 is a map demonstrating the orientation of different transducer elements in the array used for COMSOL simulation.

[0059] FIG. 28 is a graph showing simulated capacitance vs. horizontal distance curves from an array of three transducers. The graph implies the direction of the object is from transducer 2 to transducer 3.

[0060] FIG. 29 shows a simulated potential distribution map obtained from a clockwise rotation of an object.

[0061] FIG. 30 is a graph showing a phase shift in symmetrical capacitance oscillation between transducers 2 and 3 after clockwise rotation of an object.

[0062] FIG. 31 is a simulated potential distribution map used to decipher mixed linear and rotational motions.

[0063] FIG. 32 is a graph showing derived capacitance to decipher mixed linear and rotational motions.

[0064] FIG. 33 is a schematic illustration showing exemplary gestures of punch, slide left and right, and spread and pinch that can be interpreted by an exemplary apparatus.

[0065] FIG. 34 is a graph showing different waveforms of the gestures shown in FIG. 33 depending on the distance, projected area, and dynamics.

[0066] FIG. 35 is a graph showing impedance amplitude based on vertical movement of gestures with a flat hand, fist, three, and one fingertip.

[0067] FIG. 36 is a graph showing temporal variation in the impedance during the vertical movement of one finger at varying distances: 1, 2, and 4 cm.

[0068] FIG. 37 is a graph showing impedance amplitude based on the number of fingers during horizontal finger movement. The impedance amplitude increases with the number of fingers.

[0069] FIG. 38 is a graph showing invariance of triboelectricity during the change of the orientation or curvature (negative or positive) of the hand.

[0070] FIG. 39 is a graph showing that the time decay constant from an exponentially decaying impedance determines the hand's orientation: concave, convex, and flat.

[0071] FIG. 40 is a graph showing that the decay signature of impedance in the exponential pattern depends on the material: bare hand vs. nitrile and rubber gloves.

[0072] FIG. 41 is graph showing that the areal-time decay constant decreases monotonically according to the triboelectric series.

[0073] FIG. 42 is a graph showing the areal-time decay constant decreases monotonically according to the triboelectric series and its use for dynamic detection of the change of material.

[0074] FIG. 43 is a graph showing the use of the areal-time constant and peak voltage from a static-dynamic sequence to simultaneously determine the material and gesture at a distance of 6 cm from the ultrasound array.DETAILED DESCRIPTION

[0075] The following description is of exemplary embodiments and methods of use that are presently contemplated for carrying out the present invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles and features of various aspects of the present invention. The scope of the present invention is not limited by this description.

[0076] Embodiments generally relate to an apparatus 1000 including at least one ultrasound sensor 100. In some embodiments, the apparatus 1000 can be configured for contactless gesture recognition. For example, the apparatus 1000 can be configured to identify and / or interpret one or more movements of a body part (e.g., hand, head, etc.) without the need for physical contact. In some embodiments, the apparatus 1000 can be configured to be configured for material detection. For example, the apparatus 1000 can be configured to identify and / or analyze varioustypes of materials. In some embodiments, the apparatus 1000 can be configured for both contactless gesture recognition and material detection.

[0077] In particular, the apparatus can be configured to detect gestures and materials via coupled triboelectricity and electrostatic induction. The term “triboelectricity” refers to an electrical charge that can be generated between two different objects (e.g., materials), such that electrons can be transferred from one material to the other, resulting in one material becoming positively charged and the other negatively charged. More specifically, the ultrasound sensor 100 can serve as a non-contact triboelectricity generator and generate electrical energy via a triboelectric effect without the need for direct contact. The term “electrostatic induction” refers to a process by which a charged object can induce a charge on a nearby neutral object without direct contact. Electrostatic induction can occur due to the influence of the electric field created by the charged object, causing a redistribution of charges within the neutral object.

[0078] Referring to FIG. 1, embodiments of the apparatus 1000 include at least one ultrasound sensor 100. The sensor 100 can include a plurality of transducer elements 102 configured to convert physical phenomena (e.g., electrostatic induction, triboelectricity, etc.) into measurable electrical signals, which can ultimately enable collection of sensor data. This data can be transmitted to an external device such that the data can then be stored, tracked, analyzed, etc. A plurality of transducer elements 102 can offer more precise sensor data, such as data related to an object’s projected area, distance, etc., than a single transducer element.

[0079] In some embodiments, the transducer elements 102 can be arranged as an array of transducer elements. For example, the transducer elements 102 can be arranged in a two- dimensional array with structured rows and / or columns. In some embodiments, the transducer elements 102 can be closely packed. The term “closely packed” means that each transducerelement 102 may be spaced at a pre-selected closely packed distance CP, which can be 50 pm or less away from immediately adjacent transducer elements of the other adjacent transducer elements (e.g. 20-40 pm, greater than 0 pm and less than 50 pm, 10-30 pm, etc.).

[0080] For example, in a layer of transducer elements 102, there can be a first transducer element 102, a second transducer element 102, and a third transducer element 102. The second transducer element 102 can be immediately adjacent to the first and third transducer elements 102 and can be between those transducer elements 102. The second transducer element 102 can be a pre-selected closely packed distance CP away from the first transducer element 102. The second transducer element 102 can also be a pre-selected closely packed distance CP away from the third transducer element 102. The pre-selected closely packaged distance can be controlled by changing the thickness of a polyimide (PI) sheet during construction, which is pre-charged using a triboelectric material (such as hair). The pre-charged PI sheet then can be used as a spacer to closely package the transducer elements 102, where the distance between them is determined by the thickness of the PI.

