JPS58108900A - Electrostatic transducer - Google Patents

Abstract

PURPOSE:To uniform the surface charge density of an electret excellently and to improve the stability greatly by preventing charge leakage due to the supporting structure for a fixed electrode and setting the distance from a diaphragm freely. CONSTITUTION:When charges of an electret element 23 are minus, an electret structure 25 induces plus charges on the reverse side of a dielectric 24 mounted on the element 23 and minus charges having the same polarity with the element 22 on the top side, namely, performs dielectric (polarization) operation. Firstly, a switch SW connected to the dielectric 24 is closed to ground the dielectric 24, and then the switch SW is opened to obtain insulation from the earth. For example, an insulating pair of tweezers are used to mount the dielectric 24 on the surface of the electret element 23 while holding the zero charge state, thus obtaining the dielectric operation.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to an electrostatic lid transducer, in particular to a pot structure with nine fixed poles, in which a dielectric material is laminated on the surface of an electret element. Regarding.

TECHNICAL BACKGROUND OF THE INVENTION As is well known, electrets have a property in which the electric charge that is applied to them lasts semi-permanently, and they are widely used in various fields as electrostatic transducers and the like.

FIG. 1 shows the principle structure of a conventional condenser microphone using such an electret. An electret is formed by coating an electret material 12 such as a polymer film on a back electrode 11 made of a conductive metal substrate. The electret structure opening is used as a fixed pole.

Then, a diaphragm 16 made of a metal thin film or the like stretched over the retaining ring 15 via a spacer 14t made of insulating material or the like is placed opposite to the fixed pole made of the electret structure 13 as a movable pole. electric unit is configured.

When the diaphragm 16 of such an electrostatic unit is displaced by external sound pressure, the electrostatic capacitance C between the two electrodes will change, but the charge Q will change from Q=CV. (In this case, given by the electret structure JjK) is constant, when the voltage V between both electrodes is changed.

Therefore, by converting the impedance and extracting it as a low impedance via a variable voltage VT field effect transnoster FIT or the like, a capacitor microphone that electrostatically converts sound pressure into an electric signal can be realized.

Figure 2 shows the case where it is applied to a capacitor and a telephone unit.In principle, the operation is opposite to that of the condenser microphone described above. It becomes possible to convert to . In this case, a pair of electret structures 1B and 13f are connected to the holding ring 15' with the diaphragm 1- as a movable pole in the center, and a pair of electret structures 1B and 13f are placed on both sides via spacers 14 and 14, respectively. 25, a so-called Shugur type capacitor headphone unit is realized. In addition, each electrode of such a headphone unit is equipped with a signal source ms>transformer T.
An electric signal is applied through the high resistance R1R and the high resistance R1R.

By the way, as described above, an electrostatic transducer using an electret structure as a fixed pole does not require a DC power supply for polarization or biasing, unlike ordinary transducers, so it can be made simple in structure and as small as possible. It becomes possible,
This has the advantage that the price can be reduced accordingly.

However, the most important electret structure is
It has a serious drawback in that it tends to adversely affect various characteristics as a transducer due to large variations in surface charge density, that is, large unevenness in charge distribution.

FIG. 3 shows an actual measurement example of the surface charge distribution of such a conventional electret structure, in which the electret material 12 is deposited on the back electrode 11 made of an aluminum plate with an outer diameter of 60 mm to form an electret structure. However, as can be seen from the figure, it can be seen that the voltage varies within a very large range of several hundred volts.

In addition, in liilml, the flat part 17b at the center excluding the surrounding wavy uneven part Jja is a non-electret-shaped part provided for manufacturing reasons, etc.
There is a problem in that the surface charge density of the electrostatically charged portion 11b is even larger than the variation in the surrounding area and is extremely reduced, and the effective area that takes part in electrostatic action is reduced accordingly. Various conversion characteristics including the conversion efficiency of the electric type transformer and -server are further deteriorated.

In addition, in the conventional electret structure, the surface of the electret material 12 is exposed so as to be in direct contact with the air, so it has poor moisture resistance and has problems with stability over time, or has a short lifespan. It had a very serious drawback.

