JP2008147863A - Microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microphone which specifies a direction of a sound source precisely by one diaphragm. <P>SOLUTION: The microphone 100 is supported by a housing 12 at a center part, and prepares the diaphragm 16 in which an environment of the center part is displaceable in a thickness direction. First electrode pair groups 21, 23 are arranged in a front side of the diaphragm 16. Second electrode pair groups 31, 33 and third electrode pair groups 41, 43 are arranged in a rear side of the diaphragm 16. Respective electrode pairs form capacitors. A controller impresses bias voltage to the first electrode pair groups so that electrostatic capacitance held by the second and the third electrode pair groups are nearly same before receiving a sound wave. By the method, displacement of the diaphragm before receiving the sound wave is corrected in a flat status. The sound wave is received in the status. A direction of the sound source is specified by a phase difference of the electrostatic capacitance variance of the second electrode pair groups when receiving the sound wave. Since it is possible to specify the direction of the sound wave after the diaphragm is corrected in the flat status, the direction of the sound source can be specified precisely. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a microphone that identifies a direction in which sound waves propagate. A microphone that can specify the direction in which a sound wave propagates can also be used as a microphone having directivity for detecting only sound propagating from a specific direction. The present invention relates to a microphone having directivity.

Microphones that identify the direction in which sound waves propagate have been developed. If the direction in which the sound wave propagates can be specified, only the sound wave propagating from the specific direction can be received, and a microphone having directivity can be realized. The technology of Non-Patent Document 1 is known for a microphone that identifies the direction in which sound waves propagate.
In this specification, a microphone means a concept including not only a device that receives sound waves and converts them into electrical signals, but also a device that identifies the direction in which the sound waves propagate.

Nobutaka ONO, Akihito SAITO, Shigeru ANDO, "Design and Experiments of Bio-mimicry Sound Source Localization Sensor with Gimbal-Supported Circular Diaphragm", Proceeding of The 12th International Conference on Solid-State Sensors, Actuators and Microsystems, Boston June 8-12 , 2003, pp. 939-942

In the microphone of Non-Patent Document 1, four electrodes are attached to the back surface (the surface opposite to the surface receiving sound waves) of the diaphragm whose central portion is supported by the housing. The four electrodes surround the central portion of the diaphragm and are arranged at substantially equal intervals along the circumferential direction. Opposing the four electrodes, four other electrodes are fixed to the housing. A gap having a predetermined length is provided between each electrode attached to the back surface of the diaphragm and each electrode fixed to the housing so as to face the electrode. A voltage is supplied between each electrode on the diaphragm and each electrode on the housing side facing the electrode. A capacitor is formed by each electrode on the diaphragm and each electrode on the housing side facing the electrode. When the diaphragm vibrates, the gap length between the electrode on the diaphragm and the electrode on the housing side facing the electrode changes. The capacitance of the capacitor changes according to the change in the gap length.
When a sound wave is received from a certain direction, the diaphragm vibrates. Since the center part of the diaphragm is supported, the periphery of the supported center part vibrates. The vibration generated around the central portion of the diaphragm is not uniform, and a region with a large amplitude and a region with a small amplitude are distributed. The distribution depends on the propagation direction of the sound wave. The distribution change over time, that is, the phase also depends on the propagation direction of the sound wave. Therefore, the distribution (including phase) of the change in gap length between each electrode on the diaphragm and each electrode on the housing opposite to the electrode changes depending on the direction in which the sound wave propagates. That is, the distribution of the fluctuation amount of the capacitance of each capacitor also changes depending on the propagation direction of the sound wave. Therefore, the direction in which the sound wave propagates can be specified from the distribution of the variation amount of the capacitance of each capacitor. Hereinafter, the direction in which the sound wave propagates is referred to as the direction of the sound source.
According to the technique of Non-Patent Document 1, the direction of the sound source can be specified with one diaphragm. The microphone that can specify the direction of the sound source can be miniaturized.

In a microphone that specifies the direction of a sound source with a single diaphragm, the diaphragm is preferably as flat as possible. This is because a flat diaphragm is easy to vibrate. Also, if the diaphragm is flat, the correspondence between the direction of the sound source and the distribution of the variation in gap length becomes more precise. However, the diaphragm supported at the center part is likely to be deformed due to a change with time. That is, the diaphragm remains deformed even when no sound wave is received. Further, due to manufacturing tolerances and errors, the diaphragm of each microphone has an initial deformation although it is within a predetermined range. The initial deformation of the diaphragm reduces the accuracy in specifying the sound source direction. Non-Patent Document 1 does not consider deformation of the diaphragm in a state where no sound wave is received.
The present invention has been made in view of the above problems, and its purpose is a microphone that can specify the direction of a sound source with a single diaphragm, and corrects the diaphragm to a flat state before receiving sound waves. An object of the present invention is to provide a microphone that can accurately specify the direction of a sound source.

