JP2010010870A - Method of measuring surface voltage of electret and device therefor - Google Patents

Abstract

A surface voltage of an electret dielectric film can be measured more accurately.
In measuring the surface voltage of an electret dielectric film 11, a measurement electrode 37 that is driven by a vibration generating means 34 and a signal that is connected to the measurement electrode via an impedance converter 41 is measured. Means, a reference electrode 20 for the fixed electrode 10, a DC voltage source 21 for applying a DC voltage to the reference electrode 20, and a voltage measuring means for measuring the DC voltage. The electret dielectric film 11 and the reference electrode 20 The measurement electrode 37 is juxtaposed with the same surface area and height, the measurement electrode 37 is vibrated by the vibration generating means 34, and the polarity opposite to the charged charge of the electret dielectric film 11 is applied to the reference electrode 20 from the DC voltage source. Is applied, and the voltage measuring means 22 measures the direct current voltage at which the reading value of the signal measuring means 42 is minimum, and has the opposite polarity. The surface voltage of the electret dielectric film 11 with a pressure value.
[Selection] Figure 1

Description

  The present invention relates to a method and an apparatus for measuring the surface voltage of an electret provided on a fixed pole for an electret condenser microphone. More specifically, the surface voltage of the electret does not depend on a surface voltmeter and affects ambient disturbances. The present invention relates to a technique that enables appropriate measurement without being performed.

  In the electret condenser microphone unit, an electret dielectric film is provided on either the fixed pole or the diaphragm, and the electret dielectric film is electretized (polarized) to obtain a polarization voltage.

  Therefore, there is no need for a polarized power source such as a DC-CD converter, and there is an advantage that the electronic circuit of the microphone can be simplified. Further, since the electret dielectric film itself is an electrically insulating material, there is an advantage that noise due to leakage of the polarization voltage does not occur.

  For the electret dielectric film, for example, FEP (Fluorinated Ethylene Proline) is used. This type of electret material has a unique property that it is polarized when a high DC voltage is applied, for example, by corona discharge, and polarization remains even after the voltage is removed. Usually, it is charged in a nice manner from the viewpoint of the life of the charged charge.

  On the other hand, the disadvantage of using an electret material is that it is relatively difficult to control the surface voltage when applying a direct-current high voltage to form an electret, and thus aging must be performed appropriately.

  In addition, the surface voltage of the electret often tends to vary, and in the case of the back electret type in which the electret dielectric film is provided on the fixed pole side, the diaphragm may be partially adsorbed.

  In particular, since microphones used for studio sound collection are required to have high performance, careful attention is required to adjust the surface voltage due to aging, and variations in surface voltage are a serious problem. Become.

  In either case of the back electret type or the membrane electret type, when the surface voltage of the electret is high as a whole, the diaphragm is attracted to the fixed pole side and displaced. This bias-like displacement increases the electrostatic capacity, and as a result, the sensitivity increases in the same manner as the surface voltage increases equivalently, while the stability against adsorption decreases.

  The surface voltage of the electret can be measured with a commercially available non-contact type, for example, a vibration capacity type surface voltmeter. Normally, this type of surface voltmeter is designed to reduce errors due to distance, but it is impossible to measure whether the surface voltage is appropriate with the diaphragm and fixed pole assembled. .

  Therefore, in Patent Document 1, a diaphragm that is electretized on either side and a fixed pole are arranged to face each other via a spacer to actually operate as a microphone, and a power amplifier is provided by an oscillator. It is proposed to measure the surface voltage of the electret by driving a speaker at a predetermined frequency and applying sound waves to the diaphragm, taking out the change in capacitance caused by this as a measurement signal with an impedance converter. Yes.

JP 2006-174125 A

  However, in the invention described in the above-mentioned Patent Document 1, since the diaphragm is vibrated by applying sound waves to the diaphragm by a speaker, measurement errors may occur if ambient noise is mixed in. Therefore, a work environment in which ambient noise is not mixed is required, and this becomes a measurement burden.

