Earpiece-type electrode

Abstract

The earpiece-type electrode (1) intended to be inserted into an ear canal (2) is provided with: a first truncated-conical-shaped wall part (11) which is formed from an electroconductive rubber, has an approximately truncated conical shape, and has a first axis-line-direction edge part (11a) and a second axis-line-direction edge part (11b) having a larger diameter than that of the first axis-line-direction edge part (11a); and a second truncated-conical-shaped wall part (12) which is formed from an electroconductive rubber, has a dimension larger than that of the first truncated-conical-shaped wall part (11), has an approximately truncated conical shape, is arranged coaxially with the first truncated-conical-shaped wall part (11), and has a third axis-line-direction edge part (12a) connected to the second axis-line-direction edge part (11b) and a fourth axis-line-direction edge part (12b) having a larger diameter than that of the third axis-line-direction edge part (12a).

Description

earpiece-type electrodes

[0001] The present invention relates to an earpiece-type electrode that is inserted into the ear canal of a mammal, including a human, or a bird.

[0002] Japanese Patent Application Laid-Open Publication No. 2011-217986 discloses an electrode having a substantially cylindrical shape similar to the earpiece of a canal-type earphone, which is inserted into the human ear canal and used to supply electric current to the skull or measure electroencephalograms.

[0003] Earpieces for earphones used for listening to music are made of soft materials. The rubber hardness measured with a durometer type A specified in JIS K 6253 (2012) is generally 30° or less. Therefore, earpieces can easily conform to the shape and size of the ear canal, which vary from person to person.

[0004] On the other hand, earpiece-type electrodes are made of hard materials because they contain a large amount of conductive filler that enhances conductivity. The rubber hardness measured with a durometer type A is generally 60 to 70 degrees. As a result, some people experience discomfort such as a feeling of pressure or pain when wearing earpiece-type electrodes for long periods of time.

[0005] To ensure electrical connection with the living body, it is preferable for the earpiece electrode to stably contact the inner surface of the ear canal over a wide area with a certain degree of contact pressure. If the hardness of the earpiece electrode is reduced, the earpiece electrode will be more likely to buckle when inserted into the ear canal. This may result in a decrease in the contact area between the earpiece electrode and the inner surface of the ear canal or a partial decrease in contact pressure.

[0006] Since the shape and size of the ear canal vary from person to person, it is preferable to select an earpiece-type electrode of appropriate size. An earpiece-type electrode that is smaller than the ear canal may cause a decrease in the contact area with the inner surface of the ear canal and a decrease in contact pressure. An earpiece-type electrode that is larger than the ear canal may cause discomfort. However, preparing earpiece-type electrodes of various sizes increases costs.

[0007] An object of the present invention is to provide an earpiece-type electrode that fits properly to ear canals of various shapes and sizes.

[0008] A first aspect of the present disclosure is an earpiece-type electrode to be inserted into an ear canal, comprising: a first frustoconical wall portion formed of conductive rubber and having a substantially frustoconical shape, the first frustoconical wall portion having a first axial end and a second axial end having a larger diameter than the first axial end; and a second frustoconical wall portion formed of conductive rubber, having a larger dimension than the first frustoconical wall portion, having a substantially frustoconical shape, and disposed coaxially with the first frustoconical wall portion, the second frustoconical wall portion having a third axial end connected to the second axial end, and a fourth axial end having a larger diameter than the third axial end.

[0009] The earpiece-type electrode of the present invention can be fitted appropriately to ear canals of various shapes and sizes.

[0010] 1 is a cross-sectional view showing an example of use of the earpiece-type electrode of the embodiment; 2 is a front view of the earpiece-type electrode of the first embodiment; 3 is a perspective view of the earpiece-type electrode of the first embodiment; 4 is a front cross-sectional view of the earpiece-type electrode of the first embodiment; 5 is a plan view of the earpiece-type electrode of the first embodiment; 6 is a front view of the earpiece-type electrode of the second embodiment;

[0011] Various embodiments of the present invention will now be described with reference to the accompanying drawings, in which the drawings are not necessarily to scale and some features may be exaggerated or omitted.

[0012] As shown in Figure 1, an earpiece-type electrode 1 according to an embodiment is inserted into the ear canal 2 of a human, other mammal, or bird. The earpiece-type electrode 1 is made of conductive rubber. When in use, the earpiece-type electrode 1 is electrically connected to a measuring device (not shown) that measures brain waves or blood flow.

