Electromicrophone

Abstract

Electret microphone (100), with an electrically conductive membrane (110), a counter electrode (120) with at least one first hole (121) having a first distance (A1) from an edge (120a) of the counter electrode (120) and a second plurality of second holes (122) each having a second distance (A2) from the edge (120a) of the counter electrode (120), wherein the second distance (A2) is smaller than the first distance (A1), a first electrically conductive coating (131) on a first side (120b) of the counter electrode (120), and a second electrically conductive coating (132) on a second side (120c) of the counter electrode (120), wherein the at least one first hole (121) has a via (133) to electrically contact the first and second electrically conductive coatings (131, 132), wherein at least one third gap (A3) is provided between the second holes (122) and the first electrically conductive coating (131) such that the first electrically conductive coating (131) does not extend to the second holes (122), and a polarizable film (140) which extends completely over the first electrically conductive coating (131) leaving the first and second holes (121, 122) free, wherein the polarizable film (140) extends to the second holes (122).

Description

[0001] The present invention relates to an electret microphone.

[0002] An electroacoustic condenser microphone has a movable, thin, electrically conductive diaphragm (first electrode) and a stationary second electrode (counter electrode). The diaphragm can be either metallic or non-metallic and coated on both sides with an electrically conductive coating. The electrode and counter electrode are located a short distance apart, with an air gap between them. In an electret microphone, an electret layer is located on the counter electrode between the electrode and the counter electrode to generate the necessary electric field between the electrode and the counter electrode.

[0003] DE 10 2018 108 720 B4 shows an electret microphone. A conductive layer is provided on a substrate. Furthermore, a diaphragm with a conductive layer is provided. The circular substrate body can be made of a high-quality, dimensionally stable plastic. The substrate body has a hole, which is also metallized, to electrically connect the front and rear coatings. Furthermore, additional holes can be provided to provide an acoustic connection between the air volume beneath the diaphragm and a rear volume.

[0004] CN 1481654 A shows an electret microphone with a counter electrode and several holes.

[0005] It is an object of the present invention to provide an electret microphone which is better protected against humidity.

[0006] This object is achieved by an electret microphone according to claim 1.

[0007] Thus, an electret microphone is provided which has an electrically conductive membrane and a counter electrode with at least one first hole at a first distance from an edge of the counter electrode and a second plurality of second holes, each at a second distance from the edge of the counter electrode, wherein the second distance is smaller than the first distance. The electret microphone has a first electrically conductive coating on a first side of the counter electrode, and a second electrically conductive coating on a second side of the counter electrode. The at least one first hole has a via for electrically contacting the first and second electrically conductive coatings. At least a third distance is present between each second hole and the first electrically conductive coating, such that the first electrically conductive coating does not reach as far as the second holes.Furthermore, a polarizable film is provided which extends completely over the first electrically conductive coating and leaves the first and second holes free, wherein the polarizable film reaches up to the second holes.

[0008] This means that the holes near the edge are not provided with a through-hole. By keeping the area around the second holes free of the first electrically conductive coating while the foil extends to the second holes, the insulation to the edge of the counter electrode can be improved, even in the presence of moisture.

[0009] According to one aspect, the counter electrode has a center point. The at least one first hole is arranged at a first radius around the center point. The plurality of second holes is arranged at a second radius around the center point, wherein the first radius is smaller than the second radius. The counter electrode is circular with a third radius. The first electrically conductive layer is arranged at most within a fourth radius around the center point. The fourth radius is smaller than the third radius, so that an edge region of the counter electrode remains free of the first electrically conductive layer. The polarizable film covers the edge region.

[0010] According to one aspect, the fourth radius is larger than the second radius, so that the electrically conductive coating extends radially beyond the second holes. This allows the area of ​​the conductive coating to be increased.

[0011] According to one aspect, the microphone comprises a circuit board arranged opposite the second electrically conductive coating. An electrically conductive connection is provided between the circuit board and the second electrically conductive coating.

[0012] According to one aspect, an area around the second holes remains free of the first electrically conductive coating while the polarizable film extends to an edge of the second holes, so that the polarizable film covers the area.

[0013] According to one aspect, the first and second electrically conductive coatings may be configured as an electrically conductive layer.

