WO2024077311A2

WO2024077311A2 - High-capacitance ionic liquid gel/polymer matrix biocompatible materials for flexible pressure sensor

Info

Publication number: WO2024077311A2
Application number: PCT/US2024/011494
Authority: WO
Inventors: Rui NING; Jiechen WANG; Yue CAO; Hong Heather Yu
Original assignee: Futurewei Technologies, Inc.
Priority date: 2024-01-12
Filing date: 2024-01-12
Publication date: 2024-04-11

Abstract

High-capacitance flexible pressure sensors for applications such as flexible keyboards and human-machine augmented reality/virtual reality interfaces have a dielectric of an ionic liquid gel within a flexible polymer matrix. The ionic liquid gel/polymer matrix dielectric is between a pair of flexible transparent electrodes, all of which are in a biocompatible encapsulation layer

Description

HIGH-CAPACITANCE IONIC LIQUID GEL/POLYMER MATRIX BIOCOMPATIBLE MATERIALS FOR FLEXIBLE PRESSURE SENSOR

Inventors:

Rui Ning Jiechen Wang Yue Cao Hong Heather Yu

FIELD

[0001] The following is related generally to the field of human-machine interactions and, more specifically, to flexible pressure sensors.

BACKGROUND

[0002] The evolution of human-machine interactions has been pivotal in shaping the way users interact with technology. As augmented reality (AR) and virtual reality (VR) technologies become more immersive, the traditional input devices, such as rigid keyboards and touchpads, are becoming less suitable for dynamic ARA/R environments. There is a growing demand for input devices that are not only flexible, but also highly sensitive and responsive.

SUMMARY

[0003] According to one aspect of the present disclosure, a human-machine interface includes one or more capacitive sensors, each comprising a dielectric layer, a first flexible transparent electrode; a second flexible transparent electrode, and a biocompatible encapsulation layer. The dielectric layer comprises: an ionic liquid gel; and a porous flexible polymer matrix hosting the ionic liquid gel to form a composite film. The biocompatible encapsulation layer holds the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode, with the dielectric layer between the first and second flexible dielectric layers. [0004] Optionally, in the preceding aspect, the ionic liquid gel comprises polyvinyl alcohol with hydroxypropyl cellulose biopolymer fibers.

[0005] Optionally, in the preceding aspect, the ionic liquid gel comprises cholinium carboxylate ionic gel.

[0006] Optionally, in any of the preceding aspects, the polymer matrix is a piezoelectric material.

[0007] Optionally, in any of the preceding aspects, the polymer matrix comprises polyvinylidene fluoride incorporated with metal-organic frameworks.

[0008] Optionally, in any of the preceding aspects, the polymer matrix comprises modified isabgol.

[0009] Optionally, in any of the preceding aspects, the polymer matrix comprises nanomaterials incorporated polymeric monoliths.

[0010] Optionally, in any of the preceding aspects, each of the first and second electrodes comprises silver nanowires.

[0011] Optionally, in any of the preceding aspects, each of the first and second electrodes comprises poly(3,4-ethylenedioxythiophene) polystyrene sulfonate.

[0012] Optionally, in any of the preceding aspects, the encapsulation layer comprises fibroin.

[0013] Optionally, in any of the preceding aspects, the encapsulation layer comprises perfluoropolyether-dimethacrylate.

[0014] Optionally, in any of the preceding aspects, the encapsulation layer comprises aluminum nanowire grid polarizers.

[0015] Optionally, in any of the preceding aspects, the human-machine interface further comprises sensor control circuitry connected to the first and second flexible transparent electrodes of each of the capacitive sensors. [0016] Optionally, in the preceding aspect, the one or more capacitive sensors are a plurality of capacitive sensors, further comprising: a flexible backing to which is attached the plurality of capacitive sensors to form a keyboard.

[0017] Optionally, in any of the preceding two aspects, the sensor control circuitry and one or more capacitive sensors are part of a wearable device.

[0018] Optionally, in any of the three preceding aspects, the sensor control circuitry and one or more capacitive sensors are part of a touchpad.

[0019] Optionally, in any of the preceding four aspects, the sensor control is configured to provide digital output values from the one or more capacitive sensors.

[0020] Optionally, in any of the five preceding aspects, the sensor control is configured to provide analog output values from the one or more capacitive sensors.

[0021] Optionally, in any of the six preceding aspects, the human-machine interface further comprises communication and signal processing circuitry configured to receive output values of the one or more capacitive sensors from the sensor control circuitry.

