WO2018148871A1

WO2018148871A1 - Air particle filter used in microphone

Info

Publication number: WO2018148871A1
Application number: PCT/CN2017/073548
Authority: WO
Inventors: Alan Dean Michel; Guangyue LV
Original assignee: Harman International Industries, Incorporated
Priority date: 2017-02-15
Filing date: 2017-02-15
Publication date: 2018-08-23

Abstract

An air particle filter used in a microphone (20) and a microphone (20) are provided. The air particle filter includes: a conductive mesh (210); and a charged insulating electret film (211) coated on a surface of the conductive mesh (210). The microphone (20) includes: a main body of the microphone (20); and an air particle filter attached with the main body over a port (206) of the microphone (20), wherein the air particle filter includes a conductive mesh (210) and a charged insulating electret film (211) coated on a surface of the conductive mesh (210), and wherein the charged insulating electret film (211) is attached with the port (206) of the microphone (20). With the air particle filter, protection against particle contamination is provided to the microphone (20), and reliability of the microphone (20) may be improved.

Description

AIR PARTICLE FILTER USED IN MICROPHONE

FIELD

The present disclosure generally relates to a filter used in a microphone, and a microphone.

BACKGROUND

Common mesh filters used in MEMS microphone applications depend on a fact that Brownian motion and other air movements cause particles to have a random motion and path in order to touch fibers in the meshes used in the filters when the particles are going through, through Van der Wahl’s forces, the meshes entrap some of the particles that touch these fibers. However, there are still some probability of particles getting through without touching the meshes, especially during heating and cooling when the internal air in the microphone expands and contracts, which may reduce the reliability of the microphones.

SUMMARY

In an embodiment, an air particle filter used in a microphone is provided, including: a conductive mesh； and a charged insulating electret film coated on a surface of the conductive mesh.

In some embodiments, the conductive mesh may include conductive metal wires, such as stainless steel wires.

In some embodiments, a dimension of the conductive metal wires may be within a range from 20microns to 100microns.

In some embodiments, a dimension of pores defined by the conductive metal wires may be within a range from 20microns to 60microns.

In some embodiments, the conductive mesh may include conductive polymer plastic. In some embodiments, the conductive mesh may include conductive polymer plastic fiber strands. In some embodiments, the conductive mesh may be a sheet of conductive polymer with appropriately sized pores.

In some embodiments, the charged insulating electret film may be pre-charged with negative charges.

In some embodiments, the charged insulating electret film may be made of a Polytetrafluoroethylene (PTFE) material.

In some embodiments, a thickness of the charged insulating electret film may be within a range from 5microns to 20microns.

In an embodiment, a microphone is provided, including: a main body of the microphone； and an air particle filter attached with the main body over a port of the microphone, wherein the air particle filter includes a conductive mesh and a charged insulating electret film coated on a surface of the conductive mesh, and wherein the charged insulating electret film is attached with the port of the microphone.

In some embodiments, the microphone may include a port hole having a dimension within a range from 0.25mm to1mm.

In some embodiments, the conductive mesh in the microphone may include conductive metal wires, such as stainless steel wires.

In some embodiments, a dimension of the conductive metal wires of the conductive mesh in the microphone may be within a range from 20microns to 100microns.

In some embodiments, a dimension of pores defined by the conductive metal wires of the conductive mesh in the microphone may be within a range from 20microns to 60microns.

In some embodiments, the conductive mesh in the microphone may include conductive polymer plastic. In some embodiments, the conductive mesh may include conductive polymer plastic fiber strands. In some embodiments, the conductive mesh may be a sheet of conductive polymer with appropriately sized pores.

In some embodiments, the charged insulating electret film in the microphone may be pre-charged with negative charges.

In some embodiments, the charged insulating electret film in the microphone may be made of a PTFE material.

In some embodiments, a thickness of the charged insulating electret film in the microphone may be within a range from 5microns to 20microns.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other features of the present disclosure will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. Understanding that these drawings depict only several embodiments in accordance with the disclosure and are, therefore, not to be considered limiting of its scope, the disclosure will be described with additional specificity and detail through use of the accompanying drawings.

FIG. 1 is a sectional view of an air particle filter used in a microphone according to an embodiment；

FIG. 2 is a top view of a conductive mesh which is included in the air particle filter in FIG. 1 according to an embodiment；

FIG. 3 is a schematic diagram of an electric field created above a conductive mesh and distribution of charges and attracted particles according to an embodiment； and

FIG. 4 is a sectional view of a microphone according to an embodiment.