  Accordingly, an object of the present invention is to measure the surface voltage of the electret dielectric film on the fixed pole side more accurately without being affected by ambient noise or the like in a state where the diaphragm and the fixed pole are combined in a pseudo manner. There is in doing so.

  In order to solve the above problems, the present invention provides a surface voltage of an electret that measures the surface voltage of the electret dielectric film using a fixed pole for an electret condenser microphone having a polarized electret dielectric film as a fixed pole to be measured. In the measurement method, the measurement electrode driven by the vibration generating means has a smooth surface, the signal measurement means (for example, a level meter) connected to the measurement electrode via an impedance converter, and the reference to the fixed pole to be measured An electret dielectric film of the fixed electrode to be measured and the reference electrode, each including an electrode, a DC voltage source for applying a DC voltage to the reference electrode, and a voltage measuring means (for example, a voltmeter) for measuring the DC voltage With the same surface area and height with respect to the measurement electrode, and the measurement by the vibration generating means. The pole is vibrated at a predetermined frequency and amplitude, and a predetermined DC voltage having a polarity opposite to the charged charge of the electret dielectric film is applied from the DC voltage source to the reference electrode. The DC voltage that minimizes the reading value of the signal measuring means is measured.

  According to a preferred aspect of the present invention, a piezoelectric element driven by an oscillator is used for the vibration generating means.

  Further, the fixed electrode to be measured is connected to the ground at least during measurement, and the reference electrode is connected to the ground during non-measurement. In addition, an electrode having the same surface area as the electret dielectric film of the fixed electrode to be measured is used as the reference electrode.

  On the other hand, the present invention provides an electret surface voltage measuring apparatus for measuring the surface voltage of an electret dielectric film using the electret condenser microphone fixed pole having a polarized electret dielectric film as a measured fixed pole. A reference electrode for the fixed electrode to be measured, a measurement electrode having a smooth surface having a size in which the fixed electrode to be measured and the reference electrode are juxtaposed, and the measurement electrode is vibrated at a predetermined frequency and amplitude. A vibration generating means, a signal measuring means (for example, a level meter) connected to the measurement electrode via an impedance converter, and a DC voltage having a polarity opposite to the charged charge of the electret dielectric film is applied to the reference electrode A variable DC voltage source for measuring, a voltage measuring means (for example, a voltmeter) for measuring the DC voltage, and the measuring voltage The electret dielectric film of the fixed pole to be measured and the reference electrode are provided with a support housing made of an electrical insulating material juxtaposed with the same surface area and the same height. A surface voltage measurement device is also included.

  In the electret surface voltage measuring apparatus, a piezoelectric element driven by an oscillator is preferably employed as the vibration generating means.

  Further, as the impedance converter, an FET (field effect transistor) may be used as in the case of the condenser microphone.

  Further, a ground terminal for connecting the fixed pole to be measured to the ground is provided, and the fixed pole to be measured is connected to the ground at least during measurement.

  Further, a changeover switch for selectively connecting the reference electrode to either the variable DC voltage source or the ground is provided, and the reference electrode is connected to the ground during non-measurement.

  Preferably, the support housing is provided with two openings for making each part of the electret dielectric film of the fixed electrode to be measured and the reference electrode face the measurement electrode with the same surface area. The openings are preferably approximately the same size as the effective electrode surface of the electret dielectric film.

  In the present invention, when the electret dielectric film of the fixed electrode to be measured and the reference electrode are juxtaposed with the measurement electrode having the same surface area and height, the electret dielectric film is placed on the surface of the measurement electrode facing the electret dielectric film. When a charge (positive charge) opposite in polarity to the charged charge (usually a negative charge) is induced and the measurement electrode is vibrated by the vibration generating means, the measurement electrode becomes a vibration plate, and like a condenser microphone, A signal is supplied to a signal measuring means (for example, a level meter) via an impedance converter, and in this state, a predetermined DC voltage having a polarity (positive) opposite to that of the electret dielectric film charged from the DC voltage source to the reference electrode Is applied to the surface of the measurement electrode facing the reference electrode, the charge of the same polarity as the electret dielectric film charge (minus As a result, a positive charge and a negative charge are mixed on the surface of the measurement electrode, and when both charges are neutralized by changing the applied DC voltage, the signal measuring means (for example, a level meter) When the reading value is minimum (ideally zero) and the DC voltage value at that time is measured by a voltage measuring means (for example, a voltmeter), the reverse polarity value of the DC voltage value becomes the surface voltage of the electret dielectric film. .

