WO2007043729A1

WO2007043729A1 - Metal mesh phase delay device and condenser microphone including the same

Info

Publication number: WO2007043729A1
Application number: PCT/KR2006/000460
Authority: WO
Inventors: Changwon Kim; Jungmin Kim
Original assignee: Bse Co., Ltd.
Priority date: 2005-10-14
Filing date: 2006-02-08
Publication date: 2007-04-19
Also published as: KR100638512B1

Abstract

The present invention relates to a metal mesh phase delay device and a condenser microphone including the same having a small thickness and providing a uniform phase delay effect. The metal mesh phase delay device of the present invention comprises a metal mesh for delaying a phase of an acoustic wave coming in from a predetermined direction, wherein the metal mesh is plated. In addition, the condenser microphone including two or more acoustic holes for an inflow of an acoustic wave, tie microphone comprising a phase delay device for obtaining an unidirectional characteristic, by delaying a phase of the acoustic wave coming in through at least one of the two or more acoustic holes, wherein the phase delay device includes a plated metal mesh. In accordance with the metal mesh phase delay device 34 and the electret condenser microphone including the same of the present invention, a thin microphone may be manufactured and a uniform phase delay effect is provided during a mass production.

Description

METAL MESH PHASE DELAY DEVICE AND CONDENSER MICROPHONE INCLUDING THE SAME

Technical Field

[1] The present invention relates to a metal mesh phase delay device and a condenser microphone including the same, and more particularly, to a metal mesh phase delay device and a condenser microphone including the same having a small thickness and providing a uniform phase delay effect. Background Art

[2] Generally, condenser microphones are classified into an omni-directional microphone and a directional microphone. The directional microphone is divided into a bi-directional microphone and a uni-directional microphone.

[3] Particularly, the bi-directional microphone shows an '8' shaped polar pattern to an acoustic source since the bi-directional microphone reproduces an input sound from front and back and attenuates an input sound from sides. In addition, the bi-directional microphone provides an improved characteristic as the microphone is closer to an acoustic source. Therefore, the bi-directional microphone is used for extracting a sound from a specific acoustic source in a noise area such as a sports stadium.

[4] In addition, the uni-directional microphone provides an improved signal-to-noise ratio for a sound from front by maintaining a proper output for a wide front sound, and canceling an output for a sound from rear. Since the uni-directional microphone has an improved clarity, the uni-directional microphone is used for a voice recognition equipment such as a camcorder which requires a concentration on sounds from front and sides. The uni-directional microphone provides a wide output for a surrounding acoustic source including the microphone contrary to the omni-directional microphone responding sensitively to the sound from front.

[5] On the other hand, a latest microphone is manufactured using an electret which is capable of charging a charge semi-permanently contrary to a conventional microphone which requires an electric field by an external power supply. The electret condenser microphone comprises a pole plate housed in a casing, a diaphragm forming a static electric field with the pole plate, and a printed circuit board for amplifying and providing an electrical signal provided by the diaphragm and the pole plate as main components.

[6] The electret condenser microphone having the above-described configuration is used as the omni-directional microphone having an acoustic hole formed on one of the casing and the printed circuit board, or the bi-directional microphone having the acoustic hole formed on the casing and the printed circuit board. Particularly, when the acoustic holes may be formed in both the casing and the printed circuit board as in the bi-directional microphone, and an acoustic resistor (a phase delay filter) is included, the uni-directional microphone may be manufactured. The phase delay filter is used to remove the acoustic signal coming in from one direction. The phase delay filter cancels a sensitivity of the acoustic signal coming in from the one direction by adding or dividing the acoustic signals coming in through the acoustic holes of the casing and the printed circuit board.

[7] The conventional phase delay filter is manufactured using a resinoid material.

When the resinoid phase delay filter is used, a delay rate of the acoustic signal is adjusted by adjusting a power particle used for a manufacturing of the resin filter or a compression degree during the manufacturing of the resin filter.