[0013] In the example of use shown in Fig. 1, the earpiece-type electrode 1 is mechanically and electrically connected to a connecting part 3. The connecting part 3 is mechanically and electrically connected to a measuring device. The connecting part 3 has a metallic cylindrical part 4. The cylindrical part 4 is fitted onto the tip of a rubber protective tube 5.

[0014] A speaker 6 is fixed inside the cylindrical part 4. Wiring 6a for generating sound from the speaker 6 extends through the inside of the protective tube 5 and is electrically connected to the measuring device. The cylindrical part 4 has a small-diameter cylindrical portion 4a. A hook 4b is formed on the end of the small-diameter cylindrical portion 4a. The hook 4b is an annular flange that expands radially outward.

[0015] The earpiece-type electrode 1 has an inner wall 8, a tip wall 9, and an outer wall 10. The small-diameter cylindrical portion 4a is fitted into the inner wall 8. An annular hook 8a is formed on the end of the inner wall 8 opposite the tip wall 9. The hook 8a extends radially inward. The hook 8a is hooked onto the hook 4b. In this manner, the earpiece-type electrode 1 is fixed to the cylindrical part 4 and electrically connected to the cylindrical part 4. The cylindrical part 4 is electrically connected to the measuring device via a conductor 4c extending through the inside of the protective tube 5. The earpiece-type electrode 1 can be removed from the cylindrical part 4 by releasing the hooks 4b and 8a.

[0016] In this example, the earpiece electrode 1 is used with a speaker 6. That is, the earpiece electrode 1 is used as an earpiece for a canal-type earphone. The speaker 6 generates sound. The sound reaches the middle ear and inner ear through the internal space of the small-diameter cylindrical portion 4a, the internal space of the inner wall 8, and the ear canal 2. The earpiece electrode 1 supplies current to the inner surface of the ear canal 2 with which it makes contact. The earpiece electrode 1 also measures changes in electrical properties obtained from the ear canal 2, such as changes in potential and current. The measuring device diagnoses changes in brain waves or blood flow based on the changes in electrical properties obtained from the ear canal 2. This makes it possible to estimate the mental state of a subject who has heard a specific sound.

[0017] In this example, the speaker 6 is connected to the measurement device via a wire 6a, but the speaker 6 may also be connected to the measurement device wirelessly. The speaker 6 may also be omitted. The earpiece-type electrode 1 may be used to supply current to the cranium for electrovestibular stimulation without generating sound. Alternatively, the earpiece-type electrode 1 may be used to measure brain waves or blood flow without generating sound.

[0018] The conductive rubber that is the material of the earpiece-type electrode 1 contains particles and / or flakes of a conductive material. The rubber that is the matrix material is, for example, silicone rubber. The conductive material may be, for example, any of carbon black, gold (Au), platinum (Pt), silver (Ag), tungsten (W), molybdenum (Mo), copper (Cu), stainless steel, iron (Fe), silver-silver chloride (Ag / AgCl), or a mixture thereof.

[0019] <First embodiment> As shown in Figures 2 to 5, the earpiece-type electrode 1 of the first embodiment has a three-dimensional shape that is rotationally symmetric about the central axis line Ax. Figure 4 is a cross-sectional view taken along the line IV-IV in Figures 2 and 5. Because the earpiece-type electrode 1 has a rotationally symmetric shape, the same cross-sectional view as Figure 4 is obtained when cutting the earpiece-type electrode 1 along any plane that includes the central axis line Ax.

[0020] The earpiece-type electrode 1 has an inner wall 8, a tip wall 9, and an outer wall 10. As shown in Figure 1, when the earpiece-type electrode 1 is attached to a living body, the tip wall 9 faces the depth of the ear canal 2.

[0021] The outer wall 10 contacts the inner surface of the ear canal 2. The outer wall 10 has a first truncated cone-shaped wall portion 11 and a second truncated cone-shaped wall portion 12. The first truncated cone-shaped wall portion 11 and the second truncated cone-shaped wall portion 12 each have a substantially truncated cone shape. The first truncated cone-shaped wall portion 11 and the second truncated cone-shaped wall portion 12 may have a complete truncated cone shape. Alternatively, the first truncated cone-shaped wall portion 11 and the second truncated cone-shaped wall portion 12 may have an incomplete truncated cone shape, as in the walls 11 and 12 shown in FIGS. 2 to 4, but may be recognized at a glance as a truncated cone and have a shape suitable for insertion into the ear canal 2. In other words, the first truncated cone-shaped wall portion 11 and the second truncated cone-shaped wall portion 12 may have an umbrella or bowl shape without a radial center portion. The frustoconical walls 11, 12 may have slight concavities and / or convexities.

