Patent Description:
<CIT> describes a device which comprises a position sensor assembly which comprises a composite layer medium including electrically conductive magnetic particles in a nonconductive matrix material. The medium is sandwiched between contact assemblies. The particles are aligned into chains extending across the thickness of the layer, and chains include a non-conductive gap (e.g. an air space or a nonconducting layer at least on particles nearest the contact assemblies) which is bridged upon application of sufficient pressure.

<CIT> describes a pressure-sensitive, conductive elastic sheet for use in a graphics digitizing tablet through which various letters or figures can be detected, the characteristics of which are such that the contact pressure is almost constant irrespective of contact area or increases with increasing contact area. The pressure-sensitive sheet according to the present invention comprises a silicon rubber in which a number of coarse, ferromagnetic, conductive metal particles with a diameter of <NUM> to <NUM> micron are mixed with a number of fine, ferromagnetic, conductive metal particles with a diameter of <NUM> micron or less or <NUM> micron or less at a predetermined proportion in such a manner that the coarse particles are aligned vertically through the interior thereof and the fine particles are dispersed near at least one surface thereof. To properly align the particles, the sheet is allowed to set within a uniform magnetic field.

<CIT> describes a switchable pressure activated electronic device. The switchable electronic device includes a composite material disposed between two conductors. The composite material electrically connects the two conductors. When pressure is applied between them, and electrically isolates the two conductors when pressure is not applied between them. The composite includes conductive particles at least partially embedded in an insulating material. The conductive particles are disposed so that substantially all electrical connections made between the first and second conductors are through single particles.

<CIT> describes a pressure sensitive conductive sheet provided by having a plurality of ferromagnetic conductive particles dispersed in a transparent elastic member joined together and linearly aligned with the thickness direction thereby forming a linear aggregate and then having the linear aggregate segmented into a plurality conductive elements, held linearly aligned with the thickness direction, with predetermined gaps formed therebetween.

<CIT>describes electrodes and sensors having nanowires. According to an embodiment as described, a dry sensor is provided. Nanowires, such as silver nanowires, are positioned within a polymer material, such as polydimethylsiloxane (PDMS) to form an electrode. A conductive element is attached to the electrode during its formation. Example conductive elements include, but are not limited to, a contact or a wire that may be communicatively coupled to medical equipment.

Embodiments of the invention are described in the dependent claims.

Examples are disclosed that relate to magnetically aligned switching circuits. One disclosed example provides an electronic component comprising a first terminal, a second terminal, and a deformable host material arranged between the first terminal and the second terminal. Aligned magnetically within the host material is an ensemble of particles each comprising a ferromagnetic material, each particle having greater electrical conductivity than the host material. The ensemble of particles is configured to form at least one complete conduction path from the first terminal to the second terminal.

Furthermore, the claimed subject matter is not limited to implementations that solve the disadvantages identified in this disclosure.

The examples disclosed herein relate to flexible electronic componentry, including flexible, pressure-sensitive electrical switches and electrodes to be worn on the human body. The disclosed examples utilize a thin layer of deformable, host material and an ensemble of magnetically aligned conductive particles embedded therein. Under appropriate conditions, the particles form a complete conduction path through the host material, between terminals arranged on opposite sides of the host material. In wearable implementations, one of the terminals can be configured to make an electrical contact to living human skin. The opposite terminal may be configured for resilient flexibility, so that the electronic component can be worn and used on a flexible body part. In some implementations, a complete conduction path through the ensemble of particles is formed upon depression of the host material through the flexible terminal, and is broken when the depression is released. This type of component can be used as a momentary electrical switch, as one example implementation.

Aspects of this disclosure will now be described by example and with reference to the drawing figures listed above. Components, process steps, and other elements that may be substantially the same in one or more of the figures are identified coordinately and are described with minimal repetition. It will be noted, however, that elements identified coordinately may also differ to some degree. It will be further noted that the figures are schematic and generally not drawn to scale. Rather, the various drawing scales, aspect ratios, and numbers of components shown in the figures may be purposely distorted to make certain features or relationships easier to see.

