Bioelectrodes

Abstract

Provided is a bioelectrode which is capable of achieving good contact with the scalp of a subject. This bioelectrode is provided with an electrode member 20 which is brought into contact with the body of a subject. The electrode member 20 has a plate-shaped electrode part body 21 and a plurality of electrode protrusions 22 provided to protrude from an electrode protrusion forming surface 21b of the electrode part body 21. The plurality of electrode protrusions 22 is disposed in an outer circumferential section 29 of the electrode protrusion forming surface 21b of the electrode part body 21 to avoid a central section 28 of the electrode protrusion forming surface 21b. The protrusion height h of each electrode protrusion 22 from the base to the tip thereof in a direction perpendicular to the electrode protrusion forming surface 21b is 6-15 mm.

Description

[Technical field]

[0001] The present invention relates to a bioelectrode, and more particularly to a bioelectrode capable of achieving good contact with the scalp of a subject. [Background technology]

[0002] In order to diagnose the health condition of a subject in a medical facility, etc., bioelectrodes are placed on the subject's body to detect various electrical signals. For example, electroencephalograms are measured by placing electrodes on the subject's scalp.

[0003] Conventionally, as an electrode for measuring electroencephalograms, a bioelectrode having an electrode part made of conductive silicone rubber or the like has been proposed (see, for example, Patent Document 1). An example of the electrode part of such a bioelectrode is one in which a plurality of projections with sharp tips are provided on the surface side that comes into contact with the subject, and such a plurality of projections form a brush shape. In addition, the bioelectrode for measuring electroencephalograms further includes, for example, a base for mounting the electrode part, and the base is provided with a terminal for assembly with a mating part, insulating rubber for supporting the terminal, and the like.

[0004] Conventionally, in bioelectrodes for measuring electroencephalograms, the number of protrusions at the tip of the electrode is set to be large in order to increase the contact area with the subject's scalp. Hereinafter, the number of protrusions provided on the electrode may be referred to as the "protrusion number" of the electrode. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2017-74369 A Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the number of protrusions on the electrode part of the bioelectrode for measuring electroencephalograms is increased, the protrusions are arranged densely on one electrode part, so when measuring the electroencephalogram of a subject with a lot of hair, the space for storing the hair between the scalp and the electrode part is reduced. Therefore, such a bioelectrode has a problem that the electrode part is easily lifted from the scalp, and conversely, it is difficult to contact the scalp.

[0007] In addition, when detecting the brainwaves of a subject with a lot of hair, it is necessary to apply a strong pressing force to the bioelectrodes in order to prevent the bioelectrodes from floating up due to the hair and to firmly contact each electrode part with the subject's scalp. However, if the bioelectrodes are used for a long period of time while applying a strong pressing force to them as described above, a problem may occur in which the subject's scalp is painful.

[0008] In view of the above problems, the present invention provides a bioelectrode capable of achieving good contact with the scalp of a subject. In particular, the present invention provides a bioelectrode suitable for electroencephalogram measurement, capable of achieving good contact with the scalp of a subject even if the subject has a lot of hair. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides the following bioelectrode.

[0010] [1] A device comprising: an electrode member that contacts the body of a subject; The electrode member has a plate-shaped electrode body and a plurality of electrode protrusions provided so as to protrude from an electrode protrusion forming surface of the electrode body, the plurality of electrode protrusions are arranged on an outer periphery of the electrode protrusion forming surface so as to avoid a central portion of the electrode protrusion forming surface of the electrode body; a projection height from a base end to a tip end of each of the electrode projections in a direction perpendicular to the electrode projection forming surface is 6 to 15 mm; the plurality of electrode projections are arranged so as to be located on the circumference of one imaginary circle or a plurality of imaginary concentric circles on the outer periphery of the electrode projection forming surface, The electrode protrusions are disposed at equal intervals on the outer periphery of the electrode protrusion forming surface, Each of the electrode projections has an oblique cone shape with a rounded apex. At the same time, the cross-sectional area is gradually reduced from the base end to the tip end. A bioelectrode in which each of the multiple electrode protrusions is arranged to be located on the circumference and, when viewed from the center of the arrangement of the multiple electrode protrusions, the center of the tip end is located radially outward from the center of the cross section of the base end.

