FIELD OF THE DESCRIPTION

[0001] The following relates to sensing systems and materials, composed of one or more elements of sensors created from polymer composite materials to contact the skin, circuitry to detect, record, or process the signals, an interface to transport the signals from the skin surface contact material to the circuitry, a processor to collect and record the signals, and methods for the selection and optimization of such sensor and sensor materials to meet the needs of desired specifications or applications. The following also relates to selection methods for optimizing the same, where such sensor materials are optimized to non-invasively detect one or more of electrical, thermal, mechanical, or chemical signals when in contact with skin in the absence of conductive gels, and can have one or more properties that are biocompatible, flexible, soft, elastic, self-adhesive, and conductive, and are developed for continuous wear in electronic devices for consumer, health, or medical applications.

BACKGROUND

[0002] The use of electrodes on the skin is commonly practiced for the acquisition of non-invasive biopotential signals, such as electroencephalography (EEG) to study brain activity, electrooculography (EOG) to track eye motion, electromyography (EMG) to monitor muscular impulses, and electrocardiography (ECG) for monitoring heart function. For the purposes of collecting biopotential signals related to the brain and brain function, these electrodes are typically placed on locations on the head or face of a user; however, the reliable and high-quality EEG recording using conventional electrodes from these areas is challenging due to their complex topologies. Current medical grade EEG electrodes are made of gold, silver/silver chloride (Ag/AgCI), or other metals, and to ensure low skin-electrode interface impedance and high quality of signal recordings, contact to the skin is facilitated by two means: adhesive electrical conduits, such as conductive gels, and mechanical pressure, such as that created by tight head caps or adhesives. Typically, conductive gels use a saline (NaCI) or silver/silver chloride (Ag/AgCI) solution to enhance the conductivity between the electrode and skin, which requires additional preparation time, as it is recommended to clean the area of the skin before application, provide microabrasions to facilitate better signal quality, and remove any interfering hair by shaving. Head caps and adhesives require a second party to apply the electrodes, often requiring specific positioning of electrodes. However, such arrangement would not be suitable for the long-term EEG recording since the gel dries out by time and results in increasing the skin-electrode interface impedance and reducing signal to noise ratio (SNR) (Krummel, T. M. 2019).

[0003] Previous work has been done to develop sensor electrodes that do not require conductive gels or mechanical pressure. Dry electrodes made of metal films or electrically conductive polymer composites are widely used in wearable technology (Stauffer, et al., 2018; Kin, et al., 2016; Kim, et al., 2011 , Xu, et al., 2016); however, it is hard to make conformal contact between these electrodes and skin due to two main reasons: first, the complex topology of targeted recording region and in some individuals existence of hairs that avoids stable direct and intimate contact between electrodes with planar geometry and skin; second, the mechanical mismatch between the electrodes and skin results in significant motion artifacts. In one attempt to secure an electrode to the skin without conductive gels, a patent (U.S. Pat. No. 7,032,301) discloses a dry electrode that pierces the skin in order to obtain constant contact for a biopotential signal, which can irritate the skin and is not suitable for repeated wear.

[0004] Alternatively, polymer material with conductive fillers are described to be able to sense the electrical signals generated by the body (US20160089045A1 , US9591979B2), though these sensors are not optimized for certain applications, locations, or target signals, and are limited only to electrical signals.

[0005] More recently, some groups have attempted to make polymer-based sensors that are not homogeneous, made by layering different materials with specific properties to construct sensors (WO2021089593A1). Such sensors require multiple processes to fabricate due to the dissimilarity of the materials, and are not durable, as the contact boundary between different materials provide sources of failure due to bonding where breaks are more common to occur.

