FIELD OF THE INVENTION

The present invention relates to an electrode assembly, in particular dry electrode assembly, for contacting skin, in particular the scalp, of a user to receive and/or transmit an electrical signal, in particular for measuring electrical brain activity. The present invention further relates to a wearable device configured to be put at least partly around the head of a user, the wearable device comprising such electrode assembly. Also, the present invention relates to a method of manufacturing an electrode assembly for contacting skin of a user to receive and/or transmit an electrical signal. BACKGROUND OF THE INVENTION

It is known to use electrode assemblies for receiving an electrical signal indicative of the electrical brain activity, thus measuring electrical brain activity, also known as electroencephalogram (EEG). The main challenge in applying EEG electrodes is to get a low impedance contact to the scalp. One type of known electrodes is wet or gel electrodes. These wet or gel electrodes can only be used for recording from regions of the scalp without hair and most of the time after preparation of the scalp side. Also, wet or gel electrodes are often used for clinical measurements, but are not very practical for non-clinical or nonmedical application, such as sports or lifestyle consumer products.

Another type of electrodes is dry electrodes. US 4,967,038 discloses an active electrode EEG Smart Hat which is placed on the head of the patient to detect the patient's brain waves. Preferably the hat 10 includes a stretchable cloth hat body 11 having 1 to 256 rubber multicontact electrodes 12a-n. Each of the electrodes 12a consists of a pure gum rubber block, 1.0 to 2.5 cm square with four to sixteen metal tips 17 at the end of 0.5 to 1.0 cm pyramid- shaped rubber fingers 18. Wires 19 are threaded down the center of each finger and are soldered to the metal tip. The tip consists of a 2-mm tin-lead (60-70% tin, 30%-40% lead) ball. At the upper end of the electrode, the wires are soldered to a gold plated pin 30 which plugs into a connector on the flexible printed circuit board. The rubber base of each electrode is attached to the fabric hat with 1 to 4 plastic snaps 26. The flexibility of the rubber base allows the multiple fingers to adapt to the local contour of the head. The gold-plated metal pin 30 from each of the electrodes plugs into a contact spring receptacle 31 having a pair of gold-plated spring contacts 32. The receptacle is attached to a metal pad (with a plated-through hole) on the flexible non-conductive printed circuit board 34. Conductors 36, which are copper foil signal traces, conduct the signals from each electrode 12a-12n to a nearby preamplifier circuit 35 a.

However, the assembly of US 4,967,038 is quite complex and not easy to manufacture, thus also not cheap in manufacturing. Additionally, it is quite thick in direction perpendicular to the skin, which can be obtrusive for the user wearing the hat. Also, the electrical connection to the metal tips is vulnerable to breaking, in particular for prolonged wearing or usage .

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an electrode assembly, in particular a dry electrode assembly, and method of manufacturing which enables an easier and cheaper manufacturing of such electrode assembly and/or to provide a thinner electrode assembly, in direction perpendicular to the skin and/or to provide a more robust electrode assembly, in particular for prolonged wearing or usage. At the same time, the flexibility of the assembly should be preserved. It is a further object to provide a corresponding wearable device configured to be put at least partly around the head of the user, in particular for measuring electrical brain activity or an electroencephalogram (EEG).

In a first aspect of the present invention, an electrode assembly for contacting skin of a user to receive and/or transmit an electrical signal is presented. The electrode assembly comprises a flexible substrate comprising at least one through-hole, and at least one pin electrode arranged through the at least one through-hole of the flexible substrate such that a first portion of the at least one pin electrode contacts the flexible substrate and a second portion of the at least one pin electrode protrudes beyond the flexible substrate for contacting the skin.

In a further aspect of the present invention a wearable device to be put at least partly around the head of a user is presented. The wearable device comprises at least one such electrode assembly for contacting the scalp of the user, and at least one elastic element which is adapted to at least partly follow the curvature of the user's head, wherein the electrode assembly is arranged on the elastic element.

In a still further aspect of the present invention a method of manufacturing an electrode assembly for contacting skin of a user to receive and/or transmit an electrical signal is presented. The method comprises providing a flexible substrate, and arranging at least one pin electrode through at least one through-hole of the flexible substrate such that a first portion of the pin electrode contacts the flexible substrate and a second portion of the pin electrode protrudes beyond the flexible substrate for contacting the skin.