[0081] In some embodiments, the transducer elements 102 may be positioned to calculate the charge transfer between the transducer elements and the triboelectric materials. The measured charge transfer calculation shows that there exists an electrostatic force between the pre-selected Pl sheet (see 102s) and the transducer elements.

[0082] The transducer elements 102 can have any thickness extending in a thickness direction. For example, the thickness may be within 50-1000 pm (e.g. 200-750 pm., 250-420, greater than 50 pm and less than 1000 pm, etc.).

[0083] The transducer elements 102 can be made of any suitable material. In some embodiments, the transducer elements 102 can be made of a piezoelectric material. For example,the transducer elements can include 1-3 lead zirconate titanate (PZT), 0-3 PZT, zinc oxide, barium nitrate, polyvinylidene fluoride (PVDF), and / or mixtures thereof.

[0084] Some or all of the transducer elements 102 can be pre-charged (e.g., positively or negatively charged) via surface charge engineering. In particular, some or all of the transducer elements 102 can be treated or otherwise manipulated to modify their electric charge prior to assembly of a sensor 100. The transducer elements 102 can have a first surface and an opposite second surface in the thickness direction, and can further have at least one side surface extending between the first surface and an opposite second surface. In some embodiments, at least one surface of the transducer elements 102 can be pre-charged via surface charge engineering.

[0085] The ultrasound sensor 100 can further include a first electrode 104 and a second electrode 106, wherein the plurality of transducer elements 102 are positioned between the first electrode 104 and second electrode 104. The first and second electrodes 104, 106 can be configured to facilitate the flow of current or voltage to and from the transducer elements 102, and can further be configured to collect and / or measure electrical signals generated by the transducer elements 102, which can ultimately enable collection of sensor data.

[0086] The first and second electrodes 104, 106 can be any suitable electrode material. In some embodiments, the electrode material can include a conductive metal, including but not limited to copper, gold, iridium, nickel, platinum, silver, titanium, and / or mixtures thereof. In some embodiments, the conductive metal can be deposited onto a flexible substrate, including but not limited to polyimide (PI), polyamide-imide (PAI), polyethersulfone (PES), polyphenylene sulfide (PPS), polyethylene phthalates (PEN), poly(methyl methacrylate) (PMMA), polyethylene terephthalate (PET) and / or mixtures thereof. In preferred embodiments, the substrate is thermostable.

[0087] In some embodiments, the first and second electrodes are made of the same electrode material. In other embodiments, the first and second electrodes are made of different electrode materials.

[0088] The first and second electrodes 104, 106 can be charged oppositely than the transducer elements 102, such that the electrodes 104, 106 can attach or be attracted to the transducer elements 102 via normal electrostatic force. For instance, the substrate of the first and second electrodes 104, 106 can be negatively charged and the transducer elements can be positively charged, or the substrate can be positively charged and the transducer elements can be negatively charged.

[0089] An ultrasound sensor 100 can optionally include a first contact layer 108 positioned between the first electrode 104 and the transducer elements 102. The first contact layer 108 can be any suitable material, such as a conductive metal (e.g., copper, gold, iridium, lead, nickel, platinum, silver, titanium, and / or mixtures thereol), a conductive polymer, etc.

[0090] An ultrasound sensor 100 can further include a second contact layer 110 positioned between the second electrode 106 and the transducer elements 102. The second contact layer 110 can be any suitable material, such as a conductive metal (e.g., copper, gold, iridium, lead, nickel, platinum, silver, titanium, and / or mixtures thereof), a conductive polymer, etc.

[0091] In some embodiments, the first and second contact layers 108, 110 are made of the same material. In other embodiments, the first and second contact layers 108, 110 are made of different materials.

[0092] Any or all of components of the ultrasound sensor 100 can be encapsulated by, embedded within, or otherwise positioned within an elastomeric material 112 such that the components of the sensor 100 can not be exposed to surroundings. The elastomeric material 112 can beflexible / stretchable and durable, such that the apparatus can be suitable in a wearable application and be configured to accommodate various body parts and / or contours and properly function while undergoing stresses and / or deformations (bending, twisting, etc.). The elastic material 112 can include but not be limited to silicon, natural rubbers, polyurethane, polybutadiene, neoprene, and / or mixtures thereof.

[0093] The at least one ultrasound sensor 100 can be configured to collect sensor data. The sensor data can relate to gesture detection and can include motion data, location / position data, orientation data, rotation data, and / or other metrics of interest. The sensor data can additionally or alternatively relate to material detection and can include material surface data.

[0094] The sensor 100 can exhibit excellent ultrasound properties with a high bandwidth (e.g., approx. 57.1%) and high electromechanical coefficient (approx. 0.75).

[0095] Referring to FIGS. 4A, 4B, and 5, the apparatus 1000 can be hardwire connected to an input / output device 210 (e.g., a smart phone, tablet, laptop computer, personal computer, computer device of a drone or robotic device, etc.), or the apparatus 1000 can be communicatively connected to the input / output device 210 via a network connection or wireless connection (e.g., internet connection, wide area network connection, near field communication connection, Bluetooth connection, etc.).

[0096] In some embodiments, the input / output device 210 can be configured to receive data from the at least one ultrasound sensor 100 for storage and analysis. In some implementations, the input / output device 210 can be configured as a server or cloud-based service providing device for storage and analysis of the data obtained via the sensor 100. The data can be communicated to a user via display device, which can be a tablet, smart phone, laptop computer, personal computer, or other type of terminal device. The display device can be effectuated via anapplication programming interface (API) and / or use of an application stored on the display device. It is contemplated that the input / output device 210 can comprise the display device, or the display device can be a separate device.