  The microphone according to the present invention includes a diaphragm, a first electrode pair group, a second electrode pair group, a third electrode pair group, and a controller. The center part of the diaphragm is supported by the housing, and the periphery of the center part can be displaced in the thickness direction. One electrode group of the first electrode pair group is fixed to one surface of the diaphragm at a plurality of positions surrounding the central portion of the diaphragm, and the other electrode group is connected to the corresponding electrode via a gap. It is fixed to the housing at a position facing each other. One electrode group of the second electrode pair group is fixed to the other surface of the diaphragm at a plurality of positions surrounding the central portion of the diaphragm, and the other electrode group is connected to the corresponding electrode via a gap. It is fixed to the housing at a position facing each other. One electrode group of the third electrode pair group is a plurality of positions surrounding the central portion of the diaphragm, and the other of the diaphragms at a position radially inward of the diaphragm from one electrode group of the second electrode pair group The other electrode group is fixed to the housing at a position facing the corresponding electrode via a gap. The controller applies a voltage to each electrode pair of the first electrode pair group, the second electrode pair group, and the third electrode pair group, and the static electrode held by each of the second electrode pair group and the third electrode pair group. Measure the capacitance. Further, the controller is configured so that the capacitance held by each electrode pair of the second electrode pair group and the third electrode pair group satisfies a predetermined relationship when the diaphragm is not receiving sound waves. The bias voltage applied to each electrode pair is adjusted. The controller applies at least one electrode of the second electrode pair group and the third electrode pair group when the diaphragm receives sound waves in a state where the adjusted bias voltage is applied to each electrode pair of the first electrode pair group. The direction in which the sound wave propagates is specified from the change in the capacitance held by each pair of electrodes.

  Each electrode pair of the first to third electrode pair groups forms a capacitor. A capacitor group formed by each electrode pair of the first electrode pair group is referred to as a first capacitor group. A capacitor group formed by each electrode pair of the second electrode pair group is referred to as a second capacitor group. A capacitor group formed by each electrode pair of the third electrode pair group is referred to as a third capacitor group.

When a voltage is applied, the capacitor generates a Coulomb force (electrostatic attractive force) in a direction that narrows the gap. In the present invention, by using this Coulomb force, the first capacitor group is used as an actuator for correcting the deformation of the diaphragm in a state where no sound wave is received and correcting it flatly.
The second capacitor group and the third capacitor group are each disposed at a position surrounding the central portion of the diaphragm, and the third capacitor group is disposed radially inward of the second capacitor group. A capacitor has a predetermined relationship between its gap length and capacitance. When the diaphragm is deformed, the gap length of each capacitor also changes. Therefore, when the diaphragm is not receiving sound waves (that is, the diaphragm is not vibrating) and the diaphragm is in a substantially flat state, the capacitance of each capacitor of the second and third capacitor groups A predetermined relationship is established between them. For example, when the area of each electrode of the second electrode pair group and the third electrode pair group is equal, the diaphragm is not deformed and is flat, and the gap length is equal, each of the second and third capacitor groups The capacitor holds the relationship of holding substantially the same capacitance. Therefore, the controller sets each capacitor of the first capacitor group so that the relationship between the capacitances of the second and third capacitor groups becomes the above-described predetermined relationship when the diaphragm is not receiving sound waves. Adjust the applied voltage (bias voltage). Thereby, the deformation | transformation of the diaphragm in the state which has not received the sound wave can be corrected. That is, the diaphragm can be corrected to a flat state. In a state where a bias voltage is applied (that is, in a state where the diaphragm is kept flat if no sound wave is received), at least one of the second and third capacitor groups when the diaphragm receives the sound wave. The direction of the sound source is specified from the change in capacitance. Before receiving the sound wave, the direction of the sound source can be specified after correcting the diaphragm to a flat state. The direction of the sound source can be specified with high accuracy. Even if the diaphragm has deformation due to aging or manufacturing errors, the direction of the sound source can be specified with high accuracy.
It should be noted that the relationship that the capacitance held by each electrode pair of the second electrode pair group and the third electrode pair group satisfies when the diaphragm is not receiving sound waves and the diaphragm is substantially flat is different. In other words, when the diaphragm is not receiving sound waves and the diaphragm is in a substantially flat state, it is established between the capacitance held by each electrode pair of the second electrode pair group and the third electrode pair group. It is a relationship. Such a relationship can be translated into a relationship that can specify that the diaphragm is in a substantially flat state.

  In the above microphone, in particular, the second capacitor group and the third capacitor group are arranged on the outer peripheral side and the inner peripheral side of the diaphragm, respectively. As a result, even when the diaphragm is deformed into a conical shape having the central portion as the apex, the relationship between the capacitances of the second and third capacitor groups becomes a predetermined relationship. By applying a bias voltage to the capacitor, the deformation of the diaphragm can be corrected and a flat state can be obtained.

By applying the bias voltage, the deformation of the diaphragm before receiving the sound wave can be corrected. If the bias voltage for correcting the deformation of the diaphragm before receiving the sound wave and the capacitance of the second or third capacitor at that time are obtained, the direction of the sound source can be specified as follows. When the diaphragm is receiving sound waves, the capacitance of at least one of the second capacitor group and the third capacitor group is the capacitance when a bias voltage is applied without receiving sound waves. A damping voltage that maintains (that is, keeps the diaphragm flat) is applied to each capacitor of the first capacitor group. The direction of the sound source is specified from the voltage obtained by subtracting the bias voltage of each capacitor from the damping voltage applied to each capacitor of the first capacitor group.
A microphone that specifies the direction of a sound source by applying a vibration suppression voltage can be realized by a main body having the same structure as the above-described microphone main body and a controller having the following structure. The controller applies a voltage to each electrode pair of the first electrode pair group, the second electrode pair group, and the third electrode pair group, and the respective electrode pairs of the second electrode pair group and the third electrode pair group hold. Measure the capacitance. Further, when the diaphragm is not receiving sound waves, each electrode of the first electrode pair group satisfies a predetermined relationship so that the capacitance held by each electrode pair of the second electrode pair group and the third electrode pair group satisfies a predetermined relationship. Adjust the bias voltage applied to the pair. When the diaphragm is receiving sound waves, the electrostatic capacity held by each electrode pair of at least one of the second electrode pair group and the third electrode pair group is not receiving sound waves. Then, a damping voltage for maintaining the capacitance when the bias voltage is applied to each electrode pair of the first electrode pair group is applied to each electrode pair of the first electrode pair group. The direction in which the sound wave propagates is specified from the voltage obtained by subtracting the bias voltage of each electrode pair from the damping voltage applied to each electrode pair of the first electrode pair group.
While the above-mentioned microphone corrects the diaphragm before receiving the sound wave to a flat state and specifies the direction of the sound source, this microphone keeps the diaphragm flat while receiving the sound wave. The sound source direction is specified while controlling the vibration so that it is maintained. This microphone can receive a sound wave having a large amplitude because the vibration control of the diaphragm is controlled while the sound wave is being received. That is, a sound source direction specifying microphone having a wide dynamic range can be realized. In addition, since the vibration control of the diaphragm is also performed when the direction of the sound source is specified, fatigue deterioration of the diaphragm due to vibration can be suppressed. Durability can be improved.