[0014] According to one aspect, an electret microphone is provided with a diaphragm, a counter electrode, an electrically conductive coating of the counter electrode, a first plurality of holes in a first circle, and a second plurality of holes in a second circle, wherein the radius of the second circle is larger than the radius of the first circle. At least one hole in the first circle has a via that is electrically connected to the electrically conductive coating of the counter electrode. A polarizable FEP film is provided on the counter electrode, covering a top side of the counter electrode with the exception of the holes.

[0015] The foil is placed on the counter electrode in such a way that it covers the entire counter electrode, except for the first and second holes. This results in the electrode being covered with the foil, particularly in an edge region of the counter electrode, i.e., at the outer edge of the counter electrode. The foil can be, for example, a fluoroethylene-propylene foil.

[0016] By providing the foil on the counter electrode, the counter electrode can be better protected against humidity.

[0017] This ensures that the electrically conductive coating is completely covered by the foil. This prevents leakage currents even in the holes closest to the edge (i.e., the second holes), even in damp conditions.

[0018] The counter electrode can optionally be circular with a center point. A first plurality of holes is provided in a first radius around the center point. A second plurality of holes is provided in a second radius around the center point. The second radius is greater than the first radius. The counter electrode has a third radius which is greater than the first and second radii. The conductive coating on the substrate of the counter electrode does not extend to the edge of the counter electrode, but has a fourth radius which is greater than the second but smaller than the third radius. In the area between the third and fourth radii, the film is therefore located directly on the substrate. Otherwise, the conductive coating is provided between the top side of the counter electrode and the FEP film.This means that the entire free surface of the counter electrode (excluding the first and second holes) is covered by the foil.

[0019] According to one aspect of the present invention, the first holes (with the first radius) have a via that electrically connects the conductive layer on the first and second sides (top side, bottom side) of the counter electrode.

[0020] The second holes optionally do not have a corresponding through-hole.

[0021] The electret microphone according to the invention can provide a microphone which has low noise and, at the same time, high insensitivity to moisture.

[0022] Further embodiments of the invention are the subject of the subclaims.

[0023] Advantages and embodiments of the invention are explained in more detail below with reference to the drawing. Fig. 1 shows a sectional view of an electret microphone according to a first embodiment, Fig. 2 shows a plan view of a counter electrode for an electret microphone, and Fig. 3 shows a perspective view of a counter electrode for an electret microphone.

[0024] Fig. 1 shows a sectional view of an electret microphone according to a first embodiment. The electret microphone 100 has a membrane 110, a counter electrode 120 with an edge 120a, at least one first hole 121, and a plurality of second holes 122. The counter electrode 120 has a first and second side 120b, 120c. A first electrically conductive coating 131 is provided on the first side 120b, and a second electrically conductive coating 132 is provided on the second side 120c. An FEP film 140 is provided on the first side 120b of the counter electrode 120, which film covers the first electrically conductive layer 131. In addition, the film 140 also covers a region 123 of the counter electrode 120 that is not covered by the first electrically conductive coating 131. However, the film 140 does not cover either the first or the second holes 121, 122. For this purpose, the film 140 can have recesses at the corresponding locations.The at least one first hole 121 has a first distance A1 from an edge 120a of the counter electrode 120, and the majority of the second holes 122 have a second distance A2 from the edge 120a of the counter electrode 120. The second distance A2 is smaller than the first distance A1. The second holes are thus close to the edge, while the first holes are provided further away from the edge.

[0025] Optionally, the film 140 can extend to an edge of the first and second holes 121, 122. The first electrically conductive coating 131 can at least partially have a third distance A3 from an edge of the second holes 122. Thus, a section 125 with a width of the third distance A3 can be provided between the edge of the second holes 122 and the first electrically conductive coating 131. This section 125 around the second holes 122 does not have a first electrically conductive coating 131 and is covered by the film 140.

[0026] The electret microphone 100 further comprises a circuit board 150 on which the electrical and electronic components for signal processing of the electret microphone signals are provided. The circuit board 150 can optionally also include acoustic elements such as holes or damping elements. A spring 160 for contacting can be provided between the second electrically conductive layer 132 and the circuit board 150.

[0027] The electret microphone 100, and in particular the counter electrode 120, can be circular and can be placed in a housing 170. Optionally, the housing 170 radially surrounds the counter electrode 120 and the diaphragm 110.

[0028] Fig. 2 shows a plan view of a counter electrode for an electret microphone according to Fig. 1 and Fig. 3 shows a perspective view of a counter electrode 120 for an electret microphone 100 according to Fig. 1.