[8] However, when a product having a small thickness is manufactured using the conventional resin filter, a pressing and sintering method is used. Therefore, it is difficult to adjust a phase delay characteristic or maintain uniformity. Moreover, since the resin filter has a low mechanical strength, the electret condenser microphone required a separate structure for fixing the resinoid phase delay filter in the electret condenser microphone. Therefore, the conventional electret condenser microphone is disadvantageous in that a height of the electret condenser microphone is increased by thicknesses of the resin filter and the fixture structure for the resin filter.

[9] In addition, when the resinoid phase delay filter is used, the resin filter which is an insulating material blocks one of conductive paths of the diaphragm and the back electret such that a separate conductive path should be formed. Moreover, a continuity of a manufacturing process is degraded due to a housing of the resin filter and the fixture structure and the formation of the separate conductive path, which complicates the manufacturing process and increases a manufacturing cost of the electret condenser microphone.

Disclosure of Invention Technical Problem

[10] It is an object of the present invention to provide a metal mesh phase delay device and a condenser microphone including the same having a small thickness and providing a uniform phase delay effect.

[11] It is another object of the present invention to provide a metal mesh phase delay device and a condenser microphone including the same wherein a metal mesh phase delay device plated via a wet-plating process to achieve a uniform phase delay characteristic and a low manufacturing cost.

[12] It is yet another object of the present invention to provide a metal mesh phase delay device and a condenser microphone including the same, wherein various types of metal meshes that are actually manufactured and specific types and standards of applicable metal mesh are provide so that a manufacturer or a developer may manufacture the device and the microphone effectively and inexpensively. Technical Solution

[13] In order to achieve the above-described object, there is provided a metal mesh phase delay device, the device comprising a metal mesh for delaying a phase of an acoustic wave coming in from a predetermined direction, wherein the metal mesh is plated.

[14] There is also provided a condenser microphone including two or more acoustic holes for an inflow of an acoustic wave, tie microphone comprising a phase delay device for obtaining an uni-directional characteristic, by delaying a phase of the acoustic wave coming in through at least one of the two or more acoustic holes, wherein the phase delay device includes a plated metal mesh.

[15]

Advantageous Effects

[16] In accordance with the metal mesh phase delay device and the condenser microphone including the same of the present invention, the thickness may be reduced and the uniform phase delay effect may be provided.

[17] The metal mesh phase delay device and the condenser microphone including the same in accordance with the present invention is manufactured using the stainless steel to provide a durability to various environment, and a uniform phase delay characteristic using a wet-plating method, and may be manufactured at a low manufacturing cost.

[18] In accordance with the metal mesh phase delay device and the condenser microphone including the same of the present invention, a type and a standard of a most reasonable applicable mesh of various metal meshes actually manufactured are presented so that the phase delay device is manufactured at a low cost and with efficiency.

[19] In accordance with the metal mesh phase delay device and the condenser microphone including the same of the present invention, the stainless steel is used contrary to the resinoid phase delay device to maintain the characteristic thereof at a reflow temperature over 270°and to be non-oxidizing, corrosion-resistant.

[20] Finally, in accordance with the metal mesh phase delay device and the condenser microphone including the same of the present invention, yield of a product within a desired characteristic is more than 90% while that the conventional copper-sintered products and resinoid products are 50 to 60%, thereby reducing the manufacturing to one tenth of the convention products. Brief Description of the Drawings

[21] Fig. 1 is a perspective view illustrating a phase delay device in accordance with a first embodiment of the present invention.

[22] Fig. 2 is a magnified view illustrating a portion of the device shown in Fig. 1.

[23] Fig. 3 is a cross-sectional view illustrating a plated metal mesh in accordance with the first embodiment of the present invention. [24] Figs. 4 through 7 are diagrams illustrating examples of the metal mesh in accordance with a first embodiment of the present invention. [25] Fig. 8 is a perspective view illustrating a phase delay device including a metal plate in accordance with a second embodiment of the present invention. [26] Fig. 9 is a diagram illustrating a metal plate having a diameter smaller than that of a metal mesh.

[27] Fig. 10 is a diagram illustrating a donut-type metal plate.

[28] Fig. 11 is a diagram illustrating a metal plate divided into multiple pieces.