[0022] Optionally, in the preceding aspect, the communication and signal processing circuitry is connected to the sensor control circuitry with a wired connection.

[0023] Optionally, in any of the two preceding aspects, the communication and signal processing circuitry is wirelessly connected to the sensor control circuitry by a radio-frequency identification connection.

[0024] Optionally, in any of the three preceding aspects, the human-machine interface further comprises one or more output devices connected to receive output data from the communication and signal processing circuitry.

[0025] Optionally, in the preceding aspect, the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a Bluetooth channel. [0026] Optionally, in any of the two preceding aspects, the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a radio frequency channel.

[0027] Optionally, in any of the three preceding aspects, the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a near-field communication channel.

[0028] Optionally, in any of the four preceding aspects, the one or more output devices include a computer.

[0029] Optionally, in any of the five preceding aspects, wherein the one or more output devices include an augmented reality device.

[0030] Optionally, in any of the six preceding aspects, the one or more output devices include a virtual reality device.

[0031] Optionally, in any of the seven preceding aspects, the one or more output devices include a robotic device.

[0032] According to an additional aspect of the present disclosure, there is provided a method of forming a capacitive sensor, including forming a dielectric layer by: forming a porous flexible polymer matrix; and infiltrating an ionic liquid gel into the porous flexible polymer matrix to form a composite film. The method also includes: forming a first flexible transparent electrode; forming a second flexible transparent electrode; and encapsulating within a biocompatible material the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode, with the dielectric layer between the first and second flexible dielectric layers.

[0033] Optionally, the preceding aspect, forming each of the first and second flexible transparent electrodes comprises a spray coating process.

[0034] Optionally, in any of the preceding aspects of forming a capacitive sensor, encapsulating the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode comprises a layer-by-layer assembly process. [0035] Optionally, in any of the preceding aspects of forming a capacitive sensor, encapsulating the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode comprises a dip coating process.

[0036] Optionally, in any of the preceding aspects of forming a capacitive sensor, encapsulating the dielectric layer, wherein encapsulating the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode comprises an electro-spinning process.

[0037] According to a further aspect, a system includes: a plurality of capacitive sensors, a first flexible transparent electrode a second flexible transparent electrode, and a biocompatible encapsulation layer. Each of the plurality of capacitive sensors comprises: a dielectric layer, comprising an ionic liquid gel and a porous flexible polymer matrix hosting the ionic liquid gel to form a composite film. The biocompatible encapsulation layer holding the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode, with the dielectric layer between the first and second flexible dielectric layers. The system also includes: sensor control circuitry connected to the first and second flexible transparent electrodes of each of the capacitive sensors; communication and signal processing circuitry configured to receive output values of the capacitive sensors from the sensor control circuitry; and one or more output devices connected to receive output data from the communication and signal processing circuitry.

[0038] Optionally, in the preceding aspect the communication and signal processing circuitry is connected to the sensor control circuitry with a wired connection.

[0039] Optionally, in any of the preceding aspects for a system, the communication and signal processing circuitry is wirelessly connected to the sensor control circuitry by a radio-frequency identification connection.

[0040] Optionally, in any of the preceding aspects for a system, the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a Bluetooth channel. [0041] Optionally, in any of the preceding aspects for a system, the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a radio frequency channel.

[0042] Optionally, in any of the preceding aspects for a system, the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a near-field communication channel.

[0043] Optionally, in any of the preceding aspects for a system the one or more output devices include a computer.

[0044] Optionally, in any of the preceding aspects for a system the one or more output devices include an augmented reality device.

[0045] Optionally, in any of the preceding aspects for a system, the one or more output devices include a virtual reality device.

[0046] Optionally, in any of the preceding aspects for a system, the one or more output devices include a robotic device.

[0047] Optionally, in any of the preceding aspects for a system, the system further comprises a flexible backing to which is attached the plurality of capacitive sensors to form a keyboard.

[0048] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the Background. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Aspects of the present disclosure are illustrated by way of example and are not limited by the accompanying Figures for which like references indicate elements.

[0050] Figure 1 is a schematic representation of an embodiment of a capacitive- type pressure sensor.

[0051] Figure 2 illustrates the parameters that determine the value of the capacitance of the sensor.

[0052] Figure 3A illustrates the application of the pressure sensors of Figure 1 to an embodiment of a flexible keyboard with individual capacitive pressure sensor keys.

