WO2021254601A1

WO2021254601A1 - Three-dimensional electrode arrangement

Info

Publication number: WO2021254601A1
Application number: PCT/EP2020/066617
Authority: WO
Inventors: Séverine CHARDONNENS; Simon Bachmann; Andrea Fümm; Katja Junker; Moritz THIELEN; Mark Melnykowycz
Original assignee: IDUN Technologies AG
Priority date: 2020-06-16
Filing date: 2020-06-16
Publication date: 2021-12-23

Abstract

According to an aspect, there is provided an electrode arrangement. The electrode arrangement comprises an elastic element for contacting skin. The elastic element comprises a top section having top and bottom surfaces, a protrusion extending substantially centrally and orthogonally from the bottom surface along a central axis of the elastic element and two or more legs extending from the bottom surface and away from the protrusion at a first angle to the central axis and arranged to surround the protrusion symmetrically. A length of the protrusion along the central axis is shorter than a length of each leg along the central axis. The electrode arrangement further comprises a conductive connector element operatively connected to the top surface of the top section for relaying signals between the elastic element and a measurement device or a transmitter.

Description

THREE-DIMENSIONAL ELECTRODE ARRANGEMENT

TECHNICAL FIELD

The present application relates to electrodes for measuring and/or inducing biosignals.

BACKGROUND

Electrodes are conventionally used for physiological measurements and stimulation. Physiological measurements comprise measuring and monitoring a range of physiological parameters while physiological stimulation comprises tissue and neuronal stimulation. Current electrode solutions suffer from various problems and limitations, for example, poor signal quality owing to poor electrode skin contact and poor user comfort and usability. Thus, there is a need for improved electrode designs for overcoming at least some of the aforementioned limitations.

SUMMARY

According to an aspect, there is provided the subject matter of the in dependent claims. Embodiments are defined in the dependent claims.

One or more examples of implementations are set forth in more detail in the accompanying drawings and the description below. Other features will be apparent from the description and drawings, and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described with reference to the accompanying drawings:

Figures 1A, IB and 1C illustrate an example apparatus in a non- compressed state in two perspective views and in a compressed state in a side view, respectively;

Figures 2A and 2B illustrate an example apparatus and its dimensions in a side view and a cross-sectional side view;

Figures 3A and 3B illustrate an example apparatus in a cross-sectional side view and from above;

Figure 4 illustrates a conductive connector element of an example apparatus in a perspective view; and

Figure 5 illustrates exemplary headphones according to embodiments. DETAILED DESCRIPTION OF THE DRAWINGS

The following embodiments are exemplifying. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations of the text, this does not necessarily mean that each reference is made to the same embodiment(s), or that a particular feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

In the following, various references are made to conductive material, conductive surfaces and conductivity in general. In the context of this application, said terms refer specifically to electrical conductivity (as opposed to, e.g., thermal conductivity). The same applies, mutatis mutandis, to references to non- conductivity.

Example embodiments relate to an apparatus for measuring and/or inducing biosignals. The apparatus may be equally called an electrode arrangement. More particularly, example embodiments relate to an electrode for biopotential data acquisition and/or for non-invasive stimulation of biological matter such as muscle or brain tissue. According to an example embodiment, the apparatus comprises an elastic element with a conductive surface for contacting skin, the elastic element comprising a top section having a top surface and a bottom surface, a protrusion extending substantially centrally and orthogonally from the bottom surface of the top section along a central axis of the elastic element and two or more legs of equal length extending from the bottom surface of the top section and away from the protrusion at a first angle to the central axis and arranged to surround the protrusion, wherein a length of the protrusion along the central axis is shorter than a length of each of said two or more legs along the central axis; and a conductive connector element operatively connected to the top surface of the top section of the elastic element for receiving biosignals from the elastic element and for enabling transmission of said biosignals to a measurement device and/or for inducing biosignals via the elastic element according to electric signals received from a transmitter (or a transceiver). In other words, a conductive connector element serves to relay signals between the elastic element and a measurement device (i.e., a receiver or a transceiver) or a transmitter (via, e.g., a measurement cable).

A biosignal comprises a signal in a living being that can be continually measured and monitored. A biosignal may comprise an electrical or non-electrical signal. An electrical biosignal may refer to a change in electric current produced by an electrical potential difference between points in living cells, tissues organs or a cell system such as the nervous system. An electrical biosignal may comprise, for example, electroencephalogram (EEG), electrocardiogram (ECG) or electromyogram (EMG). EEG, ECG and EMG may be measured with a differential amplifier configured to register the difference between two or more electrodes attached to skin.

A bioelectrode is a mechanism configured to function as an interface between a biological structure and an electronic system. Electronic systems may be configured to passively sense, for example, measure or actively stimulate electrical potentials within the biological structures. Bioelectric potentials generated by a living being are ionic potentials that need to be converted into electronic potentials before they can be measured by conventional methods. Electrodes are configured to convert ionic potential into electronic potential. A bioelectrode is configured to convert an ionic current in a body into electronic current flowing in an electrode.

