JP2003018696A - Electret capacitor microphone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electret capacitor microphone which can also be used as an ultrasonic sensor by enlarging the characteristics up to a high frequency band while keeping the characteristics of low frequency band without increasing the size. SOLUTION: In an electret capacitor microphone where a diaphragm 25 and a back plate 27 form a capacitor and variation in the capacitance of the capacitor due to oscillation of the diaphragm 25 upon receiving a sound wave is taken out in the form of voltage variation and subjected to sound wave/ electric signal conversion, an irregular surface 42 having a large number of recesses 41 is employed on the side of the back plate 27 facing the diaphragm 25 and the diaphragm 25 is stretched on the irregular surface 42.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microphone for performing sound wave / electrical signal conversion, and more particularly, to a capacitor formed by a diaphragm and a back electrode plate, and the diaphragm vibrates when receiving a sound wave. The present invention relates to an electret condenser microphone that performs sound wave / electric signal conversion by extracting a change in capacitance as a voltage change.

[0002]

2. Description of the Related Art Electret condenser microphones of this type are widely used in portable telephone communication equipment, audio-visual equipment, etc. because they are small and have good sound quality.

FIG. 7 shows an example of a conventional general electret condenser microphone. In FIG. 7, reference numeral 1 denotes a case formed in a bottomed cylindrical shape, the bottom plate portion of which is a top plate, and the top plate 2 has a plurality of sound holes 3. Inside this case 1, from top to bottom,
The vibration plate 5 to which the spacer ring 4 is fixed, the spacer plate 6,
The back electrode plate 7, the insulating spacer cylinder 8 and the circuit board 9 are housed in an overlapping manner, the lower end edge 10 of the case 1 is bent inward, and the housed parts are assembled so as not to be extracted. An IC 11 for impedance conversion is provided on the upper surface of the circuit board 9.
Is attached and fixed.

The diaphragm 5 holds an electric charge and serves as an electret, and a capacitor is formed between the diaphragm 5 and the back electrode plate 7. As a result, when the diaphragm 5 receives a sound wave and vibrates, the inter-electrode distance (gap 12) of the capacitor is changed, the electrostatic capacitance of the capacitor is changed, and the capacitance change is changed as a voltage change. It is taken out and subjected to sound wave / electric signal conversion. The converted electric signal is impedance-converted by the IC 11, and then is guided to the outer surface of the circuit board 9 so that the terminals 11a,
It is taken out from 11a.

[0005]

As described above, such an electret condenser microphone is small and has good sound quality. Especially in the high range, the cut of the sound is good, but recently,
There has been a demand for expanding this characteristic to a higher frequency band. This is because if the characteristics can be extended to a high frequency band, the application can be expanded, such as using such an electret condenser microphone as an ultrasonic sensor. At that time, if the characteristics in the low frequency band can be maintained, the conventional use as an acoustic transducer will not be lost.

If such characteristics can be realized without enlarging the shape, the features of a small microphone are not impaired, and therefore, it has been conventionally desired to develop an electret condenser microphone satisfying the above points.

The present invention has been made in view of the above-mentioned demands, and it is possible to extend the characteristics to a higher frequency band while maintaining the characteristics of a low frequency band, and as a normal acoustic transducer. It is an object of the present invention to provide an electret condenser microphone that can be used as an ultrasonic sensor and can realize such characteristics without increasing the size of the shape.

[0008]

In order to achieve the above object, the invention as set forth in claim 1 forms a capacitor by a diaphragm and a back electrode plate opposed to the diaphragm, and In an electret condenser microphone that performs sound wave / electric signal conversion by extracting a change in the electrostatic capacity of the capacitor as a voltage change when the board receives a sound wave and vibrates, a surface of the back electrode plate facing the diaphragm. However, it is an uneven surface in which a large number of concave portions are formed, and the diaphragm is stretched on the uneven surface.

The invention described in claim 2 is characterized in that, in the invention described in claim 1, the uneven surface of the back electrode plate is formed in a curved surface projecting toward the diaphragm side.

According to a third aspect of the present invention, in the first aspect of the present invention, the diaphragm and the back electrode plate arranged to face the diaphragm form a capacitor, and the diaphragm receives a sound wave. In the electret condenser microphone that performs sound wave / electric signal conversion by taking out the change in the electrostatic capacitance of the condenser due to vibration as a voltage change, a sheet-like spacer having a predetermined pattern with a large number of through holes is formed. The vibrating plate and the back electrode plate are laminated with the sheet-like spacer interposed.

According to a fourth aspect of the invention, in the invention according to the third aspect, the areas of the plurality of through holes are set so that they have resonance points at a wide frequency.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a vertical sectional view showing an embodiment of the electret condenser microphone according to the present invention. In FIG. 1, reference numeral 21 is a case made of aluminum. The case 21 is formed into a cylindrical shape with a bottom by drawing or the like, the bottom plate portion thereof is a top plate, and the top plate 22 is provided with a plurality of sound holes 23.