The basic idea of the invention is to arrange, for example push, at least one pin electrode, in particular a plurality of pin electrodes, through a flexible substrate. A first portion of the at least one pin electrode is then in direct contact with the flexible substrate and the second portion protrudes beyond the flexible substrate for contacting the skin of the user, in particular with an end (e.g. a rounded end) of the at least one pin electrode. A pin electrode can be an electrode having an elongated body. By arranging the least one pin electrode through at least one through-hole of the substrate, the second portion can contact the skin while the first portion can be used for providing outside electrical connection. This provides for a very easy and thus cheap manufacturing of the electrode assembly. Also, a very compact or thin, in direction perpendicular to the skin, electrode assembly can be provided. Furthermore, the electrode assembly according to the present invention provides increased robustness, and thus also an increased reliability, in particular for prolonged wearing or usage (e.g. a couple of hours, days, months or years). Regular wearing or usage of the electrode assembly does not reduce or destroy its functioning. For example, it was found that even after regular usage of the electrode assembly or wearable device (e.g. a couple of months, such as 1 to 2 months) there were no broken electrical connections in the electrode assembly, and thus the signal quality did not decrease.

The flexibility of the substrate ensures movability of the pin electrodes, which is necessary for user comfort and functionality. For example, the electrode assembly needs to at least partly follow the curvature of the user's head. Thus, the flexibility is necessary for conformity to the shape of the head. The flexibility of the substrate is such that the substrate provides support for the pin electrode(s) and at the same time ensures movability of the pin electrode(s) (for example, when pressure and/or strain is applied to the electrode assembly). This can for example be achieved by selecting a specific substrate material (for example of a specific rigidity) and/or a specific substrate thickness. In particular, the flexible substrate can be in form of a sheet or be a sheet. For example, the thickness of the substrate can be much smaller (e.g. by at least an order of magnitude) than the length and width of the substrate. By properly choosing the substrate dimensions, the flexibility can also be influenced.

The second portion protrudes beyond the flexible substrate, in order to be able to contact skin through, for example, hair, as it is mostly the case when putting an electrode on the scalp of the user. However, the skin electrode assembly can, for example, also be used with a textile substrate material (e.g. cloth or clothing) since the pin electrode could also be arranged through a textile material (e.g. cloth, clothing or the like). In particular, the length of the second portion is sufficient to reach through hair or cloth, depending on the application. Also the second portion needs to have a sufficient length to reach through hair. The length needs to be sufficiently long so that the pin electrode is flexible, when pressure and/or strain is applied to the electrode assembly. However, the length of the second portion should be not so long that the pin electrode bends when contacting the skin. For example, the length of the second portion can between 1 mm and 10 mm, in particular between 4 mm and 7 mm.

The electrode assembly can preferably be used for measuring electrical brain activity, thus receiving an electrical brain activity signal, also known as measuring an electroencephalogram (EEG). Alternatively or cumulatively, the electrode assembly can also be used for stimulating electrical brain activity of the user, thus transmitting an electrical signal, also known as brain stimulation or current stimulation, in particular direct current stimulation (DCS) or alternating current stimulation (ACS). However, the electrode assembly could also be used for other measurements or stimulations, such for example measuring an electrocardiogram (ECG), an electromyogram (EMG), an electrooccluogram (EOG) or skin conductance (GSR). In any case, an outside electrical connection from the electrode assembly needs to be provided for receiving and/or transmitting the electrical signal. In this context, an outside electrical connection is meant to be any electrical connection that can receive and/or transmit the electrical signal, for example, transmit to at least one signal processing unit, such as for example an amplifier and/or a processor, or receive from at least one signal generating unit.

Preferred embodiments of the invention are defined in the dependent claims. It shall be understood that the claimed method of manufacturing or the claimed wearable device has similar and/or identical preferred embodiments as the claimed electrode assembly and as defined in the dependent claims.

In one embodiment, the at least one pin electrode comprises an end for contacting the skin, in particular a rounded end. This prevents injury of the skin and thus prevents pain for the user. However, the end of the shape can also have any other suitable shape preventing injury of the skin.

In another embodiment, the at least one pin electrode can be made of a rigid or non- flexible material. In particular, the pin electrode can be rigid or non- flexible. This provides for good electrical connection as the pin electrode does not easily break. For example, the rigid or non-flexible material can be a metal. Alternatively, the pin electrode could also be made of a flexible material. In general, being an electrode, the pin electrode is made of any suitable conducting material (e.g. metal).