DETAILED DESCRIPTIONOF EMBODIMENTS

In the following detailed description, reference is made to the accompanying drawings, which form a part hereof. In the drawings, similar symbols typically identify similar components, unless context dictates otherwise. The illustrative embodiments described in the detailed description, drawings, and claims are not meant to be limiting. Other embodiments may be utilized, and other changes may be made, without departing from the spirit or scope of the subject matter presented here. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the Figures, can be arranged, substituted, combined, and designed in a wide variety of different configurations, all of which are explicitly contemplated and make part of this disclosure.

FIG. 1 is a sectional view of an air particle filter used in a microphone according to an embodiment. Referring to FIG. 1, the air particle filter includes a conductive mesh 101 and a charged insulating electret film 103 coated on a surface of the conductive mesh 101.

FIG. 2 is a top view of the conductive mesh 101 according to an embodiment. Referring to FIGS. 1 and 2, in some embodiments, the conductive mesh 101 may include conductive metal wires, for example, stainless steel wires.

Referring to FIG. 1, in some embodiments, a cross-section of the conductive metal wires may be circular or square. In some embodiments, a dimension D1 of each conductive metal wire (i.e., black portions in FIG. 2) may be within a range from 20microns to 100microns. The dimension D1 may be a diameter or otherwise a width of each of the conductive metal wires.

In some embodiments, a dimension D2 of each pore (white portions in FIG. 2) defined at least by the conductive metal wires cannot be too small or too large. For example, to define the pores, the conductive metal wire may be arranged in a grid-like manner. In one example of the grid-like manner, the pores may be equally dimensioned. Further, as an example in FIG. 2, the dimension D2 may be a width for each pore. In some embodiments, the conductive metal wires may be coated with a charged insulating electret film 103. In such embodiments, the pores may be defined by the conductive metal wires and the charged insulating electret film 103 thereupon the conductive metal wires.

When the air particle filter is applied in a microphone, if the dimension D2 of the pores is too small, acoustic performance may be affected due to acoustic resistance. If the dimension D2 of the pores is too large, the conductive mesh 101 may be too coarse to be effective in filtering particles in the air. In some embodiments, the dimension D2 of the pores defined by the conductive metal wires may be within a range from 20microns to 60microns.

In some embodiments, the conductive mesh 101 may include conductive polymer plastic. In some embodiments, the conductive mesh may include conductive polymer plastic fiber strands. In some embodiments, the conductive mesh may be a sheet of conductive polymer with appropriately sized pores. For example, the conductive mesh 101 may be a sheet of Polyphenylene sulfide (PPS) . In some embodiments, the conductive mesh 101 may include Poly (flourene) s, Polyphenylenes, Polypyrenes, Polyazulenes, Polynaphthalene, Poly (pyrrole) s (PPY) , Polycarbozole, Polyindoles, Polyazepine, Polyaniline (PANI) , Polythiophene (PT) , Poly (3, 4-ethylenedioxythiophene) PEDOT, Poly (acetylene) s PAC or Poly (p-phenylene vinylene) PPV.

Similarly to the conductive metal wires, the conductive polymer plastic may be arranged in a grid-like manner to define the pores. And similarly to the conductive metal wires, the conductive polymer plastic may be coated with the charged insulating electret film 103. A dimension of the conductive polymer plastic may be within a range from 20microns to 100microns. A dimension of pores defined by the conductive polymer plastic may be within a range from 20microns to 60microns.

In some embodiments, the charged insulating electret film 103 may be coated on a surface of each fiber strand of the conductive mesh 101. The surface may be a portion of each strand. As an example, in FIG. 1, the portion may be a first outer region, as opposed to the entire surface, of each strand. Therefore, in the example, a second outer region of each strand may be left uncoated. In relation to the conductive mesh 101, the first outer region may be referred to as an upper or top surface, and the second outer region may be referred to as a lower or bottom surface. The first outer region and the second outer region may include the entire surface of each strand. In some embodiments, the charged insulating electret film 103 may be made of a PTFE material which possesses good insulating capacity and is an excellent electret. In some embodiments, a thickness of the charged insulating electret film 103 may be within a range from 5microns to 20microns.

In some embodiments, the charged insulating electret film 103 may be pre-charged with charges by a charging process, such as a corona charging process. In some embodiments, the charged insulating electret film 103 may be pre-charged with negative charges.

Based on the above structure of the air particle filter, an electric field is created above and within the conductive mesh 101. FIG. 3 is a schematic diagram of the electric field created above the conductive mesh 101 and distribution of charges and attracted particles according to an embodiment. In FIG. 3, only one fiber strand 1011 of the conductive mesh 101 is illustrated for example.