[0053] Figure 3B illustrates the keyboard of Figure 3A when flexed.

[0054] Figure 4 illustrates an embodiment of the connections between the capacitive-type pressure sensors and sensor control circuitry.

[0055] Figure 5 is a block diagram of an embodiment for a system based on the flexible capacitor-based sensors.

[0056] Figure 6 is a flowchart of an embodiment for forming the high-capacitance IL gel/polymer matrix pressure sensors.

[0057] Figure 7 is a flowchart of an embodiment for operating the system of Figure 5 with sensors as formed in the process of Figure 6.

DETAILED DESCRIPTION

[0058] The following presents a flexible, highly sensitive, ultra-thin, and biocompatible pressure sensors suitable for immersive augmented reality (AR), virtual reality (VR) environments, and other human-machine interaction applications. The objective is to overcome the limitations of traditional input devices and current flexible pressure sensors by leveraging the properties of high-capacitance ionic liquid gel. [0059] The making and using of embodiments of this disclosure are discussed in detail below. It should be appreciated, however, that the concepts disclosed herein can be embodied in a wide variety of specific contexts, and that the specific embodiments discussed herein are merely illustrative and do not serve to limit the scope of the claims. Further, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of this disclosure as defined by the appended claims.

[0060] The following considers human-machine interactions making use of flexible sensors for the human-machine interface, along with communication and signal processing circuitry and devices, including augmented reality and virtual reality device, controlled by control circuitry receiving inputs from the flexible sensors. Pressurebased sensors can be useful in such applications, but prior art pressure-based sensors have a number of limitations. One such limitation is the sensitivity and response time of previous pressure-based sensors, which are typically not sufficient for realistic AR/VR applications. Another limitation of previous devices relate to wearability and stability, as wearable electronic devices should combine flexible pressure sensors with biocompatibility and wearability. Achieving strong adhesion and uniform distribution of materials on substrates is important for the stability of pressure sensors, which is often a challenge in the prior art. Additionally, many materials used in current approaches for pressure sensors are not biocompatible, posing potential health risks.

[0061] The following presents embodiments of flexible pressure sensors for applications such as flexible keyboard that can address the challenges with the integration of high-capacitance ionic liquid gels with a flexible polymer matrices. This combination can provide rapid response times and anti-swelling properties, addressing the limitations of current flexible keyboards. Furthermore, the biocompatibility of the materials of embodiments can provide user safety, a concern that is often overlooked in the design of traditional input devices.

[0062] More specifically, embodiments presented here can provide a flexible, highly sensitive, and biocompatible pressure sensor suitable for immersive ARA/R keyboards and other pressure-based sensors. These embodiments can overcome the limitations of traditional input devices and current flexible pressure sensors by way of the properties of high-capacitance ionic liquid gel/polymer matrix dielectrics. [0063] In following, embodiments can include ionic liquid (IL) gel that can be synthesized from materials such as polyvinyl alcohol (PVA) with hydroxypropyl cellulose (HPC) biopolymer fibers, cholinium carboxylate ionic liquids, poly(ethylene oxide) (PEO) with deep eutectic solvents, PVA with polymerizable deep eutectic solvent (PDES), among others. The flexible polymer matrix can be made from materials like polyvinylidene fluoride (PVDF) incorporated with metal-organic frameworks (MOFs), modified isabgol, or nanomaterials incorporated polymeric monoliths. With respect to fabrication methods, processing and infiltration methods can be employed to prepare the IL gel and polymer matrix.

[0064] The embodiments can further include flexible transparent electrodes with material formulations including: ultrathin silver nanowire (AgNW) films, or Poly(3,4- ethylenedioxythiophene) Polystyrene Sulfonate (PEDOT:PSS) with mild acids, among other materials that can be used as the flexible transparent electrodes in the sensors. With respect to fabrication methods, these can include spray-coating for applying thin electrodes, ensuring uniform coverage and optimal conductivity.

[0065] With respect to an encapsulation layer for the capacitor based pressure sensors, some examples of embodiments for the material formulation can include: biocompatible (i.e. , non-toxic and not triggering an immune response) materials such as fibroin, perfluoropolyether-dimethacrylate (PFPE-DMA), liquid crystal polymer (LCP), aluminum nanowire grid polarizers, and calcium phosphate (CaP). Fabrication methods can include: layer-by-layer assembly, dip-coating, and electro-spinning methods that can be employed to create a uniform encapsulation layer, ensuring the device is safe for user interaction.