[29] Fig. 12 is a diagram illustrating a circular metal plate or a ring-type metal plate having sequentially smaller diameters.

[30] Fig. 13 is a diagram illustrating a semi-circle type cap metal plate.

[31] Fig. 14 is a diagram illustrating a cylinder type cap metal plate.

[32] Fig. 15 is a perspective view illustrating a disassembled electret microphone including the metal mesh phase delay device in accordance with the present invention. [33] Fig. 16 is a cross-sectional view illustrating the condenser microphone of Fig. 15.

Best Mode for Carrying Out the Invention [34] Fig. 1 is a perspective view illustrating a phase delay device in accordance with a first embodiment of the present invention, and Fig. 2 is a magnified view illustrating a portion of the device shown in Fig. 1. [35] Referring to Figs. 1 and 2, the phase delay device 1 in accordance with the first embodiment of the present invention comprises a metal mesh 2 for delaying a phase of an acoustic wave coming in from a predetermined direction. [36] The acoustic wave coming in is delayed, attenuated or removed by the metal mesh

2 used as the phase delay device. Therefore, a stable and effective phase delay effect may be obtained as the mesh gets denser. [37] It is preferable that a stainless steel such as is 'SUS304' used for the metal mesh 2.

When the stainless steel is used as the metal mesh 2, the metal mesh 2 is not easily oxidized, and is robust to corrosion, and is not magnetized. Therefore, defects due to an environment or a manufacturing process may be reduced. That is, when SMT

(Surface Mount Technology) is used to mount the condenser microphone on a main board or to remove the condenser microphone from the main board, the metal mesh 2 is not oxidized even if a high temperature heat is applied during a reflow. Therefore, a normal use or a reuse is possible. When the phase delay device of the present invention is used in the electret condenser microphone, a distortion of the electric field due to a magnetic force since the metal mesh 2 is not magnetized. Therefore, a performance of the condenser microphone almost identical to that of the microphone wherein a phase delay device is not used may be obtained even when the phase delay device is used a signal interference due to a small current between a diaphragm and the electret is not generated.

[38] Fig. 3 is a cross-sectional view illustrating a plated metal mesh in accordance with the first embodiment of the present invention.

[39] As shown in Fig. 3, it is preferable that the metal mesh 2 is wet-plated using a metal having a high conductivity such as a nickel, a gold, a silver or a copper to maximize the phase delay effect. Particularly, it is preferable that the nickel which has a good plating characteristic and relatively inexpensive is used. In addition, it is preferable that the wet-plating is used instead of a dry -plating. While the metal is plat ed mainly on a surface of the metal mesh 2, i.e. an exposed portion of the metal mesh 2 when the dry-plating such as a sputtering is used, the metal is plated uniformly including a gap between the mesh when the wet-plating is used.

[40] As shown in Fig. 3, the metal mesh comprises a gap between meshes in vertical direction 3/horizontal direction 5, i.e. a pore 9. When the acoustic signal is transmitted to the pore, the phase delay effect is degraded. Therefore, a porous ratio is adjusted using the wet-plating to adjust a degree of the phase delay.

[41] In addition, the reason that nickel is preferable as a plating material is that the metal mesh 2 is manufactured using the stainless steel. Nickel is relatively inexpensive compared to other metals, and is easily plated on the metal mesh 2 consisting of the stainless steel.

[42] Figs. 4 through 7 are diagrams illustrating examples of the metal mesh in accordance with the first embodiment of the present invention also showing cross- section views. Fig. 4 illustrates a plain weave metal mesh 2 that may be used as the metal mesh of the present invention, Fig. 5 illustrates a twilled weave metal mesh, and Fig. 6 illustrates a dutch weave metal mesh 2. In addition, Fig. 7 illustrates a twilled dutch weave metal mesh 2.

[43] Referring to Figs. 4 through 7, mesh types that may be used as the metal mesh of the present invention includes the plain weave metal mesh, the twilled weave metal mesh, the dutch weave metal mesh, a plain dutch weave metal mesh, the twilled dutch weave metal mesh, a twisted metal mesh, a crimped metal mesh or any other kind of metal mesh that has a dense structure. [44] The plain weave metal mesh shown in Fig. 4 is manufactured such that a vertical line 11 and a horizontal line 13 cross each other orthogonally. The plain weave metal mesh may be a square type or a rectangular type according to a distance between the vertical lines 11 and the horizontal lines 13. A pore 15 is larger than other metal meshes as shown.