[0022] The first frustoconical wall portion 11 has a first axial end portion 11 a and a second axial end portion 11 b. The second axial end portion 11 b has a larger diameter than the first axial end portion 11 a. The first axial end portion 11 a is smoothly connected to the tip wall 9. The second axial end portion 11 b is smoothly connected to the second frustoconical wall portion 12.

[0023] As shown in FIG. 2 , the inclination angle θ1 is greater than the inclination angle θ2. Here, the inclination angle θ1 is the inclination angle of the first portion 11c on the first axial end 11a side of the first truncated conical wall portion 11 with respect to the central axis Ax. The inclination angle θ2 is the inclination angle of the second portion 11d on the second axial end 11b side with respect to the central axis Ax. Furthermore, the inclination angle θ1 of the first portion 11c increases as it approaches the first axial end 11a. In this way, the inclination angle of the first truncated conical wall portion 11 with respect to the central axis Ax increases as it approaches the first axial end 11a. Therefore, when the earpiece-type electrode 1 is inserted into the ear canal 2, the first truncated conical wall portion 11 provides less stimulation to the subject.

[0024] The second frustoconical wall portion 12 has dimensions larger than those of the first frustoconical wall portion 11. The second frustoconical wall portion 12 is arranged coaxially with the first frustoconical wall portion 11. The second frustoconical wall portion 12 has a third axial end portion 12a and a fourth axial end portion 12b. The fourth axial end portion 12b has a larger diameter than the third axial end portion 12a. The third axial end portion 12a is smoothly connected to the second axial end portion 11b. The fourth axial end portion 12b is the end of the earpiece-type electrode 1 opposite the tip wall 9.

[0025] As shown in FIG. 2 , the inclination angle θ3 is greater than the inclination angle θ4. Here, the inclination angle θ3 is the inclination angle of the third portion 12c on the third axial end 12a side of the second truncated conical wall portion 12 with respect to the central axis Ax. The inclination angle θ4 is the inclination angle of the fourth portion 12d on the fourth axial end 12b side with respect to the central axis Ax. The fourth portion 12d may have a cylindrical shape instead of a truncated cone shape. That is, the inclination angle θ4 may be zero. Furthermore, the inclination angle θ3 of the third portion 12c is greater than the inclination angle θ2 of the second portion 11d.

[0026] As shown in Figure 4, the inner wall 8 has a generally truncated cone shape with the cross-sectional area on the tip wall 9 side larger than the cross-sectional area on the opposite side. The inner wall 8 is disposed inside the outer wall 10 and coaxial with the outer wall 10. An annular hook 8a is formed at the end of the inner wall 8 opposite the tip wall 9. The hook 8a extends radially inward. The tip wall 9 has a generally arcuate shape in a cross section including the central axis Ax. The tip wall 9 smoothly connects the inner wall 8 and the outer wall 10.

[0027] The dimensions of the earpiece-type electrode 1 will be described with reference to Figure 4. The height H1 of the earpiece-type electrode 1 is, for example, 7 to 11 mm. Here, the height H1 is the distance along the axial direction between the fourth axial end 12b and the tip end surface 9a. The height H2 of the second truncated conical wall portion 12 is, for example, 3 to 5 mm. Here, the height H2 is the distance along the axial direction between the fourth axial end 12b and the third axial end 12a.

[0028] The outer diameter D1 of the earpiece-type electrode 1 is, for example, 10 to 14 mm. Here, the outer diameter D1 is the outer diameter of the fourth axial end 12 b. The outer diameter D2 of the first truncated conical wall portion 11 is, for example, 9 to 12 mm. Here, the outer diameter D2 is the outer diameter of the third axial end 12 a and the outer diameter of the second axial end 11 b.

[0029] The inner diameter Dh of the hook 8a is, for example, 3 to 5 mm, and the axial length L of the hook 8a is, for example, 1 to 3 mm.

[0030] The thickness t1 of the outer wall 10 is, for example, 0.3 to 0.6 mm. The thickness t2 of the inner wall 8 is, for example, 0.5 to 0.8 mm. It is preferable that the thickness t1 is smaller than the thickness t2. In this case, the inner wall 8, which has high rigidity, prevents the earpiece-type electrode 1 from buckling. The tip wall 9 and outer wall 10, which have low rigidity, deform to follow the shape and size of the ear canal 2, reducing the stimulation provided to the subject.