In another embodiment, the flexible substrate can comprise a substrate base layer. In a variant of this embodiment, the substrate base layer can be made of an insulating material (e.g. rubber material, textile material or the like) and/or an adhesive material. In case of an insulating material, besides providing flexibility, the substrate then also insulates the pin electrode(s). In case of an adhesive material, besides providing flexibility, the substrate then also adhesively secures the at least one pin electrode (or its first portion) to the substrate (in particular as the first portion contacts the substrate adhesively). In another variant of this embodiment, the substrate base layer is a single layer. Thus, it is easy to manufacture.

Alternatively, the substrate or substrate base layer can comprise multiple layers. In this case, the layers can be selected such as to provide a desired flexibility (e.g. additional layer(s) can be added to provide more stability to the flexible substrate) and/or to improve the electrical connection and robustness.

In another embodiment, the flexible substrate comprises a foam layer. In particular the substrate base layer of the previous embodiment can be a foam layer. This material provides sufficient flexibility and support of the pin electrode(s) at the same time. In a variant of this embodiment, the foam is made of an insulating material and/or an adhesive material. In particular, the foam can be compressible. Alternatively or cumulatively, the flexible substrate can comprise any other suitable material that provides flexibility. For example, in an embodiment, the flexible substrate comprises a textile material, non-woven material (e.g. a spacer fabric) and/or polymer material.

In a further embodiment, the at least one pin electrode has an elongated body and a head protruding beyond the body. Thus, the at least one electrode has basically a nail- shape (e.g. having a rounded end). The nail-shape is particularly advantageous for arranging, e.g. pushing, the pin electrode(s) through the flexible substrate as the head can prevent the pin electrode from slipping through the through-hole. In a variant of this embodiment, a portion of the head contacts the flexible substrate. Thus, the head can provide support on the flexible substrate.

In a further embodiment, the at least one pin electrode is a single element. This provides a particularly easy way of manufacturing since simply one single element needs to be arranged or put through the flexible substrate, in particular a single nail-shaped pin electrode as mentioned above. Alternatively, the at least one pin electrode could be manufactured from multiple parts.

In a further embodiment, the flexible substrate comprises a first conductive layer forming at least part of a surface of the substrate. Placing a conductive layer on a surface of the flexible substrate enables to provide a more robust electrode assembly as the conductive layer does not easily break (for example when pressure or strain is applied). In a variant of this embodiment, the first conductive layer is continuous and/or covers most part of the first surface or substantially the entire first surface.

In another variant of this embodiment, the flexible substrate has a second surface, being on a second side on which the second portion protrudes beyond the flexible substrate, and a first surface, being on a first side opposing the second side with respect to the flexible substrate, wherein the first conductive layer forms at least part of the first surface. Placing the conductive layer on the first surface of the flexible substrate, not facing the skin, enables to provide an even more robust electrode assembly as the conductive layer on the first side does not easily break (for example when pressure or strain is applied). Also, outside electrical connection to the conductive layer can be easily made on the first side, not facing the skin. In a variant of this variant, another conductive layer forms at least part of the second surface of the substrate.

In another variant of this embodiment, the at least one pin electrode contacts the first conductive layer. This provides for a good outside electrical connection, in particular to receive and/or transmit an electrical signal, for example connecting to a cable. This variant can in particular be combined with the nail-shaped pin electrode where a portion of the head contacts the first conductive layer. This provides for a good outside electrical connection and at the same time hinders the pin electrode from slipping through the through-hole.

In a further variant of this embodiment, a plurality of wires spread over the first conductive layer for outside electrical connection to receive and/or transmit the electrical signal. This provides for a robust outside electrical connection, in particular when strain is applied to the electrode assembly and at the same time provides an improved electrical signal. Furthermore, an outside electrical connection can be provided while providing a still very thin electrode assembly.

In a still further variant of this embodiment, a second conductive layer is arranged on at least part of the first conductive layer. In combination with the previous embodiment, the second conductive layer is arranged on at least part of the first conductive layer and/or the wires. This second conductive layer can provide a better fixation of the outside electrical connection, in particular when used in combination with the wires of the embodiment described above.

In a further embodiment, an electrical connection portion protrudes beyond the flexible substrate and adapted to electrically connect the at least one pin electrode to a cable for outside electrical connection to receive and/or transmit the electrical signal.