[0097] In some embodiments, the apparatus 1000 can alternatively or subsequently be sent to a central computer device 220 (e.g., a server, an operator workstation, etc.) that can be hardwire connected to the apparatus 1000 and / or the input / output device 210, or can be communicatively connected to the apparatus 1000 and / or the input / output 210 device via a network connection and / or a wireless connection. The central computer device 220 can be configured to store, analyze, and / or display data received from the apparatus 1000 and / or input / output device 210.

[0098] In some embodiments, the collected data can be continuously streamed to the input / output device 210 and / or the central computer device 220. In other embodiments, the collected data can be periodically streamed to the input / output device 210 and / or the central computer device 220 (e.g., non-continuously at pre-determined intervals). Embodiments of the apparatus 1000 can be configured to provide real time data collection.

[0099] The input / output device 210 and / or the central computer device 220 can be a computer device that can include a processor (Proc.) connected to a non-transitory memory (Mem.) and at least one transceiver (Trcvr) for forming communicative connections with one or more other devices. The at least one transceiver (Trcvr) can include a Bluetooth module and / or other type of transceiver unit (Trcvr). The processor can be hardware (e.g., processor, integrated circuit, central processing unit, microprocessor, core processor, computer device, etc.), configured to perform operations by execution of instructions embodied in algorithms, data processing program logic, artificial intelligence programming, automated reasoning programming, etc. that can be defined by code stored in the memory. The processor can facilitate receipt, processing,and / or storage of readings from the at least one ultrasound sensor 100 and / or control transmission of the collected data to input / output device 210 and / or the central computer device220.

[0100] It should be noted that use of processors herein can include hardware, such as for example any one or combination of a Graphics Processing Unit (GPU), a Field Programmable Gate Array (FPGA), a Central Processing Unit (CPU), a microprocessor, a processor, etc. The processor can include one or more processing or operating modules. A processing or operating module can be a software or firmware operating module configured to implement any of the functions disclosed herein. The processing or operating module can be embodied as software and stored in non-transitory memory, the memory being operatively associated with the processor. A processing module can be embodied running a web application, a desktop application, a console application, etc.

[0101] The memory (Mem.) can be a non-transitory computer readable memory configured to store data. Embodiments of the memory can include a processor module and other circuitry to allow for the transfer of data to and from the memory, which can include to and from other components of a communication system. This transfer can be via hardwired links or wireless transmission communication links. The communication system can include transceivers, which can be used in combination with switches, receivers, transmitters, routers, gateways, waveguides, etc. to facilitate communications between different devices via a communication approach or protocol for controlled and coordinated signal transmission and processing to any other component or combination of components of the communication system. The transmission can be via a communication link, which can be a wireless type of communication connection and / or a wired type of connection.

[0102] The computer or non-transitory machine-readable medium can be configured to store one or more instructions thereon. The instructions can be in the form of algorithms, program logic, etc. that cause the processor to execute any of the functions disclosed herein.

[0103] The processor can be in communication with other processors of other devices (e.g., additional external device, a computer system, a laptop computer, a desktop computer, etc.). An exemplary other device can be a Bluetooth enabled device, near field communication device, etc. Any of those other devices can include any of the exemplary processors disclosed herein as well as transceivers or other communication devices / circuitry to facilitate transmission and reception of wireless signals or other type of communicative connections.

[0104] Either the input / output device 210 and / or the central computer device 220 can be configured to be connected to other input devices and output devices. Examples of input devices can include a scanner device (e.g., scanner), a microphone, a keyboard, a touch screen, a button, a sensor a detector, or other type of input device. Examples of output devices can include a display, a printer, a speaker, or other type of output device.

[0105] As noted above, once collected data is transmitted to the input / output device 210 and / or the central computer device 220, the data can be analyzed and evaluated to determine an output. For example, the data can be processed and evaluated to determine hand gestures and / or materials. In some embodiments, the data can be processed using artificial intelligence or machine learning algorithms stored on the input / output device 210 and / or the server central computer device 220. In particular, the input / output device 210 and / or the server central computer device 220 can run a program that uses the collected data along with a module trained via a machine learning process that received the collected sensor data and processes that data to determine an output.

[0106] Regarding hand gesture recognition, it is contemplated that recognition can be based on coupled triboelectrification and electrostatic induction, which can depend on the projected area and the distance between a sensor 100 and the object to be measured (e.g., the object providing the gesture). A dynamic gesture contributes to the triboelectrification of the apparatus 1000, which results in changes in capacitance and impedance that can be measured. For example, an estimated or precise location and / or direction of the object’s motion can be analyzed by simultaneously collecting impedance and capacitance of the sensor 100.

[0107] In some embodiments, the sensor 100 can be configured to collect data related to horizontal movement of the object. Alternatively or additionally, the sensor 100 can be configured to collect data related to direction of rotation of the object. As a result, a sensor 100 can be used to decipher any general motion, which can be presented as a combination of liner and rotational motions.

[0108] Compared to a single transducer element, a plurality of transducer elements 102 can provide more precise information regarding an object’s projected area and distance for sensing. For example, more than one sensor 100 placed at different orientations can help decipher an object’s horizontal information (e.g., a smaller distances between the object and first and second sensors can result in higher capacitances than that for a third sensor; moreover, increasing capacitance for the first sensor one and decreasing capacitance for the second sensor and almost unchanged capacitance for the third sensor can signify that the object is moving in a direction from the second sensor to the first sensor).