Purpose of the Invention Therefore, the present invention has been made in view of the above-mentioned points, and has been developed to improve the stability of the electret surface by uniformizing the surface charge density of the electret. By using an electret structure formed by laminating a dielectric material on the surface of the element as a fixed pole, the structure prevents charge leakage due to the supporting structure of the fixed pole and allows the distance from the diaphragm to be freely set. In this way, it is an object of the present invention to provide an extremely good electrostatic transducer in which the conversion characteristics are as excellent as possible and the conversion characteristics are as good as possible.

Summary of the invention That is, the electrostatic transducer according to the present invention has the following features:
electret, which uses charges induced on the dielectric layered on the surface of the electret element to make the electret surface charge density uniform and stable;
) The structure is used as a fixed pole, but the dielectric layered on the electret element is made smaller than the spacer, and the fixed pole is moved a predetermined distance through the spacer without the armpit dielectric touching the spacer. It has a special gIL in that it is configured such that it is supported so as to be opposed to the diaphragm.

An Example of Sound Generation First, the principle of the electret structure used in the ζO invention will be explained.

That is, as shown in FIG. 4, the back electrode 21K, which is made of a highly conductive metal base and has the same potential as the ground, is connected to the back electrode 21K, for example, P P ,
On the electret element 23 formed by depositing an electret material 22 made of a polymer film such as TFI or FKP and converting it into an electret, a conductive metal having a larger area and shape than the electret element 23 is formed. An electret structure is constructed by laminating four dielectric bodies 24 made of a material or an organic material in a state insulated from the ground, so that charges of the same sign as those of the electret element 23 appear on the surface of the dielectric bodies 240. This has been realized.

Here, the dielectric material 24 differs from the fact that it usually refers only to an insulator; however, as mentioned above, the dielectric material 24 is a conductive metal material and an organic material (
(This will be described later) is also referred to as otm. In addition, organic materials here include thermoplastic and thermosetting resin materials, composite materials that combine these with different materials, and dielectric materials such as glass, and have a volume resistivity of 10120 - Kokufu. A general term for so-called insulating materials.

Then, the electret structure 25 configured as described above
When the electric charge of the electret element 23 has a negative sign O, the back side of the dielectric 24 placed on the electret element 23 has a positive sign ■, and the front side @ has a negative sign of the same electric charge as the element 22. A phenomenon such as that induced by the charge of O] dielectric (
polarization) effect is brought about. In this case, the presence of the dielectric 24 not only causes the above-mentioned dielectric effect, but also
As will be described later, it is important that the surface charge density of the electret structure 25 is well made uniform and its stability is ensured.

FIG. 5 shows a specific example of obtaining the electret structure 25 realized as described above.
When the switch SW connected to 4 is closed, the dielectric 2
4t - Same potential as earth! After setting it to J zero charge state,
When switch swt is opened, it becomes insulated from ground.

Then, for example, using an insulating force, a zero-charge state lI
! If the wrinkled dielectric material 24 is placed on the surface of the electret element 23 up to a point t where t is maintained, a dielectric effect will be produced as described above.

In this case, if the dielectric 24 is a conductive metal material, charges will be induced instantaneously, but if it is an insulating material, it will take a certain amount of time (for example, 30 (about 1 minute).

Furthermore, when the switch SW is closed again from such an induced state, if the dielectric material 24 is made of metal, the electric charge disappears immediately to zero potential, but in the case of an insulating material (however, in the case of a fluororesin type material, the electric charge disappears immediately) In the case of Oka et al., the charge gradually decreases and disappears, so that it has a certain time constant with respect to the movement of charge.

No. ** shows a case where the dielectric 24 is made of glass with a smaller area shape than the electret element as an example of a different body of Rin. (The electric charge of the electret element alone is approximately 700V.
It was confirmed that the dielectric charge of the glass dielectric material was induced to about 5 sovs degrees with respect to K. Note that the glass dielectric 2
4m is advantageous when the surface potential needs to be adjusted because the fall time from the dielectric state when the switch SW is closed again is relatively fast for ABS resin-based materials and slow for metal materials. be.