  According to the microphone of the present invention, the microphone can specify the direction of the sound source with a single diaphragm, and the direction of the sound source can be accurately specified by correcting the deformation of the diaphragm in a state where no sound wave is received. it can.

Embodiments of a microphone according to the present invention will be described below with reference to the drawings.
The microphone 100 according to the present embodiment includes a microphone body 10 and a controller 50. First, the structure of the microphone body 10 will be described. The controller 50 will be described later.
FIG. 1 is a schematic cross-sectional view of the microphone body 10. The microphone body 10 includes a housing 12 and a substantially circular diaphragm 16. FIG. 2 is a plan view when the diaphragm 16 is viewed from the front side. FIG. 3 is a plan view when the diaphragm 16 is viewed from the back side. The cross section of the diaphragm 16 shown in FIG. 1 shows the cross section of the diaphragm 16 when viewed along the AA line in FIG. 2 and along the BB line in FIG. Here, the front side of the diaphragm 16 is a side facing the opening 18 of the housing 12 as shown in FIG.
The diaphragm 16 has a central portion 16 a fixed to the housing 12. The diaphragm 16 has flexibility so that the periphery of the center portion 16a can be displaced in the thickness direction (Z direction of the coordinate system shown in FIG. 1). A surface of the housing 12 that faces the back surface of the diaphragm 16 is referred to as a base surface 12a. A part of the housing 12 forms a wall surface extending from the base surface 12a around the diaphragm 16 in the Z direction. The wall surface extends on the front side of the diaphragm 16 so as to surround the peripheral portion of the front surface of the diaphragm 16. A surface of the housing 12 that faces the front surface of the diaphragm 16 is referred to as a peripheral cover surface 12b.
The housing 12 has an opening 18 on the front side of the diaphragm 16. The diaphragm 16 receives a sound wave propagating through the opening 18 of the housing 12 and vibrates in the Z direction.

As illustrated in FIG. 2, flat electrodes 21 a, 22 a, 23 a, and 24 a are attached to the front surface of the diaphragm 16. In FIG. 1, only the electrodes 21a and 23a are shown, and the electrodes 22a and 24a are not shown. As shown in FIG. 2, each of the electrodes 21a-24a has a fan shape, and is attached to the front surface of the diaphragm 16 at a plurality of positions surrounding the central portion 16a. The electrodes 21a-24a are arranged at equal intervals along the circumferential direction of the diaphragm 16.
As shown in FIG. 1, the electrode 21b is fixed to the peripheral cover surface 12b of the housing 12 at a position facing the electrode 21a. Similarly, the electrode 23b is fixed to the peripheral cover surface 12b of the housing 12 at a position facing the electrode 23a. Although not shown, the electrodes 22b and 24b are fixed to the peripheral cover surface 12b of the housing 12 at positions facing the electrodes 22a and 24a, respectively. A gap length d is provided between the electrodes 21a and 21b, between the electrodes 22a and 22b, between the electrodes 23a and 23b, and between the electrodes 24a and 24b.

As shown in FIG. 3, electrodes 31 a, 32 a, 33 a, 34 a, 41 a, 42 a, 43 a, and 44 a are attached to the back surface of the diaphragm 16. In FIG. 1, only the electrodes 31a, 33a, 41a, and 43a are shown, and the electrodes 32a, 34a, 42a, and 44a are not shown. As shown in FIG. 3, each of the electrodes 31a to 34a has a fan shape, and is attached to the back surface of the diaphragm 16 at a plurality of positions surrounding the central portion 16a. The electrodes 31 a to 34 a are arranged at equal intervals along the circumferential direction of the diaphragm 16. As shown in FIG. 3, the electrodes 41 a to 44 a each have a sector shape, and are a plurality of positions surrounding the central portion 16 a, at positions radially inside the diaphragm 16 from the electrodes 31 a to 34 a. Attached to the back surface of the diaphragm 16. The electrodes 41 a to 44 a are arranged at equal intervals along the circumferential direction of the diaphragm 16.
As shown in FIG. 1, the electrodes 31b, 33b, 41b, and 43b are fixed to the base surface 12a of the housing 12 at positions facing the electrodes 31a, 33a, 41a, and 43a, respectively. Although not shown, the electrodes 32b, 34b, 42b, and 44b are fixed to the base surface 12a of the housing 12 at positions facing the electrodes 32a, 34a, 42a, and 44a, respectively. A gap length d is provided between the electrodes facing each other. As will be described later, the gap length d is a gap length when the diaphragm 16 is not receiving sound waves and the diaphragm 16 is flat and not deformed.
As shown in FIGS. 1 to 3, the electrodes 21 a and 31 a are arranged at positions facing each other with the diaphragm 16 in between. Similarly, the electrodes 22a and 32a, the electrodes 23a and 33a, and the electrodes 24a and 34a are arranged at positions facing each other with the diaphragm 16 in between.
All the electrodes have the same area.