[0014] [2] The above-mentioned [1 ] The bioelectrode described. Effect of the Invention

[0015] The bioelectrode of the present invention has the effect of realizing good contact with the subject's scalp. In addition, the bioelectrode of the present invention has the effect of eliminating the need for excessive pressing of the electrode, and reducing the pain of the scalp during measurement. In particular, even for subjects with a lot of hair, subjects with long hair, subjects with a large volume of hair (in other words, thick hair), etc., stable contact with the scalp can be achieved. [Brief description of the drawings]

[0016] [Figure 1] 1 is a front view showing a schematic diagram of a bioelectrode according to an embodiment of the present invention; [Diagram 2] FIG. 2 is a bottom view of the bioelectrode shown in FIG. [Diagram 3] 3 is a cross-sectional view taken along the line AA in FIG. 2. [Figure 4] FIG. 1 is an explanatory diagram showing an example in which a bioelectrode is used for measuring electroencephalograms. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. It should be understood that the present invention is not limited to the following embodiment, and that appropriate design changes, improvements, etc. may be made based on the ordinary knowledge of a person skilled in the art without departing from the spirit of the present invention.

[0018] Fig. 1 is a front view showing a schematic diagram of a bioelectrode according to an embodiment of the present invention. Fig. 2 is a bottom view of the bioelectrode shown in Fig. 1. Fig. 3 is a cross-sectional view taken along line AA in Fig. 2. Fig. 4 is an explanatory diagram showing an example in which the bioelectrode is used for measuring electroencephalograms.

[0019] As shown in Figs. 1 to 3, the bioelectrode 1 includes an electrode member 20 having a plate-shaped electrode body 21 and a plurality of electrode protrusions 22 provided so as to protrude from the electrode protrusion forming surface 21b of the electrode body 21. The electrode member 20 makes it possible to detect (take out) a biosignal of the subject through a connector, for example, by contacting the tip side portions of the plurality of electrode protrusions 22 with the body (skin) of the subject. The bioelectrode 1 is used, for example, as a bioelectrode for measuring brain waves. In this case, the bioelectrode 1 is attached to the head of the subject so that the tip side portions of the plurality of electrode protrusions 22 of the electrode member 20 contact the scalp of the subject. For example, as shown in Fig. 4, by arranging a plurality of bioelectrodes 1 at desired locations on the head of the subject 60, various electrical signals such as brain waves of the subject 60 can be detected.

[0020] The bioelectrode 1 can be suitably used to sense an electrical signal from the subject's body, transmit an electrical stimulus to the subject, or perform both the sensing and transmission, by bringing the electrode protrusions 22 of the electrode member 20 into contact with the body of the subject. Specifically, the bioelectrode 1 can be used as the bioelectrode 1 for, for example, a medical measuring instrument, a wearable measuring instrument, a health monitoring instrument, etc. In particular, the bioelectrode 1 can be suitably used when measuring an electroencephalogram as an electrical signal.

[0021] The bioelectrode 1 of this embodiment further includes a support member 10 for supporting the electrode member 20. The support member 10 is made of an electrically insulating material. For example, the support member 10 can be made of silicone rubber or the like. In the bioelectrode 1 of this embodiment, the support member 10 is formed in a disk shape. The support member 10 has a support surface 10a that supports the electrode member 20, and a back surface 10b opposite to the support surface 10a. In addition, a through hole 10c is formed in the center of the support member 10, penetrating the support member 10 in the thickness direction (i.e., penetrating from the support surface 10a to the back surface 10b) (see, for example, FIG. 3).

[0022] The support member 10 need only have a configuration corresponding to the support surface 10a, the back surface 10b, and the through-holes 10c, and is not necessarily required to be formed in a disk shape.

[0023] In the bioelectrode 1, the electrode member 20 is made of, for example, conductive rubber, and has an electrode body 21 supported by the support member 10 and a plurality of electrode protrusions 22 protruding from the electrode body 21 to the opposite side of the support member 10 as described above. An example of the conductive rubber is so-called conductive silicone rubber containing silicone rubber and metal particles. An example of the silicone rubber is liquid silicone rubber that cures at room temperature. An example of the metal particles is silver particles. The liquid silicone rubber that cures at room temperature is a silicone rubber that is liquid or paste-like before curing and undergoes a curing reaction at 20°C to 100°C to become a rubber elastic body. The silver particles may include aggregated particles (aggregates) in which a plurality of silver particles (primary particles) are aggregated together, or flake-shaped silver particles.