[0029] The counter electrode 120 has at least one hole 121, or a first plurality of holes 121, which can be arranged on a circle around a center point M of the counter electrode with a first radius r1. The counter electrode 120 has a plurality of second holes 122, which can be arranged on a circle around the center point M of the counter electrode 120 with a second radius r2. A first electrically conductive coating or layer 131 is applied to the counter electrode 120 (i.e., on a first side 120b). The electrically conductive layer 131 does not cover the first and second holes 121, 122.

[0030] The counter electrode 120 has an edge 120a, can be circular, and can have a third radius r3. The first electrically conductive layer 131 has a maximum fourth radius r4. The third radius r3 is larger than the first, second, and fourth radii r1, r2, and r4. The fourth radius r4 is smaller than the third radius r3 and larger than the second radius r2. The second radius r2 is larger than the first radius r1.

[0031] The at least one first hole 121 has a first distance A1 from an edge 120a of the counter electrode 120, and the plurality of second holes 122 have a second distance A2 from the edge 120a of the counter electrode 120. The second distance A2 is smaller than the first distance A1. The first plurality of holes 121 can optionally be arranged in a circle with the first radius r1 around a center point M of the counter electrode 120. The second plurality of holes 122 are arranged around a further circle with a larger radius (second radius r2) around the center point M of the counter electrode. Optionally, the arrangement of the holes 121 and 122 can deviate from a circular shape. What is crucial is that the second plurality of holes is arranged closer to an outer edge 120a of the counter electrode than the first plurality of holes 121. Optionally, only a single first hole 121 may be provided, which is further away from the edge 120a of the counter electrode 120 than the second holes 122.

[0032] The film 140 completely covers the first electrically conductive coating or layer 131 on the first side 102b of the counter electrode 120. Optionally, the film 140 can be provided in a circle around the center point M with a fifth radius r5, wherein the fifth radius r5 is greater than the maximum fourth radius r4 of the electrically conductive layer 131. The radius r5 can optionally correspond to the radius r3. Thus, a region 123 is provided at the edge 120a of the counter electrode 120, which is covered by the film 140 but not by the first electrically conductive coating. In this region, the film 140 lies directly on the counter electrode 120.

[0033] Between an edge of the second holes 122 and the first electrically conductive coating, a region 125 with a width of the third distance A3 can be provided, which is also only covered by the film 140 but not by the first electrically conductive coating 131.

[0034] Because the electrically conductive layer 131 does not extend to the edge 120a of the counter electrode 120 and because the film 140 extends beyond the edge of the conductive layer 131 and thus completely covers it in the edge region, electrical insulation from the housing 170 can be achieved. This reliably prevents leakage currents to the housing 170, even in the event of significant moisture buildup.

[0035] According to one aspect of the present invention, the first holes 121 have a via 133, by means of which the first and second electrically conductive coatings or layers 131, 132 are electrically connected to one another. Optionally, the second electrically conductive layer 132 can be coupled to a circuit board 150 by means of the conductive spring 160.

[0036] According to one aspect of the present invention, the FEP film 140 covers the entire surface of the counter electrode 120 with the exception of the first and second holes 121, 122. Thus, the film 140 also covers the edge region 123 of the counter electrode 120.

[0037] According to one aspect of the present invention, only the first holes 121 have a via 133, while the second holes 122 have no via.

[0038] As in Fig.As shown in Figure 1, the first electrically conductive coating 131 in the region of the second holes 122 can each have a third distance A3 from the respective hole 122, while the film 140 extends to the edge of the second holes 122, so that the first electrically conductive coating completely covers the area 123 at the second holes 122. In this way, the conductive layer 131 is covered with a highly insulating layer in the region of the second holes 122 near the edge in order to reliably prevent leakage currents from the conductive layer 131 to the housing 170, even in high humidity conditions.

[0039] According to one aspect of the present invention, the substrate of the counter electrode is made of ceramic and is therefore highly insulating.

[0040] After the electrically conductive layer 131, 132, 133 has been applied to the counter electrode substrate, the foil 140 can be placed thereon. Optionally, the electrically conductive layer 131, 132, 133 can be applied using a sputtering process.

[0041] The electret microphone according to the invention maximizes its resistance to high humidity. This is achieved despite its small size and thus the small surface area of ​​the counter electrode, enabling very low self-noise.