[0109] In some embodiments, the sensor 100 can also be configured to collect data related to the orientation and / or curvature of the object. The time decay constant can be exploited from an exponentially declining impedance or exponentially increasing capacitance. Forexample, by keeping an object at rest (e.g., stationary) with respect to the sensor 100, electrostatically induced charges at the surface of the transducer elements 102 can result in different time constants for estimating object orientation. The time decay constant T in the equation for exponentially decaying impedance can increase or decrease as theobject switches orientations, and the differences in decay profiles (or the dynamics of exponential charge decay) can therefore be attributed to the different electrostatic charge distributions modulated by the curvature of the object.

[0110] It is therefore contemplated that the apparatus 1000 and / or at least one sensor 100 can interpret the general motion and / or orientation of any object without any using any imaging techniques, equipment, etc.

[0111] In some embodiments, the sensor 100 can be configured to decipher gestures up to 10 cm in distance (e.g. greater than 0 cm up to 10 cm) or other suitable distance (e.g. in a range of greater than or equal to 0 cm up to 40 cm, (e.g. in a range of greater than or equal to 0 cm up to 100 cm, etc.).

[0112] Regarding material detection, an object / material can be detected by noting that an exponential decay in impedance can be due to the exponential decay in charge from the object / material, which can be consistent with charging decay in an electron thermionic emission mode. The surface charge during the thermionic emission is given by Equation (1):

[0113] where 4()is the Richardson constant of a free electron, T is the temperature of the material to be detected, A is the projected area of the object, W is the height of the materialpotential barrier (unique to a material), Axis approximately a constant given by Ax= XAW / Qs, with AV / as the change in the potential barrier height due to the surface electric field and A as the material-specific factor, and k is the Boltzmann factor. Solving Equation (1) gives the surface charge Qsthat decays according to Equation (2):where S is the material -specific constant given by The sensor 100 can becharged by an object / material to exponentially increase the surface charge Qs. The exponential increase in the sensor 100 can result in in the exponential decay of impedanceTherefore, the time decay constant T is given by T , implying that the areal-time decayconstant is a material-specific constant rather than a simple time decayconstant. Finding the material-specific areal-time decay constant can therefore allow for detection of various materials.

[0114] It is therefore contemplated that the apparatus 1000 and / or at least one sensor 100 can detect the material of any object without any using any imaging techniques, equipment, etc.

[0115] Embodiments of the apparatus 1000 can be configured as at least one sensor 100, such as a plurality of sensors 100. For example, in embodiments including a plurality of sensors 100, each sensor 100 can operate and collect data independently with no interference between their signals. Embodiments of the apparatus 1000 can include one sensor, two sensors, three sensors, four sensors, five sensors, six sensors, seven sensors, eight sensors, nine sensors, ten sensors, etc.

[0116] In use, the apparatus 1000 and / or the sensor 100 can be configured to be placed on a human body part (e.g., arm, hand, finger, etc,), robotic device, vehicular device, drone device, etc.

[0117] Embodiments of the apparatus 1000 described herein can be employed in a variety of industries and applications wherein detection of hand gestures or materials can be necessary or advantageous. For example, the apparatus described herein can be used in augmented and virtual reality application (e.g., gaming), driver-assistive system, gesture-based biometrics, interactive display, human-robot-interaction applications, rescue operations, health monitoring applications, finger motion tracking (e.g., sign language translations), among other applications.

[0118] Embodiments generally also relate to methods of making an apparatus 1000 and sensor 100. Referring to FIG. 2, transducer elements 102 can be constructed by providing a piezoelectric material and charging the surface of the material, such that the transducer elements 102 can be charged (e.g., positively or negatively charged). This surface charge engineering allows for the attachment of an oppositely charged film to form an array of element / film / element. After a sufficient array is constructed, the film can be removed. The transducer elements 102 can be embedded in an elastomeric material (e.g., before or after addition of additional components).

[0119] Referring to FIG. 3, electrodes 104, 106 can be formed attaching / laminating a substrate and a conductive metal to form an electrode material, and laser scribing the electrode material to form the electrodes 104, 106. The electrodes 104, 106 can further be transfer printed. The electrodes 104, 106 can then be attached to the transducer elements 102 to form the sensor100. Alternatively, first and second contact layers 108, 110 can be placed between the first andsecond electrodes 104, 106 and the transducer elements 102, respectively. The components of the sensor 100 can be embedded in an elastomeric material.

[0120] The apparatus 1000 and / or at least one sensor 100 can be manufactured without the use of a microscope.EXAMPLES

[0121] EXAMPLE 1 : Exemplary Apparatus and Sensor Construction and Components

[0122] An exemplary embodiment of an apparatus and a sensor was constructed, and the scope of this application is not be limited to the particular embodiment described below.

[0123] Materials'. Prime-graded silicon (Si) substrate (p-doped, 100) was purchased from Alpha Nanotech, USA. PDMS kit (SYLGARD™ 184 Silicone Elastomer) was purchased from the Dow Chemical Company, USA. Piezoelectric 1-3 PZT-5A composite transducers with a thickness of 200 pm and 420 pm were purchased from Del Piezo Specialties, USA. The transducers were diced using ADT 7100 dicing saw (thickness 150 pm), Advanced Dicing Technologies, Israel. Ecoflex 0030 (Part A and B) was purchased from Smooth-On, USA.Pyralux® copper / polyimide film (Cu / PI of 9 pm / 12 pm) and Kapton® PI film (thickness: 12, 30, 50, and 100 pm) were purchased from DuPont™, USA. Water-soluble tape 5414 was obtained from 3M™, USA. Silver epoxy EPO-TEK H20E was purchased from Epoxy Technologies, USA. Isopropyl alcohol (IPA) was purchased from VWR International, USA.