[45] Since the twilled weave metal mesh has a pore 18 smaller than that of the plain weave metal mesh shown in Fig. 4, the twilled weave metal mesh shown in Fig. 5 is manufactured to be denser than the plain weave metal mesh. The twilled weave metal mesh is manufactured by crossing two of vertical lines 16 and two of the horizontal line 17.

[46] The dutch weave metal mesh (or a plain dutch weave metal mesh) shown in Fig. 6 is manufactured by increasing a distance between the vertical lines 19 and crossing two the horizontal line 20 for a single vertical line 19. The dutch weave metal mesh is much denser and has small pore rate compared to the plain weave metal mesh.

[47] Fig. 7 illustrates a metal mesh having an improved structure to complement disadvantages of the metal meshes of Figs. 4 through 6, wherein the twilled dutch weave metal mesh is illustrated. Specifically, the plain weave metal mesh, the twilled weave metal mesh and the dutch weave metal mesh have relatively lower mesh density compared to twilled dutch weave metal mesh. This means that the plain weave metal mesh, the twilled weave metal mesh and the dutch weave metal mesh have a relatively larger pore compared to the twilled dutch weave metal mesh. The twilled dutch weave metal mesh is manufactured such that the vertical line 22 is attached at both sides of the horizontal line 21 wherein both the twilled weave and the dutch weave are applied. The twilled dutch weave metal mesh has a density two times higher than that of the twilled weave metal mesh.

[48] As described above, the plain weave metal mesh, the twilled weave metal mesh and the dutch weave metal mesh have a larger pore ratio than the twilled dutch weave metal mesh. Therefore, it is difficult to reduce the pore ratio by plating the plain weave metal mesh, the twilled weave metal mesh and the dutch weave metal mesh. For instance, while a desired pore ratio may be achieved by one or two plating processes in case of the twilled dutch weave metal mesh, multiple plating processes should be carried out to reduce a size of the pore or a complicated metal mesh should be used in case of the plain weave metal mesh, the twilled weave metal mesh and the dutch weave metal mesh. Therefore, it is preferable that the twilled dutch weave metal having the high density is used. However, the crimped weave metal mesh and the twisted weave metal mesh may also be used.

[49] Table 1 illustrates a relation the number of metal lines, i.e. the number of meshes per inch, a diameter of the metal line and the size of the pore of the twilled dutch weave metal.

[50] Table 1

[51] Referring to Table 1, the number of meshes per inch, the diameter of the metal line and the size of the pore are shown. [52] Particularly, when 165/800 mesh and 80/800 mesh are compared, a difference in the sizes of the pore ranges from 20 to 40 according to the number of the vertical line and the horizontal line. In addition, when 165/1600 mesh and 165/800 mesh are compared, the size of the pore is one half while the mesh of the horizontal line is two times.

[53] In addition, with respect to the diameter, while a metal line having a diameter of 0.113/0.07 mm is used in case of 80/800 mesh, a metal line having a relatively small diameter of 0.07/0.053mm is used for the 165/800 mesh. The diameter of the line is directly related to a thickness of the metal mesh. Therefore, when the diameter of the mesh is increased, a thickness of the phase delay device is also increased. In addition, the size of the pore is increased as the diameter of the line is increased.

[54] Therefore, considering the mesh of vertical and horizontal line, the diameter of the line and the size of the pore, it is preferable that the twilled dutch weave metal having the 165/800 mesh and the diameter of 0.07/0.053 is used to embody the phase delay device. However, a selection of the mesh may change according to a use. Therefore, it is preferable that the mesh having the small pore is selected. Mode for the Invention

[55] Fig. 8 is a perspective view illustrating a phase delay device including a metal plate in accordance with a second embodiment of the present invention.