<FIG> shows one view of an example electronic component <NUM> of a wearable electronic device <NUM>. Electronic component <NUM> is an electrode intended to contact the living human skin of the device wearer. In some implementations, the electronic component may be five to ten millimeters in diameter. In other implementations, the electronic component may be larger or smaller, and may have any desired shape. In <FIG>, electronic component <NUM> is held against the wearer's skin by flexible band <NUM> of electronic device <NUM>. In other implementations, replaceable adhesive pads or tape may be used to secure the electronic component to the wearer's skin. The pads or tape may include a pressure-activated, hypoallergenic adhesive that yields to lift-off force.

<FIG> provides another view of electronic component <NUM>. The electronic component includes a first terminal <NUM>, a second terminal <NUM>, and a thin layer of deformable host material <NUM> arranged between the first and second terminals. The host material may be stretchable, bendable, and/or depressible. In some implementations, the host material is an electrical insulator. Further, in some implementations, the host material may comprise a soft, thermosetting, elastomeric polymer, such as silicone. Soft rubbers and thermoplastic materials are equally envisaged.

First terminal <NUM> and second terminal <NUM> each comprise one or more conductive materials, but are otherwise not particularly limited, either in form or in composition. In some implementations, the first and second terminals may be metallic. In other implementations, the first and second terminals may be formed from a conducting composite material, such as a graphite polymer composite. In some implementations, the first and second conductors may be nominally flat or plate-like. Curved terminals are also envisaged.

First terminal <NUM> provides electronic conduction through the interior of host material <NUM>. In <FIG>, the first terminal is coupled electrically to analog-to-digital (A/D) convertor <NUM> of wearable electronic device <NUM>. This configuration enables various forms of electrical monitoring of the wearer's physiology, including galvanic skin-resistance monitoring and electrocardio- or electroencephalographic monitoring, for example. More generally, the electrical monitoring may include detection and/or measurement of any electric current, voltage, or charge from the wearer's body. In some implementations, a wire electrically coupled to the first terminal may be used to conduct current or charge from the wearer's body to a remote monitoring device.

In some implementations, first terminal <NUM> may be resiliently deformable-e.g., to enable electronic component <NUM> to be worn over a flexible body part. The first terminal may comprise eutectic gallium indium (EGaIn), for example. With a conductivity of <NUM> x <NUM><NUM> siemens per meter (S / m) and a melting point of <NUM>, EGaIn is a liquid conductor at room temperature and at human skin and body temperature. An EGaIn first terminal will conform to its container (the deformable host material) at these temperatures, thereby maintaining the flexibility of the host material. The thickness of the first electrode may be one millimeter or less, in some implementations. In other implementations, the first electrode may have any other suitable thickness. To lessen the risk of detachment, damage to, or corrosion of the first terminal, the first terminal may be fully encapsulated and contained by the host material.

Second terminal <NUM> provides conductivity over a continuous area of a surface of host material <NUM> (the lower surface in <FIG>). In skin-wearable implementations, the second terminal may be configured to form an electrical contact to living human skin. Hair follicles and dead outer layers of human skin are liable to be dry and resistive. Accordingly, some skin-contact technologies use one or more fine, macroscopic needles to penetrate the resistive outer layer of skin and access moister, living tissue. Naturally, however, this approach may irritate the wearer's skin. In lieu of macroscopic needles, and referring now to <FIG>, second terminal <NUM> of electronic component <NUM> may include a large number of microscopic filaments <NUM>. The microscopic filaments of the second terminal may be stuck in (e.g. immobilized by and/or adhered to) the surface host material <NUM> which is opposite first terminal <NUM>. In <FIG>, microscopic filaments <NUM> are embedded directly in host material <NUM>; in other implementations, a conductive interface layer may be provided to couple the host material to the microscopic filaments of the second terminal.