[0006] Polymer composite based electrodes are mechanically flexible but most of them are stiffer than skin (Stauffer, et al., 2018; Kin, et al., 2016; Kim, et al., 2011). That is because most of the electrically conductive fillers such as carbon nanotubes (CNT), graphene and metallic nanoparticles have high Young’s modulus and in order to achieve full percolation and high electrical conductivity required for EEG, relatively high weight percentage of these nano materials are added to the polymer precursor. In most cases this will affect the mechanical characteristics of the polymer composites drastically and consequently will result in the mechanical mismatch between the skin and sensors, high skin- electrode interface impedance, low quality of signal recording, low signal to noise ratio and motion artifact. In order to address such issues, forming conformal contact to skin is necessary, but making such contact especially on complex topologies using conventional electrodes with planar contact-surface without the use of wet-gels is a challenge. Recently, polymer composites based dry sensors with pillarstructures formed at their contact-surface have been developed, however these sensors are not suitable for mobile and long-time sensing during daily activity due to unstable contact to skin (Hwang, et al., 2018; Krahn, et al., 2011 ; Kwak, et al., 2011 ; Thanh- Vinh, et al., 2011). Sensing using such sensors significantly suffers from motion artifacts. The innovation disclosed herein describes effective sensors and hardware that enable reliable recording of biopotential signals of interest. These sensors are capable of recording signals from the area behind the ears, and within the ears’ canals using proper sensors. Furthermore, the sensors must be mechanically soft, have low electrode-skin interface and form stable and conformal dry contact to skin in order to avoid motion artifacts in long term recording during daily activities. The innovation presented herein discloses sensor materials, designs, systems, and selection methods capable of achieving such desired signals from the skin of a user.

SUMMARY OF THE DESCRIPTION

[0007] In one aspect, the enclosed relates to sensing systems optimized to sense high fidelity signals of one or more of electrical, mechanical, thermal, or chemical signals from the surface of the human skin, the sensing system composed of one or a combination of one or more sensors created from one or more polymer composite materials and designed as skin-contact sensors to optimize sensing the signals from dry or wet contact with the skin; circuitry to detect, record, or process said signals sensed by the materials in contact with the skin; an interface to transport the signal from the contact surface of the polymer composite material to the circuitry; a processor to collect and record the signals or provide determinations based on the signals; where the polymer composite materials having been selected and optimized using a selection method designed to choose materials and fabrication processes to meet the needs or specifications of intended applications or desired signals.

[0008] In a further aspect, the system can be a system that requires circuitry, such as those incorporated into electronic devices, wearable devices, or e-skin applications; or purely a sensor, such as tattoo electrodes and other sensors made with composite polymer material.

[0009] In a further aspect, the materials and systems are less susceptible to noise or artifacts, such as movement, interference from hair, skin conditions, sweat, temperature or other conditions.

[0010] In a further aspect, the electrical signals that are sensed can be one or more of electroencephalography (EEG), electrooculography (EOG), electromyography (EMG), or electrocardiography (ECG), and the signals can be used raw or processed to provide indications of auditory attention, auditory attention envelope of sound, visual attentional direction, physical orientations of the user’s head, gaze, and trunk, saccades, blink, facial movements, jaw movements, emotions, fatigue, activity level, temperature, injury, illness, disease, sleep state, narcolepsy, seizures, blood oxygen level, pH level, and other indicators regarding the status of the user.

[0011] In a further aspect, the system can be configured to provide that the blink signal is a function (f) of one or more or an average of multiple signals from the left amplified voltages Vleft, signal=f(Vleft), or right amplified voltages Vright, signal=f(Vright) or from the difference between one or more or an average of multiple signals of the left and right amplified voltages Vleft and Vright, signal=f(Vleft— Vright) .

[0012] In a further aspect, the processor can accept data in, but not limited to, the following forms and their combinations: raw data, filtered data, low-pass filtered data, bandpass filtered data, averaged data, subtraction of left from right data, subtraction of right from left data, subtraction of left average from right average, subtraction of right average from left average, etc. [0013] In a further aspect, the material is a composite material composed of specific measurements or ratios of a matrix of at least one polymer and filler inclusions of at least one material, the polymer matrix composed of one or more of thermoplastic elastomers, TPU, P/PC acrylonitrile- butadiene- styrene, ABS, styrenic block copolymer TPS, PP/PE, styrene- ethylene- butadiene- styrene, TPE, polyetherimide copolymer, low density polyethylene copolymer, or other such material as appreciated by someone skilled in the art; and wherein the filler elements could be conductive, such as one or a combination of carbon-based particles such as graphite, graphene, single-walled carbon nanotubes, multi-walled carbon nanotubes, carbon black, or carbon nanofibers; silica-based particles, such as glass, zirconia or silica, in microstructures such as spheres, flakes, leaves or dendrites; metal-based particles, such as silver, gold, copper, nickel, aluminum, chromium, titanium, tungsten, in the form of nanowires, spheres, flakes, or dendrites; or metal-coated particles, including organic, in-organic, carbon fiber, or others as appreciated by a person skilled in the art. Furthermore, the polymer matrix and/or composite has traits of one or more of biocompatible, flexible, soft, conductive, or adhesive.