[0066] Figure 1 is a schematic representation of an embodiment of a capacitive- type pressure sensor. The capacitive-type pressure sensor 101 includes an ionic liquid (IL) gel/polymer matrix dielectric layer 103 disposed between upper and lower flexible transparent electrodes 105A and 105B. An encapsulation layer 107 encapsulates matrix dielectric layer 103 and transparent electrodes 105A and 105B. The pressure sensor 101 combines the IL gel/polymer matrix 103, flexible transparent electrodes 105A/105B, and the encapsulation layer 107 and can be formed, by example, using transfer printing, layer-by-layer lamination, and solution processing methods. The materials (such as PVA with HPC biopolymer fibers and cholinium carboxylate ILs) used to synthesize the IL gel in the IL gel/polymer matrix layer 103 provide rapid response times due to the inherent high capacitive densities. This allows the pressure sensors of Figure 1 to provide a flexible, highly sensitive, ultra-thin, and biocompatible pressure sensor suitable for immersive AR/VR environments and other applications, overcoming the limitations of traditional input devices and current flexible pressure sensors by leveraging the properties of the high-capacitance ionic liquid gel. The embodiment of Figure 1 illustrates a sensor that has a square shape, but depending on the application, other shapes (e.g., non-square rectangular, round) can be used.

[0067] Capacitive-type pressure sensors can be used in human-machine interfaces such as flexible touch keyboards and wearable sensors, for example, for AR/VR applications, leveraging the properties of high-capacitance IL gel/polymer matrix. Embodiments of the IL gel of the dielectric 103 can use materials such as PVA with HPC biopolymer fibers and cholinium carboxylate ionic liquids to synthesize the IL gel, as these materials ensure rapid response times due to their inherent high capacitance density.

[0068] Embodiments of the polymer matrix of the dielectric 103 can use materials such as PVDF incorporated with MOFs, modified isabgol, or nanomaterials incorporated polymeric monoliths are used to create the flexible polymer matrix. PVDF is known for its piezoelectric properties, making it a useful material for pressure sensing applications. When combined with MOFs or modified Isabgol, the matrix remains flexible, has anti-swelling properties, and can be easily fabricated into a porous structure, ensuring that the matrix can host the IL effectively and maintain flexibility.

[0069] Embodiments of the flexible transparent electrodes 105A/105B can use materials such as AgNWs and PEDOT:PSS with mild acids. AgNWs are known for their high transparency and flexibility, making them very suitable for applications where visibility and flexibility are of major importance. PEDOT:PSS, when treated with mild acids, offers high conductivity, making it suitable for flexible capacitive pressure sensor. [0070] A touch keyboard or other user input device can incorporate such capacitive-type pressure sensors, which consists of two flexible transparent electrodes and the IL/polymer matrix film between them. The sensitivity (S) of the capacitive pressure sensor is calculated from

where Co is the initial capacitance, AC is the relative change of capacitance, and P is the applied pressure.

[0071] Figure 2 illustrates the parameters that determine the value of the capacitance of the sensor. The electrodes 105A and 105B have a separation of a distance d and area A. The capacitance C of a capacitor constructed of two parallel plates, both of area A and separated by a distance d, is (for d sufficiently small with respect to the smallest chord of A), to a high level of accuracy is given by C= £ (A/d), where £ is permittivity of the dielectric (here the IL gel/matrix layer) between the plates. Consequently, for an initial separation do and relative change in distance of Ad, the sensitivity can be expressed as S= -b(Ad/do)/5P for when the electrodes stay parallel and which will be a good approximation as the sensor undergoes moderate amounts of flex.

[0072] As the pressure-based sensors can detect minute changes in pressure based on user applied pressure, they can provide accurate inputs readings, ensuring user experience and system reliability. Another important factor is response time, including both rise time (the duration it takes for the sensor to react from an inactive state to a state of recognition, which is crucial for real-time applications) and fall time (the speed at which the sensor returns to its baseline after detecting a stimulus, which determines its readiness for subsequent inputs). A further important factor is wearability and biocompatibility, since, for wearable devices, the sensor's comfort on the skin and its non-toxic nature are important to ensure user comfort and health. Additionally, stability is important to provide consistent and reliable performance over time, regardless of environmental factors, for long-term applications and user trust.