  Therefore, according to the present invention, the electret dielectric film on the fixed pole side is not affected by ambient noise or the like in a state in which the diaphragm and the fixed pole are combined in a pseudo manner (an aspect close to the actual use state). Can be measured more accurately.

  As main components, vibration generating means (preferably piezoelectric elements), impedance converters (preferably FETs for condenser microphones) and level meters, DC power supplies, and reference electrodes may be used. Since it is not a simple part, the measuring device can be constructed at low cost.

  Also, for example, when charged charge leakage occurs in the electret dielectric film or measurement electrode measurement system, the measured value drifts greatly with respect to the voltage applied to the reference electrode. Can be done appropriately.

  Next, although FIG. 1 demonstrates embodiment of this invention, this invention is not limited to this. FIG. 1 is a schematic diagram schematically showing the configuration of an electret surface voltage measuring apparatus according to the present invention.

  As shown in FIG. 1, this surface voltage measuring apparatus uses an electret dielectric film 11 using a reference electrode 20 with an electret condenser microphone fixed pole 10 having an electret dielectric film 11 on one surface as a measured fixed pole. Measure the surface voltage. Note that the electret dielectric film 11 is negatively charged by the polarization process. Although not shown, this surface voltage measuring device includes a ground terminal for grounding the fixed electrode 10 during measurement.

  The reference electrode 20 is preferably an electrode having the same surface area as the electret dielectric film 11. At the time of measurement, a predetermined DC voltage is applied to the reference electrode 20. For this reason, this surface voltage measuring device is a measurement power source system, and a DC voltage source 21 with variable output voltage connected to the reference electrode 20 via a switch 23, and a voltmeter (voltage measuring means) 22 for measuring the output voltage. With.

  In addition, the surface voltage measuring device includes a support housing 30 for juxtaposing the fixed electrode 10 and the reference electrode 20 at the time of measurement. The support housing 30 is made of an electrical insulating material such as synthetic resin or ceramic.

  In the case 30, support columns 32, 32 having the same height and standing at predetermined intervals are erected. A diaphragm 33 made of a metal plate is stretched between the upper ends of the columns 32 and 32. On the lower surface side of the diaphragm 33, a piezoelectric element 34 as a vibration generating means is provided.

  One drive electrode 35 for the piezoelectric element 34 is attached to the lower surface of the piezoelectric element 34. In this embodiment, the diaphragm 33 is also used as the other drive electrode for the piezoelectric element 34, and an oscillator (oscillator) 38 is connected between the diaphragm 33 and the drive electrode 35. In this embodiment, the diaphragm 33 side is grounded, but the drive electrode 35 side may be grounded.

  A measurement electrode 37 is provided on the upper surface of the vibration plate 33 via an electrical insulating material 36. The measurement electrode 37 has a surface area larger than the combined surface area of the fixed electrode 10 and the reference electrode 20, and the surface thereof is preferably smooth.

  As shown in FIG. 1, the fixed electrode 10 and the reference electrode 20 are juxtaposed on the upper surface of the support housing 30 in a non-contact manner. However, the electret dielectric film 11 and the reference electrode 20 of the fixed electrode 10 are disposed. In order to face the measurement electrode 37 with the same surface area, two openings 31a and 31a having the same diameter are formed on the upper surface of the support housing.

  Thereby, the electret dielectric film 11 of the fixed electrode 10 and the reference electrode 20 are placed by placing the fixed electrode 10 and the reference electrode 20 on the upper surface of the support housing 30 so as to be positioned in the openings 31a and 31a. It faces the measurement electrode 37 with the same surface area and the same height. The openings 31a and 31a preferably have a size corresponding to the effective electrode surface of the electret dielectric film 11.