[56] Referring to Fig. 8, the metal mesh described with reference to Figs. 1 through 7 provides more improved phase delay effect as the density of the mesh is increased. However, when a dense metal mesh is manufactured using a current manufacturing technology, a manufacturing cost is drastically increased. Therefore, it is difficult to produce select the dense metal mesh. More specifically, when only the above- described metal mesh is applied to obtain the phase delay effect, an amount of the acoustic signal passing through the metal mesh may be increased excessively. In order to complement this, a metal plate is employed in accordance with the second embodiment of the present invention to adjust the amount of delivered the acoustic signal, and compensate for deficient mechanical strength of the metal mesh.

[57] A metal mesh 45 of the present invention is manufactured as a plate type as shown in Fig. 8. In this case, a metal plate 46 is disposed on an upper or a lower portion of the metal mesh. The metal plate 46 prevents the excessive acoustic signal from reaching the metal mesh 45 or passing through the metal mesh 45 to be emitted. More specifically, the acoustic signal coming in from a direction of the metal plate 46 with respect to the metal mesh 45 passes the metal plate 46 first. A good amount of the acoustic signal is eliminated, attenuated by the metal plate 46 and a portion thereof reaches the metal mesh 45 through a hole 47 of the metal plate 46. The acoustic wave delivered from the metal plate 46 is again delayed or attenuated by the metal mesh 45 to be emitted. The metal plate 46 may comprises one or more holes 47 for delivering the acoustic signal (or acoustic pressure). The sound delivered from outside or the sound emitted by the metal mesh 45 is delivered through the hole 47. While a size and the number of holes varies according to the phase delay effect of the metal mesh 45, the hole is not required to be formed.

[58] Figs. 9 through 12 illustrate various examples of the metal plate. Fig. 9 is a diagram illustrating a metal plate having a diameter smaller than that of a metal mesh, and Fig. 10 is a diagram illustrating a donut-type metal plate. In addition, Fig. 11 is a diagram illustrating a metal plate divided into multiple pieces, and Fig. 12 is a diagram illustrating a circular metal plate or a ring-type metal plate having sequentially smaller diameters.

[59] A metal plate 49 shown in Fig. 9 may be manufactured to have a diameter 2 Dl smaller than that of a metal mesh 48. When the metal plate 49 having the smaller diameter than the metal mesh 48 is used, the acoustic signal passes through the circumference of the metal plate 49, i.e. an edge portion of the metal mesh 48. More specifically, most of the acoustic signal is blocked by the metal plate 49 to be lost and a portion of the acoustic signal passes through a gap due to a difference in diameters of the metal plate 49 and the metal mesh 48 to be adjusted. The metal plate 49 having the smaller diameter than the metal mesh 48 may comprise a plurality of holes to improve sound volume adjustment effect.

[60] Fig. 10 illustrates the donut-type metal plate 51. Since the donut-type metal plate

51 of Fig. 10 has an outer diameter almost identical to a metal mesh 50, it is preferable that the metal plate 51 is manufactured to form a single body with the metal mesh 50. In addition, in case that the metal plate 51 is manufactured to form the single body, the metal plate 51 maintains the metal mesh 50 when installed in a device using the metal mesh 50. The amount of the acoustic wave reaching the metal mesh 50 may be adjusted by adjusting the size of holes 52 formed at a center portion of the donut-type metal plate 51.

[61] Fig. 11 illustrates a metal plate 54 divided into multiple pieces, wherein the amount of the acoustic wave reaching the metal mesh may be adjusted by adjusting a gap formed between the pieces of the metal plate 54.

[62] Finally, Fig. 12 illustrates a circular metal plate or a ring-type metal plate 57 having sequentially smaller diameters. In case of the embodiment shown in Fig. 10, the amount of the acoustic wave reaching the metal mesh is adjusted by adjusting the size of the hole 52 formed at the center portion of the donut-type metal plate 51. However, a case wherein the amount of the acoustic wave reaching a metal mesh 56 should be reduced more when the metal plate 51 is used may occur. In this case, the amount of the acoustic wave may easily be controlled by inserting one or more rings having a smaller diameter to the hole 52 of Fig. 10. That is, a gap 58 formed between rings may be utilized or the size of the innermost hole may be adjusted to control the amount of the acoustic wave. In addition, this method is advantageous in that the ring-type metal plate 57 having a certain diameter may be used for the metal mesh 56 having a different diameter. Therefore, ready-made products may be used as is.