[0073] Embodiments for the IL gel/polymer matrix composite file can achieve high sensitivity (e.g., ~1.194 kPa^-1) and fast response times (e.g., ~40 ms) for the sensors, such as the flexible keyboard of Figures 3A and 3B discussed below, due to the high elastic modulus of materials like PVDF, and the low viscosity IL gel cause almost no delay to the response. Additionally, the IL gel helps to form an electric double layer at the dielectric-electrode interfaces, which separates the positive and negative charges leading to a high capacitance density.

[0074] With respect to the encapsulation layer 107, embodiments can be made of biocompatible materials like fibroin, PFPE-DMA, LCP, aluminum nanowire grid polarizers, and CaP materials to ensure the device is safe for user interaction. These materials can be chosen for their biocompatibility, ensuring that the device is safe for skin contact. LCP and CaP are known for their stability and insulation properties, making them ideal for encapsulating electronic devices. The integration of these materials ensures both functionality and safety for the user.

[0075] Figure 3A illustrates the application of the pressure sensors of Figure 1 to an embodiment of a flexible keyboard 301 with individual capacitive pressure sensor keys. The keyboard includes a flexible backplate 311 on which are mounted a number of sensors 101. As illustrated in Figure 3A, some of the sensors can be larger than others to mimic a traditional keyboard’s arrangement. The individual sensors could, for example, be laid out in a standard computer keyboard layout, such as the QWERTY arrangement, or other layout, depending on the application. For example, different numbers of sensors could be on wearables or arranged on backplates or for control devices for ARA/R applications, machinery control, gaming, and other uses. In some examples, such as the keyboard example of Figure 3A, the pressure sensors would be used to provide a binary output value (i.e., either pressed or not), but other embodiments could use digital output of higher numbers of bits or analogue output values. Each of the electrodes 105A and 105B for each sensor will be electrically connected by a lead to sensor control circuitry that provide charge to the electrodes and detect changes in capacitance due to the pressure applied. This is illustrated in Figure 4.

[0076] Figure 3B repeats the elements of Figure 3A, but illustrates the keyboard in a flexed condition. For example, this could illustrate the keyboard when attached as a wearable sensor array. Although again illustrated arranged similarly to a standard keyboard, other such flexible sensor arrays could have differing numbers and arrangements of the sensors depending on the particular application of the embodiment.

[0077] Figure 4 illustrates an embodiment of the connections between the capacitive-type pressure sensors and sensor control circuitry. Figure 4 shows two pressure sensors 101-1 and 101-N of a group of N connected to sensor control circuitry 421. As discussed with respect to Figures 1 and 2, each of the pressure sensors includes a pair of electrodes 105A and 105B with an IL gel/polymer matrix dielectric 103 within the encapsulation layer 107. The electrodes 105A and 105B of each pressure sensor is connected to a corresponding lead 413 and 415 to be electrically connected to the sensor control circuitry 421 . The sensor control circuitry 421 can charge the electrodes and individually monitor the change in capacitance of the sensors 101 -1 to 101 -N based and changes in electrode separation based on applied pressure. Depending on the application, embodiments can have a sensor control circuit may only be connected to a single pressure sensor or a single sensor control circuit may be connected to multiple pressure sensors, such as where the keyboard 301 could has a single control circuit for all of its sensors.

[0078] Figure 5 is a block diagram of an embodiment for a system based on the flexible capacitor-based sensors. As in Figure 4, the sensor control circuitry 421 is connected to pressure sensors 101 -1 to 101 -N, where the system can include multiple numbers of such sensor control circuitry 421 that can have different numbers of pressure sensors attached. Sensor control circuitry 421 is connected to exchange signals with communications and processing circuitry 523, where this can be a wired connection or wireless connection, depending on the embodiment. For example, a radio-frequency identification (RFID) wireless embodiment could be used as an energy source from the communication and signal processing circuit 523 for the sensor control circuitry 421 and for exchanging of signals. The communication and signal processing circuit 523 can provide power and control signals to the sensor control circuitry 421 and the sensor control circuitry 421 can provide the sensor outputs to the communication and signal processing circuit 523, where, depending on the embodiment, the sensor outputs can be digital (such as the binary outputs of the keyboard example), analogue, or a combination of these. [0079] The communication and signal processing circuit 523 can be connected to one or more output devices 525 either by wired or wireless channels, such as Bluetooth, NearLink, WiFi, or radio frequency (RF), such as microwave communication or near-field communication (NFC), for example. The output devices can include a computer, such as when the sensors are used (as in Figures 3A and 3B) as part of a keyboard, in a mouse, and in a gaming controller. Other output devices for which a keyboard can be used as an input device can include televisions or smart appliances, for example. Other examples can include various examples of machinery and AR/VR machines, such as robotics, for 2D or 3D control in real space or cyberspace.