  The surface voltage measuring apparatus includes a level meter (signal measuring means) 42 connected to the measuring electrode 37 via an impedance converter 41 as a signal measuring system. A high input impedance FET (field effect transistor) is preferably used for the impedance converter 41, and an impedance conversion circuit of a capacitor microphone can be substituted.

  The switch 23 included in the measurement power supply system has a live contact 23a and a ground contact 23b connected to the DC voltage power supply 21. In this embodiment, the ground contact 23b is grounded via the diaphragm 33. It is connected.

  According to the present invention, as an example, the surface voltage of the electret dielectric film 11 of the fixed pole 10 is measured as follows.

  First, the switch 23 is switched to the ground contact 23 b side to ground the reference electrode 20, and the fixed electrode 10 and the reference electrode 20 are opened on the upper surface of the support housing 30 with the fixed electrode 10 grounded. The electret dielectric film 11 of the fixed electrode 10 is placed on the portions 31 a and 31 a so as to face the measurement electrode 37.

  As a result, a positive charge is induced on the surface of the portion of the measuring electrode 37 facing the electret dielectric film 11, and this is equivalent to the case where a DC voltage (between grounding) is applied to the measuring electrode 37 from the outside ( DC voltage bias). Since the fixed pole 10 is grounded, the potential of the fixed pole itself does not change.

  Here, a drive signal having a predetermined frequency and a predetermined amplitude is given from the oscillator 38 to the piezoelectric element 34 to operate the piezoelectric element 34 to vibrate the measurement electrode 37. As a result, the capacitance between the fixed electrode 10 and the measurement electrode 37 changes, and an electric signal corresponding to the frequency and amplitude of the oscillator 38 is output from the impedance converter 41 according to the principle of operation of the condenser microphone. In response, the level meter indicates a predetermined reading.

  Next, the switch 23 is switched to the live contact 23 a side, and a positive (predetermined) predetermined voltage is applied from the DC voltage source 21 to the reference electrode 20. As a result, a negative charge is induced on the surface of the portion of the measurement electrode 37 facing the reference electrode 20, and the positive charge on the measurement electrode 37 previously induced is gradually neutralized.

  In this way, when the neutralization of the positive charge proceeds, it is as if the DC voltage bias is lowered, and in the completely neutralized state, the output of the impedance converter 41 is lost, so the reading of the level meter 42 Is minimized (ideally zero).

  At this time, a voltage having a polarity opposite to the DC voltage applied to the reference electrode 20 is equal to the surface voltage of the electret dielectric film 11.

  Therefore, while looking at the level meter 42, the DC voltage applied to the reference electrode 20 is swept from the low voltage to the high voltage, and the DC voltage when the reading of the level meter 42 shows the minimum is obtained by the voltmeter 22. By measuring, the surface voltage of the electret dielectric film 11 can be obtained with the reverse polarity voltage of the measured voltage.

  In addition, since the charge of the reference electrode 20 is discharged by switching the switch 23 to the ground contact 23b side after the measurement and connecting the reference electrode 20 to the ground, there is no trouble in performing the next measurement.

  As described above, according to the present invention, in a state where the diaphragm and the fixed pole are combined in a pseudo manner (a mode close to the actual use state), the fixed pole side is not affected by ambient noise or the like. The surface voltage of the electret dielectric film can be measured more accurately.

  As main components, vibration generating means (preferably piezoelectric elements), impedance converters (preferably FETs for condenser microphones) and level meters, DC power supplies, and reference electrodes may be used. Since it is not a simple part, the measuring device can be constructed at low cost.

  Also, for example, when charged charge leakage occurs in the electret dielectric film or measurement electrode measurement system, the measured value drifts greatly with respect to the voltage applied to the reference electrode. Can be done appropriately.

  In addition, since the two openings 31a and 31a formed in the support housing 30 have the same diameter, the surface area (opposing area) of the fixed electrode 10 and the reference electrode 20 with respect to the measurement electrode 37 is the same. The fixed electrode 10 and the reference electrode 20 do not have to have the same shape.

  For example, a control unit such as a microcomputer may be prepared to adopt an automatic control method.