[0031] The earpiece-type electrode 1 of this embodiment has two truncated cone-shaped wall portions 11, 12 of different sizes. This allows the earpiece-type electrode 1 to fit appropriately to ear canals 2 of various shapes and sizes. Therefore, the earpiece-type electrode 1 stably contacts the inner surface of the ear canal 2 over a wide area with a certain degree of contact pressure. This also reduces the need to prepare earpiece-type electrodes 1 in a large number of sizes.

[0032] When the earpiece-type electrode 1 is attached to a living body, the first truncated conical wall 11 is directed deeper into the ear canal 2 than the second truncated conical wall 12. The first portion 11c of the first truncated conical wall 11 is directed deeper into the ear canal 2 than the second portion 11d. As shown in FIG. 2 , the inclination angle θ1 of the first portion 11c with respect to the central axis Ax is greater than the inclination angle θ2 of the second portion 11d. Therefore, the first truncated conical wall 11 can be smoothly inserted into the ear canal 2. Furthermore, when the diameter of the ear canal 2 is small, the second portion 11d is likely to come into surface contact with the inner surface of the ear canal 2 over a wide contact area.

[0033] When the earpiece-type electrode 1 is attached to a living body, the third portion 12c of the second truncated cone-shaped wall portion 12 is oriented deeper into the ear canal 2 than the fourth portion 12d. The inclination angle θ3 of the third portion 12c with respect to the central axis Ax is greater than the inclination angle θ2 of the second portion 11d and greater than the inclination angle θ4 of the fourth portion 12d. Therefore, when the diameter of the ear canal 2 is large, the second truncated cone-shaped wall portion 12 can be smoothly inserted into the ear canal 2. Furthermore, the third portion 12c and / or the fourth portion 12d are likely to come into surface contact with the inner surface of the ear canal 2 over a wide contact area.

[0034] Second Embodiment As shown in Figures 6 to 9, the earpiece-type electrode 20 of the second embodiment also has a three-dimensional shape that is rotationally symmetric about the central axis Ax. Figure 8 is a cross-sectional view taken along the arrows VIII-VIII in Figures 6 and 9. Because the earpiece-type electrode 20 has a rotationally symmetric shape, the same cross-sectional view as Figure 8 will be obtained when the earpiece-type electrode 20 is cut along any plane that includes the central axis Ax.

[0035] The earpiece-type electrode 20 has features in common with the earpiece-type electrode 1 of the first embodiment, and therefore a description of these features will be omitted.

[0036] The outer wall 10 of this embodiment has a first frustoconical wall portion 11, a second frustoconical wall portion 12, and a third frustoconical wall portion 13. The third frustoconical wall portion 13 has larger dimensions than the second frustoconical wall portion 12. The third frustoconical wall portion 13 has a generally frustoconical shape. The third frustoconical wall portion 13 is arranged coaxially with the first frustoconical wall portion 11 and the second frustoconical wall portion 12. The third frustoconical wall portion 13 has a fifth axial end portion 13a and a sixth axial end portion 13b. The sixth axial end portion 13b has a larger diameter than the fifth axial end portion 13a. The fifth axial end portion 13a is smoothly connected to the fourth axial end portion 12b. The sixth axial end 13 b is the end of the earpiece-type electrode 1 opposite the tip wall 9 .

[0037] The dimensions of the earpiece-type electrode 20 will be described with reference to FIG. 8 . The height H1 of the earpiece-type electrode 20 is, for example, 9 to 13 mm. Here, the height H1 is the distance along the axial direction between the sixth axial end 13 b and the tip end surface 9 a. The height H3 of the third truncated conical wall portion 13 is, for example, 2 to 4 mm. Here, the height H3 is the distance along the axial direction between the sixth axial end 13 b and the fifth axial end 13 a. The height H2 of the second truncated conical wall portion 12 is, for example, 3 to 5 mm. Here, the height H2 is the distance along the axial direction between the fourth axial end 12 b and the third axial end 12 a.

[0038] The outer diameter D1 of the earpiece-type electrode 20 is, for example, 11 to 15 mm. Here, the outer diameter D1 is the outer diameter of the sixth axial end 13b. The outer diameter D2 of the first truncated conical wall portion 11 is, for example, 9 to 12 mm. Here, the outer diameter D2 is the outer diameter of the third axial end 12a and the outer diameter of the second axial end 11b. The outer diameter D3 of the second truncated conical wall portion 12 is, for example, 10 to 14 mm. Here, the outer diameter D3 is the outer diameter of the fifth axial end 13a and the outer diameter of the fourth axial end 12b.