[0080] The system presented by Figure 5 presents a number of improvements over previous pressure based sensors through its use flexible pressure sensor for AR/VR input device applications based on the properties of the high-capacitance IL gel/polymer matrix. The inherent flexibility of the materials and design ensures user comfort, especially in dynamic AR/VR environments where adaptability and conformability are crucial. The use of a high-capacitance IL gel ensures that the keyboard is highly responsive as the high capacitance translates to a rapid response time and heightened sensitivity of the keyboard or other applications, providing realtime feedback to users. The encapsulation of the pressure sensor using biocompatible materials ensures that the device is safe for user interaction, prioritizing user safety and comfort. The embodiments present here also can provide low-cost, scalable processing, such as solution processing, printing, lamination, and spray coating methods. The design principles and materials are also versatile, allowing designs to be adapted and transferred to other materials and structures, offering flexibility in application.

[0081] Figure 6 is a flowchart of an embodiment for forming the high-capacitance IL gel/polymer matrix pressure sensors. At 600, the dielectric layer 103 of the composite film is formed, where this includes the formation of flexible polymer matrix at 601 and infiltrating an ionic liquid gel into the porous polymer matrix at 603. Solution processing and infiltration method can be employed to prepare the IL gel and polymer matrix. The IL gel can be synthesized from materials such as PVA with HPC biopolymer fibers, cholinium carboxylate ILs, PEO with deep eutectic solvents, PVA with PDES, and others. The flexible polymer matrix can be made from materials like PVDF incorporated with MOFs, modified isabgol, or nanomaterials incorporated polymeric monoliths.

[0082] The flexible transparent electrodes 105A and 105B are formed at 605, where fabrication methods can include spray-coating for applying thin electrodes, ensuring uniform coverage and optimal conductivity. Material formulations can include ultrathin AgNW films, PEDOT:PSS with mild acids, and among other materials that can be used as the flexible transparent electrodes in the sensors.

[0083] The flexible transparent electrodes 105A and 105B and IL gel/polymer matrix 103 of the dielectric are then encapsulated within a biocompatible material at 607. Fabrication methods can include layer-by-layer assembly, dip-coating, and electro-spinning methods to create a uniform encapsulation layer, ensuring the device is safe for user interaction. Fabrication formulations can include biocompatible materials like fibroin, PFPE-DMA, LCP, aluminum nanowire grid polarizers, and CaP.

[0084] Figure 7 is a flowchart of an embodiment for operating the system of Figure 5 with sensors as formed for the process of Figure 6. At 701 the communication and signal processing circuity 523 wireless as RFID signals to the sensor control circuitry 421 and sensors 101 -1 to 101-N. In response to user inputs by applying pressure to the sensors 101 -1 to 101 -N, at 703 the sensor signals are received at communications and signal process circuitry 523, where these can be digital, analogue, or a combination of signals. The output devices 525 are then controlled by the user inputs at 705.

[0085] The presented embodiments for pressure sensors can be ultra-thin, allowing for seamless integration into various applications without adding bulk, and flexible, ensuring that they can conform to different surfaces and shapes, making it ideal for wearable and bendable applications. The lightweight design promotes portability and easy transportation and, if needed, they can be easily integrated with (or placed on top of) a rigid and foldable thin piece of material, transforming it into a flat and stable keyboard. The integration of high-capacitance IL gel with a flexible polymer matrix can provide rapid response times, anti-swelling properties, and flexibility. [0086] Embodiments for the pressure sensors can provide large amounts of design flexibility. By adjusting the IL gel's refractive index, the pressure sensor's transparency can be controlled, so that it can be made transparent or opaque based on the application's requirements or user preferences. The energy source can be wired, or an RFID based wireless energy source, which can obviate the necessity for cumbersome wiring and mitigate the weight and form factor challenges associated with conventional battery systems. The capacitive flexible pressure sensor can have very high sensitivity, ensuring accurate keypress detection and giving users the capability to adjust the sensitivity based on their typing habits and preferences, allowing for a personalized typing experience. By reacting quickly to pressure changes, the sensors can provide real-time feedback and high accuracy in dynamic environments.

