Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Microphone capsule only
Reexamination Certificate
2000-08-11
2003-07-15
Barnie, Rexford (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Microphone capsule only
C038S137000
Reexamination Certificate
active
06594369
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electret capacitor microphone.
2. Prior Art
Electret capacitor microphones are often provided with a thin diaphragm having a thin metal film facing toward an opening in a metal casing and a fixed electrode opposed thereto, and utilize the principal of a change in capacity between the diaphragm and the fixed electrode dependently on the vibration of the diaphragm due to a sound wave. The diaphragm utilizes a thin metallized electret material on a surface thereof, and a capacitor is formed between the diaphragm and the fixed electrode. A change in capacity is converted into a current or voltage change through a solid state device, the sound wave being fetched as an electric signal.
Conventional electret capacitor microphones have been provided in a cylindrical metal casing
5
which disposes a diaphragm
4
made of an electret material with a metal layer deposited or other method on the surface and has a sound hole
21
in the central part of an upper surface facing to the diaphragm
4
, as shown in FIG.
13
. In the casing, a fixed electrode
6
is fixed just behind the diaphragm
4
with a capacitance gap
32
through a thin gap ring spacer
61
between the fixed electrode
6
and the diaphragm
4
. Furthermore, a depressed dielectric
27
accommodating a solid state device
8
and a printed circuit board
29
are located in a lower part of the casing
5
, and the casing is crimped to a peripheral edge
52
on the back face of the printed circuit board
29
, using a crimping portion
52
of the opening of the metal casing
5
.
In the conventional example, an input lead
81
of the solid state circuit device
8
is connected to a fixed electrode
26
, and an output lead
82
penetrates through the special dielectric
27
and the printed circuit board
29
and is connected to a pad electrode
83
on a bottom face. On the other hand, the diaphragm
4
is conducted to the metal casing
5
through a film ring
41
.
Recently, electret capacitor microphones have been required to be light and small-sized. However, in the conventional microphone technique, a large number of parts have been required and the thickness the crimping portion and the pad electrode could not be reduced.
Moreover, in the conventional microphones, since the dielectric and the printed circuit board have been utilized, it has been impossible to satisfy the demand for a reduction in size and weight of the whole microphone.
Conventional electret capacitor microphones are not suitable for mass-production and have had a low productivity. The reason is because parts from the fixed electrode
6
to the printed circuit board
29
are previously assembled as an amplifier block and each part of the assembly is individually disposed in the metal casing
5
and is finally crimped with the crimped portion
52
.
In the conventional electret capacitor microphones, since the metal casing is crimped with a substrate, and then the uncertainty of fixation of each part causes microphone failure in use and reduces the yield of the microphone products.
Conventionally, soldering pad electrodes
83
, which are takeoff connection portions, have been attached neat a center of the circuit board
29
so that it has been hard to carry out mounting a solid circuit device
8
on the circuit board
29
by soldering the pad electrode
83
, and the conventional microphones have had a risk of short-circuiting the circuit board.
A main component of the microphone restricting a reduction in size has been a metal casing
5
. A solid circuit device
8
including a transistor or an integrated circuit which normally has a square shape is accommodated on the circuit board with useless space because a conventional metal casing is cylindrical. In addition, the cylindrical metal casing
5
is hard to handle for mounting and to position. Furthermore, even if a sound hole is to have a complicated shape, processing is hard.
The metal casing
5
is apt to transmit a surrounding mechanical vibration, has an adverse influence on the diaphragm and supplies a noise to an electric signal, resulting in a deterioration in microphone performance.
Since the output leads was provided through the printed circuit board, pad electrodes for soldering was required to bury holes through which the leads pass airtightly.
A diaphragm
24
is a membrane of fluoro-polymer membrane such as polyfluoroethylene, polypropylene (FEP), or polyester polymer such as Mylar (registered trademark), and has a thermal resistance limited. Therefore, it has been hard to solder the microphone onto the printed circuit board by heating.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a compact and thin electret capacitor microphone by reducing the number of parts constituting the capacitor microphone as much as possible.
Another object of the present invention is to provide an electret capacitor microphone capable of being assembled with mechanical fixation and electrical connection of parts carried out readily.
Another object of the present invention is to provide an electret capacitor microphone capable of being simply and reliably mounted in a small size onto another printed circuit board.
The elecret capacitor microphone of the present invention includes a casing formed of a dielectric and having a bottomed hollow portion which accommodates a combination of a diaphragm and a fixed electrode apart from each other at regular capacitance interval and a solid state device fox converting, into an electric signal, a change in an electrostatic capacity between a diaphragm and the fixed electrode, thereby forming an electret capacitor microphone.
Electret capacitor microphone will be hereinafter referred to as microphone, simply.
A dielectric casing can directly fix the parts in the hollow portion, eliminating the need for use of a printed circuit board for fixing a special insulator member and solid state circuit according to the conventional example, thereby decreasing the number of parts to be used.
Furthermore, an opening of the casing can be covered with a metal cover having a sound hole to penetrate sound from the outside of the casing to the interior of the hollow and fixed by bonding to the periphery of the opening. As a result, the microphone according to the present invention has a high mass-productivity.
Furthermore, in the microphone of the present invention, the casing may contain the solid state device in parallel to the combination of diaphragm and fixed electrode in its hollow. The combination and the solid state device are arranged laterally so that the whole thickness of the casing is further reduced to make the microphone much thinner.
In the present invention, preferably, the hollow portion of the casing may be divided into two partial hollow portions, in which case the combination of the fixed electrode and the diaphragm may be located in one of the hollow portions and the solid state device is placed in the other hollow portion.
Furthermore, it is preferable that the microphone according to the present invention should have cover for covering the opening of the hollow portion. The cover can also be shared by the fixed electrode, where the cover and the diaphragm are arranged facing to each other to constitute a capacitance gap.
In the present invention, one or more recesses for absorbing a sound preferably may be formed on the bottom of the hollow portion of casing, to eliminate an influence on the diaphragm of a reflected wave to be generated with deduced volume of the hollow portion. The recesses means a depessed portion which is at a lower level than a bottom level of the hollow portion accommodating the solid state device. The vibration of the diaphragm caused by the sound wave makes a wave to the back side toward the hollow bottom. The recess serves to increase a volume under the diaphragm the in the casing to form a release passage for the reflected wave which passage prevents the reflected wave of the diaphragm from interference with the diaphragm, and to comp
Barnie Rexford
Hogan & Hartson LLP
Kyocera Corporation
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