[0124] Fabrication of Transducer Elements'. The diced 1-3 PZT composite was rubbed with hair samples to engineer surface charges on its side surfaces (FIG. 2). The positively charged 1-3 PZT composite was then placed sufficiently close to a negatively charged PI thin film (thickness: 12 or 30 pm) for attachment due to normal electrostatic force (FIG. 2).Repeating the steps aligned and attached another 1-3 PZT composite to the thin PI, forming aclosely packed PZT / PI / PZT. Next, a thin polymethyl methacrylate (PMMA) mold was prepared with a hollow opening covered by water-soluble tape on which the aligning experiment was performed. Similarly, a water-soluble tape was used again as a mask for the top gold contact along with the previously placed water-soluble tape, thus protecting both the top and bottom contacts (FIG. 2). After raising the temperature to 100°C, the PI film was easily removed from the PZT / PI / PZT to form closely packed transducer elements. For PZT with a thickness of 200 pm, the water-soluble mask was placed on the top gold contact after the PI removal, whereas the 420 pm-thick PZT used the water-soluble mask on top contact before the PI removal (FIG. 2). Then the Ecoflex precursor was poured into the mask-protected 1 -3 PZT composite array suspended using the water-soluble tape on the PMMA mold. After curing at 80°C for 15 min, the sandwiched 1-3 PZT composite array was kept in water to dissolve the water-soluble mask. Removing the PMMA mold resulted in a flexible array with closely packed 1-3 PZT composite elements embedded in the cured Ecoflex matrix (FIG. 2). The whole fabrication process was performed without using any microscope.

[0125] Fabrication of Stretchable Sensor. The fabrication started by spin-coating (SPIN150i, RK-AHT, Germany) the PDMS precursor solution (10:1) at 800 rpm for 30 seconds on a Si substrate. The Cu / PI film was surface activated using ultraviolet light (PSD Series Digital Ultraviolet Ozone System, Novascan, USA) for 3 min for bonding with PDMS / Si (FIG. 3). The bonded Cu / PI on PDMS / Si substrate was pulse ablated (SPI Lasers, UK) to engrave the top or bottom electrode (FIG. 3). The laser parameters (wavelength: 1040 - 1200 nm, pulse energy: 0.4 mJ, pulse duration: 250 ns, speed: 200 mm / s) were optimized to maximize the yield of ablated Cu similar to those reported previously. After laser ablation of Cu / PI, the unwanted carbon formed on the PI side was removed using IPA. A thicker Ecoflex film (1:1) was prepared on Sisubstrate at 1000 rpm for 30 s for the bottom electrode, whereas a thinner Ecoflex film (1:1) was spin-coated on PMMA substrate (for improved transparency during placement) at 2000 rpm at 60 s for the top electrode. The patterned top and bottom Cu / PI electrodes were transfer-printed from donor PDMS to receiver Ecoflex substrate using water-soluble tape after 7 min of surface activation (FIG. 3). After dissolving water-soluble tape with water (FIG. 3), the previously prepared 1-3 PZT composite transducer array (thickness of 200 or 420 pm) was aligned and bonded to the bottom electrode using the silver epoxy EPO-TEK H20E followed by baking at 150°C for 10 min (FIG. 3). Similarly, the top electrode on the transparent Ecoflex / PMMA substrate was aligned with the 1-3 PZT composite array and bonded using silver epoxy. Next, the device between the top PMMA and bottom Si substrates was uniformly packaged using Ecoflex without forming any bubbles. After curing Ecoflex at 80°C for 15 min, both substrates were separated to result in a stretchable ultrasound array (FIG. 3).

[0126] EXAMPLE 2: Characterizations of Constructed Sensor

[0127] Optical Characterization'. Because of manual operation in the fabrication processes and the nonvanishing gap between the PZT and PI thin film (thickness of 12 or 30 pm) in the closely packed array (thickness of 420 pm), the gap between two adjacent transducer elements or kerf is larger than the thickness of the PI film. The optical images obtained from Digital Microscope (AmScope, USA) showed a kerf of ~20 (or 40) pm between the 12 (or 30) pm-thick PI film and PZT in the PZT / PI / PZT stack array (FIG. 7) due to the higher (or lower) triboelectric effect.

[0128] Triboelectric Characterization of PZT and Hair. The surface charge engineering or electrification of PZT using hair based on the difference between their triboelectric properties was characterized by using a triboelectric nanogenerator (TENG). PZT and hair stacks wereatached to Cu electrodes for constructing the TENG (FIG. 8). The TENG was pressed and released at an interval of 0.5 s to observe the charge transfer. The TENG was further tapped at a frequency of 2 Hz for voltage measurement (an air gap of 0.5 cm between the two films).Because PZT is triboelectrically positive compared to hair, positive charges are induced on the active boundary of the PZT transducer, with negative charges on the active region of the hair. The contact electrification between hair and PZT gives a surface charge transfer density of 29 pC / m2measured using Autolab (Metrohm) (FIG. 9) and an open-circuit voltage of ~20 V measured using an oscilloscope (SDS1202X-E, Siglent Technologies) (FIG. 10).

[0129] Triboelectric Characterization of Pl and PZT. Close placement of the positively charged PZT transducer elements near the negatively charged PI thin film produced the electrostatic attraction force that depends on the charge transfer between the active surface of two materials. The surface charge transfer density between PI film and PZT decreases from 115.3 to 68 pC / m2as the thickness of the PI film increases from 12 to 100 pm measured using Autolab (Metrohm) (FGI. 11). The open-circuit voltage also drops from 53 to 25 V due to the increased thickness from 12 to 100 pm (FIG. 12). Therefore, the electrostatic force is sufficient to hold a thin PI film of 12 pm against its gravity (FIG. 13) but fails to attach the PI film of 100 pm (FIG. 14).