In a variant of this embodiment, a shielding comprising an insulating layer and a third conductive layer is arranged on the insulating layer. The insulating layer, in particular a dielectric layer, and the third conductive layer form a shielding in order to protect the electrode assembly from disturbing electrical signals in the environment of the electrode assembly. Thus, vulnerability to environmental noise is reduced. This also improves the signal quality. In particular, the third conductive layer can be electrically connected to ground.

In a variant of this variant, the shielding covers an area corresponding at least to the flexible substrate and the electrical connection portion. This provides for a good shielding of the unshielded pin electrode(s) and electrical connection portion, while at the same time providing a very thin electrode assembly.

In a further embodiment, a plurality of pin electrodes is arranged in an array, each pin electrode arranges through a respective through-hole of a plurality of through-holes. A plurality of pin electrodes can provide a better electrical signal compared to a single pin electrode.

In an embodiment of the wearable device, the wearable device further comprises at least at least one signal processing unit, such as for example an amplifier and/or a processor, to which the electrical signal is transmitted, and/or at least one signal generating unit, from which the electrical signal is received. This enables the processing or generation of the electrical signal in the wearable device itself.

In another embodiment of the wearable device, the wearable device further comprises a wireless transmission link for wirelessly transmitting the electrical signal. This provides for a wearable device that can wirelessly communicate with a central station.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter. In the following drawings

Fig. 1 shows a schematic cross section of an electrode assembly according to an embodiment, Fig. 2 shows a cross section of an electrode assembly according to another embodiment,

Fig. 3 shows a perspective view of an electrode assembly according to an embodiment,

Figs. 4a-c show different manufacturing steps of a method of manufacturing an electrode assembly according to an embodiment,

Fig. 5 shows a top view of an electrode assembly with wires according to an embodiment,

Fig. 6 shows a wearable device according to an embodiment,

Fig. 7 shows an enlarged portion of the wearable device of Fig. 6,

Fig. 8 shows a top view of a portion of the wearable device of Fig. 1.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 shows a schematic cross section of an electrode assembly 2 according to an embodiment. The electrode assembly 2 can contact skin 8 of a user to receive and/or transmit an electrical signal. The electrode assembly 2 comprises a flexible substrate 10 of a thickness d. The substrate material and the substrate thickness d can be selected such that the flexible substrate 10 provides support for the pin electrodes 20 but at the same time remains movability of the pin electrodes 20. In Fig. 1, the substrate comprises a (single) substrate base layer 18. The flexible substrate 10 can comprise any suitable flexible material, in particular a foam layer. For example, the substrate base layer or foam layer can be textile, non-woven or a polymer layer.

The flexible substrate 10 comprises at least one through-hole 12, in particular a plurality of through-holes. For illustration purposes, three through-holes are shown in Fig. 1. The electrode assembly 2 further comprises at least one pin electrode 20, in particular a plurality of pin electrodes. For illustration purposes, three pin electrodes are shown in Fig. 1. The pin electrodes 20 are arranged in an array 9. The number of pin electrodes 20 can be any suitable number, for example between 10 and 30 pin electrodes, for example 19 pin electrodes. The pin electrode(s) 20 can be made of any suitable conducting material, such as a metal material. Each pin electrode 20 is arranged through a respective through-hole 12 of the flexible substrate 10 such that a first portion 22a of the pin electrode 20 contacts the flexible substrate 10 and a second portion 22b of the pin electrode 20 protrudes beyond the flexible substrate 10 for contacting the skin. In particular, the pin electrode 20 comprises an end 21 for contacting the skin 8, such as the rounded end 21 shown in Fig. 1. The first portion 22a has a length Li which equals the thickness d of the substrate 10. The second portion 22b has a length L ₂ which can depend on the specific application. For example, when the electrode assembly needs to contact the scalp 8a of the user through hair, the length L ₂ of the second portion 22b needs to be sufficiently long to reach through hair. Also, the length L ₂ needs to be sufficiently long, so that the pin electrode 20 is flexible, when pressure and/or strain is applied to the electrode assembly 2. However, the length L ₂ should not be so long, that the pin electrode 20 bends when contacting the skin 8. For example, the length L ₂ of the second portion 22b can be between 1 mm and 10 mm, in particular between 4 mm and 7 mm.