[0087] Keyboard embodiments can use a Lego-like reconfigurable layout where the desired number of sensors for a particular application can be attached to a backplate, providing users with the flexibility to customize the sensor layout based on specific application needs and user preferences, enhancing its versatility. This versatility for ergonomic design allows for the keyboard to be configured in multiple configurations: it could manifest as a split keyboard or adopt a traditional non-split layout. The design is inherently adaptable, allowing for easy adjustments to various shapes and sizes to cater to user preferences and ergonomic needs. When configured as a split keyboard, the sensors can be strategically arranged in a split fashion. Despite this, the entire keyboard remains a singular, cohesive piece of material, ensuring structural integrity. Embodiments can have a foldable design for convenience, with the sensor's foldable design ensures it can be easily stored and transported, making it highly convenient for users on the go. This design feature also adds to its versatility, allowing it to be used in various settings and scenarios.

[0088] It is understood that the present subject matter may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this subject matter will be thorough and complete and will fully convey the disclosure to those skilled in the art. Indeed, the subject matter is intended to cover alternatives, modifications and equivalents of these embodiments, which are included within the scope and spirit of the subject matter as defined by the appended claims. Furthermore, in the following detailed description of the present subject matter, numerous specific details are set forth in order to provide a thorough understanding of the present subject matter. However, it will be clear to those of ordinary skill in the art that the present subject matter may be practiced without such specific details.

[0089] Aspects of the present disclosure are described herein with reference to flowchart illustrations and/or block diagrams of methods, apparatuses (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable instruction execution apparatus, create a mechanism for implementing the functions/acts specified in the flowchart and/or block diagram block or blocks.

[0090] The description of the present disclosure has been presented for purposes of illustration and description but is not intended to be exhaustive or limited to the disclosure in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the disclosure. The aspects of the disclosure herein were chosen and described in order to best explain the principles of the disclosure and the practical application, and to enable others of ordinary skill in the art to understand the disclosure with various modifications as are suited to the particular use contemplated.

[0091] For purposes of this document, each process associated with the disclosed technology may be performed continuously and by one or more computing devices. Each step in a process may be performed by the same or different computing devices as those used in other steps, and each step need not necessarily be performed by a single computing device.

[0092] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

CLAIMS What is claimed is:

1. A human-machine interface, comprising: one or more capacitive sensors, each comprising: a dielectric layer, comprising: an ionic liquid gel; and a porous flexible polymer matrix hosting the ionic liquid gel to form a composite film; a first flexible transparent electrode; a second flexible transparent electrode; and a biocompatible encapsulation layer holding the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode, with the dielectric layer between the first and second flexible dielectric layers.

2. The human-machine interface of claim 1 , wherein the ionic liquid gel comprises polyvinyl alcohol with hydroxypropyl cellulose biopolymer fibers.

3. The human-machine interface of any of claims 1 -2, wherein the ionic liquid gel comprises cholinium carboxylate ionic gel.

4. The human-machine interface of any of claims 1 -3, wherein the polymer matrix is a piezoelectric material.

5. The human-machine interface of any of claims 1 -4, wherein the polymer matrix comprises polyvinylidene fluoride incorporated with metal-organic frameworks.

6. The human-machine interface of any of claims 1 -5, wherein the polymer matrix comprises modified isabgol.

7. The human-machine interface of any of claims 1 -6, wherein the polymer matrix comprises nanomaterials incorporated polymeric monoliths.

8. The human-machine interface of any of claims 1 -7, wherein each of the first and second electrodes comprises silver nanowires.

9. The human-machine interface of any of claims 1 -8, wherein each of the first and second electrodes comprises poly(3,4-ethylenedioxythiophene) polystyrene sulfonate.

10. The human-machine interface of any of claims 1 -9, wherein the encapsulation layer comprises fibroin.

11. The human-machine interface of any of claims 1 -10, wherein the encapsulation layer comprises perfluoropolyether-dimethacrylate.

12. The human-machine interface of any of claims 1 -11 , wherein the encapsulation layer comprises aluminum nanowire grid polarizers.

13. The human-machine interface of any of claims 1 -12, wherein the encapsulation layer comprises calcium phosphate.

14. The human-machine interface of any of claims 1 -13, further comprising: sensor control circuitry connected to the first and second flexible transparent electrodes of each of the capacitive sensors.