The electrode 21a and the electrode 21b make a pair, and the electrodes 21a and 21b are collectively referred to as an electrode pair 21. Since the electrode 21a and the electrode 21b are arranged to face each other, when a voltage is applied between the electrodes, the electrode pair 21 functions as a capacitor that holds a predetermined capacitance. Therefore, hereinafter, the electrode pair 21 may be referred to as a capacitor 21. Similarly, the electrodes 31 a and 31 b are collectively referred to as an electrode pair 31 or a capacitor 31. Similar designations are used for the other electrodes.
The pair of electrodes forming each capacitor are parallel to each other when the diaphragm 16 is not receiving sound waves and is in a flat state that is not deformed.
The electrode pairs 21, 22, 23, and 24 arranged on the front side of the diaphragm 16 are collectively referred to as a first electrode pair group 20. The electrode pairs 21, 22, 23, and 24 may be referred to as capacitors 21, 22, 23, and 24, respectively, and these capacitor groups may be collectively referred to as a first capacitor group 20. Similarly, the electrode pairs 31, 32, 33, and 34 disposed on the back side of the diaphragm 16 are referred to as a second electrode pair group 30 or a second capacitor group 30. The electrode pairs 41, 42, 43, and 44 disposed on the inner side in the radial direction from the second electrode pair group 30 on the back side of the diaphragm 16 are referred to as a third electrode pair group 40 or a third capacitor group 40.

  Next, the microphone controller 50 will be described. FIG. 4 shows a block diagram of the controller 50. The “upper electrode” shown in FIG. 4 means an electrode (electrodes 21b, 22b, 23b, and 24b) fixed to the housing 12 among the electrodes of the electrode pair group 20. The “lower electrode” shown in FIG. 4 is an electrode (electrodes 31b, 32b, 33b, 34b, 41b, 42b, 43b, fixed to the housing 12 among the electrodes of the electrode pair group 30 and the electrode pair group 40. And 44b). The “diaphragm electrodes” shown in FIG. 4 are all electrodes (electrodes 21a, 22a, 23a, 24a, 31a, 32a, 33a, 34a, 41a, 42a, 43a, and 44a) attached to the diaphragm 16. Means.

The controller 50 includes a capacity detection circuit 52, a vibration suppression circuit 54, and a sound source direction specifying circuit 56. Next, an outline of each circuit will be described. The operation of the controller 50 will be described later.
Each electrode of the diaphragm electrode and the lower electrode is connected to the capacitance detection circuit 52. That is, each capacitor of the second capacitor group 30 and the third capacitor group 40 is connected to the capacitance detection circuit 52. Each electrode of the diaphragm electrode is grounded to the ground of the controller 50.
The capacitance detection circuit 52 applies a constant voltage to each capacitor of the second capacitor group 30 and the third capacitor group 40 (that is, applies a constant voltage to each electrode of the lower electrode), and the second capacitor. The capacitance of each capacitor in the group 30 and the third capacitor group 40 is detected. The capacitance detection circuit 52 outputs a voltage value proportional to the detected capacitance to the vibration suppression circuit 54.
The damping circuit 54 applies a predetermined voltage to each upper electrode so that the voltage value output from the capacitance detection circuit 52 is constant. That is, a predetermined voltage is applied to each upper electrode so that the capacitance held by each capacitor of the second capacitor group 30 and the third capacitor group 40 is constant. A method for obtaining the voltage value output from the damping circuit 54 will be described later.
The output voltage of the damping circuit 54 is applied to each upper electrode and is input to the sound source direction specifying circuit 56. The sound source direction specifying circuit 56 specifies the direction of the sound source from the input voltage (the voltage applied to each upper electrode by the damping circuit 54). A method for specifying the direction of the sound source will be described later.

Next, the operation of the controller 50 will be described.
The controller 50 executes the next process in a state where the diaphragm 16 does not receive sound waves before specifying the direction of the sound source. The controller 50 adjusts the voltage applied to each capacitor of the first capacitor group 20 to correct the plane of the diaphragm 16 when not receiving sound waves to a flat state.

  Deformation and correction of the diaphragm 16 will be described. A state in which the diaphragm 16 is parallel to the base surface 12a is referred to as a reference state. Here, “deformation” means that at least a part of the diaphragm 16 when not receiving sound waves deviates from the reference state. A state in which the diaphragm 16 is not deviated from the reference state when no sound wave is received is referred to as a flat state of the diaphragm 16. In other words, “the state in which the diaphragm 16 is flat” is a state in which one electrode of each electrode pair is parallel to the other electrode.

The gap length d between both electrodes of each electrode pair is a value in the reference state. Since the periphery of the diaphragm 16 is flexible in the direction perpendicular to the surface (the Z direction in FIG. 1), each portion except for the central portion 16a of the diaphragm 16 is easily displaced in the Z direction. . When the diaphragm 16 receives a sound wave, each part of the diaphragm 16 is displaced in the Z direction by the sound pressure. However, each part of the diaphragm 16 does not receive the sound wave due to a change with time or a manufacturing error of the microphone. Sometimes it is deformed.
As the gap length between both electrodes of each electrode pair changes, the capacitance held by each capacitor also changes. Since all the electrodes have the same area, when the gap length of each capacitor is equal and the voltage applied to each capacitor is also equal, the capacitance held by each capacitor is equal. A constant voltage is applied to each capacitor of the second capacitor group 30 and the third capacitor group 40 by the capacitance detection circuit 52. Therefore, in the reference state, the capacitance of each capacitor is equal. The electrostatic capacity held by the capacitors of the second capacitor group 30 and the third capacitor group 40 in the reference state (that is, the gap length of the capacitors of the second capacitor group 30 and the third capacitor group 40 is d). Let C be the capacity.