The flexible substrate 10 has a second surface 10b which is on a second side B where the second portion 22b protrudes beyond the flexible substrate 10. This second side B is the side facing the skin 8. The flexible substrate 10 further has a first surface 10a which is on a first side A opposing the second side B with respect to the flexible substrate 10. The thickness d of the flexible substrate is defined between the first surface 10a and the second surface 10b. On the first surface 10a or first side A an electrical connection portion 27 is arranged which protrudes beyond the flexible substrate 10 and is adapted to electrically connect the pin electrodes 20 to each other and/or to a cable 25, in particular a (shielded) coax-cable or the like, (not shown in Fig. 1) for outside electrical connection to receive and/or transmit the electrical signal. The electrical signal is then transmitted to at least one signal processing unit, e.g. an amplifier and/or a processor, and/or is received from at least one signal generating unit.

In Fig. 1 each pin electrode 20 has a nail-shape having an elongated body 22 and a head 24 (e.g. flat head) protruding beyond the elongated body 22. The elongated body 22 comprises the first portion 22a and the second portion 22b. The elongated has a length L (L = Li+L ₂ ). The A portion of the head 24(e.g. the lower portion in Fig. 1) contacts the flexible substrate 10, in particular the first surface 10a of the substrate 10. The head 24 is arranged on the first side A and the rounded end 21 of the pin electrode 20 is arranged on the second side B facing the skin 8. In the embodiment of Fig. 1 each pin electrode 20 is a single element. This is a particularly advantageous since simply one single element needs to be arranged or put through the substrate 10. However, alternatively, the pin electrode 20 may also comprise at least two separate elements.

The through-holes 12 may have any suitable size conforming to the size of the pin electrode 20, in particular conforming to the diameter of the body 22 of the pin electrode 20. More specifically, the diameter of the through- hole may be bigger than the diameter of the body 22 of the pin electrode 20, but smaller than the diameter of the head 24 of the pin electrode 20. For example, the diameter of the through-hole 12 can be in a range of 0.1 mm to 5 mm, in particular 0.2 to 1mm, for example 0.6 mm.

Fig. 2 shows a cross section of an electrode assembly 2 according to another embodiment. The basic structure of the electrode assembly 2 is the same as just explained with reference to Fig. 1. Additionally, the flexible substrate 20 comprises a first conductive layer 26 forming at least part of a surface of the substrate 10. In the embodiment of Fig. 1, the first conductive layer 26 forms at least part of the first surface 10a of the flexible substrate 10. The first conductive layer 26 is adapted to electrically connect the pin electrodes 20 to each other. The first conductive layer 26 can be any type of suitable conductive layer providing sufficient conductivity, such as for example a polymeric or metallic layer. If the substrate base layer 18 is an adhesive foam layer, the first conductive layer 26 can for example be a conventional conductive tape applied to the substrate base layer 18 on the first side 10a. In particular, the first conductive layer 26 can be a continuous layer, for example covering most or all part of the first surface 10a.

Also, a conductive layer could be applied to both the first side and the second side. For example, the conductive layer 26 forms at least part of the first surface 10a and another conductive layer (not shown in Fig. 2) can form at least part of the second surface 10b of the substrate 10. When the substrate 10 (or substrate base layer 18) comprises multiple layers, the layers can be selected such as to provide a desired flexibility. Thus, additional layer or layers can be added to provide more stability to the flexible substrate. Also, it or they can be added to improve the electrical connection and robustness (e.g. in case the first conductive layer 26 does not contact the pin electrode 20 properly). Alternatively to the embodiment shown in Fig. 2, the first conductive layer could form at least part of the second surface 10b of the flexible substrate 10 (facing the skin).

In Fig. 2, after the pin electrodes 20 are arranged through the through-holes 12 of the flexible substrate 10, a plurality of (thin) wires 28 are spread over the first conductive layer 26 for outside electrical connection. For outside electrical connection, to receive and/or transmit the electrical signal, the electrode assembly 2 further comprises an electrical connection portion 27 protruding beyond the flexible substrate 10. The electrical connection portion 27 is adapted to electrically connect the at least pin electrode 20 to a cable 25, in particular a (shielded) coax cable or the like. The electrical signal is then transmitted to at least one signal processing unit, e.g. an amplifier and/or a processor, and/or is received from at least one signal generating unit. As can be seen in Fig. 2, the wires 28 are spread over the first conductive layer 26 contacting the first conductive layer 26, and also contacting the heads 24 of the pin electrodes 20. Thus, electrical connection is provided between the pin electrodes 20 over the electrical connection portion 27 to the cable 25.