[0014] In a further aspect, the properties, such as hardness modulus or volume resistivity, can be adapted to a desired value based on traditional electrodes or a gold standard for a particular field of application.

[0015] In a further aspect, the surface is surface treated to enhance specific properties of the material, which treatment can be one or more of an exposure of internal structure, chemical treating, coating, or other processes.

[0016] In a further aspect, the sensor design can be optimized for data collection given the location of application, such as hairless skin surface contact, hairy skin surface contact, in-ear skin surface contact, skin surface contact on the face, etc.; the intended use, and the target signals.

[0017] In a further aspect, the sensor geometry, design, or mechanical properties are optimized to attain the target signals for the desired location, including, but not limited to, flat surface contact, comb pillar contact, webbed contact, clamping contact, scaffolding contact, vacuum contact through suction, etc. [0018] In a further aspect, the sensor is optimized to be used in a specific configuration among one or more other sensors, such configuration can include one or both of a ground electrode and reference electrode located to result in highest signal to noise ratio to capture desired signals, where such electrodes can be located on the same side of the head with active electrodes on the opposite side of the head, in positions around the ear, on the mastoid area, in the ear, on the nose, on the forehead, on the temple, or other locations across the face or head, or others.

[0019] In a further aspect, the sensor is optimized to be incorporated into electronic devices, wearable electronic devices, smart clothing or fabric, skin-worn patches, or other items to contact the skin.

[0020] In a further aspect, one or more faces of the sensor has specified microstructures and/or macrostructures on its surface.

[0021] In a further aspect, one or more faces of the sensor creates a vacuum between the skin and sensor, resulting in reduced movement between the skin and sensor and higher contact reliability to enhance the transfer of signals from the skin to the electrode.

[0022] In a further aspect, the sensor is optimized to transmit data to a device.

[0023] In a further aspect, a sensor fabrication process involves creating sensors with specific geometries and sizes from a mixture of conductive polymer composite material; the fabrication process involving one or more of mixing raw elements using a mixer, spreading a mixture using a roller, casting a raw mixture into molds, manipulating the viscosity, adhesiveness, or surface tension of a raw mixture to achieve a desired geometry, curing a raw mixture to preserve a desired geometry, including by the means of applying one or more of heat, chemical curing agents, plasma, coating treatment, UV treatment, dehydration, or extended exposure to ambient conditions.

[0024] In a further aspect, a material selection method, wherein inputs can be entered into a platform that can include one or more desired applications or properties and outputs a list of one or more optimal materials in, interpolated from, or extrapolated from a database to achieve desired applications or properties. Inputs can take into consideration aspects such as the human physiology, distance of sensors to the source of signal activity, properties of skin in the desired region of application, such as conductivity, presence of hair, perspiration, etc., as well as desired applications, measures of electrical conductivity, hardness, chemical sensitivity, adhesiveness, flexibility, thermal conductivity, or gold standard specifications.

[0025] In a further aspect, the platform can involve applying filters to a database to provide a list of one or more suitable materials, applying linear or non-linear models such as artificial neural network models, including deep and/or shallow artificial neural network models, wherein the models can be one or more of a combination of predictive models.

[0026] In a further aspect, the database can include material data from one or more of published literature, experimentation results, simulation results, or other sources of data.

[0027] In a further aspect, the material selection platform outputs can include materials and associated specifications for one or both of relevant fabrication processes and designs to meet the input specifications, including information regarding materials, material weight percentages, material molecular, nano-, micro-, or macro-structures, polymer matrix material weight percentage, filler material weight percentage, mixing process, shaping process, curing process, ideal geometry, and other relevant information.