[0042] The inventive design of the first electrically conductive layer on the (upper) side of the substrate of the counter electrode ensures that a reduction in the capsule capacity is avoided while at the same time increasing the resistance to moisture.

[0043] The increase in moisture resistance is achieved by not applying the electrically conductive layer 131, 132, 133 in the edge region 123 of the substrate of the counter electrode 120. Furthermore, the electrically conductive layer is adapted in the region of the second holes 122 such that no electrically conductive coating is provided in a region between the second holes and the edge of the substrate of the counter electrode. The electrically conductive coating 131, 132, 133 is provided essentially in the region between adjacent second holes 122 and in the direction of the edge 120a. In particular, the holes in the outer circle and their immediate surroundings are exposed. Furthermore, a polarizable FEP film is placed over the surface of the counter electrode such that only the first and second holes 121, 122 remain exposed.

[0044] According to one aspect of the present invention, the electrically conductive layer 131, 132, 133 is a gold layer and can be applied by sputtering.

[0045] The electret microphone according to the invention ensures that the counter electrode of the electret microphone is electrically insulated from the surrounding metal housing. This can be achieved, for example, by the electrically conductive first and second layers not extending to the housing 170, but leaving the area 123 exposed. This can reduce leakage currents. Furthermore, it is desirable to have the largest possible electrically conductive area in order to increase the capacitance of the electret microphone and thus reduce its inherent noise.

[0046] According to the invention, a counter electrode is provided with a substrate made of a highly insulating material, such as ceramic, which has first and second holes. The holes can be used to adjust the acoustic frequency response. The surface of the counter electrode is completely covered (except for the holes) with an electrically polarized FEP film. The first electrically conductive layer is provided on top of the counter electrode substrate. The FEP film extends to the edge of the counter electrode, leaving only the first and second holes untouched.

[0047] Preferably, the first holes 121 (with a small radius) are used for through-hole plating. This is advantageous because it provides a large distance from the housing 170, which also reduces leakage currents.

[0048] Thus, an electret microphone with the largest possible electrode surface is provided, which reliably prevents leakage currents with respect to the surrounding housing, which can be caused by excessive humidity.

Claims

[1] Electret microphone (100), with an electrically conductive membrane (110), a counter electrode (120) having at least one first hole (121) with a first distance (A1) from an edge (120a) of the counter electrode (120) and a second plurality of second holes (122) each with a second distance (A2) from the edge (120a) of the counter electrode (120), wherein the second distance (A2) is smaller than the first distance (A1), a first electrically conductive coating (131) on a first side (120b) of the counter electrode (120), and a second electrically conductive coating (132) on a second side (120c) of the counter electrode (120), wherein the at least one first hole (121) has a through-contact (133) to electrically contact the first and second electrically conductive coatings (131, 132), wherein at least a third distance (A3) is present between the second holes (122) and the first electrically conductive coating (131), so that the first electrically conductive coating (131) does not reach as far as the second holes (122), and a polarizable film (140) which extends completely over the first electrically conductive coating (131) and leaves the first and second holes (121, 122) free, wherein the polarizable film (140) reaches up to the second holes (122). [2] Electret microphone (100) according to claim 1, wherein the counter electrode (120) has a center point (M), wherein the at least one first hole (121) is arranged at a first radius (r1) around the center point (M) wherein the plurality of second holes (122) are arranged at a second radius (r2) around the center point (M), the first radius (r1) being smaller than the second radius (r2), wherein the counter electrode (120) is circular with a third radius (r3), wherein the first electrically conductive coating (131) is arranged at most within a fourth radius (r4) around the center point (M), wherein the fourth radius (r4) is smaller than the third radius (r3), so that an edge region (123) of the counter electrode (120) remains free of the first electrically conductive coating (131), wherein the polarizable film (140) covers the edge region (123). [3] Electret microphone (100) according to claim 2, wherein the fourth radius (r4) is larger than the second radius (r2) such that the electrically conductive coating (131) extends radially beyond second holes (122). [4] Electret microphone (100) according to one of claims 1 to 3, further comprising a printed circuit board (150) arranged opposite the second electrically conductive coating (132), wherein an electrically conductive connection (160) is provided between the circuit board (150) and the second electrically conductive coating (132). [5] Electret microphone (100) according to one of claims 1 to 4, wherein an area (125) around the second holes (122) remains free of the first electrically conductive coating (131), wherein the polarizable film (140) extends to an edge of the second holes (122) so that the polarizable film (140) covers the area (125).

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