  That is, the output of the impedance converter is A / D converted, the digital signal is input to a comparator in which a threshold value corresponding to the minimum value of the level meter 42 is set, and the output of the voltmeter 22 is A / D converted. The control unit reads the DC voltage at the time when the output of the comparator is output, and displays the voltage value of the opposite polarity on the display as the surface voltage of the electret dielectric film. Is possible.

The schematic diagram which shows schematically the structure of the surface voltage measuring apparatus of the electret by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Fixed electrode 11 Electret dielectric film 20 Reference electrode 21 DC voltage source 22 Voltmeter (voltage measuring means)
23 switch 30 support housing 31a opening 33 diaphragm 34 piezoelectric element 37 measurement electrode 41 impedance converter 42 level meter (signal measurement means)

Claims (12)

In the electret surface voltage measuring method for measuring the surface voltage of the electret dielectric film, using the electret condenser microphone fixed pole having a polarized electret dielectric film as a measured fixed pole,
A measurement electrode having a smooth surface driven by vibration generating means, a signal measurement means connected to the measurement electrode via an impedance converter, a reference electrode for the fixed pole to be measured, and a DC voltage applied to the reference electrode A DC voltage source for applying the voltage, and voltage measuring means for measuring the DC voltage,
The electret dielectric film of the fixed pole to be measured and the reference electrode are juxtaposed with the same surface area and height with respect to the measurement electrode, and the measurement electrode is vibrated at a predetermined frequency and amplitude by the vibration generating means. In addition, a predetermined DC voltage having a polarity opposite to the charged charge of the electret dielectric film is applied from the DC voltage source to the reference electrode, and the measured value of the signal measuring means is minimized by the voltage measuring means. A method for measuring the surface voltage of an electret, characterized in that the DC voltage is measured.   2. The electret surface voltage measuring method according to claim 1, wherein a piezoelectric element driven by an oscillator is used as the vibration generating means.   3. The electret surface voltage measurement method according to claim 1, wherein the measured fixed pole is connected to the ground at least during measurement.   4. The electret surface voltage measurement method according to claim 1, wherein the reference electrode is connected to ground during non-measurement.   5. The electret surface voltage measuring method according to claim 1, wherein an electrode having the same surface area as the electret dielectric film of the fixed electrode to be measured is used as the reference electrode. In the electret surface voltage measuring device for measuring the surface voltage of the electret dielectric film, using the electret condenser microphone fixed pole having a polarized electret dielectric film as a measured fixed pole,
A reference electrode for the fixed electrode to be measured, a measurement electrode having a smooth surface having a size in which the fixed electrode to be measured and the reference electrode are juxtaposed, and vibration for vibrating the measurement electrode at a predetermined frequency and amplitude Generating means, signal measuring means connected to the measurement electrode via an impedance converter, and a variable DC voltage source for applying a DC voltage having a polarity opposite to the charged charge of the electret dielectric film to the reference electrode And a voltage measuring means for measuring the DC voltage, and an electrical insulating material for juxtaposing the electret dielectric film of the fixed electrode to be measured and the reference electrode with the same surface area and the same height with respect to the measurement electrode. An electret surface voltage measuring device comprising a support housing.   7. The electret surface voltage measuring apparatus according to claim 6, wherein the vibration generating means comprises a piezoelectric element driven by an oscillator.   8. The electret surface voltage measuring apparatus according to claim 6, wherein an FET is used as the impedance converter.   9. The electret surface voltage measuring device according to claim 6, further comprising a ground terminal for connecting the fixed pole to be measured to the ground.   10. The electret surface voltage measuring device according to claim 6, further comprising a changeover switch for selectively connecting the reference electrode to either the variable DC voltage source or the ground. .   The support housing is provided with two openings for making the electret dielectric film of the fixed pole to be measured and each part of the reference electrode face the measurement electrode with the same surface area. The surface voltage measuring device for electrets according to any one of claims 6 to 10.   12. The electret surface voltage measuring device according to claim 11, wherein each of the openings has substantially the same size as an effective electrode surface of the electret dielectric film.

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