[0024] The conductive rubber forming the electrode member 20 may contain, instead of silver particles, other conductive metal particles or carbon-based material particles (carbon black, carbon nanotubes, etc.), and may also contain reinforcing materials, fillers, and various additives as appropriate.

[0025] The electrode body 21 of the electrode member 20 preferably has the same shape as the support member 10. That is, in the bioelectrode 1 of this embodiment, the electrode body 21 is formed in a disk shape. The electrode body 21 has a supported surface 21a supported by the supporting surface 10a of the support member 10, and an electrode protrusion forming surface 21b opposite to the supported surface 21a.

[0026] The multiple electrode protrusions 22 are formed to protrude from the electrode protrusion-forming surface 21b of the electrode body 21. The multiple electrode protrusions 22 are arranged on the outer periphery 29 of the electrode protrusion-forming surface 21b so as to avoid the central portion 28 of the electrode protrusion-forming surface 21b of the electrode body 21.

[0027] The bioelectrode 1 of this embodiment has a particularly important configuration with respect to the projection height h of each electrode projection 22 arranged on the outer circumferential portion 29 of the electrode projection forming surface 21b as described above. That is, in the bioelectrode 1 of this embodiment, the projection height h from the base end to the tip end of each electrode projection 22 in the direction perpendicular to the electrode projection forming surface 21b is 6 to 15 mm. Hereinafter, the projection height h from the base end to the tip end of each electrode projection 22 in the direction perpendicular to the electrode projection forming surface 21b may be simply referred to as the "projection height h of the electrode projection 22."

[0028] In the bioelectrode 1, the electrode protrusions 22 with a protrusion height h of 6 to 15 mm are arranged only on the outer periphery 29 of the electrode protrusion forming surface 21b, and the central portion 28 of the electrode protrusion forming surface 21b surrounded by such electrode protrusions 22 becomes a space for storing the subject's hair. The space in the central portion 28 has a spatial height equivalent to the protrusion height h of the electrode protrusions 22, and the subject's hair can be well stored in the space. Therefore, the bioelectrode 1 can achieve good contact with the subject's scalp, and it is not necessary to press the bioelectrode 1 excessively against the subject, and pain on the scalp during measurement can be reduced. In particular, stable contact with the scalp can be achieved even for subjects with a lot of hair, subjects with long hair (for example, women who are growing their hair), subjects with a large volume of hair (in other words, thick hair), etc.

[0029] If the projection height h of the electrode projection 22 is less than 6 mm, the spatial height of the center 28 of the electrode projection forming surface 21b is too low, and the subject's hair may not be able to be sufficiently accommodated in the space of the center 28. For example, the average hair thickness is generally 0.085 mm, and the number of hairs growing per unit area of ​​the subject's scalp is 208 / cm. 2 In the following, the number of hairs per unit area is called "hair density (hairs / cm 2 )"

[0030] Here, when multiple bioelectrodes 1 are arranged on the head of subject 60 as shown in FIG. 4 to detect electrical signals such as brain waves, the back of the head of subject 60, indicated by measurement point Oz, is affected by hair from above, etc., and is therefore a location where the bioelectrode 1 is more likely to float. Point x in FIG. 4 is the range where hair is expected to overlap and be affected when measuring at measurement point Oz, and the length from measurement point Oz to point x is 5 mm. For this reason, if the length of the range where hair is expected to overlap and be affected is set to 5 mm, the average hair thickness (mm) and hair density (lengths / cm) for the above-mentioned general subjects will be 2 ), the number of hairs per unit length is 14 / cm, the number of hairs in the linear range up to that range (5 mm) is 72, and the hair volume (in other words, the height of the overlapped hairs) when all the hairs in the linear range up to that range (5 mm) are overlapped is 6 mm. Therefore, by making the projection height h of electrode projection 22 6 mm or more, the subject's hair can be well contained in the space of central portion 28 surrounded by electrode projection 22.