[0130] Ultrasound Characterization of Sensor. The fabrication of a stretchable, closely packed high-frequency ultrasound array facilitated by surface charge engineering is frequency- adaptable with consistent acoustic performance for both thick (420 pm) and thin (200 pm) 1-3 PZT composite arrays. The thick 1-3 PZT composite showed a resonant frequency of 3.7 MHz and an anti-resonant frequency of 5.63 MHz, resulting in an exceptionally high effective electromechanical coefficient of 0.75 (FIG. 15). The impedance and phase angle spectra werecharacterized using LCR Meter (IM 3536-01, Hioki). In contrast, the thin 1-3 PZT composite results in a higher resonant frequency of 7.4 MHz and an anti-resonant frequency of 9 MHz, with an effective electromechanical coefficient of 0.56 (FIG. 16). The pulse-echo response of the thick 1-3 PZT composite corresponds to a central frequency of 3.94 MHz with an excellent wide bandwidth of 57.1% and a spatial pulse length of 1.5 ps characterized using pulser-receiver (Panametric 5077PR, Olympus) (FIG. 17). In comparison, the pulse-echo response of the thin 1- 3 PZT composite shows a central frequency of 7.3 MHz with a wide bandwidth of 52.3% and an extremely narrow spatial pulse length of 0.5 ps (FIG. 18). The excellent ultrasound characteristics of the fabricated closely packed ultrasound array are consistent with recent literature reports.

[0131] Contactless Triboelectric Characterization of Sensor; Acting as a non-contact triboelectric nano generator, the stretchable ultrasound array embedded in the silicone elastomer provides opportunities for the contactless gesture and material recognition. The dynamic gesture contributes to the triboelectrification of the device, resulting in changes in capacitance, thus, the impedance measured using LCR Meter (IM 3536-01, Hioki). The impedance analysis of the ultrasound array was performed by providing 1 V across the electrode with corresponding resonant frequencies, i.e., 7.3 MHz for 200 pm and 3.9 MHz for 420 pm 1-3 PZT composite array, respectively.

[0132] EXAMPLE 3: Evaluating Contactless Triboelectrification

[0133] We conducted a study evaluating the mechanism of contactless triboelectrification of an exemplary sensor as designed above in Example 1.

[0134] Recognition was based on coupled triboelectrification and electrostatic induction, which depends on the projected area and the distance between the transducer and the object.Because the frequency range of the ultrasound (7.3 MHz) is orders of magnitude higher than the frequency of the human gesture (~1 Hz), the impedance variation with a gesture cannot be realized using a time-of-flight mechanism as revealed by the simulation in COMSOL (FIGS, 19A-19B). To simulate contactless triboelectricity, both the object and the transducer were grounded. A potential of 1 V was applied across the transducer, and a surface charge density of 25 pC / m2was applied to the object (experimentally validated by the charge transfer from the human hand to the ultrasound array) (FIG. 20). The simulated potential distribution (FIG. 21) and normalized displacement current nomi (FIG. 22) for contactless triboelectrification between the object and transducer generated the capacitance variation due to the horizontal motion of the object. The capacitance reached a maximum when the object was closest (horizontal distance of 7.5 cm from the left boundary) to the transducer (FIG. 23), which was consistent with the mechanism of electrostatic induction or capacitive sensing (capacitance is inversely proportional to distance).

[0135] EXAMPLE 4: Mechanical Simulation of Stretchable Arrays

[0136] We conducted a mechanical simulation of an exemplary sensor as designed above in Example 1.

[0137] Compared with a single transducer, an array of transducers can provide more precise information regarding the object's projected area and distance for capacitive sensing. The design of the array can first consider the mechanical stability of the large stretchable array. In the proof-of-the-concept demonstration, the closely packed ultrasound array was designed to be placed on the three phalanges - distal, middle, and proximal - of the index finger of an adult male. The serpentine interconnects connect the three closely packed ultrasound arrays, increasing the ultrasound array's mechanical stretchability. The mechanical simulation of the device (cross-section shown in FIG. 24) using Abaqus shows that the maximum principal strain in Cu interconnects upon finger bending with a radius of 3.5 cm and 2.5 mm locally at the finger joint (3 cm and 5 cm from the Meta Carpo Phalangeal Joint, making 30° relative to each other, as shown in FIG. 25) is only 0.44%, which is much lower than its fracture strain (FIG. 26).

[0138] EXAMPLE 5: Gesture Recognition Via Sensor

[0139] We conducted a study evaluating the gesture recognition capabilities of an exemplary sensor as designed above in Example 1.

[0140] After placing the stretchable ultrasound array on the index finger with different phalanges orienting at different angles, the projected area and distances between the device and the object were changed. The precise location and direction of the object's motion can be analyzed by simultaneously sampling the impedance and capacitance of the ultrasound array. For example, three transducers placed at different orientations (FIG. 27) can help decipher the object's horizontal motion. The smaller distance between the object and transducers 2 and 3 resulted in higher capacitance than that for transducer 1. Moreover, the increasing capacitance for transducer 3 and decreasing capacitance for transducer 3 with almost unchanged capacitance for transducer 1 signified that the object's moving direction is from transducer 2 to 3 (FIG. 28). Along with horizontal movement, the capacitances of the three transducers can also interpret the direction of rotation (FIG. 29). The clockwise rotation of the object can be mapped by comparing the phase shift in the symmetrical capacitance oscillation between transducers 2 and 3, where transducer 2 reaches its maximum value (at 6 cm) before transducer 3 (at 9 cm) (FIG. 30). As a result, the array can be used to decipher any general motions, which can be represented as a combination of linear and rotational motions (FIG. 31). For instance, the initial (at 0 cm) higher value of transducer 2 together with reaching its maximum value (at 6 cm) before transducer 3 (at9 cm) inferred that the object moves to the right with clockwise rotation (FIG. 32). The simulation with just three transducers shows that an ultrasound array can be used to interpret the general motion of the object, even without any imaging technique.