To improve the electrical connection, the electrode assembly 2 further comprises a second conductive layer 36 arranged on at least part of the first conductive layer 26 and/or the wires 28. More specifically, as shown in Fig. 2, the second conductive layer 36 is arranged on the heads 24 of the pin electrodes. The second conductive layer 36 can be of the same material as the first conductive layer 26 as explained above, or can be of different material.

In the embodiment of Fig. 2, an adhesive layer 37 is arranged on the second conductive layer 36 in order to attach a shielding. The shielding comprises an insulating layer 45 and a third conductive layer 46 arranged on the insulating layer 45. The insulating layer

45 can for example be a dielectric layer. The third conductive layer 46 can be of the same material as the first and/or second conductive layers as explained above, or can be of different material. For example, the second conductive layer 26 can be heated to a temperature near or above a melting point of its material, and then cooled down. This improves the electrical connection and robustness. However, any other suitable technique can also be used.

The shielding comprising the insulating layer 45 and the third conductive layer

46 covers an area corresponding to the flexible substrate 10 and the electrical connection portion 27. This means, that the shielding covers the unshielded flexible substrate 10, pin electrodes 20 and the unshielded electrical connection portion 27. The shielding may, for example, protrude beyond the flexible substrate 10 at least as far as also the unshielded electrical connection portion 27 protrudes beyond the flexible substrate 10. For example, the shielding can protrude between 1 cm and 10 cm, for example 5 cm, on one or both sides of the flexible substrate 10. Also, for example, the shielding can protrude on both (or all) sides of the substrate 10 (e.g. in order to shield against wires in an elastic band). The third conductive layer 46 is electrically connected to ground, in particular using an electrical connector 48 attached to the third conductive layer 46, for example by soldering, and leading to the cable 25 for ground connection, as can be seen in Fig. 2.

In general, sufficient adhesion of each of the described layers can be achieved by using any suitable adhesion technique. For example, the layer(s) can be adhered using a glue, such as a conductive glue for conductive layer(s), e.g. in liquid form, or with a solid backing. Fig. 3 shows a perspective view of an electrode assembly 2 for contacting skin 8 or scalp 8a according to an embodiment of a user, in particular an electrode assembly as shown in Fig. 2. The electrode assembly 2 comprises a flexible substrate 10 and an array 9 of pin electrodes 20. The top layer shown in Fig. 3 may for example be the second conductive layer 36, the adhesive layer 37, the insulating layer 45, or the third conductive layer 46. A cable 25 is provided for outside electrical connection. As can be seen in Fig. 3, the flexible substrate 10 is in form of a sheet. Here, the thickness d of the substrate 10 is much smaller (e.g. by at least an order of magnitude) than the length and width of the substrate.

Figs. 4a to 4e show different steps of a method of manufacturing an electrode assembly 2 as previously explained, in particular an electrode assembly as shown in Fig. 2. In a first step, shown in Fig. 4a, a flexible substrate 10 is provided having a first conductive layer 26 on its first surface 10a. The first conductive layer 26 can, for example, be applied to a substrate base layer 18 in a previous step. Alternatively, a conductive layer can be applied to both the first side and the second side (on the first surface 10a and the second surface 10b of the substrate 10). In particular, the first conductive layer 26 can be a continuous layer covering most or all part of the first surface 10a.

Next, as shown in Fig. 4b, at least one through-hole 12 is provided in the flexible substrate 10. For example, the through-hole 12 can be drilled through the substrate 10 (both the base layer 18 and the first conductive layer 26) by any conventional technique. For example, a template may be used for drilling, such as a polytetrafluoroethylene (PTFE) block as a template. Alternatively, the through-hole 12 can for example only be first provided in the first conductive layer, and this perforated first conductive layer 12 can then be applied to the substrate base layer 18.