[63] Figs. 13 and 14 illustrate examples of a cap metal plate, wherein Fig. 13 illustrates a semi-circle type cap metal plate, and Fig. 14 illustrates a cylinder type cap metal plate.

[64] The semi-circle type cap metal plate 61 or the cylinder type cap metal plate 63 is attached to a first surface of metal meshes 60 and 62 to support the metal meshes 60 and 62. Particularly, as shown in Fig. 14, an hole for passing through the acoustic signal is formed at a lower portion of the cylinder, i.e. a corresponding surface of the metal mesh 62 to maintain a certain distance between the metal mesh 62 and the hole. An inner diameter of the semi-circle type cap metal plate 61 or the cylinder type cap metal plate 63 may be almost identical to those of the metal meshes 60 and 62 contrary to Figs. 13 and 14 such that the metal meshes 60 and 62 may be fixed inside the metal plates 61 and 63. It is preferable that the metal plates 61 and 63 are used when the distance between the metal plates 61 and 63 and the metal meshes 60 and 62 can be maintained as well as when a surface for forming the hole is widened and the metal meshes 60 and 62 is easily supported.

[65] Fig. 15 illustrates the electret microphone including the metal mesh phase delay device in accordance with the present invention, wherein a most widely used back type electret condenser microphone is shown. In addition, Fig. 16 illustrates a cross-section of the condenser microphone of Fig. 15.

[66] Referring to Figs. 15 and 16, the electret microphone including the metal mesh phase delay device in accordance with an embodiment of the present invention comprises a phase delay device 34 consisting of a metal mesh. In addition, the electret microphone including the metal mesh phase delay device 34 comprises a casing 30, a diaphragm 31, a spacer ring 32, a back electret plate 33, a first base ring 35, a second base ring 36 and a printed circuit board 37.

[67] The casing 30 houses the diaphragm 31, the spacer ring 32, the back electret plate

33, the phase delay device 34, the first base ring 35 and the second base ring 36 to protect the same from an external shock. The printed circuit board 37 may be housed in the casing 30 or may be attached outside the casing 30 according to a bonding method. In addition, the casing 30 blocks an external acoustic noise and electromagnetic noise, and electrically connects the diaphragm 31 and the printed circuit board 37. Therefore, the casing 30 is manufactured to have a polygon or a circular cylinder shape such as a container (vessel) having a one open end portion. In addition, a first acoustic hole 38 is formed at a closed end portion of the casing 30. the open end of the casing 30 is curled while the printed circuit board 37 is housed in the casing 30, or bonded to the printed circuit board 37 by resistance welding, laser welding or bonding. The casing 30 consists of highly conductive metals such as aluminum, copper or alloys thereof to block the noises. The casing 30 may be plated with gold or nickel to improve an electrical conductivity and prevent a corrosion.

[68] The diaphragm 31 forms a static electric field with the back electret plate 33, and varies an electric field of the static electric field by vibrating according to an acoustic pressure of the acoustic signal transmitted through acoustic holes 38 and 39. For this, the diaphragm 31 comprises a vibrating film 31b and a polar ring the polar ring 31a. Particularly, the vibrating film 31b is manufactured using a film such as a PET (Polyethylene Terephthalate) having a thickness of a few micrometers so that the vibrating film 31b vibrates according to a small acoustic pressure. The vibrating film 31b is coated with metals such as nickel, silver or gold using a sputtering in order to have a conductivity.

[69] On the other hand, the polar ring 31a fixes and supports the vibrating film 31b. The polar ring 31a secures a vibrating space and also provides a conductive path.

[70] The spacer ring 32 is disposed between the diaphragm 31 and the back electret plate 33, and maintains that the diaphragm 31 is parallel to the back electret plate 33 having a predetermined distance therebetween. In addition, the spacer ring 32 is manufactured using a material having a high insulation characteristic such as an acrylic resin so that the diaphragm 31 is electrically insulated from the back electret plate 33.