[0141] The gesture recognition can be highlighted by a few commonly used gestures such as vertical punch, slide right-left, and spread-pinch. The temporal dynamics of these gestures (FIG. 33) can be observed by the measured impedance. Different from spread-pinch and slide left-right gestures that are presented at approximately 4 cm above the sensor, the vertical punch gesture varied in distance to result in an increased amplitude of approximately 0.2 ft (FIG. 34). The vertical movement of gestures with the flat hand, punch, three, and one fingertip at 2 Hz exhibited reduced impedance amplitude due to decreased projected area, which all diminished with the increase in the distance (FIGS. 35-36). For example, a flat hand covered approximately 95 cm2to result in an impedance amplitude of 0.65 Q, whereas one fingertip, comprising approximately 3.5 cm2surface area, produces an amplitude of 0.15 Q at 1 cm above the sensor. The contactless gesture recognition sensor worked for a distance of approximately 10 cm in length above the sensor. For the horizontal movement of fingers, the impedance amplitude increased from 0.07 G to 0.36 G as the number of fingers (placed 4 cm above at a frequency of 0.5 Hz) increases from one to five (FIG. 37), which was consistent with the tread observed in FIG. 35.

[0142] Although the triboelectrification between the transducer and the object depends on the projected area and distance, it cannot determine the hand's orientation or curvature (negative vs. positive) (FIG. 38). To address this challenge, we exploited the time decay constant from an exponentially declining impedance or exponentially increasing capacitance. By keeping the object at rest (or stationary) with respect to the transducer, electrostatically induce charges atthe transducer surface would result in different time constants for estimating the curvature of the hand's orientation. The time decay constant T in the exponentially decaying impedance Z = Z^-^ increased from 72.7 to 366.3 sec as the hand switched from the convex (fitting exponential data with R2= 0.9998) to concave orientation (R2= 0.991 ) (FIG. 39). The differences in decay profiles (or the dynamics of exponential charge decay) are attributed to the different electrostatic charge distributions modulated by the curvature of the hand.

[0143] EXAMPLE 6: Material Detection Via Sensor

[0144] We conducted a study evaluating the material detection capabilities of an exemplary sensor as designed above in Example 1.

[0145] Keeping an object stationary to the sensor can provide the exponential decay of impedance, whereas the triboelectrification induced by the dynamic motion of the object can lead to local oscillation of the impedance, with the mean impedance remaining constant globally. The exponential decay signature of impedance can also depend on the material (e.g., nitrile and rubber gloves vs. bare hand) and the trend of decay can be consistent with the triboelectric series. The highly positive bare human hand has a decay constant of 104.8 sec, whereas the negatively charged rubber shows a decay constant of 86.9 sec (FIG. 40). The decay in impedance of the ultrasound array signifies an increase in the capacitance of the ultrasound element across the top and bottom electrodes, which implies the equivalent capacitor between the device and human finger is charging the ultrasound capacitance while discharging itself. As the voltage supplied across the electrodes is constant (1 V), the decrease in capacitance accounts for the charge transferred. Therefore, the exponential decay in the impedance is due to the exponential decay in the charge from the human body surface, which is consistent with charging decay in the electronthermionic emission mode. The surface charge Qsduring the thermionic emission is given byEquation (1):

[0146] where 40is the Richardson constant of a free electron, is the temperature, A isthe surface area, W is the height of the potential barrier, is approximately a constant given bywith AW as the change in the potential barrier height due to the surface electricfield and A as the material-specific factor, and k is the Boltzmann factor. Solving Equation (1) gives the surface charge Qsthat decays according to Equation (2):

[0147] where S is the material-specific constant given by The devicehuman body capacitor charges the ultrasound capacitor to exponentially increase the surface charge Qson the ultrasound capacitor. The exponential increase in the capacitor results in the exponential decay of impedance Therefore, the time decay constant T is given by T =1 / AS, implying that the areal-time decay constantis a material-specific constant rather than a simple time decay constant. By fitting the exponentially decaying impedance, the areal-time decay constant decreases monotonically from the highly positive human body (1.13 m2sec) to negatively charged PDMS (0.02 m2sec) (FIG. 41).

[0148] EXAMPLE 7: Sequential Contactless Material and Gesture Recognition

[0149] We conducted a study evaluating the detection sequential contactless material and gesture recognition capabilities of an exemplary sensor as designed above in Example 1.