Now, as shown in FIG. 5, consider a case where the diaphragm 16 is deformed so as to be inclined along the X-axis when it does not receive a sound wave. At this time, the gap length of the electrode pair 31 is shorter than d. When the diaphragm 16 is inclined, both electrodes of the electrode pair are not parallel, and the gap length in one electrode pair is not constant. The gap length here means the average gap length in each electrode pair.
As shown in FIG. 5, the gap length of the electrode pair 31 when the diaphragm 16 is tilted is d−Δd1. The gap length of the electrode pair 41 is d−Δd2. Since the diaphragm 16 is supported by the central portion 16a, when the diaphragm 16 is tilted along the X axis, if the gap length is shortened on the left side of FIG. 5, the gap length is increased on the right side of FIG. . When the gap length of the electrode pair 31 is (d−Δd1), the gap length between the electrode pair 31 and the electrode pair 33 at the target position across the center portion 16a is (d + Δd1). When the gap length of the electrode pair 41 is (d−Δd2), the gap length between the electrode pair 41 and the electrode pair 43 at the target position across the center portion 16a is (d + Δd2).
Since the gap length and the capacitance are in inverse proportion, the capacitance increases as the gap length decreases. Conversely, the capacitance decreases as the gap length increases. The capacitance of the capacitor 31 whose gap length is (d−Δd1) is (C + ΔC1). Similarly, the capacitance of the capacitor 41 is (C + ΔC2), the capacitance of the capacitor 43 is (C−ΔC2), and the capacitance of the capacitor 33 is (C−ΔC1).
As described above, when the diaphragm 16 is tilted along the X axis, the capacitance of the capacitors 31 and 41 located on the left side of the central portion 16a in FIG. The capacitance of 43 decreases. When the diaphragm 16 is tilted along the X axis in the direction opposite to that of FIG. 5, the capacitances of the capacitors 31 and 41 located on the left side of the central portion 16a in FIG. The capacitances of the capacitors 33 and 43 positioned increase.

When a voltage is applied, the capacitor generates a Coulomb force (electrostatic attractive force) in a direction that narrows the gap. In the microphone 100 of the present embodiment, the first capacitor group disposed on the front surface of the diaphragm 16 is used as an actuator for correcting the deformation of the diaphragm 16. As shown in FIG. 5, when the diaphragm 16 is inclined along the X axis, the controller 50 applies a voltage to the capacitor 21 arranged on the right side of the first capacitor group on which the capacitance has increased. Apply. Then, the electrode 21a is attracted to the electrode 21b by the electrostatic attraction force. The gap of the capacitor 21 is shortened. On the other hand, when the electrode 21a is attracted to the electrode 21b, the distance between the electrode pair 21 and the electrode pair 23 at the target position is increased with the central portion 16a of the diaphragm 16 in between. The gap length between the electrodes 23a and 23b is increased. The shorter gap between the capacitors 21 means that the gap length between the capacitors 31 and 41 is increased. Similarly, increasing the gap length of the capacitor 23 means that the gap length of the capacitors 33 and 43 is shortened.
The controller 50 applies the second capacitor group 30 and the third capacitor group 40 to the capacitor 21 until the capacitance of the capacitor located on the right side of the central portion 16a is equal to the capacitance of the capacitor located on the left side. Increase the voltage. By doing so, the gap length of each of the capacitors 31, 41, 33, and 43 can be returned to the original gap length d. That is, the diaphragm 16 tilted along the X axis can be corrected to be parallel to the base surface 12 a of the housing 12. The voltage applied to the capacitor 21 so that the capacitance of each capacitor of the second capacitor group 30 and the third capacitor group 40 maintains the same value is referred to as a bias voltage.
Similarly, when the diaphragm 16 is inclined along a line parallel to the XY plane, a predetermined bias voltage is applied to a predetermined capacitor of the first capacitor group 20, so that the diaphragm 16 is attached to the base surface of the housing 12. It can correct in a state parallel to 12a. That is, the deformation of the diaphragm 16 can be corrected to the original reference state. More specifically, among the capacitors of the second capacitor group 30 and the third capacitor group 40, a first capacitor (first capacitor group 20) arranged at a position overlapping with the capacitor having an increased capacitance when viewed from the Z-axis direction. A voltage may be applied to any one of the capacitors.