[71] The back electret plate 33 (or dielectric plate) forms the static electric field with the diaphragm 31, and converts the acoustic signal to an electrical signal. The back electret plate 33 comprises an electret high molecular film 33a and a back electret the back electret 33b. The electret high molecular film 33a is semi-permanently charged with a charge, and an electric field is formed by the charge. The electret high molecular film 33a may be formed by heating and pressing a high molecular film such as PTFE (Poly Tetra Fluoro Ehtylene), PFA (Perfluoroalkoxy) or FEP (Fluoroethylenepropylene) to the back electret 33b, and then injecting the charge using an electron injector. In addition, the back electret 33b is manufactured using metals such as copper, bronze, brass or phosphor bronze.

[72] The first base ring 35 (or a conductive base ring) provides a conductive path between the back electret plate 33 and the printed circuit board 37, fixes and supports components housed between the casing 30 and the first base ring 35, and forms a space between the back electret plate 33 and other components and the printed circuit board 37.

[73] The second base ring 36 (or an insulation base ring) is disposed between the back electret plate 33 and the casing 30 to insulate the back electret plate 33 form the casing 30 and fixes the diaphragm 31. The second base ring 36 is manufacture to have a cylindrical shape having a space therein. An outer surface of the cylinder is in contact with the casing 30, and the back electret plate 33, the phase delay device 34 and the first base ring 35 is housed therein. The second base ring 36 may be manufactured to have a height almost identical to that of the casing 30 such that the diaphragm 31 and the spacer ring 32 may be housed therein. The second base ring 36 is manufactured using a material having a high insulation characteristic and a high strength characteristic.

[74] The printed circuit board 37 amplifies and filters a change in the static electric field generated by the diaphragm 31 and the back electret plate 33. The change is then converted to an electrical signal and provided to outside. For this, the printed circuit board 37 comprises an amplifying device such as a field effect transistor, and a multilayer ceramic capacitor 40 consisting of one or more capacitors for filtering the noise. Since the amplifying device and the capacitor are vulnerable to external light, and a terminal is formed on the printed circuit board, the multilayer ceramic capacitor 40 is formed on the printed circuit board such that the multilayer ceramic capacitor 40 is disposed inside the space formed by the first base ring 35. In addition, a second acoustic hole 39 is formed in the printed circuit board 37.

[75] As described with reference to Figs. 1 through 7, the phase delay device 34 is manufactured using a metal mesh having a high mesh density per unit area. The phase delay device 34 is disposed in the electret condenser microphone and delays, attenuates or removes the phase of the acoustic signal coming in through the first acoustic hole 38 or the second acoustic hole 39 so that the electret condenser microphone is unidirectional. More specifically, the phase delay device 34 is disposed at a position close to one of the first acoustic hole 38 and the second acoustic hole 39 with respect to the diaphragm 31 and the back electret plate 33 so that the acoustic signals coming in through one of the first acoustic hole the first acoustic hole 38 and the second acoustic hole 39 is delayed and attenuated. For instance, when the phase delay device 34 is disposed between the back electret plate 33 and the second acoustic hole 39 as shown in Fig. 15, the acoustic signal coming through the first acoustic hole reaches the diaphragm 31 and the back electret plate 33 without any loss or attenuation. On the other hand, the acoustic signal coming in through the second acoustic hole 39 is attenuated and delayed by the phase delay device 34 to be transmitted to the diaphragm 31 and the back electret plate 33. Through this process, the electret condenser microphone having the phase delay device 34 has a uni-directional characteristic, the phase delay device 34 may be disposed at various positions such as between an inner surface of the printed circuit board 37 and the first base ring 35, outside of the printed circuit board 37 (a surface wherein the casing is not bonded), inside the polar ring 31a of the diaphragm, between the diaphragm 31 and the casing 30, and outside the casing 30. The position of the phase delay device 34 may differ according to a direction required for the phase delay when the electret condenser microphone is installed, a manufacturing method of the electret condenser microphone, and a structure of the electret condenser microphone. In addition, the metal plate described with reference to Fig. 14 may be used together with the phase delay device. While it is preferable that the metal plate is inserted between the phase delay device and one of the first acoustic hole and the second acoustic hole, the metal plate may be disposed at a position where the phase delay effect is expected, i.e. on an inner or an outer surface of the casing around the acoustic holes. The position of the metal plate may be freely selected considering a direction of the acoustic signal to be attenuated and a structure of the el ectret condenser microphone. The phase delay device 34 may be the phase delay device described with reference to Figs. 1 through 14 or the phase delay device including the metal plate. Therefore, a detailed description is hereby omitted.