There are different types of electrodes such as surface electrodes, microelectrodes, internal electrodes and needle electrodes. Surface electrodes are types of electrodes applied to the skin of a subject. Surface electrodes are typically used in ECG, EEG and EMG measurements.

There are different types of electrodes such as wet electrodes, dry electrodes, active electrodes and passive electrodes. Wet electrodes use electrolytic gel material as conductor between the skin and the electrode. Dry electrodes typically comprise a single metal, such as stainless steel, that acts as a conductor between the skin and the electrode. Active electrodes typically comprise a pre-amplification module that allows amplifying a signal before additional noise is added between the electrode and a system that might capture, process or amplify the signal. Passive electrodes extend the connection from the conductive material to the equipment capturing, processing or amplifying the signal.

Another way to classify electrodes is to divide them into two- dimensional (2D) and three-dimensional (3D) electrodes. Two-dimensional electrodes allow for biopotential measurements on any sufficiently flat part of the body (e.g., on the arm). One exception to this is biopotential measurements through a dense hairy scalp or any other considerably hairy part of a body of a human or an animal. Three-dimensional electrodes have a more volumetric structure compared to the two-dimensional electrodes which allows for biopotential measurements in three-dimensional spaces. The geometry and dimensions of the three-dimensional electrode may be adjusted to meet the demands of a particular use case. For example, three-dimensional electrodes may enable biopotential measurements through hair. However, the problem of designing a three-dimensional electrode which would simultaneously provide good electrode-skin contact and thus high signal quality as well as high user comfort during the measurements is not a straightforward task.

Figures 1A and IB show an example of an apparatus 100 [equally called an electrode arrangement] according to an embodiment in two perspective views. Namely, Figure 1A shows the apparatus from "above" and Figure IB shows the apparatus from "below". Figure 1C shows an example of an apparatus 100 or specifically the elastic element 101 of said apparatus 100 during operation when it is pushed against a skin of a user. According to an example embodiment, the apparatus 100 is configured to measure and/or monitor electrical biosignals on skin, preferably even through thick hair. The apparatus 100 may be or comprise a three-dimensional electrode. Said electrical biosignals may comprise, for example, ECG, EEG and/or EMG signals. The operation and geometry of the apparatus according to embodiments are discussed next in relation Figures 1A, IB and 1C while exemplary dimensions according to embodiments are discussed, thereafter, in relation to Figures 2A and 2B.

The apparatus 100 comprises two distinct parts or elements which are operatively connected to each other: an elastic element 101 (a bottom part] and a conductive connector element 102 [a top part]. The elastic element 101 is the part which is contacting the skin during measurements while the conductive connector element 102 acts as an intermediary between the elastic element and a measurement device or instrument (i.e., enabling a mechanical and electrical connection or an interface for the measurement instrument]. Owing to their different functions, the two parts 101, 102 may be made of different materials. The elastic element 101 may be also conductive, that is, it may be made of a conductive material or at least have a conductive surface. In the following, the two parts 101, 102 are discussed in detail.

The elastic element 101 for contacting skin comprises a top section 103 and a protrusion 104 and two or more legs 105 [eight legs in the illustrated example] extending from the top section 103. The top section 103 may have a top surface 109 facing the conductive connector element 102 and a bottom surface 108 from which the other parts 104, 105 of the elastic element 101 extend. The top and botom surfaces 109, 108 may be substantially opposite to each other. As illustrated in Figures 1A, IB and 1C, the top section 103 may be shaped like a (short) cylinder though other shapes may also be employed such as any other prism or a frustum. In the case of a top section 103 shaped like a prism or a frustum, the top surface 109 and the bottom surface 108 may specifically correspond to the bases of the prism or frustum.

The protrusion 104 (or a central protrusion) extends substantially centrally and orthogonally from the bottom surface of the top section 103 along a central axis 110 of the elastic element 101. Said central axis 110 may act as a central axis of (radial) symmetry for the elastic element 101 as depicted in Figures 1A and IB (and also in Figure 2B). The length of the protrusion 104 along the central axis 110 is shorter than the length of each of said two or more legs 105 along the central axis 110. Thus, when the apparatus 100 is placed on a flat surface (or even a slightly curved surface such as a surface defined by a top of a scalp) with the elastic element 101 facing the surface and no external pressure is applied to it, the apparatus 100 stands only on said two or more legs 105 (i.e., the protrusion 104 is not touching said surface). Only when enough force (that is, force along the central axis 110) is applied on the apparatus 100 causing the spreading of the two or more legs 105, does the protrusion 104 touch the surface. Obviously, if said surface is curved, as opposed to being totally flat, as is the case often with a surface of the skin, the curvature of the surface serves to facilitate both the spreading of said two or more legs 105 and the touching of the skin by the protrusion 104 when force is applied on the apparatus 100. The protrusion 104 may be shaped, for example, like a prism (e.g., a cylinder) or a frustum (e.g., a conical frustum), optionally with rounded edges. In the example illustrated in Figures 1A, IB and 1C, a rounded conical frustum is used with the larger base of the frustum being arranged against the top section 103. The prism or frustum may be specifically a right prism or a right frustum, respectively.