[0031] In addition, subjects with thick, dense hair had an average hair thickness of about 0.150 mm and a hair density of 300 strands / cm 2 The average hair thickness (mm) and hair density (lengths / cm 2), the number of hairs per unit length is 17 / cm, the number of straight hairs in the above range (5 mm) is 87, and the hair volume when all the straight hairs above the above range (5 mm) are overlapped is 13 mm. Therefore, if the projection height h of the electrode projection 22 is secured to be 15 mm, the hair can be well stored in the space of the center portion 28 surrounded by the electrode projection 22, even in the case of a subject with thick hair and high hair density. If the projection height h of the electrode projection 22 exceeds 15 mm, the projection height h of the electrode projection 22 becomes excessive, and the removability from the mold when forming the electrode projection 22 may be deteriorated. Also, from the viewpoint of reducing the space of the bioelectrode 1, it is not preferable that the projection height h of the electrode projection 22 is excessive.

[0032] Regarding the arrangement of the electrode protrusions 22 on the outer periphery 29 of the electrode protrusion forming surface 21b, a circular arrangement is preferable with respect to the outer periphery 29 of the electrode protrusion forming surface 21b from the viewpoint of balance. For example, it is preferable that each of the electrode protrusions 22 is arranged so as to be located on the circumference of a virtual circle 25 on the outer periphery 29 of the electrode protrusion forming surface 21b. Note that the virtual circle may be one virtual circle or multiple virtual concentric circles. However, the arrangement of the electrode protrusions 22 is not limited to the above, and for example, the shape drawn by connecting the points at which the multiple electrode protrusions 22 are arranged may be a triangle, a rectangle, or the like.

[0033] The electrode protrusions 22 are preferably arranged at equal intervals on the outer periphery 29 of the electrode protrusion-forming surface 21b. The intervals between two adjacent electrode protrusions 22 do not need to be strictly equal, but may be approximately equal. The arrangement of the electrode protrusions 22 is not limited to the above-mentioned embodiment, and may have a certain arrangement pattern in which, for example, the intervals between two adjacent electrode protrusions 22 on the outer periphery 29 of the electrode protrusion-forming surface 21b are not all the same, and may have two or more types of intervals. Furthermore, for example, the electrode protrusions 22 may be arranged randomly on the outer periphery 29 of the electrode protrusion-forming surface 21b.

[0034] There is no particular limit to the number of electrode protrusions 22 disposed on the outer periphery 29 of the electrode protrusion forming surface 21b, and the number can be appropriately determined depending on the size of the electrode protrusion forming surface 21b, etc.

[0035] There is also no particular limitation on the shape of each electrode protrusion forming surface 21b, as long as the protrusion height h is 6 to 15 mm and is formed to protrude from the electrode protrusion forming surface 21b of the electrode body 21. Here, an example of the shape of the electrode protrusion forming surface 21b will be described using the electrode protrusion forming surface 21b of the bioelectrode 1 shown in Figures 1 to 3 as an example.

[0036] As in the bioelectrode 1 shown in Figs. 1 to 3, for example, each of the electrode protrusions 22 is preferably formed so that the cross-sectional area gradually decreases from the base end (root portion) toward the tip end, in other words, as it moves away from the electrode protrusion forming surface 21b. For example, each of the electrode protrusions 22 has a circular cross section, and the diameter gradually decreases from the base end toward the tip end. It is preferable that the center C1 of the cross section of the base end of each of the electrode protrusions 22 is disposed so as to be located on the circumference of the virtual circle 25 on the outer periphery 29 as described above. In such a configuration, it is not necessary that the center C1 of the cross section of the base end of each of the electrode protrusions 22 is located strictly on the circumference of the virtual circle 25, but it is sufficient that it is located approximately on the circumference.

[0037] The tip of each of the electrode protrusions 22 is preferably formed in a hemispherical shape. Moreover, each of the electrode protrusions 22 is preferably formed such that the center C2 of the tip (also referred to as the center of the cross section of the tip) is located radially outward from the center C1 of the cross section of the base end when viewed from the arrangement center O of the electrode protrusions 22. For example, such an electrode protrusion 22 has an oblique cone shape with a rounded apex of the tip. By configuring in this way, it is possible to ensure a wider space in the center 28 of the electrode protrusion forming surface 21b surrounded by the electrode protrusions 22.

[0038] In the bioelectrode 1, the connector 30 is formed as a snap button connector. More specifically, the connector 30 is formed as a male connector in a snap button connector. The connector 30 includes a first conductive member 40 and a second conductive member 50 that are fitted together, for example, as shown in FIG.