In some implementations, microscopic filaments <NUM> of second terminal <NUM> may take the form of conductive nanowires-e.g., silver (Ag) or other metal nanowires and/or nanowires of a semiconductor or semi-metal, such as carbon. Nanowires useful for this purpose may be single- or multi-walled, and have any suitable dimensions. , Example Ag nanowires may have a diameter of <NUM> ± <NUM> nanometers (nm) and a length of up to <NUM> microns (µm). In other examples, Ag nanowires for filamentous second terminal <NUM> may have other suitable dimensions. In some implementations, the nanowires or other microscopic filaments of the second terminal may be randomly oriented. In other implementations, the nanowires may be oriented in specific direction and/or angle relative to the surface being contacted.

Returning now to <FIG>, aligned within host material <NUM> is an ensemble <NUM> of particles <NUM>, each particle having greater electrical conductivity than the host material. In some examples, the host material is an electrical insulator (e.g., having a bulk conductivity of <NUM>-<NUM>S / m or less in some examples), and each particle is a conductor (e.g., having a bulk conductivity of <NUM><NUM> S / m or more in some examples). Accordingly, the ratio of the bulk electrical conductivity of the particles to that of the host material may be <NUM><NUM> or greater in some examples. The ensemble of particles may be configured to form, at least under some conditions, at least one complete conduction path from first terminal <NUM> to second terminal <NUM>. To that end, each particle <NUM> may include a highly conductive and a corrosion-resistant outer surface <NUM>, as shown in <FIG>. Moreover, at least some of the particles may be in contact with each other, at least under some conditions. To facilitate alignment of the particles, each particle may include a ferromagnetic core material <NUM>. As a non-limiting example, the ensemble of particles may include one or more of Ag-coated nickel and Ag-coated ferromagnetic oxide particles. The particles may have any suitable size, and may vary in size between implementations. In implementations in which the host material is arranged in a layer of about <NUM> microns in thickness, each particle may be about <NUM> to <NUM> in diameter. For example, Ag coated nickel particles <NUM> in diameter (<NUM>% Ag by weight) and/or Ag coated iron oxide <NUM> in diameter (<NUM>% Ag by weight) may be used.

The guest-host assembly disclosed herein may provide various advantages over composite materials in which an insulating flexible polymer is loaded with a random dispersion of conductive particles. For example, low-density dispersions may exhibit poor conductivity, because the probability of forming a complete conduction path with low particle densities is low. High-density dispersions may be suitably conductive, but at the expense of various desirable properties of the host polymer, such as flexibility, castability, adhereability, and material hygiene.

In some implementations, a complete conduction path through the ensemble <NUM> of particles <NUM> may not be maintained under all conditions. For instance, the ensemble may form a complete conduction path from first terminal <NUM> to second terminal <NUM> only upon oriented depression of host material <NUM>. More specifically, the conduction path may form as a result of initially separated particles moving into contact with each other as the host material is depressed in a direction parallel to the direction of alignment of the ensemble of particles. Depression of the host material may be transmitted readily through first terminal <NUM>, in configurations in which the first terminal itself is deformable. This scenario is shown in <FIG>. In some implementations, the host material may remain deformed-and the particles may remain in contact-even after the depression of the host material is released. An electronic component configured in this manner may be used as a pressure-activated electrical contact. In other examples, when the host material is resiliently deformable, the conduction path may be broken upon release of the oriented depression of the host material. Thus, the breaking of the conduction path may result from the particles moving out of contact with each other, as the oriented depression is released. An electronic component configured in this manner may be used as a pressure-sensitive, momentary switch.

Also envisaged is a switching implementation in which conductive particles <NUM>, initially in contact, separate from each other in response to oriented depression of host material <NUM>. The oriented depression in this case may be perpendicular to the direction of alignment of the ensemble of particles, and parallel to the first and second terminals. This scenario is shown in <FIG>.