The two or more legs 105 extend from the bottom surface 108 of the top section 103 and away from the protrusion 104 at a first angle a] to the central axis (or equally to the longitudinal direction of the protrusion 104). Moreover, the two or more legs 105 may be arranged to surround the protrusion 104 symmetrically (or at least substantially symmetrically). The spacing between adjacent legs may be constant and/or they may be arranged in a radially symmetric manner in relation to the central axis 110. In some embodiments, three or more legs 105 may be provided so as to improve stability of the structure and to increase the overall skin-leg contact area. In other embodiments, four or more legs, five or more legs, six or more legs, seven or more legs or eight or more legs may be provided. As illustrated in Figures 1A, IB and 1C, the number of the two or more legs 105 may be, for example, eight. Also as illustrated in Figures 1A, IB and 1C, the ends of two or more legs 105 may be rounded for improving the user comfort.

The two or more legs 105 may be of equal length. However, in other embodiments, all of said two or more legs 105 may not be of equal length. In such embodiments, the apparatus 100 may be specifically adapted for a specific placement on skin taking into account the curvature of the area of insertion.

Each of the two or more legs 105 may be straight though they may be adapted to curve when force is applied. In some alternative embodiments (not illustrated in Figures 1A, IB and 1C), each of the two or more legs 105 may comprise a first straight section extending from the bottom surface 108 at the first angle and a second straight section (mechanically and electrically) connected to an end of the first straight section (i.e., to the end not connected to the bottom surface 108) and forming a second angle with the central axis. Preferably, the second angle is larger than the first angle.

During the operation of the apparatus (e.g., during measurements of biosignals), the elastic element 101 is pushed against the skin of a person (or an animal) so that the two or more legs 105 are spread wider apart (i.e., are deformed) and the protrusion 104 may, consequently, also be touching the skin of the user substantially increasing the total contact area of the elastic element 101. This operation is illustrated in Figure 1C. Specifically in Figure 1C, a scenario, where the protrusion 104 (in addition to all of the eight legs 105) is touching the skin of the user, is illustrated. The curving dashed line 111 illustrates the skin of the user at a central cut-plane of the elastic element 101. Similar curvature is assumed in Figure 1C also for an orthogonal central cut-plane (i.e., a central cut-plane extending into the figure) meaning that the elastic element 101 is deformed in a symmetric manner.

The apparatus 100 may be especially well-suited for measuring biosignals through dense hair (e.g., dense hair of a scalp) as the hair is able to pass through the two or more legs 105 which, in turn, enables the two or more legs 105 (or at least one of them) to reach the skin. To achieve such desired operation in an optimal manner, the material of the elastic element 101 must be carefully chosen. For example, if the material is too hard, it may cause considerable discomfort for the user. Also, the skin-leg contact area may be reduced if the material is too hard which may cause the performance of the apparatus 100 to deteriorate (e.g., measured signal quality using the apparatus 100 may be reduced]. On the other hand, if the material is too soft, the two or more legs 105 may not bend in the desired manner. For example, the two or more legs 105 may, as opposed to spreading apart, bend inwardly toward the protrusion 104.

The apparatus 100 may operate in a reciprocal manner so that it may not only be used for measuring biosignals, but also for inducing biosignals. The latter application may be used, for example, for stimulating brain tissue. Similar to as described in the previous paragraph for the measurement functionality, the stimulation of the brain tissue may be possible using the apparatus 100 even through dense hair thanks to the multi-legged structure of the apparatus 100. Similar requirements for the material of the elastic element 101 as described in the previous paragraph may apply also for this alternative application.

In general, the elastic element 101 may be made of a conductive material, a non-conductive elastic material which is coated with a conductive material or a conductive elastic material which is coated with a conductive material. In the last case, the coating may be specifically used for improving the skin-electrode contact, while the bulk conductivity of the conductive elastic material provides, predominantly, the conductive path to the conductive connector element 102.

In some embodiments, the conductive ink is injected in a small funnel in the two or more legs 105 in order to protect the overall conductivity from degradation due to repeated use. In such embodiments, the coating may be applied only to the end of the two or more legs 105, the inner side of the two or more legs 105 and the central protrusion 104.

In a typical embodiment, the elastic element 101 is made of a (soft] thermoplastic elastomer which is coated with a conductive ink. A conductive ink is a type of ink infused with a conductive material such as silver or graphite. In general, said conductive material may be a conductive metal, a conductive carbonaceous material, an ionic substance or an intrinsically conductive polymer. In other embodiments, a thin metal layer may be employed instead of the conductive ink.