FIG. 7 shows one index of stability over time (leakage characteristics) of the charge induced on the surface of the dielectric 24 as described above. The same applies to the case of the system), and good stability is obtained without any change from the initial state. Furthermore, in case of an insulating material such as Mu18 resin, for example, leakage subsides after about 5 minutes from the initial state, and good stability is obtained thereafter.

By the way, such stability is achieved because the electret structure Lj places the electric body 24 on the surface K11 of the electret element 23, so that the surface of the element 23 is ff1lit, unlike in the conventional case. This is helped by the fact that it is not exposed so that it is in direct contact with the air. By protecting the surface of the electret element 23 with the dielectric material 24, it is not only highly moisture resistant, which is advantageous in terms of stability over time, but also makes it as stable as possible to extend its service life. This is because it is possible to ensure sex.

Note that if the surface of the electret element 230 is provided with wave-like irregularities as shown in FIG. It will be possible to add even more stability on top of this.

Figure 9 shows the electret structure L! This shows an actual measurement example of the surface charge distribution of the electret material 2 on the back electrode JJa made of an arsenium plate with an outer diameter of
A dielectric material 24k having the same area shape as the electret 2a is placed on the element 23h.
This is the distribution state of charges induced on the surface of the dielectric 24b. That is, as can be seen from this figure, the surface charge density is uniform in all parts and hardly varies, unlike in the conventional case. Note that the slight decrease near both ends in the figure is due to the accuracy of the measuring instrument and is not essential.

In FIG. 9, the surrounding wavy uneven portion xxb
The central flat part 22 @ except for the non-electret part is a non-electret part provided for manufacturing reasons as in the conventional case, but there is no change in the center part of the surface of the dielectric 24b corresponding to the non-electret part. No deterioration was observed, and a uniform charge density was obtained, comparable to that of the surrounding area. However, unlike the conventional case, even if there is a non-electret portion, the effective area that takes part in the electrostatic action will not be reduced in the slightest; in this respect, the electrostatic transformer - It becomes possible to significantly improve various conversion characteristics including conversion efficiency as a sensor.

That is, the electret structure formed by placing the dielectric material 24 on the electret element 23 as described above not only exhibits a phenomenon of inducing a predetermined charge based on the electret charge on the surface of the dielectric material 24, but also exhibits a phenomenon in which the dielectric material 24 is In addition to the improved stability brought about by the protection effect of the electret element 23, the surface charge 1! brought about by the surface charge uniformization effect. It has now become clear that it has the extremely excellent advantage of making the f degree as uniform as possible.

FIG. 10 shows a basic example of a transducer using the above-described electret structure 26 as a fixed pole, and in this example, it is applied to a microphone.

In other words, it has a predetermined distance via a space 34 from the diaphragm 33 which is mounted on a conductive retaining ring 32 on the front surface 11 of the metal case 31 and is supported in good condition. This supports the electret structure ZS which becomes a fixed pole. Note that 35 is an insulator base that supports the bottom of the electret structure 1j-,
36 is an extraction electrode for a fixed electrode.

However, in the configuration of this basic example, the electret structure used as a fixed pole has a spacer 34 on the dielectric 24 laminated on the electret element 23.
Since it is supported so as to be opposed to the diaphragm 33 in contact with the diaphragm 33, the electric charge induced on the dielectric 24 can leak through the spacer 34 with high uniformity and stability. Therefore, there was a problem in that high sensitivity could not be achieved.

In addition, in the case of this basic example, the distance between the fixed pole and the diaphragm 33 is uniquely determined by the thickness of the diaphragm 34, so there is less freedom in design in various aspects. It also had the problem of being inhibited.

Next, the present invention, which is an improvement on the problems of the above-mentioned basic example, will be described as an embodiment of the present invention when applied to a microphone.