15. The human-machine interface of claim 14, wherein the one or more capacitive sensors are a plurality of capacitive sensors, further comprising: a flexible backing to which is attached the plurality of capacitive sensors to form a keyboard.

16. The human-machine interface of any of claims 14-15, wherein the sensor control circuitry and one or more capacitive sensors are part of a wearable device.

17. The human-machine interface of any of claims 14-16, wherein the sensor control circuitry and one or more capacitive sensors are part of a touchpad.

18. The human-machine interface of any of claims 14-17, wherein the sensor control is configured to provide digital output values from the one or more capacitive sensors.

19. The human-machine interface of any of claims 14-18, wherein the sensor control is configured to provide analog output values from the one or more capacitive sensors.

20. The human-machine interface of any of claims 14-19, further comprising: communication and signal processing circuitry configured to receive output values of the one or more capacitive sensors from the sensor control circuitry.

21 . The human-machine interface of claim 20, wherein the communication and signal processing circuitry is connected to the sensor control circuitry with a wired connection.

22. The human-machine interface of any of claims 20-21 , wherein the communication and signal processing circuitry is wirelessly connected to the sensor control circuitry by a radio-frequency identification connection.

23. The human-machine interface of any of claims 20-22, further comprising: one or more output devices connected to receive output data from the communication and signal processing circuitry.

24. The human-machine interface of claim 23, wherein the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a Bluetooth channel.

25. The human-machine interface of any of claims 23-24, wherein the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a radio frequency channel.

26. The human-machine interface of any of claims 23-25, wherein the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a near-field communication channel.

27. The human-machine interface of any of claims 23-26, wherein the one or more output devices include a computer.

28. The human-machine interface of any of claims 23-27, wherein the one or more output devices include an augmented reality device.

29. The human-machine interface of any of claims 23-28, wherein the one or more output devices include a virtual reality device.

30. The human-machine interface of any of claims 23-29, wherein the one or more output devices include a robotic device.

31. A method of forming a capacitive sensor, comprising: forming a dielectric layer, comprising: forming a porous flexible polymer matrix; and infiltrating an ionic liquid gel into the porous flexible polymer matrix to form a composite film; forming a first flexible transparent electrode; forming a second flexible transparent electrode; and encapsulating within a biocompatible material the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode, with the dielectric layer between the first and second flexible dielectric layers.

32. The method of claim 31 , wherein forming each of the first and second flexible transparent electrodes comprises: a spray coating process.

33. The method of any of claims 31 -32, wherein encapsulating the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode comprises a layer-by-layer assembly process.

34. The method of any of claims 31 -33, wherein encapsulating the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode comprises a dip coating process.

35. The method of any of claims 31 -34, wherein encapsulating the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode comprises an electro-spinning process.

36. A system, comprising: a plurality of capacitive sensors, each comprising: a dielectric layer, comprising: an ionic liquid gel; and a porous flexible polymer matrix hosting the ionic liquid gel to form a composite film; a first flexible transparent electrode; a second flexible transparent electrode; and a biocompatible encapsulation layer holding the dielectric layer, the first flexible transparent electrode, and the second flexible transparent electrode, with the dielectric layer between the first and second flexible dielectric layers; sensor control circuitry connected to the first and second flexible transparent electrodes of each of the capacitive sensors; communication and signal processing circuitry configured to receive output values of the capacitive sensors from the sensor control circuitry; and one or more output devices connected to receive output data from the communication and signal processing circuitry.

37. The system of claim 36, wherein the communication and signal processing circuitry is connected to the sensor control circuitry with a wired connection.

38. The system of any of claims 36-37, wherein the communication and signal processing circuitry is wirelessly connected to the sensor control circuitry by a radiofrequency identification connection.

39. The system of any of claims 36-38, wherein the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a Bluetooth channel.

40. The system of any of claims 36-39, wherein the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a radio frequency channel.

41 . The system of any of claims 36-40, wherein the one or more output devices are connected to receive output data from the communication and signal processing circuitry are connected to wirelessly over a near-field communication channel.

42. The system of any of claims 36-41 , wherein the one or more output devices include a computer.

43. The system of any of claims 36-42, wherein the one or more output devices include an augmented reality device.

44. The system of any of claims 36-43, wherein the one or more output devices include a virtual reality device.

45. The system of any of claims 36-44, wherein the one or more output devices include a robotic device.

46. The system of any of claims 36-45, further comprising: a flexible backing to which is attached the plurality of capacitive sensors to form a keyboard.