The thermoplastic elastomer used as the elastic element 101 may be any thermoplastic elastomer. Namely, the thermoplastic may be any of the following types: styrenic block copolymers, TPS (TPE-s], thermoplastic polyolefinelastomers, TPO (TPE-o], thermoplastic vulcanizates, TPV (TPE-v or TPV], thermoplastic polyurethanes, TPU (TPU], thermoplastic copolyester, TPC (TPE-E], thermoplastic polyamides, TPA (TPE-A] and not classified thermoplastic elastomers, TPZ. For example, TPU or TPS (styrene-ethylene-butylene-styrene, SEBS, or SEBS compound] may be employed in a typical embodiment. In some other embodiments, a silicone rubber (with addition or condensation crosslinking] or a thermoplastic silicone may be employed as the elastic element 101. In other embodiments, a polyurethane (PUR] or a polyvinyl chloride may (PVC] may be employed as the elastic element 101.

In some embodiments, the thermoplastic elastomer used as the elastic element 101 may have a hardness in a range of 20-100 using Shore A hardness scale, preferably in a range of 60-90 using Shore A hardness scale. With this limitation, a middle ground between user comfort and desired operation (i.e., legs spreading outwardly, not folding into themselves] is achieved.

The conductive connector element 102 (a top part] is adapted to receive measured biosignals from the elastic element 101 and provide means (e.g., a connector mechanism] for transmitting said measured biosignals further to a measurement device or instrument. In contrast to the elastic element 101, the conductive connector element 102 may not be physically touching the skin of the user during conventional operation of the apparatus 100.

The conductive connector element 102 may comprise two parts or sections: a base section 107 operatively connected (and/or electrically connected and/or mechanically connected] to the top surface 109 of the top section 103 of the elastic element 101 and a connector 106 extending from the base section 107 and away from the elastic element 101 for enabling an electrical connection using a connection mechanism to a measurement device. For example, the connector 106 may extend substantially to an opposite direction compared to the elastic element 101. Alternatively, the connector 106 may extend (at least in part] along a direction substantially parallel to the top surface 109.

The base section 107 maybe connected to the top surface 109 of the top section 103 of the elastic element 101, for example, using an adhesive or as a part of a 2K injecting molding process, so as to enable the operative or electrical connectivity. The base section 107 may have a similar shape as discussed above for the top section 103 of the elastic element 101. Namely, the base section 107 may be shaped, for example, like a cylinder (as illustrated in Figures 1A and IB] or some other (right] prism or a (right] frustum. The base section 107 may be substantially aligned with the top section 103 of the elastic element 101 and/or the base section 107 and the top section 103 may have substantially the same cross section (e.g., a circular cross section as in the illustrated example).

The connector 106 enables an electrical connection to a measurement device (e.g., a receiver) and/or to a transmitter using a connection mechanism for, e.g., displaying, storing and/or analyzing a measured biosignal and/or for transmitting a signal to the elastic element 101 (and further as a biosignal through the skin of a subject). The electrical connection achieved using the connection mechanism maybe a mechanical (or wired) connection (e.g., a measurement cable such as an electrode lead wire). Correspondingly, the connector 106 may be a connector for a measurement cable or for a measurement device (e.g., comprising an enclosure with internal wiring). In some embodiments, the connector 106 may correspond to or form a part of a snap joint (as illustrated in Figures 1A, IB and 1C). One advantage of using a snap joint is that it is easy to attach and typically compatible with most commercially available cables, measurement devices and transmitters. A snap joint may be equally called a snap fit joint.

The conductive connector element 102 may be made of a conductive material (e.g., a metal), a non-conductive material embedded with one or more conductive filler materials (e.g., with conductive filler particles or other conductive filler elements) or a non-conductive material coated with a conductive material (or multiple conductive materials). One or more other materials, in addition to this primary material, may also be used, in some embodiments, for the conductive connector element 102, especially for the connector 106.

In the case where the conductive connector element 102 is made of a non-conductive material embedded with one or more conductive filler materials, the non-conductive material may be, for example, any (hard) thermoplastic material (e.g., a thermoplastic or a thermoplastic elastomer) or a duromer (i.e., a crosslinked polymer). The non-conductive material used for the conductive connector element 102 may be at least harder than the non-conductive material (e.g., thermoplastic polymer) used for the elastic element 101. Some examples of materials which may be employed are: ABS, ABS/PC, PC, polypropylene (PP), polyethylene (PE), polyamide (PA) (6; 6,6; 6;12; 12; 11; 6,10), polystyrene (PS), polyoxymethylene (POM), TPU (hard, amorphous), styrene acrylonitrile (SAN), polysulfone (PSU), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyether sulfone (PES), polyester, polyetherimide (PEI), polyetheretherketone (PEEK), polyetherketone (PEK) and PUR. The polyethylene (listed above] may be low-density polyethylene (LDPE), high-intensity polyethylene (HDPE) or ultra-high-intensity polyethylene (UHDPE).