[0039] The inner diameter Dh of the hook 8a is, for example, 3 to 5 mm, and the axial length L of the hook 8a is, for example, 1 to 3 mm.

[0040] The thickness t1 of the outer wall 10 is, for example, 0.3 to 0.6 mm. The thickness t2 of the inner wall 8 is, for example, 0.5 to 0.8 mm. It is preferable that the thickness t1 is smaller than the thickness t2. In this case, the inner wall 8, which has high rigidity, prevents the earpiece-type electrode 20 from buckling. The tip wall 9 and outer wall 10, which have low rigidity, deform to conform to the shape and size of the ear canal 2, reducing the stimulation provided to the subject.

[0041] The earpiece-type electrode 20 of this embodiment has three truncated cone-shaped wall portions 11, 12, and 13 of different sizes. This allows the earpiece-type electrode 20 to fit appropriately to ear canals 2 of various shapes and sizes. Therefore, the earpiece-type electrode 20 stably contacts the inner surface of the ear canal 2 over a wide area with a certain degree of contact pressure. This also reduces the need to prepare earpiece-type electrodes 20 in a large number of sizes.

[0042] When the earpiece-type electrode 20 is attached to a living body, the first truncated conical wall 11 is directed deeper into the ear canal 2 than the second truncated conical wall 12. The first portion 11c of the first truncated conical wall 11 is directed deeper into the ear canal 2 than the second portion 11d. As shown in FIG. 6 , the inclination angle θ1 of the first portion 11c with respect to the central axis Ax is greater than the inclination angle θ2 of the second portion 11d. Therefore, the first truncated conical wall 11 can be smoothly inserted into the ear canal 2. Furthermore, when the diameter of the ear canal 2 is small, the second portion 11d is likely to come into surface contact with the inner surface of the ear canal 2 over a wide contact area.

[0043] Furthermore, the inclination angle θ1 of the first portion 11c increases as it approaches the first axial end 11a. Thus, the inclination angle of the first truncated cone-shaped wall portion 11 with respect to the central axis Ax increases as it approaches the first axial end 11a. Therefore, when the earpiece-type electrode 1 is inserted into the ear canal 2, the first truncated cone-shaped wall portion 11 provides less stimulation to the subject.

[0044] When the earpiece-type electrode 20 is attached to a living body, the third portion 12c of the second truncated cone-shaped wall portion 12 is oriented deeper into the ear canal 2 than the fourth portion 12d. The inclination angle θ3 of the third portion 12c with respect to the central axis Ax is greater than the inclination angle θ2 of the second portion 11d and greater than the inclination angle θ4 of the fourth portion 12d. Therefore, when the diameter of the ear canal 2 is large, the second truncated cone-shaped wall portion 12 can be smoothly inserted into the ear canal 2. Furthermore, the third portion 12c and / or the fourth portion 12d are likely to make surface contact with the inner surface of the ear canal 2 over a wide contact area. The fourth portion 12d may be cylindrical rather than truncated cone-shaped. In other words, the inclination angle θ4 may be zero.

[0045] As shown in FIG. 6 , the inclination angle θ5 is greater than the inclination angle θ6. Here, the inclination angle θ5 is the inclination angle of the fifth portion 13c on the fifth axial end 13a side of the third truncated cone-shaped wall portion 13 relative to the central axis Ax. The inclination angle θ6 is the inclination angle of the sixth portion 13d on the sixth axial end 13b side relative to the central axis Ax. The inclination angle θ5 of the fifth portion 13c is greater than the inclination angle θ4 of the fourth portion 12d. Therefore, when the diameter of the ear canal 2 is larger, the third truncated cone-shaped wall portion 13 can be smoothly inserted into the ear canal 2, and the fifth portion 13c and / or the sixth portion 13d are likely to make surface contact with the inner surface of the ear canal 2 over a wide contact area. The sixth portion 13d may be cylindrical rather than truncated cone-shaped. That is, the inclination angle θ6 may be zero.