That is, as shown in IEI IIIK, a conductive retaining ring 4 is attached to the front surface of the metal case 41, which serves as a grounding path.
The electret structure 25'f, which serves as a fixed pole, is supported at a predetermined distance via a spacer 44 with respect to the diaphragm 43, which is supported and supported in a stretched state on the electret structure 25'f.
In this case, the dielectric body 24' of the electret structure 25' is smaller than the spacer 44, and the spacer 44 is smaller than the dielectric body 24'.
It differs from the basic example described above in that it is supported directly on the electret element 23' rather than on the electret element 23'. Note that 45 is a pace (To) and 46 is an extraction electrode.

Therefore, according to the electrostatic transducer (micron in this case) K configured as described above, it becomes a fixed pole with a space in which the spacer 44 does not substantially come into contact with the dielectric J4'. Since the electret structure 2 J' is supported so as to be opposed to the diaphragm 43 at a predetermined distance, the charge induced on the dielectric body 14' does not leak through the spacer 44, so that It becomes possible to achieve high sensitivity.

In addition, in the case of , the distance between the fixed pole and the diaphragm 43 is not uniquely determined only by the thickness of the spacer 44, but can be arbitrarily set by the thickness of the dielectric 24'. This makes it possible to ensure design freedom in terms of stocks.

Figure 12 shows the electret structure 2 used in this invention.
An example of actual measurement of the surface charge density of 5' is shown. That is,
This is a back electrode 21 made of an aluminum plate or the like with an outer diameter of 60 mm.
4) With the same diameter as that on a, an electret material zxht such as chemical resin is deposited to form an electret element 23&A metal body is crimped or vapor-deposited concentrically with it and has an outer diameter of about 46mmφ. In the case where the dielectric material 24' is laminated, the surface charge density induced on the dielectric material j4', which has a diameter substantially smaller than that of the electret element 23a by '4b', is similar to that of the principle configuration shown in FIG. It can be seen that it is uniform in all parts with almost no variation.

It goes without saying that this invention is not limited to the embodiments described above and illustrated, and that various modifications and applications can be made without departing from the gist of the invention.

Effects of the Invention Therefore, as detailed above, according to the present invention, a dielectric material is laminated on the surface of the electret element so that the electret surface charge density can be uniformized well and the stability can be greatly improved. When using the electret structure formed by the electret structure as a fixed pole, it is possible to prevent charge leakage due to the support structure of the skeleton fixed pole, and to improve the conversion characteristics by setting the distance from the diaphragm. This makes it possible to provide an extremely efficient electrostatic transducer that can be used as a tortoise with excellent performance.

[Brief explanation of drawings]

Figures 1 and 2 are illustrations of the basic configuration of conventional condenser microphones and capacitors, and Figure 3 shows the surface charge density of the conventional electret structure used in Figures 1 and 2. Actual measurement diagram, Figure 4 is a configuration explanatory diagram for explaining the principle of the electret structure used in this invention, Figures 5 and 6 are diagrams showing a specific example of Figure 4, and Figure 7 is a wc4 diagram showing the dielectric structure. Fig. 8 is a diagram showing another example of Fig. 4, and Fig. 9 is an actual measurement diagram illustrating the surface charge density of the electret structure shown in Fig. 4. 10 and 11 are structural explanatory diagrams showing a basic example and an embodiment of the present invention when the electret structure shown in FIG. 4 is applied to a condenser microphone, and FIG. 12 is an electret structure used in FIG. 11. FIG. 2 is an actual measurement diagram illustrating the surface charge density of FIG. 211... Back electrode, 22a... Electret material,
XS*...Electret element, 24'...Dielectric, 25'...Electret structure (fixed pole), 41.
... Case, 42 ... Holding ring, 43 ... Vibration plate (movable pole), 44 ... Spacer, 45 ... Pace,
46...Extraction electrode.

Claims (1)

[Claims] In an electrostatic transducer in which a fixed pole is placed opposite a diaphragm serving as a movable pole at a predetermined distance via a spacer, the fixed pole is placed on an electret element and is made smaller than the spacer. An electrostatic transducer characterized in that the spacer is inserted between the electret element and the diaphragm without contacting the dielectric.