US-12621611-B2 - Electret microphone

US12621611B2US 12621611 B2US12621611 B2US 12621611B2US-12621611-B2

Abstract

An electret microphone is provided. It comprises an electrically conductive membrane and a counter-electrode having 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. The second distance is shorter than the first. The microphone includes a first electrically conductive coating on a first side of the counter-electrode and a second electrically conductive coating on a second side. The at least one first hole comprises a via to electrically contact the first and second coatings. A third distance is provided between the second holes and the first coating so that the first coating does not extend to the second holes. The microphone further comprises a polarizable film extending completely over the first coating while leaving the first and second holes free, and extending to the second holes.

Inventors

Stephan Leschka
Dominic Haul

Assignees

SENNHEISER ELECTRONIC SE & CO. KG

Dates

Publication Date: 20260505
Application Date: 20230531
Priority Date: 20220603

Claims (4)

1 . An electret microphone, comprising: an electrically conductive membrane; a counter-electrode having at least one first hole having a first distance from an edge of the counter-electrode and a second plurality of second holes each having a second distance from the edge of the counter-electrode, wherein the second distance is shorter than the first distance; a first electrically conductive coating directly on a first side of the counter electrode and a second electrically conductive coating directly on a second side of the counter-electrode, wherein the at least one first hole comprises a via in order to electrically contact the first and second electrically conductive coating, wherein at least a third distance is provided in each case between the second holes and the first electrically conductive coating so that the first electrically conductive coating does not reach as far as the second holes, and the second holes are isolated from the first conductive coating; and a polarizable film which covers the first side of the counter electrode and extends completely over the first electrically conductive coating and thereby leaves free the first and second holes.
2 . An electret microphone according to claim 1 , wherein the counter-electrode has a midpoint, wherein the at least one first hole is arranged in a first radius around the midpoint, wherein the plurality of second holes is arranged in a second radius about the midpoint, wherein the first radius is smaller than the second radius, wherein the counter-electrode is configured to be circular with a third radius, wherein the first electrically conductive coating is arranged maximally in a fourth radius about the midpoint, wherein the fourth radius is smaller than the third radius so that an edge region of the counter-electrode remains free from the first electrically conductive coating, wherein the polarizable film covers the edge region.
3 . An electret microphone according to claim 1 , further comprising: a printed circuit board which is arranged opposite to the second electrically conductive coating, wherein an electrically conductive connection is provided between the printed circuit board and the second electrically conductive coating.
4 . An electret microphone according to claim 1 , wherein a region around the second holes remains free of the first electrically conductive coating, wherein the polarizable film extends as far as an edge of the second holes so that the polarizable film covers the region.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority under 35 U.S.C. § 119(b) to German Patent Application No. 102022114073.3, filed Jun. 3, 2022, the entirety of which is herein incorporated by reference. FIELD OF DISCLOSURE The present invention relates to an electret microphone. BACKGROUND An electro-acoustic capacitor microphone comprises a movable, thin, electrically conducting membrane (first electrode) and a fixed second electrode (counter-electrode). The membrane can either be metallic or non-metallic and can be provided with an electrically conducting coating on one or both sides. The electrode and the counter-electrode are located at a short distance from one another with an interposed air gap. In an electret microphone an electret layer is located on the counter-electrode between the electrode and the counter-electrode in order to generate the necessary electric field between the electrode and the counter-electrode. DE 10 2018 108 720 B4 discloses an electret microphone. A conductive layer is provided on a substrate. Furthermore, a membrane is provided with a conductive layer. The circular substrate body can be made from a high-quality, shape-resistant plastic. The substrate body has a bore which is also metallized in order to electrically connect the front and rear coating to one another. Further bores can also be provided in order to provide an acoustic connection between the air volume under the membrane and a rear volume. SUMMARY OF THE INVENTION It is an object of the present invention to provide an electret microphone which is better protected against air humidity. This object is achieved by an electret microphone according to Claim 1. Thus, an electret microphone is provided which comprises an electrically conductive membrane and a counter-electrode having at least one first hole having a first distance from an edge of the counter-electrode and a second plurality of second holes each having a second distance from the edge of the counter-electrode, wherein the second distance is shorter 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 comprises a via in order to electrically contact the first and second electrically conductive coating. At least a third distance is provided in each case between the second holes and the first electrically conductive coating so 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 thereby leaves free the first and second holes, wherein the polarizable film extends as far as the second holes. Thus, the holes near the edges are not provided with a via. As a result of the region around the second holes remaining free of the first electrically conductive coating whereas the film extends as far as the second holes, the insulation towards the edge of the counter-electrode can be improved even when moisture is present. According to one aspect, the counter-electrode has a mid-point. The at least one first hole is arranged in a first radius around the mid-point. The plurality of second holes is arranged in a second radius about the mid-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 maximally in a fourth radius about the mid-point. The fourth radius is smaller than the third radius so that an edge region of the counter-electrode remains free from the first electrically conductive layer. The polarizable film covers the edge region. According to one aspect, the fourth radius is greater than the second radius so that the electrically conductive coating extends radially beyond second holes. Thus, the area of the conductive coating can be enlarged. According to one aspect, the microphone comprises a printed circuit board which is arranged opposite to the second electrically conductive coating. An electrically conductive connection is provided between the printed circuit board and the second electrically conductive coating. According to one aspect, a region around the second holes remains free from the first electrically conductive coating whereas the polarizable film extends as far as an edge of the second holes so that the polarizable film covers the region. According to one aspect, the first and second electrically conductive coating can be configured as an electrically conductive layer. According to one aspect, an electret microphone is provided with a membrane, 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