[0039] The first conductive member 40 and the second conductive member 50 are formed of, for example, stainless steel. One end of the first conductive member 40 is embedded in the electrode body 21 of the electrode member 20, and extends through the support member 10, with the other end protruding from the back surface 10b of the support member 10. The second conductive member 50 is arranged on the back surface 10b of the support member 10 in a state where it is fitted to the other end side of the first conductive member 40. Then, the electrode member 20 of the bioelectrode 1 is electrically connected to the outside by attaching (fitting) a female connector (not shown) of the snap button type connector to the second conductive member 50. That is, the connector 30 is configured such that a part of it is embedded in the electrode body 21 of the electrode member 20, and extends through the support member 10, with the connection part with the outside being located on the back surface 10b of the support member 10.

[0040] For example, the electrode member 20 of the bioelectrode 1 is electrically connected to the measurement device by mounting (fitting) a female connector attached to the tip of a lead wire of the measurement device to the second conductive member 50. The measurement device is a device for inputting biosignals detected by a plurality of electrode protrusions 22 of the electrode member 20 of the bioelectrode 1 and processing, displaying, analyzing, etc., the input biosignals, and is not particularly limited, but examples of the measurement device include an electroencephalogram measurement device, a wearable information device, and a health monitoring device.

[0041] The first conductive member 40 and the second conductive member 50 will be specifically described with reference to Fig. 3. The first conductive member 40 and the second conductive member 50 are formed in a cylindrical shape with a flange and a bottom.

[0042] The first conductive member 40 has a first bottomed cylindrical portion 41 having an open end 41a at one end and a closed end 41b at the other end, and a first flange portion 42 extending radially outward from the open end 41a of the first bottomed cylindrical portion 41. The outer diameter of the first bottomed cylindrical portion 41 is set to be substantially the same as the diameter of the through hole 10c of the support member 10. A fitting portion 43 that is recessed in the radial direction is formed in a portion of the outer circumferential surface of the first bottomed cylindrical portion 41 near the closed end 41b. The first flange portion 42 is slightly inclined so that the outer side is located closer to the closed end 41b of the first bottomed cylindrical portion 41 than the inner side in the radial direction.

[0043] The first conductive member 40 is embedded in the electrode portion main body 21 of the electrode member 20 mainly on the surface of the first flange portion 42 opposite to the first bottomed cylindrical portion 41 side, the first bottomed cylindrical portion 41 is inserted into the through hole 10c of the support member 10 (i.e., extends through the support member 10), and a portion on the closed end 41b side of the first bottomed cylindrical portion 41 (including the fitting portion 43) protrudes from the back surface 10b of the support member 10. In the following, the surface of the first flange portion 42 opposite to the first bottomed cylindrical portion 41 side will be referred to as the "embedded surface".

[0044] The second conductive member 50 has a second bottomed cylindrical portion 51 having an open end 51a at one end and a closed end 51b at the other end, and a second flange portion 52 extending radially outward from the open end 51a of the second bottomed cylindrical portion 51. The second bottomed cylindrical portion 51 is formed so that the inner diameter increases from the open end 51a toward the closed end 51b. The inner diameter of the open end 51a of the second bottomed cylindrical portion 51 is set to be approximately the same as the outer diameter of the fitting portion 43 formed on the outer circumferential surface of the first bottomed cylindrical portion 41 of the first conductive member 40. The side surface and the bottom surface of the second bottomed cylindrical portion 51 are connected by a smooth curved surface. The second flange portion 52 has an inclined portion inclined so that the outer side is farther away from the closed end 51b of the second bottomed cylindrical portion 51 than the inner side in the radial direction.

[0045] The second conductive member 50 has the opening end 51a of the second bottomed cylindrical portion 51 fitted and fixed into the fitting portion 43 of the first bottomed cylindrical portion 41 of the first conductive member 40 by crimping or the like, thereby forming the connector 30 of the bioelectrode 1.