In the switching implementation shown in <FIG>, the electrical resistance of electronic component <NUM> as measured from first terminal <NUM> to second terminal <NUM> may originate at a very high value in the absence of oriented depression, remain at that value through weak oriented depression, and drop abruptly to a low value when at least one complete conduction path through host material <NUM> is formed. The resulting resistance-versus-depression characteristic is shown in <FIG> at A. This behavior may be observed when host material <NUM> is substantially insulating, and relatively few conduction paths are formed and broken in the host material. In other implementations, when a higher density of conduction paths is available, the resistance drop responsive to depression may be more gradual, as shown at B. In general, the resistance-versus-depression characteristic of electronic component <NUM> may be tuned by controlling such parameters as the resistivity of the host material, the resistivity of the particles, the bulk loading of the particles in the host material, and the and the detailed geometry of the ensemble <NUM> of aligned particles (e.g., the area-wise density of columns, the orientation of columns with respect to the depression, etc.).

The manner of incorporating the ensemble <NUM> of aligned particles <NUM> in host material <NUM> is not particularly limited. In some examples, the ensemble of particles may be mixed into the host material in the uncured and/or fluid state, and aligned under the influence of a magnetic field applied during solidification of the host material. In this manner, the particles align along magnetic field lines penetrating the host material. In particular, the magnetic field lines may be arranged between shielded dead zones, in which no particles are aligned. <FIG> shows aspects of an example method <NUM> to fabricate an electronic component <NUM>, of the kind described above.

At <NUM> of method <NUM>, a substrate (e.g., a mold) is treated with a polymer-release agent to promote facile release of the electronic component <NUM> from the mold, and to prevent complete encapsulation of the nanowire second terminal (vide infra). Alternatively, a smooth substrate (such as glass or a silicon wafer) can be thoroughly cleaned and left untreated.

At <NUM> a solvent suspension of microscopic filaments, such as nanowires, is deposited onto the surface of the substrate, and the solvent is allowed to evaporate. For example, an ethanolic suspension of Ag nanowires may be drop-cast onto the substrate. At <NUM> uncured poly(dimethylsiloxane) (PDMS) resin, or other uncured soft rubber, is prepared, and conductive ferromagnetic particles (such as silver coated nickel or silver coated ferromagnetic oxide) are mixed in. The resin may comprise Sylgard <NUM> from Dow Corning, and/or various other fluid elastomer resins. Alternatively, the particles may be mixed into a molten thermoplastic, or host material liquefied by incorporation of volatile solvent.

At <NUM> a thin layer of the above mixture is deposited onto the substrate, over the drop-cast nanowires. This can be achieved using either a bladed applicator or a spin coater. At <NUM> a magnetic field is applied perpendicular to the substrate, with the field strength decreasing with increasing distance above the substrate. This can be achieved by placing a strong magnet below the substrate. <FIG> shows an example polymer curing stage <NUM> for forming an ensemble of aligned particles in a polymer host material. In some implementations, a patterned, magnetically soft magnetic shield <NUM> may be positioned between permanent magnet <NUM> and substrate <NUM>, to provide a plurality of dead zones in which no particles are aligned. In this arrangement, the particles within the polymer host material will align perpendicular to the substrate, spanning the thickness of the polymer host material. In other implementations, the magnetic shield may be omitted, and 'repulsion' among the magnetic field lines may have the effect of aligning the particles along plural, non-intersecting paths through the host material.

The electron micrographs of <FIG> show one, non-limiting example of an ensemble of particles magnetically aligned in a silicone host material. The perspective in <FIG> is approximately normal to the host-material layer; the perspective in <FIG> is oblique to the host-material layer.

Returning now to <FIG>, at <NUM> the polymer host material may be cured, solidified and/or hardened. Thermal and/or photochemical curing may be employed in some examples. In other examples, a molten thermoplastic host material may be cooled to effect solidification, or volatile solvent may be evaporated, etc. At <NUM>, eutectic gallium indium is deposited onto the surface of the polymer host material. At <NUM>, the eutectic gallium indium first terminal is encapsulated by casting additional uncured polymer host material overtop. <FIG> shows an electron micrograph of a final layered structure of electronic component <NUM>, in one non-limiting example.