Next, consider a case where the diaphragm 16 is deformed into a conical shape with the central portion 16a as a vertex as shown in FIG. In other words, consider a case where the peripheral edge of the diaphragm 16 is deformed in a direction approaching the base surface 12a. At this time, the gap lengths of all the capacitor groups of the second capacitor group 30 and the third capacitor group 40 are shorter than the length d in the reference state. The gap length of the second capacitor group 30 (capacitors 31 and 33 in the second capacitor group 30 are shown in FIG. 6 and the capacitors 32 and 34 are not shown) located on the outer peripheral side of the diaphragm 16 is (D−Δd3). At this time, the capacitance of each capacitor of the second capacitor group 30 is (C + ΔC3). A third capacitor group 40 (in FIG. 6, capacitors 41 and 43 of the third capacitor group 40 are shown, and the capacitors 42 and 44 are not shown in the figure) located on the radially inner side (inner peripheral side) of the diaphragm 16. The gap length is (d−Δd4). At this time, the capacitance of each capacitor of the third capacitor group 40 is (C + ΔC4). Since the second capacitor group 30 is located on the outer peripheral side of the third capacitor group 40, (d−Δd3) <(d−Δd4). When this is expressed in terms of capacitance, (C + ΔC3)> (C−ΔC4).
At this time, the controller 50 applies a voltage to all the capacitors in the first capacitor group 20. The controller 50 increases the voltage applied to each capacitor of the first capacitor group until the capacitance of each capacitor of the second capacitor group 30 is substantially equal to the capacitance of each capacitor of the third capacitor group 40. By doing so, the diaphragm 16 deformed into a conical shape can be corrected to a flat state. A bias voltage is a voltage applied to each capacitor of the first capacitor group when the capacitance of each capacitor of the second capacitor group 30 is substantially equal to the capacitance of each capacitor of the third capacitor group 40.

  When the diaphragm 16 is deformed in the direction opposite to that in FIG. 6, that is, when the peripheral edge of the diaphragm 16 is deformed away from the base surface 12 a of the housing 12, the first capacitor group (first electrode) The functions of the pair group 20 and the second capacitor group (second electrode pair group) 30 may be reversed. That is, the second capacitor group 30 is used as an actuator. When a bias voltage is applied to each capacitor of the second capacitor group 30, the peripheral portion of the diaphragm 16 is displaced in a direction approaching the base surface 12 a of the housing 12. That is, the diaphragm 16 deformed into a conical shape can be corrected to the original reference state. Instead of the second capacitor group 30, the capacitance of the first capacitor group 20 is detected. If the controller 50 detects the capacitance of each capacitor of the first capacitor group 20 and the third capacitor group 40 and increases the voltage applied to the second capacitor group 30 until the detected capacitances coincide with each other, Good. By doing so, even when the peripheral portion of the diaphragm 16 is deformed in a direction away from the base surface 12a of the housing 12, the diaphragm 12 can be moved by the electrostatic attractive force generated by each capacitor of the second capacitor group 30. It can be corrected to a flat state.

Next, the operation when the controller 50 specifies the propagation direction of the sound wave received by the diaphragm 16, that is, the direction of the sound source will be described. The controller 50 stores the aforementioned bias voltage. Further, the controller 50 stores the capacitance of each capacitor of the second capacitor group 30 in a state in which the deformation of the diaphragm 16 is corrected by applying a bias voltage.
When receiving a sound wave, each part of the diaphragm 16 vibrates. The controller 50 applies a voltage to each capacitor of the first capacitor group 20 so as to suppress vibration of each part of the diaphragm 16. Specifically, a voltage is applied to each capacitor of the first capacitor group 20 so that the capacitance of each capacitor of the second capacitor group 30 matches the stored capacitance. When a voltage is applied to each capacitor of the first capacitor group 20, the peripheral edge of the diaphragm 16 is attracted to the front side by the electrostatic attractive force generated by the first capacitor group 20, and as a result, the second capacitor group 30. As described above, the capacitance of each capacitor changes.
The voltage applied to each capacitor of the first capacitor group 20 when the capacitance of each capacitor of the second capacitor group 30 matches the stored capacitance is referred to as a damping voltage. Since the sound pressure received by each part of the diaphragm 16 changes with time, the damping voltage also changes with time. The time-dependent change in the damping voltage applied to each capacitor in the first capacitor group 20 represents the time-dependent change in vibration at the position where each capacitor is disposed.
The sound source direction specifying circuit 56 subtracts the value of the bias voltage from the value of the damping voltage applied to each capacitor of the first capacitor group 20. The voltage after subtraction is called a differential voltage. The damping voltage includes a voltage (bias voltage) for correcting the diaphragm 16 to be flat and a voltage for suppressing vibration of the diaphragm 16 due to sound waves. Therefore, the differential voltage represents a change with time of vibration of each part of the diaphragm 16 corrected to the reference state.
The sound source direction specifying circuit 56 specifies the direction of the sound source from the difference voltage corresponding to each capacitor of the first capacitor group 20.

The principle of specifying the direction of the sound source will be briefly described with reference to FIG. An XZ coordinate system having the origin O as the center of the diaphragm 16 is set as shown in FIG. Assume that the sound source is at position S. The angle θ formed by the line connecting the position S of the sound source and the coordinate origin O and the Z axis is the direction of the sound source. The diaphragm 16 is vibrated by the sound wave propagating from the sound source at the position S. The vibration at the position P1 on the diaphragm 16 is W1, and the vibration at the position P2 on the diaphragm 16 is W2. The distance between the sound source position S and the position P1 is L1, and the distance between the sound source position S and the position P2 is L2. When the distances L1 and L2 are different, the vibration W1 at the position P1 and the vibration W2 at the position P2 vibrate in different phases. The phase difference between the vibration W1 at the position P1 and the vibration W2 at the position P2 depends on the direction of the position S of the sound source. Therefore, the direction (angle θ) of the sound source can be obtained from the phase difference between the vibration W1 at the position P1 and the vibration W2 at the position P2. For example, when the vibration W1 and the vibration W2 are in phase, the direction of the sound source is the direction in which the Z axis extends.
As described above, the difference voltage obtained by subtracting the value of the bias voltage of each capacitor from the value of the damping voltage applied to each capacitor of the first capacitor group 20 corresponds to each of the diaphragms 16 corrected to the reference state. It represents the change over time of the vibration of the part. Therefore, the direction of the sound source can be specified from the phase difference of the difference voltage of each capacitor of the first capacitor group 20.