In general, a conductive filler material may be defined as a conductive material that is added to a polymer matrix in order to functionalize the latter with electric conductivity. The conductive filler materials may be, for example, conductive metals, conductive carbonaceous materials, intrinsically conductive polymers and conductive ionic liquids. Possible geometries for conductive filler materials may be, for example, conductive particles of different sizes and geometries (e.g. spherical, flake, tubes, nano-tubes, nano-sized fibers], fibers and ionic liquids (salts, that are liquid, i.e., molten, at operation temperature, forming very small droplets inside the polymer matrix]. Said conductive particles may be, for example, metal or carbonaceous particles. The metal particles may be, for example, silver, steel, aluminum or nickel particles. By embedding one or more conductive filler materials to the non-conductive material, the overall conductivity should be rendered high enough to enable efficient transmission of the measured signal from the elastic element 101 to the connector 106 of the conductive connector element 102. Preferably, the material of the conductive connector element 102 should be, despite the high content of the one or more conductive filler materials, suitable for injection molding.

The apparatus 100 may be manufactured using injection molding, hot pressing and/or foam casting. In some embodiments, specifically 2K injection molding may be used for molding both the elastic element 101 and the conductive connector element 102 in a single or two-step (overmolding] injection molding process. In some embodiments, 3D-printing or additive manufacturing (e.g., fused deposition modeling, stereolithography or selective laser sintering] may be used for manufacturing the conductive connector element 102 or at least the connector 106. Alternatively, the conductive connector element 102 or at least the connector 106 may be manufactured using subtractive manufacturing, e.g., computer numerical control (CNC] milling.

The apparatus 100 may also comprise components that enable manufacturing of the apparatus 100. For example, the apparatus 100 may comprise different kinds of layers and/or structures to support the apparatus and make manufacturing of the apparatus 100 easier.

In some embodiments, a particular combination of materials for the elastic element 101 and the conductive connector element 102 may be employed. Specifically, the material for the elastic element 101 may be a soft thermoplastic elastomer and the material for the conductive connector element 102 may be a hard thermoplastic. Examples of such material combinations according to embodiments are:

• the soft thermoplastic elastomer used for the elastic element 101 is TPU (with Shore A 70), and the hard thermoplastic used for the conductive connector element 102 is PC or PC/ ABS, or

• the soft thermoplastic elastomer used for the elastic element 101 is TPS (SEBS/SEBS Compound), and the hard thermoplastic used for the conductive connector element 102 is PP or PE.

The material combinations listed above may be especially well-suited for 2K injection molding because of their melt processing parameters and their adhesion to each other.

Figures 2A and 2B show an example of an apparatus 100 according to an embodiment in a side view and in a cross-sectional view. Specifically, Figure 2B shows a cross sectional view of a central cross section A-A shown in Figure 2A. The apparatus 100 illustrated in Figures 2A and 2B may be the same apparatus as illustrated in Figures 1A, IB and 1C. The reference signs denoting different parts of the apparatus 100 have been left out of Figures 2A and 2B merely for clarity of presentation.

Figure 2A denotes various dimensions of the apparatus 100 as follows:

• W3 is a width of the base section 107 of the conductive connector element 102 as well as of the top section 103 of the elastic element 101,

• W4 is a width of the connector 106 of the conductive connector element 102,

• ti is a thickness of the base section 107 of the conductive connector element

102,

• t2 is a width of the top section 103 of the elastic element 101,

• hi is a height (or length) of the connector 106 of the conductive connector element 102,

• hi is a height (or length) of each leg 105 measured along the central axis 110 of the elastic element 101 and

• /?3 is a height (or length) of protrusion 104 of the elastic element 101 along the central axis 110 of the elastic element 101 (i.e., along the longitudinal direction of the protrusion 104).

In the illustrated non-limiting example, the dimensions are defined as follows: W3 - 10.09 mm, W4 = 4 mm, ti - 0.8 mm, t2 - 0.5 mm, hi - 3 mm, hi - 5.07 mm and hi = 3 mm. In some embodiments, the dimensions maybe selected from the following value ranges: W3 = 5-15 mm, W4 = 2-8 mm, ti = 0.1-5 mm, t2 = 0.25-2 mm, hi = 1.5- 6 mm, /?2 = 2.5-11 mm and /?3 = 1.5-6 mm.

In some embodiments, a ratio of the length of the protrusion 104 along the central axis 110 and the length of each leg 105 along the central axis 110, that is, the ratio h-i/h , has value in a range of 0.4-0.7. In the illustrated example, the ratio L3//22 has a value of 0.55.