In some embodiments, the charged insulating electret film 103 is pre-charged with negative charges, and accordingly, negative charges are located on the top of the conductive mesh 101. The created electric field is relatively strong to ionize and attract nearby air particles. As opposite charges attract, positive particles above the conductive mesh 101 may be attracted to the charged insulating electret film 103, i.e., the top of the conductive mesh 101. Specifically, the positive particles are accelerated by the electric field in the direction of the field lines around the conductive mesh 101 until they hit a surface of the charged insulating electret film 103 and then are held on the surface of the charged insulating electret film 103 through electrostatic and Van der Wahl’s forces.

Besides, due to the negative charges located on the top of the conductive mesh 101, induced positive charges are generated at a location of the top surface of the conductive mesh 101 near edges of the charged insulating electret film 103. As a result, negatively charged particles above the conductive mesh 101 may be attracted thereto.

The negative particles in the charged insulating electret film 103 are balanced by an equal number of positive induced charges at the surface of the conductive mesh 101. As the electric field is created above the conductive mesh 101, there is no charge on the lower surface of the conductive mesh 101, and the lower surface of the conductive mesh 101 has a net charge of zero. Therefore, no particles below the conductive mesh 101 are attracted to the conductive mesh 101.

From above, based on the air particle filter, particles above the conductive mesh 101 are attracted to the conductive mesh 101, and particles below the conductive mesh 101 are not attracted to the conductive mesh 101 and thus do not go through the conductive mesh 101.

When the air particle filter is applied in a microphone, the top surface of the conductive mesh 101 faces a main body of the microphone, and the lower surface of the conductive mesh 101 faces outside, so as to attract particles that are already inside the main body of the microphone to the conductive mesh 101 and not attract particles outside. Therefore, the particles outside are prevented from going through the conductive mesh 101 to damage inner mechanical structures inside the microphone.

FIG. 4 is a sectional view of a Micro-Electro-Mechanical System (MEMS) microphone according to an embodiment. Referring to FIG. 4, a main body of the MEMSmicrophone 20 includes a diaphragm 201, a back plate 202, a silicon die 203, an MEMS substrate 204, a solder 205, a Printed Wire Board (PWB) port 206, a cavity 207 defined by the silicon die 203, a first hole 208 in the MEMS substrate 204 and a second hole 209 in the PWB port 206. The microphone 20 further includes an air particle filter for preventing the main body from being damaged by particles. The air particle filter may include a conductive mesh 210 and a charged insulating electret film 211 coated on a surface of the conductive mesh 210. In some embodiments, the air particle filter may be attached to the main body of the microphone with a high strength adhesive. Referring to FIG. 4, the charged insulating electret film 211 is attached with the PWB port 206 by an adhesive layer 212.

In some embodiments, the conductive mesh 210 may be made of conductive metal wires, for example, stainless steel wires, or conductive polymer plastic, for example, PPS.

In some embodiments, the first hole 208 in the MEMS substrate 204 may have a dimension, such as a diameter, within a range from 0.25mm to about 1mm, and the second hole 209 in the PWB port 206 may have a dimension, such as a diameter, within a range from 0.2mm to about 1mm. In some embodiments, a dimension D1 of the conductive mesh 210 may be much smaller than the dimensions of the first hole 208 and the second hole 209, for example, within a range from 20microns to 100microns. For example, when the conductive mesh 210 includes conductive metal wires, the dimension D1 of the conductive metal wires may be within the range from 20microns to 100microns. As another example, when the conductive mesh 210 includes conductive polymer plastic, the dimension D1 of the conductive polymer plastic may be within the range from 20microns to 100microns.

In some embodiments, a dimension D2 of pores defined by the conductive mesh 210 cannot be too small or too large. If the dimension D2 of the pores is too small, acoustic performance may be affected due to acoustic resistance. If the dimension D2 of the pores is too large, the conductive mesh 210 may be too coarse to be effective in filtering particles in the air. In some embodiments, the dimension D2 of the pores defined by the conductive mesh 210 may be within a range from 20microns to 60microns.

In some embodiments, the charged insulating electret film 211 may be coated on a surface of each fiber strand of the conductive mesh 210. The surface may be a portion of each strand. As an example, in FIG. 4, the portion may be a first outer region, as opposed to the entire surface, of each strand. Therefore, in the example, a second outer region of each strand may be left uncoated. In relation to the conductive mesh 210, the first outer region may be referred to as an upper or top surface, and the second outer region may be referred to as a lower or bottom surface. The first outer region and the second outer region may include the entire surface of each strand. In some embodiments, the charged insulating electret film 211 may be made of a PTFE material which possesses good insulating capacity. In some embodiments, a thickness of the charged insulating electret film 211 may be within a range from 5microns to 20microns.