The microphone 100 of the above embodiment determines a bias voltage for correcting the deformation of the diaphragm 16 before specifying the direction of the sound source. When specifying the direction of the sound source, the direction of the sound source is specified based on the difference voltage obtained by subtracting the bias voltage from the vibration suppression voltage. That is, the direction of the sound source is specified in consideration of the influence of deformation of the diaphragm 16 in a state where no sound wave is received. Thereby, even if the diaphragm 16 is deformed, the direction of the sound source can be accurately specified. In other words, the direction of the sound source can be specified by correcting the deformation of the diaphragm in a state where no sound wave is received.
Since this microphone controls vibration control even when receiving sound waves, the vibration plate does not vibrate greatly. Therefore, even in the case of a sound wave having a large amplitude, the direction in which the sound wave propagates can be specified. That is, a wide dynamic range can be ensured. Moreover, since this diaphragm does not vibrate greatly, this microphone can reduce fatigue deterioration of the diaphragm.

  The microphone 100 can specify the direction of the sound source from the phase difference of the difference voltage. Therefore, when the phase difference of the difference voltage matches a specific phase difference, a signal obtained by converting a sound wave may be output. A specific phase difference means a sound wave propagating from a specific direction. Therefore, it is possible to realize a microphone that outputs only a sound wave propagating from a specific direction as a signal. That is, a microphone having high directivity can be realized.

A modification of the microphone 100 will be described.
In the microphone 100 of the above embodiment, the direction of the sound source is specified from the difference voltage obtained by subtracting the bias voltage from the vibration suppression voltage. The direction of the sound source can be specified as follows without applying the damping voltage.
Once the bias voltage is determined, the controller 50 continues to apply the bias voltage to each upper electrode. In this state, the diaphragm 16 receives sound waves. The diaphragm 16 corrected to a flat state by the bias voltage vibrates by receiving sound waves. The capacitances of the capacitors of the second capacitor group 30 and the third capacitor group vary with the vibration of the diaphragm 16. Since the second capacitor group 30 or the third capacitor group 40 is disposed at a position surrounding the center of the diaphragm 16, the phase of the change in the capacitance of each capacitor depends on the direction of the sound source. Therefore, the direction of the sound source can be specified from the phase difference of the capacitance change of each capacitor of at least one of the second capacitor group 30 and the second capacitor group 40.

One electrode group of each electrode pair of the first electrode pair, the second electrode pair, and the third electrode pair may be a common electrode. This is because one electrode of the electrode pair forming the capacitor can be shared as a ground. For example, when the diaphragm itself is formed of a conductive material, the diaphragm itself becomes a common electrode. Of all the electrode pairs, the electrode to which the diaphragm 16 is attached can be shared by one electrode. The number of electrodes can be reduced.
The number of electrode pairs of the first electrode pair, the second electrode pair, and the third electrode pair may be any number as long as it is plural.

  In the above embodiment, the bias voltage for correcting the diaphragm to a flat state is determined so as to satisfy the relationship in which the capacitances of the capacitors of the second capacitor group and the third capacitor group have the same value. This is because the electrodes of each electrode pair (capacitor) have the same area and the same gap length when the diaphragm 16 is flat. The relationship to be satisfied by the capacitance of each capacitor for determining the bias voltage is not limited to the above relationship. The relationship may be a relationship that satisfies the capacitances of the capacitors of the second capacitor group 30 and the third capacitor group 40 when the diaphragm is not receiving sound waves and the diaphragm is substantially flat. . For example, when the gap lengths of the capacitors of the second capacitor group and the third capacitor group are equal, and the area of the electrodes of the capacitors of the second capacitor group is twice the area of the electrodes of the capacitors of the third capacitor group. The relationship to be satisfied is as follows. The capacitance of each capacitor in the second capacitor group is equal, the capacitance of each capacitor in the third capacitor group is equal, and the capacitance of each capacitor in the second capacitor group is equal to the static value of each capacitor in the third capacitor group. The relationship is twice the electric capacity. Further, when the diaphragm is not receiving sound waves and the diaphragm is substantially flat, if the gap length of the second electrode pair group is different from the gap length of the third electrode pair group, the bias voltage is set to The relationship to be satisfied by the capacitance of each capacitor for determination is also different from the relationship exemplified above. Generally speaking, the relationship that the capacitance of each capacitor for determining the bias voltage should satisfy is that when the diaphragm is not receiving sound waves and the diaphragm is in the reference state, This is a relationship established between the capacitance held by each electrode pair of the three electrode pair group.

The inventors have developed a microphone that can accurately specify the direction of a sound source with a single diaphragm before filing this application. The relationship between the microphone and the microphone of the embodiment will be described below. The microphone has a structure in which the third electrode pair group is excluded from the microphone of the above embodiment.
Even with a microphone having no third electrode pair group (third capacitor group), the diaphragm can be corrected to a flat state. The capacitance of each capacitor of the second capacitor group in a state where the diaphragm is flat is measured in advance. The measured value at this time is referred to as a reference capacitance. Before receiving the sound wave, a bias voltage is applied to the first capacitor group so that the capacitance of the second capacitor group becomes equal to the reference capacitance. By doing so, the deformation of the diaphragm before receiving the sound wave can be corrected. However, the measured capacitance value is not always measured at a constant value due to the influence of temperature or the like even if the gap length is constant. That is, even if the gap length is the same, the currently measured capacitance does not always match the reference capacitance measured in the past. On the other hand, the microphone of the embodiment vibrates based on the relative relationship between the capacitance of the second capacitor group disposed on the outer peripheral side of the diaphragm and the capacitance of the third capacitor group disposed on the inner peripheral side. Correct the deformation of the plate. The microphone according to the present embodiment uses the relative relationship between the capacitances of the second and third capacitor groups that are simultaneously measured, and thus is not easily affected by the temperature or the like described above. The diaphragm can be corrected (controlled) to a flat state with high accuracy.
Note that the microphone developed by the inventors before the filing of the present application is disclosed in detail in Japanese Patent Application No. 2005-167742 (not disclosed at the time of filing this application).