The width of the protrusion 104 may be defined as follows. As described above and illustrated also in Figure 2A, the protrusion 104 may be shaped like a frustum (e.g., a rounded conical frustum), that is, it may taper along its length. In the illustrated example, the diameter of the protrusion 104 is 3.45 mm at the wide end and 3.235 mm at the narrow end (before the rounded section at the very end). In some embodiments, the diameter of the protrusion 104 (defined, e.g., as a conical frustum) along its whole length may be defined to be at least larger than the second width W2 (see Figure 2B). Additionally or alternatively, the diameter of the protrusion 104 (defined, e.g., as a conical frustum) along its whole length may be defined to be at least smaller than a width defined as W3-2WI.

As discussed in relation to Figures 1A, IB and 1C, the legs 105 of the apparatus 100 extend from the top section 103 of the elastic element 101 at a first angle relative to the central axis of the elastic element and away from the (central) protrusion 104. The first angle is denoted as a in Figure 2A. The first angle should be selected so that spreading apart of the two or more legs 105 of the apparatus 100 when force is applied on the apparatus 100 occurs in the desired way without the use of excessive force. T 0 this end, the first angle a may be selected from a range of 15° - 60°, preferably from a range of 19° - 40°. In the illustrated example, the first angle has a value of 24.1°.

Referring to Figure 2B, each leg 105 of the apparatus 100 has a first width wi (i.e., a maximum width) along a first cross-sectional direction of a corresponding leg and a second width W2 (i.e., a maximum width) along a second cross-sectional direction of the corresponding leg orthogonal to the first cross- sectional direction. The second cross-sectional direction may specifically be defined to be orthogonal to the central axis 110 of the elastic element 101 and to a longitudinal direction of the corresponding leg (as is the case in Figure 2B). In some embodiments, the second width W2 maybe defined to be larger than the first width wi so as to maximize the skin-leg contact area. In some embodiments, the ratio between the first width and the second width W1/W2 may be defined to be within a range of 0.5 - 0.9, preferably within a range 0.7 - 0.8. The cross section of each leg 105 may be of any shape within the aforementioned limitations. For example, each leg 105 may have an elliptical cross section along a plane defined by said first and second cross-sectional directions, as illustrated in Figures 2A and 2B. In the illustrated example, the first and second widths (defining, here, major and minor axes of an elliptical cross section, respectively] have values wi = 1.19 mm and w 2 = 1.61 mm. To give another example, the cross section may have a shape of a rounded rectangle with edges of the rectangle being arranged along the first and second cross-sectional directions. The definitions according to embodiments as discussed in this paragraph provide the benefit of increased electrode-skin contact surface and thus improved signal quality during measurements.

Figures 3A and 3B show an example of an apparatus 300 according to an alternative embodiment in a cross-sectional side view and in a view directly from above. According to an example embodiment, the apparatus 300 is configured to measure and/or monitor electrical biosignals on skin, preferably even through thick and/or dense hair. The apparatus 300 may be or comprise a three- dimensional electrode or an electrode arrangement.

The apparatus 300 illustrated in Figures 3A and 3B may correspond, for the most part, to the apparatus 100 discussed above in relation to Figures 1A, IB, 1C, 2A and 2C. Namely, the elements 300 to 307, 309 may correspond to elements 100 to 107, 109 of Figures 1A, IB, 1C, 2A and 2C, apart from the differing features to be specified below.

Similar to the above embodiments, the apparatus 300 comprises an elastic element 301 with a conductive surface for contacting skin and a conductive connector element 302. Moreover, the elastic element 301 comprises a top section 303 having a top surface 309 and a bottom surface, similar to the above embodiments. However, in contrast to the above embodiments, the top section 303 of the elastic element 301 comprises a cavity (ora depression] with the top surface 309 having an opening (its only opening] into said cavity. The conductive connector element 302 is contained (or embedded], at least in part, within said cavity.

Similar to as discussed for above embodiments, the conductive connector element 302 may comprise a base section 307 operatively connected to the top section 303 of the elastic element 301 and a connector 306 extending from the base section 307 and away from the elastic element 301. Here, specifically the base section 307 may be contained (or embedded], at least in part, within said cavity while the connector 306 is positioned outside the cavity so that it is still possible to connect a measurement cable to said connector 306. The cavity may be formed so as to tightly conform to the shape of the base section 307 (or vice versa).

The base section 307 may have various different shapes. In the illustrated example, the base section 307 has a shape of a cuboid with corrugations 311 arranged along two opposing longitudinal faces of the cuboid or along all four longitudinal faces of cuboid. The corrugations may extend along a direction orthogonal to the longitudinal direction (i.e., they may extend into and/or out of Figure 3A) so as to wholly cover the corresponding longitudinal face of the cuboid. Said corrugations 311 serve to fix the top section 303 of the elastic element 301 and the base section 307 of the conductive connector element 302 firmly together (i.e., to enable efficient mechanical interlocking between the two elements 303, 307). In other embodiments, the base section 307 maybe shaped like a prism (e.g., a cylinder) or a frustum. Also in these alternative embodiments, corrugations may be provided along longitudinal faces of the base section 307. In some embodiments, corrugations may also be provided in the top section 303 of the elastic element 301 within the cavity for further improving the interlocking between the two elements 303, 307.