In some embodiments, the charged insulating electret film 211 may be pre-charged with charges by a charging process, such as a corona charging process. In some embodiments, the charged insulating electret film 211 may be pre-charged with negative charges.

With the above structure, an electric field is created above and within the conductive mesh 210. In some embodiments, if the charged insulating electret film 211 is pre-charged with negative charges, negative charges may be located on the top of the conductive mesh 210. As opposite charges attract, positive particles above the conductive mesh 210 may be attracted to the charged insulating electret film 211, i.e. , the top of the conductive mesh 210. Specifically, the positive particles are accelerated by the electric field in the direction of the field lines around the conductive mesh 210 until they hit a surface of the charged insulating electret film 211 and then are held on the surface of the charged insulating electret film 211.

Besides, due to the negative charges located on the top of the conductive mesh 210, induced positive charges are generated at a location of the top surface of the conductive mesh 210 near edges of the charged insulating electret film 211. As a result, negatively charged particles above and within the conductive mesh 210 may be attracted thereto.

The negative particles in the charged insulating electret film 211 are balanced by an equal number of positive induced charges at the surface of the conductive mesh 210. As the electric field is created above the conductive mesh 210, there is no charge on the lower surface of the conductive mesh 210, and the lower surface of the conductive mesh 210 has a net charge of zero. Therefore, no particles below the conductive mesh 210 are attracted to the conductive mesh 210, that is, no particles outside the microphone 20 are attracted to the conductive mesh 210.

From above, based on the air particle filter, particles inside the microphone are attracted to the conductive mesh, and particles outside the microphone are not attracted to the conductive mesh. In this way, protection against particle contamination is provided to the microphone.

Even if the microphone is disposed in an environment where temperature or pressure changes or in an environment exposed to smoke or larger concentrations of dust particles, where some particles go through the conductive mesh into the main body of the microphone, the air particle filter consisting of the conductive mesh and the charged insulating electret film can attract the particles inside the mesh or inside the microphone to prevent the particles from damaging mechanical structures of the microphone. Besides, the air particle filter will not attract particles from the outside into the microphone. That is to say, only the particles which are already located inside the microphone or go through the conductive mesh due to the environment are attracted by the conductive mesh.

In this way, reliability of the microphone may be improved, and further Mean Time Between Failure (MTBF) of the microphone may be increased to a relatively high level.

While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims.

Claims

An air particle filter used in a microphone, comprising:

a conductive mesh； and

a charged insulating electret film coated on a surface of the conductive mesh.
The air particle filter according to claim 1, wherein the conductive mesh comprises conductive metal wires.
The air particle filter according to claim 2, wherein a dimension of the conductive metal wires is within a range from 20microns to 100microns.
The air particle filter according to claim 1, wherein the conductive mesh defines pores.
The air particle filter according to claim 4, wherein the pores comprise a dimension that is within a range from 20microns to 60microns.
The air particle filter according to claim 1, wherein the conductive mesh comprises conductive polymer plastic.
The air particle filter according to claim 1, wherein the charged insulating electret film is pre-charged with negative charges.
The air particle filter according to claim 1, wherein the charged insulating electret film is made of a Polytetrafluoroethylene (PTFE) material.
The air particle filter according to claim 1, wherein a thickness of the charged insulating electret film is within a range from 5microns to 20microns.
A microphone, comprising:

a main body of the microphone； and

an air particle filter attached with the main body over a port of the microphone,

wherein the air particle filter comprises a conductive mesh and a charged insulating electret film coated on a surface of the conductive mesh, and

wherein the charged insulating electret film is attached with the port of the microphone.
The microphone according to claim 10, wherein the microphone comprises a port hole having a dimension within a range from 0.25mm to 1mm.
The microphone according to claim 10, wherein the conductive mesh comprises conductive metal wires.
The microphone according to claim 12, wherein a dimension of the conductive metal wires is within a range from 20microns to 100microns.
The microphone according to claim 10, wherein the conductive mesh defines pores.
The microphone according to claim 14, wherein the pores comprise a dimension that is within a range from 20microns to 60microns.
The microphone according to claim 10, wherein the conductive mesh comprises conductive polymer plastic.
The microphone according to claim 10, wherein the charged insulating electret film is pre-charged with negative charges.
The microphone according to claim 10, wherein the charged insulating electret film is made of a Polytetrafluoroethylene (PTFE) material.
The microphone according to claim 10, wherein a thickness of the charged insulating electret film is within a range from 5microns to 20microns.
The microphone according to claim 12, wherein the conductive metal wires are made of stainless steel.