[0150] The material and gesture recognition with the stretchable ultrasound array can provide the possibility to holistically detect the object's chemical composition and physical motion sequentially. The device could dynamically detect the change of material by analyzing the variation in the impedance slope. The time constant in the exponentially decaying impedance increases from 87.4 sec (R2= 0.981) for rubber gloves to 105.2 sec (R2= 0.998) for bare hands (FIG. 42). The material and gesture can be sequentially deciphered by following the analysis sequence from the static to the dynamic phase. The static phase is utilized for material detection by extracting the time decay constant of 105.93 sec (R2= 0.994) and an amplitude of 0.15 £2 (FIG. 43). Given that the area of the object is 108 cm2, the material is confirmed to be a human hand according to the areal-time decay constant of 1.14 nrsec. Moreover, the gesture is predicted to be three fingers with prior information about the object's distance of 4 cm from the device. By exploiting the temporal impedance readout from the ultrasound array, the projected area and distance of the object can be dynamically estimated. Following the estimated projected area and distance, the static-dynamic analysis sequence can be used to retrieve the areal -time constant and impedance waveform, deciphering the material property and relative motion or gesture.

[0151] It should be understood that modifications to the embodiments disclosed herein can be made to meet a particular set of design criteria. For instance, the number of or configuration of components or parameters can be used to meet a particular objective.

[0152] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposes of illustration only. Other alternative embodiments can include some or all of the features of thevarious embodiments disclosed herein. For instance, it is contemplated that a particular feature described, either individually or as part of an embodiment, can be combined with other individually described features, or parts of other embodiments. The elements and acts of the various embodiments described herein can therefore be combined to provide further embodiments.

[0153] It is the intent to cover all such modifications and alternative embodiments as can come within the true scope of this invention, which is to be given the full breadth thereof. Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points. Thus, while certain exemplary embodiments of the apparatus and process and / or utilization and methods of making and using the same have been discussed and illustrated herein, it is to be distinctly understood that the invention is not limited thereto but can be otherwise variously embodied and practiced within the scope of the following claims.

Claims

What is claimed is:

1. An apparatus comprising: at least one ultrasound sensor, comprising: a plurality of transducer elements, wherein the plurality of transducer elements are surface charged, and wherein the transducer elements are closely packed such that each of the transducer elements is spaced 50 pm or less from immediately adjacent transducer elements of the plurality of transducer elements, a first electrode, and a second electrode, wherein the plurality of transducer elements are positioned between the first electrode and the second electrode; and an input / output device configured to receive data from the at least one ultrasound sensor, wherein the data comprises gesture recognition data and / or material detection data.

2. The apparatus of claim 1, wherein the gesture recognition data comprises measured changes in capacitance and / or impedance collected by the at least one ultrasound sensor.

3. The apparatus of claim 2, wherein the gesture recognition data further comprises measured changes in a time decay constant collected by the at least one ultrasound sensor.

4. The apparatus of claim 1, wherein the material detection data comprises measured changes in a real-time decay constant given by:wherein r is a time decay constant of a material to be detected, A is a projected surface area of the material to be detected, W is a height of the potential barrier of the material to be detected, k is a Boltzmann factor, T is a temperature of the material to be detected, and S’ is a material-specific constant.

5. The apparatus of claim 1, further comprising: a central computer device configured to receive data from the at least one ultrasound sensor and / or the input / output device.

6. The apparatus of claim 1, wherein the plurality of transducer elements are arranged in a two-dimensional array.

7. The apparatus of claim 1, wherein the plurality of transducer elements include 1-3 lead zirconate titanate.

8. The apparatus of claim 1, wherein the first electrode comprises a first conductive metal on a first substrate, and the second electrode comprises a second conductive metal on a second substrate.

9. The apparatus of claim 1, wherein the at least one ultrasound sensor further comprises:a first contact layer positioned between the first electrode and the plurality of transducer elements; and a second contact layer positioned between the second electrode and the plurality of transducer elements.

10. The apparatus of claim 1 , wherein the at least one ultrasound sensor is embedded within an elastomeric material.

11. The apparatus of claim 1 , wherein the at least one ultrasound sensor is configured for contactless gesture recognition.

12. The apparatus of claim 11, wherein the at least one ultrasound sensor is configured for gesture recognition within 10 cm.

13. A method of collecting gesture recognition data and / or material detection data, comprising: providing an apparatus comprising: at least one ultrasound sensor, comprising: a plurality of transducer elements, wherein the transducer elements are closely packed such that each of the transducer elements is spaced 50 pm or less from immediately adjacent transducer elements of the plurality of transducer elements, and wherein the plurality of transducer elements are surface charged, a first electrode, anda second electrode, wherein the plurality of transducer elements are positioned between the first electrode and the second electrode; collecting the gesture recognition data and / or the material detection data via the ultrasound sensor; and transmitting the collected gesture recognition data and / or the material detection data to an input / output device for evaluation of the collected gesture recognition data and / or the material detection data.

14. The method of claim 13, wherein collecting the gesture recognition data comprises: measuring changes in capacitance and / or impedance via the at least one ultrasound sensor.

15. The method of claim 14, wherein collecting the gesture recognition data further comprises: measuring changes in a time decay constant via the at least one ultrasound sensor.

16. The method of claim 13, wherein collected the material detection data comprises: measuring changes in an areal-time decay constant given by:wherein T is a time decay constant of a material to be detected, A is a projected surface area of the material to be detected, W is a height of the potential barrier of the material to bedetected, k is a Boltzmann factor, T is a temperature of the material to be detected, and S’ is a material-specific constant.

17. The method of claim 13, further comprising: transmitting the collected gesture recognition data and / or the material detection data to a central computer device for evaluation of the collected gesture recognition data and / or the material detection data.

18. The method of claim 13, wherein collecting the gesture recognition data and / or the material detection data via the ultrasound sensor is completed without any imaging techniques.

19. The method of claim 13, wherein the at least one ultrasound sensor is configured for contactless gesture recognition.

20. The apparatus of claim 19, wherein the at least one ultrasound sensor is configured for gesture recognition within 10 cm.

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