In another step, shown in Fig. 4c, a pin electrode 20 is arranged through a through-hole 12 such that the first portion 22a of the pin electrode 20 contacts the flexible substrate 10 and the second portion 22b of the pin electrode 20 protrudes beyond the flexible substrate 10 for contacting the skin. For simplification, only one pin electrode 20 and one respective through-hole 12 are depicted in Figs. 4a to 4e. It will be understood that a plurality of pin electrodes 20 and respective through-holes 12 may be provided. Instead of providing a through-hole 12 prior to arranging the pin electrode 20 through the through-hole 12, the through-hole 12 may also be provided while arranging the pin electrode 20 through the flexible substrate 10. For example, the substrate 10 can have a rigidity that allows a pin electrode to be pushed through the substrate 10 by applying an appropriate amount of force. As can be seen in Fig. 4c, the pin electrode 20 contacts the flexible substrate 10, more specifically the first conductive layer 26. In particular, a portion of the head 24 (e.g. the lower portion of the head 24) contacts the flexible substrate 10, or more specifically the first conductive layer 26.

To provide an improved outside electrical connection and/or electrical signal, in a next step shown in Fig. 4d, a plurality of wires 28 are spread over the first conductive layer 26 for outside electrical connection. The arrangement of the wires 28 is shown in an exemplary manner in Fig. 5 showing a top view of an electrode assembly with wires 28 according to an embodiment, in particular the embodiment shown in Fig. 2. The wires 28 contact the first electrical layer 26 and the head 24 of the pin electrode 20. Further, an electrical connection portion 27 protruding beyond the flexible substrate 10 is attached to the substrate, more specifically the first conductive layer 26, by any suitable technique, such as, for example, soldering. The electrical connection portion 27 electrically connects the pin electrode(s) 20 and the wires 28 to a cable 25 for outside electrical connection.

For a better fixation of the electrical connection, a second conductive layer 36 is arranged on the first conductive layer 26 and the wires 28, as shown in Fig. 3e. For example, the second conductive layer 26 can be heated to a temperature near or above a melting point of its material, and then cooled down. This improves the electrical connection and robustness. However, any other suitable technique can also be used.

The second conductive layer 36 can provide an even surface in order to apply further layers. For example a shielding, as previously explained, can be applied, or the electrode assembly 2 can also be directly attached to an elastic element, as will be explained later. Thus, in a further step an adhesive layer 37 may be applied to the second conductive layer 36. Then, an insulating layer 45 may be applied to the adhesive layer 37 and

subsequently a third conductive layer 46 may be applied to the insulating layer 45.

Preferably, the shielding comprising the insulating layer 45 and the third conductive layer 46 is prepared before its application to the adhesive layer 37. In this case, first the insulating layer 45 and the third conductive layer 46 are attached to each other, and then this shielding is simply attached to the adhesive layer 37. In an additional step, a connector 48 may be attached to the third conductive layer 46 for ground connection by any suitable technique, for example by soldering.

An example of an exemplary manufacturing method is given in the following. First, a substrate base layer in form of an adhesive foam layer is provided. Then, a first conductive layer in form of a conductive black tape is applied to both sides/surfaces of the 2- sided adhesive foam layer. Subsequently, through-holes (e.g. 0.6mm) are drilled in the tape using a PTFE block as template. Then, the perforated tape is placed onto the PTFE block. Afterwards, each of the pin electrodes (e.g. 19 pin electrodes) is arranged or put through a respective through-hole. Then, (thin) wires having a sufficient length are provided (e.g. by stripping) over the length of the first surface of the substrate. The wires are spread (evenly) across the pin electrodes. Afterwards, the wires are fixated by applying a second conductive layer in form of a black conductive tape on top. To improve fixation, the black tape is heated using a heating block provided. Subsequently, an (insulating) adhesive layer is applied in form of an (insulating) adhesive tape over the entire back surface of the electrode. Then, insulating (dielectric) layer in form of an insulating (dielectric) foil is applied onto the adhesive tape. A portion of the insulating (dielectric) foil protrudes beyond the substrate (sticks out) over a sufficient length (e.g. at least 5 mm), in particular in all directions beyond the substrate (outside the backing). Subsequently, a third conductive layer in form of an adhesive copper foil is applied onto the insulating (dielectric) foil. Finally, a ground connector (e.g. wire of the coax cable) can be soldered to the copper foil.

Fig. 6 shows a front view of a wearable device 1 according to an embodiment. Fig. 7 shows a front view of a portion of the wearable device of Fig. 6, and Fig. 8 shows a top view of a portion of the wearable device of Fig. 6.