BRIEF DESCRIPTION OF THE FIGURES

[0028] Embodiments will now be described by way of example only with reference to the appended drawings wherein:

[0029] FIG. 1 is a representation of the microstructure of a polymer-filler composite with no fillers 101 , tube-shaped or wire-shaped fillers, such as single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, nanofibers, nanowires, or other tube-shaped or wire-shaped fillers 102; particleshaped fillers, such as carbon black, graphene, or other carbon, silica, or metal based structures in the form of spheres, flakes, leaves, or dendrites 103; and a combination of tube-shaped, wire-shaped, or particle-shaped fillers 104. [0030] FIG. 2 depicts a schematic illustration of a top isometric view of an in- ear sensor design 201 , bottom isometric view of an in-ear sensor design 202, isometric view of a comb sensor designed to reach past hair 203, and base view of a comb sensor design 204.

[0031] FIG. 3 is a block diagram of a material and fabrication process selection model, with inputs such as desired sensing capabilities, characteristics, and/or gold standard specifications 301 ; model selection of material and fabrication processes from existing database 302; and output material with associated fabrication processes 303.

DETAILED DESCRIPTION

[0032] The described innovations are sensor systems, materials, and selection methods, including polymer material sensor material, design, fabrication process, and selection platform that is capable of detecting signals from the surface of the skin. The sensing systems can contain sensing materials fabricated to contact the skin independently of or in combination with one or more of circuitry to detect, record, or process signals, an interface to transport signals from the contact surface to the circuitry, and a processor to collect and record signals or to provide determinations based on the signals. The sensing system can be a subsystem of a larger sensor system, system, or device, or can be an independent sensur such as tattoo electrodes. The sensing system is optimized to achieve desired signals or increase signal to noise ratio of desired signals. The enclosed polymer material observes properties of flexibility, elasticity, hardness, conductivity, chemical sensitivity, and biocompatibility, and can be tuned to raise or lower certain characteristics in order to optimize the material for an intended purpose. Resulting properties of the polymer-filler composite material are subject to many factors, including composition, fabrication, and design; thus this patent explains their interdependence and the process by which materials can be tuned to achieve specific properties.

[0033] First, its properties are affected primarily by its composition. The composite material involves a polymer matrix composed of one or more polymers, with a certain weight distribution of filler materials. Polymer matrices can be one or more of thermoplastic elastomers, TPU, P/PC acrylonitrile- butadiene- styrene, ABS, styrenic block copolymer TPS, PP/PE, styrene- ethylene- butadiene- styrene, TPE, polyetherimide copolymer, low density polyethylene copolymer, or other polymer materials. Filler materials can be one of multiple elements, or a combination of elements, and generally fall into one of three categories: carbon-based, silica-based, and metal-based. Carbon-based filler materials include carbon particles with varying natural and synthetic geometries, such as graphite, graphene, carbon black, single- or multi-walled carbon nanotubes, or carbon nanofibers. Silica-based particles are made of materials such as glass, zirconia or silica, and come in varying microstructures, such as spheres, flakes, leaves or dendrites. Metal-based filler materials can be made from silver, gold, copper, nickel, aluminum, chromium, titanium, tungsten, or other metals, and can take the microstructures of nanowires, spheres, flakes, dendrites, or metal-coated particles.