Inside the case 21, from the top,
Vibration plate 25 with spacer ring 24 fixed, back electrode plate 2
7, the insulating spacer cylinder 28 and the circuit board 29 are stacked and housed, the lower end edge 30 of the case 21 is bent inward, and the housed parts are assembled so as not to be extracted.

That is, the vibrating plate 25 is accommodated below the top plate 22 of the case 21 at a predetermined interval. The vibrating plate 25 is, for example, a single-sided FEP Teflon (registered trademark), where aluminum or nickel is vapor-deposited on the upper surface in the figure, and semi-permanently holds an electric charge, and is an electret.

The vibrating plate 25 has an outer periphery fitted inside the case 21, and an upper surface thereof is fixed to a lower surface of a spacer ring 24 which is in contact with an inner surface of the top plate 22.
The spacer ring 24 maintains a distance from the top plate 22. The spacer ring 24 is made of brass here.

A back electrode plate 27 is accommodated below the vibrating plate 25. The back electrode plate 27 is fixed in a recess 28a formed inside the upper end of an insulating spacer cylinder 28 inserted in contact with the inner surface of the case 21, and is insulated from the case 21. There is. The insulating spacer tube 28 is
Here, it is a synthetic resin molded product.

The back electrode plate 27 has a surface (upper surface in the drawing) facing the vibrating plate 25 as an uneven surface 42 having a large number of recesses 41 as illustrated in FIG. Surface) 4
2 so that the diaphragm 25 is directly stretched on the concave portion 2
The bottom surface height position L of 8a is set.

The inside of the insulating spacer cylinder 28 is the back space of the back electrode plate 27, and there is a circuit board 29 therein.
An IC 31 for impedance conversion, which is fixed to the upper surface of, is accommodated. The insulating spacer cylinder 28 is also used for the back electrode plate 2.
7 also serves as a spacer between the circuit board 29 and the circuit board 29.

In the electret condenser microphone thus constructed, the diaphragm 25 and the back plate 2
7. More specifically, the bottom surface (recess bottom surface group) of the recesses 41 of the uneven surface 42 of the back electrode plate are opposed to each other through the gap 32 to form a capacitor. The gap 32 corresponds to the distance between the capacitors.

As a result, when the diaphragm 25 vibrates in response to the sound wave entering through the sound hole 23, the inter-electrode distance (gap 32) of the capacitor is changed, and the electrostatic capacity of the capacitor is changed. The change in capacitance is extracted as a change in voltage to perform sound wave / electric signal conversion. The converted electric signal is subjected to impedance conversion by the IC 31, and then taken out from the terminals 31a and 31a of the IC 31 led out to the outer surface side of the circuit board 29.

According to the experiments conducted by the inventors, the electret condenser microphone in which the concavo-convex surface 42 is formed on the surface of the back electrode plate 27 facing the diaphragm 25 can be used as, for example, an ultrasonic sensor. The characteristics could be expanded to a high frequency band (30 kHz or more). Moreover, while maintaining such high-frequency characteristics, while maintaining the characteristics of the low frequency band for use as a normal acoustic transducer,
In addition, it could be realized without enlarging the shape. Also,
According to the above-described embodiment, the spacer plate 6 according to the related art is used.
(See FIG. 7) is not necessary, and the number of parts and the number of steps for assembling parts into the case 21 can be reduced.

In the above embodiment, the surface of the back electrode plate 27 facing the diaphragm 25 is formed flat and the uneven surface 42 is formed on the flat opposite surface. However, the uneven surface 42 is formed on the curved facing surface.
May be formed. That is, as shown in FIG. 3, the surface of the back electrode plate 27 facing the diaphragm 25 (see FIG. 1; the same applies hereinafter) is formed into a curved surface projecting toward the diaphragm 25, and the curved surface The concavo-convex surface 42 may be formed on the opposing surface. According to this, by the simple work of pressing the back electrode plate uneven surface 42 against the diaphragm 25 side, the uneven surface 42 (back electrode plate 27
The vibrating plate 25 can be satisfactorily stretched on the surface facing the vibrating plate 25).

The same effect as that of the above-described electret condenser microphone can be obtained also by using the sheet-like spacer 51 shown in FIG. Hereinafter, the electret condenser microphone of the present invention using such a sheet spacer 51 will be described. Figure 4
(A) is a plan view of the sheet-like spacer 51, (b) is a vertical central cross-sectional view of the same (a), and as shown in the drawing,
The sheet-like spacer 51 has a circular outer shape, and a large number of through holes 52 are formed to form a predetermined pattern. Here, the copper foil having a thickness of about 0.03 to 0.09 mm is subjected to an etching treatment to form a sheet-like spacer 5 having a predetermined pattern.
I got 1.