Figure 4 shows an example of a conductive connector element 402 of an apparatus (i.e., an electrode arrangement) according to an alternative embodiment in a perspective view. The illustrated conductive connector element 402 corresponds for the most part to the conductive connector element 102 discussed above in relation to Figures 1A, IB, 1C, 2A and 2B. The conductive connector element 402 comprises a base section 407 (to be operatively connected to the top surface of the top section of the elastic element) and a connector 406 extending from the base section 407 (and away from the elastic element). However, two significant differences exist between the two conductive connector elements 102, 402.

Firstly, a bottom surface 420 of the base section 407 of the conductive connector element 402 is a structured surface (i.e., a surface with a surface pattern), as opposed to being a flat surface as in the previous embodiments. Specifically, in the illustrated example of Figure 4, the bottom surface 420 has a honeycomb structure. In general, any structured surface may be employed as the bottom surface 420. For example, the bottom surface 420 may comprise a two- dimensional periodic arrangement of two-dimensional elements such as circles, squares or triangles, a two-dimensional periodic arrangement of holes or bumps, a honeycomb structure, a woven or punched mesh, a periodic arrangement of ridges or any combination thereof. A corresponding structured surface may be provided for the top surface of the top section of the elastic element. Specifically, the top surface of the top section may exhibit an inverse surface structure (i.e., a surface structure with an inverse surface shape) compared to the bottom surface 420 of the base section 407 (e.g., bumps instead of holes).

The use of structured surfaces provides the benefit of increased contact surface between the conductive connector element 402 and the elastic element enabling more efficient transmission of signals through the interface between them. Moreover, the structured surfaces may be mechanically interlocked enabling increased adhesion between the conductive connector and elastic elements.

Secondly, a protrusion 421 extends (substantially) centrally and orthogonally from the bottom surface 420 of the base section 407 (along a central axis of the conductive connector element). A matching cavity (i.e., a cavity conforming to the shape of the protrusion 421) may be comprised in the elastic element. Said matching cavity may be located specifically on the top surface of the top section of the elastic element though it may penetrate all the way to the protrusion extending from said top element (making said protrusion partially hollow). The protrusion and the matching cavity act to facilitate the alignment of the conductive connector element 402 and the elastic element and to maintain said alignment. Moreover, with the protrusion 421 of the conductive connector element 402 and the matching cavity in the elastic element, the contact surface between said two elements is further increased which enables even more efficient transmission of signals through the interface between them.

In some embodiments, only one of the two features discussed in relation to elements 420, 421 may be implemented.

The electrode arrangement according to any of the embodiments described above may be specifically used for measuring biosignals through skin of a scalp or through other (densely) hairy section of skin of a human or an animal.

In some use cases, one or more electrode arrangements according to any of the embodiments discussed above may be integrated into a wearable item or a piece of equipment so that the one or more electrode arrangements are operational (i.e., touching the skin of the user) when a user is wearing said wearable item or piece equipment. As an example, Figure 5 illustrates a set of headphones 500 (or equally a pair of headphones) into which two electrode arrangements 501, 502 according to embodiments have been integrated. Specifically in Figure 5, a first electrode arrangement 501 has been integrated into a headband 503 of the set of earphones 500 and a second electrode arrangement 502 has been integrated into one of the earpieces 504 [or earpads) of the set of headphones 500. When the set of headphones 500 are worn, the first electrode arrangement 501 is positioned and oriented to face the scalp of the user while the second electrode arrangement 502 positioned and oriented to face a temporal area of the head of the user.

In general, a set of headphones 500 according to embodiments may comprise one or more electrode arrangements 501, 502 (or one or more apparatuses) according to any embodiment discussed above for contacting skin of a user while the user is wearing the set of headphones 500. Said one or more electrode arrangements 501, 502 maybe integrated into a headband 503 of the set of headphones 500 and/or into one or more of the earpieces 503 of the set of headphones 500.

The set of headphones 500 may or may not comprise a microphone, that is, they may or may not correspond to a headset.

In some embodiments, one or more electrode arrangements according to embodiments may be integrated into a headband (or specifically, an Alice band having a horseshoe-shape) or earmuffs. The placement and orientation of the one or more electrode arrangements may be similar to as discussed in relation to Figure 5 for the set of earphones (though, in the case of a headband, the placement according to element 502 may not be possible).

It will be obvious to a person skilled in the art that, as the technology advances, the inventive concept can be implemented in various ways. The embodiments are not limited to the examples described above but may vary within the scope of the claims.

Claims

1. An electrode arrangement comprising: an elastic element with a conductive surface for contacting skin, the elastic element comprising a top section having a top surface and a bottom surface, a protrusion extending substantially centrally and orthogonally from the bottom surface of the top section along a central axis of the elastic element and two or more legs extending from the bottom surface of the top section and away from the protrusion at a first angle to the central axis and arranged to surround the protrusion, wherein a length of the protrusion along the central axis is shorter than a length of each of said two or more legs along the central axis; and a conductive connector element, operatively connected to the elastic element, for relaying signals between the elastic element and a measurement device or a transmitter.