[0034] These sensor materials contain specific formulas and ratios of polymer and filler, and undergo specific fabrication processes that further tune their properties; and thus, the second condition to affect the properties of the material is its fabrication process. Generally, the process is as follows. First, polymer and filler materials are measured to precise weight ratios. These materials are then mixed together to achieve an even distribution, or dispersion, of filler materials in the polymer matrix, to achieve most predictable results. Mixing can be performed with standard mixers, single, dual, or multi screw turners, stirrers, rollers and mills, kneaders, or other mechanical mixing methods. Additionally, distributed materials can be further processed by placement in the presence of a magnetic field. This is used to align filler particles to conduct electricity in specified directions. Then, the material is shaped. Flat geometries are achieved by rolling, spin coating, pressing, or other similar techniques, typically followed by cutting to achieve specific shapes. Thin cords are produced through extrusion. More complex geometries are achieved through mold casting. To do this, a negative impression is created in a secondary material of higher hardness. The conductive filler is then poured, injected, or otherwise “cast” into the mold. Alternate methods to manipulate the geometry are also performed. For instance, glass beads may be dipped onto the surface of a polymer precursor, then removed to a certain distance and suspended, capitalizing on the adhesiveness and surface tension of a material in order to create “tulip-like” structures with a cup at the end of a stem. To solidify the material, it undergoes a curing process. Curing is often catalyzed or accelerated using a variety of curing methods. Most commonly, this is performed by “baking” the material at a certain temperature for a period of time, though curing can also be performed by exposure to ultraviolet (UV) light, chemical curing agents, plasma, coating treatment, or extended time. After the material is finalized, a coating can be applied to change the surface properties of the material. For instance, a typical example of this would be the coating using a conductive ink, such as Ag/AgCI, to tune the surface conductivity properties of a material, or other surface treatments to expose the conductive filler materials. In this fabrication process, by manipulating one or more of these steps, additional material properties can be achieved. For instance, by curing a material such as PDMS at a higher temperature, it is possible to make the resulting material more brittle; conversely, by curing the material at a lower temperature, the material will be more pliable.

[0035] Finally, because of the many variables that affect the ability to detect signals from the surface of human skin, geometry is another element that can dramatically influence a sensor’s performance. Surface-contact sensors, such as the material sensors described in this patent, achieve highest performance when movement and other disturbances are limited. Thus, sensors must be designed to reduce movement and maintain consistent contact between the sensor and the skin. For in-ear sensors, this can be achieved by manipulating the geometry of the sensor to comfortably anchor within the ear or ear canal. For skin-surface applications, because of both macro-scale variables, such as the presence of hair, and micro-scale variables, such as level of perspiration, this can be achieved macroscopically, with the design of pillars to reach past hair or suction cup geometries to anchor to the skin similar to a sucker on an octopus’s tentacles, or microscopically, with an adhesive surface structure with ridges or hooks similar to the feet of a gecko.

[0036] Thus, the material can detect biopotential signals, such as electroencephalography (EEG), electrooculography (EOG), electromyography (EMG), or electrocardiography (ECG); temperature; chemical properties, such as perspiration moisture level, pH level, glucose concentration, and others.

[0037] Because of the many variables affecting the characteristics and quality of the composite polymer material, a selection method is developed to select the optimal material given a set of requirements or intended characteristics. Such selection methods can involve a database composed of data from literature, experimental data, data derived from simulations, or other sources, applying filters to said database to provide a list of one or more suitable materials, with their associated fabrication processes and designs, or linear or non-linear models, such as artificial neural network models. These predictive models can input conditions, desired applications, properties, or locations into the model can include one or more of a range of sensing specifications, such as electrical conductivity, thermal conductivity, chemical sensitivity, or other traits; a range of mechanical properties, such as hardness, tensile strength, elasticity, impact resistance, brittleness, toughness, viscosity, or other traits; a range of chemical properties, such as biocompatibility, reactivity, flammability, oxidizability, and other traits; and a gold standard specifications as used in the industry. The model searches the database, and produces an output of material selections and fabrication processes that can meet the desired properties. Furthermore, additional materials can be output based on interpolation or extrapolation techniques. In this way, using the gold standard, a material can be reverse engineered to determine the optimal materials and processes to develop the material with the properties.

[0038] Resulting sensor systems can be configured as part of a larger sensor system, system, or device. These can be used to provide signals to be processed, wherein the processor can accept data in, but not limited to, the following forms and their combinations: raw data, filtered data, low-pass filtered data, bandpass filtered data, averaged data, subtraction of left from right data, subtraction of right from left data, subtraction of left average from right average, subtraction of right average from left average, etc. Collected data can be collected by the sensing system and processed to provide indications of auditory attention, auditory attention envelope of sound, visual attentional direction, physical orientations of the user’s head, gaze, and trunk, saccades, blink, facial movements, jaw movements, emotions, fatigue, activity level, temperature, injury, illness, disease, sleep state, narcolepsy, seizures, blood oxygen level, pH level, and other indicators regarding the status of the user.

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