The structure formed in method <NUM> allows for a highly conductive second terminal suitable for skin contact, bridged through the ensemble of aligned conductive aligned particles into a eutectic gallium indium first terminal, thereby creating a soft stretchable electronic component for a device. This component may easily conform to the skin and can be utilized as a thin film bioelectrode, measuring electrical signals from the body. In some implementations, as described above, the electrode may further provide pressure-sensitive resistance and/or switching. It may be used, for example, as a switch fully embedded in an elastomeric housing of an electronic device. A switch configured in this manner may be well-protected from environmental conditions, such as condensing moisture, skin-care products, immersion in water, etc..

Another example provides an electronic component comprising a first terminal; a second terminal; a deformable host material arranged between the first terminal and the second terminal; and, aligned magnetically within the host material, an ensemble of particles each having greater electrical conductivity than the host material, the ensemble of particles forming a complete conduction path from the first terminal to the second terminal.

In some implementations, the first terminal may be resiliently deformable. In some implementations, the first terminal may comprise eutectic gallium indium. In some implementations, the first terminal may be fully encapsulated by the host material. The second terminal is filamentous. In some implementations, the second terminal may form an electrical contact to living human skin. In some implementations, each particle may be about <NUM> to <NUM> microns in diameter. In some implementations, the host material may be an electrical insulator. In some implementations, the host material may include a thermosetting polymer. In some implementations, the host material may include silicone. In some implementations, each particle may include a ferromagnetic material and a conductive outer surface. In some implementations, the ensemble of particles may include one or more of silver-coated nickel and silver-coated ferromagnetic oxide particles. In some implementations, the ensemble may form the conduction path upon depression of the host material and may break the conduction path upon release of depression of the host material.

Another example provides a pressure-sensitive electrical switch comprising: a first terminal; a second terminal; a deformable host material arranged between the first terminal and the second terminal; and, aligned within the host material, an ensemble of particles each having greater electrical conductivity than the host material, the ensemble forming a complete conduction path from the first terminal to the second terminal upon depression of the host material and breaking the conduction path upon release of depression of the host material.

In some implementations, the ensemble of particles may be magnetically aligned. In some implementations, the ensemble of particles may be aligned during solidification of the host material, along magnetic field lines arranged between shielded dead zones in which no particles are aligned. In some implementations, forming and breaking the complete conduction path may result from the particles moving in and out of contact with each other with depression and release of depression of the host material.

Another example provides a method to fabricate an electronic component for a wearable device. The method comprises: depositing a filamentous second terminal configured to form an electrical contact against living human skin; depositing a deformable host material over the second terminal; magnetically aligning an ensemble of particles within the host material, each particle having greater electrical conductivity than the host material; and, depositing the first terminal onto the host material, opposite the second terminal, such that the ensemble of particles forms a complete conduction path from the first terminal to the second terminal.

In some implementations, the second terminal may become immobilized in the host material upon solidification of the host material. In some implementations, the second terminal may include conductive nanowires.

Claim 1:
An electronic component, comprising:
a first terminal (<NUM>);
a second terminal (<NUM>);
a deformable host material (<NUM>) arranged between the first terminal (<NUM>) and the second terminal (<NUM>); and
aligned within the host material (<NUM>), an ensemble of particles, the particles each comprising a ferromagnetic material and each having greater electrical conductivity than the host material (<NUM>), the ensemble of particles forming a complete conduction path from the first terminal (<NUM>) to the second terminal (<NUM>) upon depression of the host material (<NUM>) and wherein the conduction path is broken when the depression is released, wherein the second terminal (<NUM>) is filamentous and is suitable for forming an electrical contact to living human skin.