2. The electrode arrangement according to claim 1, wherein the two or more legs are of equal length and/or are arranged to surround the protrusion symmetrically.

3. The electrode arrangement according to claim 1 or 2, wherein the two or more legs comprise three or more legs.

4. The electrode arrangement according to any preceding claim, wherein the two or more legs comprise eight or more legs.

5. The electrode arrangement according to any preceding claim, wherein the conductive connector element is operatively connected to the top surface of the top section of the elastic element.

6. The electrode arrangement according to claim 5, wherein the conductive connector element comprises: a base section operatively connected to the top surface of the top section of the elastic element; and a connector extending from the base section and away from the elastic element for enabling connection using a connection mechanism to the measurement device or the transmitter.

7. The electrode arrangement according to claim 6, wherein the top surface of the top section of the elastic element and a bottom surface of the base section of the conductive connector element are structured surfaces having inverse surface structures compared to each other.

8. The electrode arrangement according to claim 6 or 7, wherein the base section comprises a protrusion extending substantially centrally and orthogonally from the bottom surface of the base section along the central axis of the conductive connector element and the elastic element comprises a cavity opening on the top surface and conforming to a shape of the protrusion of the conductive connector element.

9. The electrode arrangement according to any of claims 1 to 4, wherein the top section of the elastic element comprises a cavity opening on the top surface and the conductive connector element is embedded, at least in part, into said cavity.

10. The electrode arrangement according to claim 9, wherein the conductive connector element comprises a base section embedded into the cavity of the top section of the elastic element; and a connector extending from the base section and away from the elastic element for enabling connection using a connection mechanism to the measurement device or the transmitter.

11. The electrode arrangement according to any preceding claim, wherein each of the two or more legs has a first width along a first cross-sectional direction of a corresponding leg and a second width along a second cross-sectional direction of the corresponding leg orthogonal to the first cross-sectional direction, the second cross-sectional direction being orthogonal to the central axis of the elastic element and to a longitudinal direction of the corresponding leg and the second width being larger than the first width.

12. The electrode arrangement according to claim 11, wherein each of the two or more legs has an elliptical cross section along a plane defined by said first and second cross-sectional directions.

13. The electrode arrangement according to any preceding claim, wherein the first angle is selected from a range of 15° - 60°.

14. The electrode arrangement according to any preceding claim, wherein a ratio of the length of the protrusion along the central axis and the length of each of said two or more legs along the central axis has value in a range of 0.4- 0.7.

15. The electrode arrangement according to any preceding claim, wherein the elastic element is made of a conductive elastic material, of a non- conductive elastic material coated with a conductive material or a conductive elastic material coated with a conductive material.

16. The electrode arrangement according to any preceding claim, wherein the elastic element is made of a soft thermoplastic elastomer coated with a conductive ink.

17. The electrode arrangement according to claim 16, wherein the soft thermoplastic elastomer has a hardness in a range of 20-100 using Shore A hardness scale.

18. The electrode arrangement according to claim 16, wherein the soft thermoplastic elastomer has a hardness in a range of 60-90 using Shore A hardness scale.

19. The electrode arrangement according to any preceding claim, wherein the conductive connector element is made of a conductive material, a non- conductive material embedded with one or more conductive filler materials or a non-conductive material coated with a conductive material.

20. The electrode arrangement according to any preceding claim, wherein the conductive connector element is made of a hard thermoplastic embedded with one or more conductive filler materials.

21. The electrode arrangement according to any preceding claim, wherein the elastic element is made of a soft thermoplastic elastomer coated with a conductive ink and the conductive connector element is made of a hard thermoplastic embedded with one or more conductive filler materials and one of following material combinations for the soft thermoplastic elastomer and the hard thermoplastic is employed: the soft thermoplastic elastomer is thermoplastic polyurethane, TPU, and the hard thermoplastic is polycarbonate, PC, or PC/acrylonitrile-butadiene- styrene, ABS, or the soft thermoplastic elastomer is a styrenic block copolymer, TPS, and the hard thermoplastic is polypropylene, PP, or polyethylene, PE.

22. The electrode arrangement according to any preceding claim, wherein the connector forms a part of a snap joint.

23. The electrode arrangement according to any preceding claim, wherein the electrode arrangement has been manufactured using 2K injection molding.

24. A set of headphones comprising one or more electrode arrangements according to any preceding claim for contacting skin of a user of the set of headphones.

25. The set of headphones according to claim 24, wherein the one or more electrode arrangements are integrated into a headband of the set of headphones and/or into one or more earpieces of the set of headphones.

26. The use of the electrode arrangement according to any of claims 1 to 23 for measuring biosignals through skin of a scalp or through other densely hairy section of skin of a human or an animal.