Specific examples of the present invention have been described above in detail, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.
Further, the technical elements described in the present specification or drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology exemplified in this specification or the drawings can achieve a plurality of purposes at the same time, and has technical utility by achieving one of the purposes.

FIG. 1 is a schematic cross-sectional view of a microphone body. FIG. 2 is a plan view of the diaphragm as viewed from the front side. FIG. 3 is a plan view of the diaphragm as viewed from the back side. FIG. 4 is a block diagram of a microphone controller. FIG. 5 is a diagram illustrating a state in which the diaphragm is deformed so as to be inclined along the X axis. FIG. 6 is a diagram illustrating a state in which the diaphragm is deformed in a conical shape with the central portion at the top. FIG. 7 is a diagram for explaining the principle of specifying the direction of the sound source.

Explanation of symbols

100: Microphone 10: Microphone body 12: Housing 16: Diaphragm 21, 22, 23, 24, 31, 32, 33, 34, 41, 42, 43, 44: Electrode pair 50: Controller 52: Capacitance detection circuit 54: Damping circuit 56: Sound source direction specifying circuit

Claims (4)

A diaphragm whose center is supported by the housing and whose periphery is displaceable in the thickness direction;
One electrode group is fixed to one surface of the diaphragm at a plurality of positions surrounding the central portion of the diaphragm, and the other electrode group is fixed to the housing at a position facing each corresponding electrode via a gap. A first electrode pair group,
One electrode group is fixed to the other surface of the diaphragm at a plurality of positions surrounding the center of the diaphragm, and the other electrode group is fixed to the housing at a position facing each corresponding electrode via a gap. A second electrode pair group,
One electrode group is fixed to the other surface of the diaphragm at a plurality of positions surrounding the central portion of the diaphragm and inside the diaphragm in the radial direction from one electrode group of the second electrode pair group. A third electrode pair group fixed to the housing at a position where the other electrode group faces the corresponding electrode via a gap;
A controller, and that controller
A voltage is applied to each electrode pair of the first electrode pair group, the second electrode pair group, and the third electrode pair group,
Measure the capacitance held by each of the second electrode pair group and the third electrode pair group,
When the diaphragm is not receiving sound waves, each electrode pair of the first electrode pair group is set so that the capacitance held by each electrode pair of the second electrode pair group and the third electrode pair group satisfies a predetermined relationship. Adjust the bias voltage to be applied,
With the adjusted bias voltage applied to each electrode pair of the first electrode pair group, at least one of the second electrode pair group and the third electrode pair group when the diaphragm receives sound waves. A microphone characterized in that a direction in which a sound wave propagates is specified from a change in capacitance held by each electrode pair. A diaphragm whose center is supported by the housing and whose periphery is displaceable in the thickness direction;
One electrode group is fixed to one surface of the diaphragm at a plurality of positions surrounding the central portion of the diaphragm, and the other electrode group is fixed to the housing at a position facing each corresponding electrode via a gap. A first electrode pair group,
One electrode group is fixed to the other surface of the diaphragm at a plurality of positions surrounding the center of the diaphragm, and the other electrode group is fixed to the housing at a position facing each corresponding electrode via a gap. A second electrode pair group,
One electrode group is fixed to the other surface of the diaphragm at a plurality of positions surrounding the central portion of the diaphragm, and at a position radially inward of the diaphragm from one electrode group of the second electrode pair group, A third electrode pair group fixed to the housing at a position where the other electrode group faces the corresponding electrode via a gap;
A controller, and that controller
A voltage is applied to each electrode pair of the first electrode pair group, the second electrode pair group, and the third electrode pair group,
Measure the capacitance held by each of the second electrode pair group and the third electrode pair group,
When the diaphragm is not receiving sound waves, each electrode pair of the first electrode pair group is set so that the capacitance held by each electrode pair of the second electrode pair group and the third electrode pair group satisfies a predetermined relationship. Adjust the bias voltage to be applied,
When the diaphragm is receiving sound waves, the electrostatic capacity held by each electrode pair of at least one of the second electrode pair group and the third electrode pair group is not receiving sound waves. And applying a damping voltage for maintaining the capacitance when the bias voltage is applied to each electrode pair of the first electrode pair group to each electrode pair of the first electrode pair group,
A microphone characterized in that a direction in which sound waves propagate is specified from a voltage obtained by subtracting the bias voltage of each electrode pair from a damping voltage applied to each electrode pair of the first electrode pair group.   The predetermined relationship is satisfied by the capacitance held by each electrode pair of the second electrode pair group and the third electrode pair group when the diaphragm is not receiving sound waves and the diaphragm is substantially flat. The microphone according to claim 1, wherein the microphone has a relationship.   The microphone according to any one of claims 1 to 3, wherein an area of each electrode of the second electrode pair group is substantially equal to an area of each electrode of the third electrode pair group.

Images