In Fig. 6 the wearable device 1, configured to be put at least partly around the head of a user, comprises at least one electrode assembly 2 as previously explained, for example with reference to Fig. 1 or 2. In particular, the wearable device 1 comprises a plurality of electrode assemblies, for example four electrode assemblies 2 as shown in Fig. 6. Further, the wearable device 1 comprises at least one elastic element 11 which is adapted to at least partly follow the curvature of the user's head. The electrode assembly 2 is arranged on the elastic element 11. In particular, the wearable device comprises a plurality of elastic elements 11, for example two elastic elements 11 as shown in Fig. 6. In an example, the wearable device 1 enables positioning of the electrode assembly 2 on a user's scalp 8a. The wearable device 1 or electrode assembly 2 can preferably be used for measuring electrical brain activity, thus receiving an electrical brain activity signal, also known as measuring an electroencephalogram (EEG). In another example, the wearable device 1 or electrode assembly 2 can also be used for stimulating electric brain activity of the user, thus transmitting an electrical signal, also known as brain stimulation or current stimulation, in particular direct current stimulation (DCS) or alternating current stimulation (ACS).

However, the wearable device or electrode assembly could also be used for other measurements or stimulations, such as for example measuring an electrocardiogram (ECG), an electromyogram (EMG), an electrooculogram (EOG), or skin conductance (GSR).

The wearable device 1 of Fig. 6 is a headphones comprising a headpiece 3 (also referred to in this description by "unit" or "housing"), made of firm but flexible material and having the shape of a headband, and earpieces 5. The device furthermore comprises a positioning arrangement consisting of two projection elements 7 and a positioning strap 13. The projection elements 7 are used for positioning the plurality of electrode assemblies 2 (each comprising an electrode array 9 and a substrate 10), elastic elements (bands) 11 and the positioning strap 13 at the inner side of the housing 3. The two projection elements 7 project the ends of the positioning strap 13 against the auricles 14 of the user, when the housing is put around the user's head. At the inner side of the positioning strap small springs 16 are placed. The ends of the elastic bands 11 are also fixed to the projection elements 7 close to the points at which the ends of the positioning strap 13 are fixed to the projection elements 7. The positioning strap 13 is used for positioning the electrode assemblies 2 at predefined positions on the scalp 8a. It is fixed to the plurality of the electrode assembly 2 or flexible substrate 10 by means of fixations 15, as shown in Figs. 7 and 8. It comprises openings 17 with a diameter of approximately 15 mm through which the pin electrode arrays 9 protrude when the elastic bands 11 exert pressure on the electrodes. To cope with the variety in head sizes and shapes the positioning strap 13 is divided in two halves with a connecting elastic band 19 between them to guarantee good mechanical contact to the scalp 8a all over the circumference. The reference electrode position of two electrode arrays 9 (or electrode assemblies 2) is set by the spring loaded fixation point of the two halves of the positioning strap as close as possible to the T3/T4 locations of the International 10/20 System. The two halves of the positioning strap have the ears as mechanical reference via the main headphone- clamp The sense electrode arrays positioned at C3 and C4 according to the International

10/20 System (according to which C3-C4 refer to central sites for picking up the activity in the posterior regions of head) are fixed at the other ends of both of the positioning strap parts. In this way all electrode arrays 9 (or electrode assemblies 2) are positioned in their right places in one simple action by just putting on the headphones in the usual way by the user. In this regard it is to be noted that the wearable device 1 may be something else than

headphones, for example a (Alice) band, cap, helmet, glasses, etc.

Due to the stress or strain on the elastic bands 11 caused by the stretching thereof, which at its turn is caused by the insertion of the user's head in the housing (which pushes the positioning strap 13 and the elastic bands 11 upwards), the elastic bands 11 press the arrays of electrodes on the user's scalp, resulting in an effective contact of the electrodes to the scalp.

An eventually additional (active) body ground electrode, normally a wrist (- strap) electrode, could be added in the middle on top of the head (EEG Cz location). The body ground electrode is typically used in amplifiers for biosignal measuring to improve the signal quality. Cabling and electronics (e.g. signal processing unit or signal generating unit) which may be integrated in the headphones or in an external device are not depicted in Figs. 6 to 8. Test results from testing of the described wearable device 1 and electrode assembly 2 showed that the dry electrode assemblies can measure for example difference in Eyes Open vs. Eyes Closed alpha activity, or Difference in Relaxed vs. Mental Activity (Alpha

Desychronization) .

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims.

In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

Any reference signs in the claims should not be construed as limiting the scope.