[0046] Next, an example of a manufacturing method of the bioelectrode 1 will be described. However, the manufacturing method of the bioelectrode 1 is not limited to the following method. In the following description, the connector 30 is assumed to be attached to the support member 10 in advance. Specifically, the first bottomed cylindrical portion 41 of the first conductive member 40 is inserted into the through hole 10c of the support member 10 from the closed end 41b side, and the open end 51a of the second bottomed cylindrical portion 51 of the second conductive member 50 is fitted into the fitting portion 43 of the first bottomed cylindrical portion 41 of the first conductive member 40 protruding from the back surface 10b of the support member 10, thereby forming an assembly of the support member 10 and the connector 30 in advance. Therefore, in the following manufacturing method, the connector 30 is treated as a member provided on the support member 10 side.

[0047] In manufacturing the bioelectrode 1, first, liquid or paste-like conductive rubber containing silicone rubber and metal particles is stirred, and the stirred conductive rubber is poured into a mold (cavity) having the shape of the electrode member 20. As a result, the conductive rubber is formed into the shape of the electrode member 20 within the mold.

[0048] Next, the support member 10 with the connector 30 attached, i.e., the assembly of the support member 10 and the connector 30, is placed on the conductive rubber in the molding die with the support surface 10a of the support member 10 facing downward. As a result, the support surface 10a of the support member 10 is placed on a portion corresponding to the supported surface 21a of the electrode portion main body 21 made of conductive rubber formed in the shape of the electrode member 20. In addition, the embedding surface of the first flange portion 42 of the first conductive member 40 is embedded in a portion corresponding to the electrode portion main body 21 made of conductive rubber formed in the shape of the electrode member 20.

[0049] Next, the conductive rubber molded into the shape of the electrode member 20 is crosslinked with the assembly of the support member 10 and the connector 30 placed thereon. This causes the conductive rubber formed into the shape of the electrode member 20 to harden, and the first conductive member 40 and the electrode member 20 are integrated. That is, the connector 30 and the electrode member 20 having a plurality of electrode body bodies 21 are molded into one piece. In this way, the support member 10, the electrode member 20, and the connector 30 are integrated. Thereafter, the integrated support member 10, the electrode member 20, and the connector 30 are removed from the mold, and post-processing is performed as necessary, thereby manufacturing the bioelectrode 1. [Industrial Applicability]

[0050] The bioelectrode of the present invention can be used as a bioelectrode for contacting a subject's body and sensing electrical signals from the subject's body, transmitting electrical stimuli to the subject, or performing both the sensing and transmission described above. [Explanation of symbols]

[0051] 1: Bioelectrode 10: Support member 10a: Support surface 10b: Back 10c: Through hole 20: Electrode material 21: Electrode body 21a: Supported surface 21b: Electrode protrusion forming surface 22: Electrode protrusion 25: Virtual circle 28: Central part 29: Outer periphery 30: Connector 40: First conductive member 41: First bottomed cylindrical part 41a: Open end 41b: Closed end 42: First flange part 43: Fitting part 50: second conductive member 51: Second bottomed cylindrical section 51a: Open end 51b: Closed end 52: Second flange part 60: Subject C1: Center of the cross section of the base end of the electrode protrusion C2: Center of tip of electrode protrusion h: Projection height O: Center of arrangement of multiple electrode protrusions Oz: Measurement point x: location

Claims

1. An electrode member is provided for contacting the body of the subject, The electrode member has a plate-shaped electrode body and a plurality of electrode protrusions provided so as to protrude from an electrode protrusion forming surface of the electrode body, the plurality of electrode protrusions are arranged on an outer periphery of the electrode protrusion forming surface so as to avoid a central portion of the electrode protrusion forming surface of the electrode body; a projection height from a base end to a tip end of each of the electrode projections in a direction perpendicular to the electrode projection forming surface is 6 to 15 mm; each of the plurality of electrode projections is disposed so as to be located on the circumference of one imaginary circle or a plurality of imaginary concentric circles on the outer periphery of the electrode projection-forming surface, and the plurality of electrode projections are disposed at equal intervals on the outer periphery of the electrode projection-forming surface; A bioelectrode, wherein each of the multiple electrode protrusions has an oblique conical shape with a rounded apex, and is formed so that the cross-sectional area gradually decreases from the base end to the tip end, and each of the multiple electrode protrusions is arranged to be located on the circumference, and is formed so that the center of the tip end is located radially outward from the center of the cross section of the base end when viewed from the center of the arrangement of the multiple electrode protrusions.

2. 2. The bioelectrode according to claim 1, which is used for measuring electroencephalograms of a subject.

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