[0046] Although the above describes the embodiments, the present invention is not limited thereto. For example, the outer wall 10 may have four or more truncated cone-shaped wall portions. The inner wall 8, the distal wall 9, and the outer wall 10 may be formed from the same material or different materials. For example, the rubber matrix material of the distal wall 9 and the outer wall 10 that contact the living body may be softer than the matrix material of the inner wall 8 that does not contact the living body. In this case, the inner wall 8, which has high rigidity, prevents buckling of the earpiece-type electrode 1, while the distal wall 9 and the outer wall 10, which have low rigidity, deform to conform to the shape and size of the ear canal 2, thereby reducing the stimulation provided to the subject.

[0047] The earpiece-type electrodes 1, 20 may be used without the speaker 6 (FIG. 1). In this case, the distal wall 9 does not need to have an opening for transmitting sound to the subject's middle and inner ear. The earpiece-type electrodes 1, 20 may have a solid core portion instead of the inner wall 8.

[0048] 1, 20 Earpiece-type electrode 2 Ear canal 8 Inner wall 9 Tip wall 10 Outer wall 11 First truncated cone-shaped wall portion 11a First axial end 11b Second axial end 11c First portion 11d Second portion 12 Second truncated cone-shaped wall portion 12a Third axial end 12b Fourth axial end 12c Third portion 12d Fourth portion 13 Third truncated cone-shaped wall portion 13a Fifth axial end 13b Sixth axial end 13c Fifth portion 13d Sixth portion

Claims

1. An earpiece-type electrode that is inserted into the ear canal, a first frustoconical wall portion formed of a conductive rubber and having a generally frustoconical shape, a first axial end; a second axial end having a larger diameter than the first axial end; a first frustoconical wall having a a second frusto-conical wall portion formed of a conductive rubber, the second frusto-conical wall portion having a larger dimension than the first frusto-conical wall portion, the second frusto-conical wall portion having a generally frusto-conical shape, and the second frusto-conical wall portion being coaxially disposed with the first frusto-conical wall portion; a third axial end connected to the second axial end; and a fourth axial end having a larger diameter than the third axial end; a second frustoconical wall having having an inclination angle of a first portion located at a first axial end of the first frustoconical wall portion relative to the central axis is greater than an inclination angle of a second portion located at a second axial end of the first frustoconical wall portion relative to the central axis; an inclination angle of a third portion located on the third axial end side of the second frustoconical wall portion with respect to the central axis is greater than an inclination angle of the second portion and is greater than an inclination angle of a fourth portion located on the fourth axial end side of the second frustoconical wall portion with respect to the central axis; Earpiece-type electrodes.

2. The first truncated cone-shaped wall portion and the second truncated cone-shaped wall portion each have a rotationally symmetric shape about a central axis line.

2. The earpiece-type electrode according to claim 1.

3. In the first portion, the inclination angle increases toward the first axial end.

3. The earpiece-type electrode according to claim 1 or 2.

4. An earpiece-type electrode to be inserted into the ear canal, a first frustoconical wall portion formed of a conductive rubber and having a generally frustoconical shape, a first axial end; a second axial end having a larger diameter than the first axial end; a first frustoconical wall having a a second frusto-conical wall portion formed of a conductive rubber, the second frusto-conical wall portion having a larger dimension than the first frusto-conical wall portion, the second frusto-conical wall portion having a generally frusto-conical shape, and the second frusto-conical wall portion being coaxially disposed with the first frusto-conical wall portion; a third axial end connected to the second axial end; and a fourth axial end having a larger diameter than the third axial end; a second frustoconical wall having a third frustoconical wall portion formed of a conductive rubber, having a dimension larger than that of the second frustoconical wall portion, having a generally frustoconical shape, and disposed coaxially with the second frustoconical wall portion; a fifth axial end connected to the fourth axial end; a sixth axial end having a larger diameter than the fifth axial end; a third frustoconical wall having An earpiece-type electrode having

5. an inclination angle of a first portion located at a first axial end of the first frustoconical wall portion relative to the central axis is greater than an inclination angle of a second portion located at a second axial end of the first frustoconical wall portion relative to the central axis; an inclination angle of a third portion located at the third axial end side of the second frustoconical wall portion with respect to the central axis is greater than an inclination angle of the second portion and is greater than an inclination angle of a fourth portion located at the fourth axial end side of the second frustoconical wall portion with respect to the central axis; an inclination angle of a fifth portion located on the fifth axial end side of the third frustoconical wall portion with respect to the central axis is greater than an inclination angle of the fourth portion and is greater than an inclination angle of a sixth portion located on the sixth axial end side of the third frustoconical wall portion with respect to the central axis; 5. The earpiece-type electrode according to claim 4.