[76] In addition, the phase delay device 34 may be applied to a front type and a foil type in addition to the back type, and also to a structure using an integrated base ring. A washer spring for maintaining an inter pressure between components may be used for the above-described electret condenser microphone other than the phase delay device 34. A detailed description for the washer spring is disclosed by a patent application filed by the applicant. Therefore the detailed description is hereby omitted. Industrial Applicability

[77] In accordance with the metal mesh phase delay device 34 and the electret condenser microphone including the same of the present invention, a thin microphone may be manufactured and a uniform phase delay effect is provided during a mass production.

[78]

[79]

[80]

Claims

[I] A metal mesh phase delay device, the device comprising a metal mesh for delaying a phase of an acoustic wave coming in from a predetermined direction, wherein the metal mesh is plated.

[2] The device in accordance with claim 1, wherein the metal mesh comprises a stainless steel.

[3] The device in accordance with claim 2, wherein the metal mesh is wet-plated.

[4] The device in accordance with one of claims 1 through 3, wherein the metal mesh is plated with one of a copper, a gold, a silver and a nickel. [5] The device in accordance with one of claims 1 through 3, wherein the metal mesh is weaved via one of a plane weave, a twilled weave, a plain dutch weave, a twilled dutch weave, a twist weave and a crimped weave. [6] The device in accordance with one of claims 1 through 3, wherein the metal mesh includes 165 or more horizontal metal lines per inch horizontally, and 800 or more vertical metal lines per inch. [7] The device in accordance with claim 6, wherein each of the vertical metal lines has a diameter of no more than 0.071mm, each of the horizontal metal lines has a diameter of no more than 0.053mm. [8] The device in accordance with one of claims 1 through 3, further comprising at least one metal plate disposed at a position where the sound wave is delivered to the metal mesh or a position where the sound wave is discharged. [9] The device in accordance with claim 8, wherein the metal plate comprises at least one hole. [10] The device in accordance with claim 8, wherein the metal plate has a shape of a cap.

[I I] A condenser microphone including two or more acoustic holes for an inflow of an acoustic wave, tie microphone comprising a phase delay device for obtaining an uni-directional characteristic, by delaying a phase of the acoustic wave coming in through at least one of the two or more acoustic holes, wherein the phase delay device includes a plated metal mesh.

[12] The microphone in accordance with claim 11, wherein the metal mesh comprises a stainless steel.

[13] The microphone in accordance with claim 12, wherein the metal mesh is wet- plated.

[14] The microphone in accordance with one of claims 11 through 13, wherein the metal mesh is plated with one of a copper, a gold, a silver and a nickel.

[15] The microphone in accordance with one of claims 11 through 13, wherein the metal mesh is weaved via one of a plane weave, a twilled weave, a plain dutch weave, a twilled dutch weave, a twist weave and a crimped weave. [16] The microphone in accordance with one of claims 11 through 13, wherein the metal mesh includes 165 or more horizontal metal lines per inch horizontally, and 800 or more vertical metal lines per inch. [17] The microphone in accordance with claim 16, wherein each of the vertical metal lines has a diameter of no more than 0.071mm, each of the horizontal metal lines has a diameter of no more than 0.053mm. [18] The microphone in accordance with one of claims 11 through 13, further comprising at least one metal plate disposed at a position where the sound wave is delivered to the metal mesh or a position where the sound wave is discharged. [19] The microphone in accordance with claim 18, wherein the metal plate comprises at least one hole. [20] The microphone in accordance with claim 18, wherein the metal plate has a shape of a cap.