Such a sheet spacer 51 is shown in FIG.
By arranging in place of the spacer plate 6 of the conventional electret condenser microphone shown in FIG. 1, the through hole 52 acts similarly to the recess 41 of the back electrode plate 27 in FIG.

That is, as shown in FIG. 5, the uneven surface 42 (see FIG. 1) is not formed on the back electrode plate 57,
The surface is flat like the prior art (back electrode plate 7 in FIG. 7). Then, the back electrode plate 57 and the vibration plate 25 are laminated and arranged with the sheet spacer 51 interposed therebetween. In FIG. 5, the same symbols as those in FIG. 1 indicate the same or corresponding parts. According to this, the diaphragm 25 and the sheet-like spacer 5
1 and the upper surface portion of the back electrode plate 57 facing each through hole 52 face each other through each through hole 52 to form a capacitor, and the electret having a different structure having the same operation and effect as the electret condenser microphone shown in FIG. A condenser microphone is obtained.

Even when such a sheet-like spacer 51 is used, as shown in FIG. 6, the surface (upper surface in the drawing) of the back electrode plate 57 facing the vibration plate 25 (see FIG. 1) is changed to the vibration plate. You may form in the curved surface shape which protrudes toward the 25 side. According to this, the upper surface of the back electrode plate 57 is attached to the sheet-like spacer 51.
Also, the sheet-like spacer 51 and the diaphragm 25 can be properly stretched on the back electrode plate 57 by a simple operation of pressing the diaphragm 25 side against the diaphragm 25 side.

The uneven surface 42 of the back electrode plate 27 shown in FIG.
Pattern of the concave portions 41 ... (Shape, opening area,
Setting pattern such as position. same as below. ) And the formation pattern of the through holes 52 ... Of the sheet-like spacer 51 shown in FIG. 4 are not limited to the examples shown in FIGS. That is,
In the example shown in FIGS. 1 and 4, a large number of honeycomb-shaped concave portions 41 and through holes 52 having different areas (opening areas) are provided to have resonance points in a wide range of high frequencies.
A large number of one to several kinds of honeycomb-shaped concave portions 41 and through holes 52 having different areas may be provided to have a resonance point in a high frequency range different from the above example.

[0028]

As described above, according to the present invention, in the electret condenser microphone, it is possible to extend the characteristics to a higher frequency band while maintaining the characteristics of the low frequency band, and to use a normal acoustic transducer. Can be added to the application as, for example, an ultrasonic sensor, and such characteristics can be achieved without increasing the shape.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of an electret condenser microphone according to the present invention.

2 is a top view showing an example of a recess forming pattern of the back electrode plate in FIG. 1. FIG.

3 is a vertical cross-sectional view showing an example in which the upper surface of the back electrode plate in FIG. 1 is formed in a curved shape.

FIG. 4 is a diagram showing an example of a sheet-like spacer used in place of the uneven surface of the back electrode plate in FIG.

5 is a longitudinal sectional view showing an embodiment of the electret condenser microphone of the present invention including the sheet-like spacer shown in FIG.

6 is a vertical cross-sectional view showing an example of a back electrode plate having a curved upper surface when the sheet-like spacer shown in FIG. 4 is used.

FIG. 7 is a vertical sectional view of a conventional electret condenser microphone.

[Explanation of symbols]

25 diaphragm 27 back plate 41 recess 42 uneven surface

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ryuichi Uchida             1-12-17 Kamirenjaku, Mitaka City, Tokyo             Den Co., Ltd. F-term (reference) 5D021 CC03

Claims (4)

[Claims] 1. A capacitor is formed by a diaphragm and a back electrode plate disposed opposite to the diaphragm, and a change in the electrostatic capacitance of the capacitor caused by the diaphragm vibrating in response to a sound wave changes a voltage. In the electret condenser microphone that performs sound wave / electric signal conversion, the surface of the back electrode plate facing the diaphragm is an uneven surface in which a large number of concave portions are formed, and the vibration is formed on the uneven surface. An electret condenser microphone with a stretched board. 2. The electret condenser microphone according to claim 1, wherein the uneven surface of the back electrode plate is formed into a curved surface projecting toward the diaphragm side. 3. A vibrating plate and a back electrode plate arranged opposite to the vibrating plate form a capacitor, and a change in the capacitance of the capacitor due to the vibration of the vibrating plate upon receiving a sound wave is changed by a voltage. In the electret condenser microphone for performing sound wave / electric signal conversion, a sheet-like spacer having a large number of through holes and forming a predetermined pattern is provided, and the diaphragm and the back electrode are interposed with the sheet-like spacer interposed. An electret condenser microphone in which plates are stacked. 4. The electret condenser microphone according to claim 3, wherein each of the plurality of through holes has its area set so as to have a resonance point at a wide frequency.