JPS6133506B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a highly sensitive piezoelectric electroacoustic transducer.

Conventionally, in piezoelectric electroacoustic transducers using ceramic piezoelectric plates, diaphragms as shown in FIGS. 1, 2, and 3 have been used. FIG. 1 shows a typical sounding device, in which full-surface electrodes are used on both sides of a ceramic piezoelectric plate. Figures 2 and 3 are for a sounding body used in combination with a self-excited oscillation circuit.The electrode on the side that is bonded to the metal plate is a full-surface electrode, and the electrode on the opposite side has two electrodes: a main electrode and a return electrode. It is divided into.

In Figures 1 to 3, each figure (a) is a perspective view of the diaphragm, each figure (b) is a diagram of the electrode pattern on the surface of the ceramic piezoelectric plate that is not bonded to the metal plate, and each figure (c) is a diagram of the electrode pattern on the surface of the ceramic piezoelectric plate that is bonded to the metal plate. FIG. In these figures, 1 is a metal plate, 2
is a ceramic piezoelectric plate, 3 and 3' are full-surface electrodes on the front and back surfaces, 4 is a main electrode, and 5 is a return electrode. The diaphragms shown in FIGS. 1 to 3 are all clamped at their peripheral edges and attached (not shown) to form a piezoelectric electroacoustic transducer.

Figure 4 shows the voltage sensitivity when used as a sound receiver and when used as a sounding body when the resonant frequency is kept constant and ceramic piezoelectric plate thickness/metal plate thickness = 1, and (diameter of ceramic piezoelectric plate)/ (metal plate clamp diameter) is shown as a curve. Usually the clamp diameter is 2 to 3 times larger than the diameter of metal plate 1.
mm is selected as the smaller value. Here, the electrodes include a full-surface electrode 3 having a diameter equal to the diameter of the ceramic piezoelectric plate 2;
It was set to 3'. From Figure 4, the voltage sensitivity (curve) as a sound receiver reaches its maximum at around (diameter of ceramic piezoelectric plate)/(clamp diameter of metal plate) = 0.5, but the voltage sensitivity (curve) as a sounding body is around 0.85. It can be seen that the maximum value is .

Conventionally, in the configurations shown in Figures 1 to 3, (diameter of ceramic piezoelectric plate)/(diameter of metal plate clamp) was
It was chosen to be around 0.65 to 0.95. This is because converters with these configurations are mainly used as sounding bodies such as buzzers and telephone receivers, and are designed with emphasis on sensitivity as a sounding body.

However, if this is used as a sound receiver as it is, the voltage sensitivity will be low (compared to the highest voltage sensitivity).
(3dB lower) resulting in a decrease in the S/N ratio. Conversely, if the design focuses on voltage sensitivity as a sound receiver, the voltage sensitivity as a sounder will be low (more than 6 dB lower than the maximum). In the end, there was a drawback that it was necessary to design two types of diaphragms for different uses, or to sacrifice the sensitivity of one or both.

This invention was made in order to solve the above-mentioned drawbacks and at the same time to further increase the sensitivity of the sound receiving body. is provided in the center of the piezoelectric plate. Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 5 shows a diaphragm for a sound receiver showing an embodiment of the present invention. Figure 5a is a perspective view of the diaphragm;
Figure b is a diagram of the electrode pattern on the side that is not bonded to the metal plate, and Figure 5c is a diagram of the electrode pattern on the side that is bonded to the metal plate. In these figures, 1 is a metal plate, 2 is a ceramic piezoelectric plate, 3' is a full-surface electrode, and 4 is a ceramic piezoelectric plate.
a is an electrode.

Regarding the diaphragm for a sound receiver shown in FIG. 5, a high sensitivity sound receiver can be realized by providing an electrode 4a in the center.

The relationship between the diameter of the electrode 4a and voltage sensitivity will be described in detail below.

Figure 6 shows, as an example, (diameter of ceramic piezoelectric plate)/(diameter of metal plate clamp) = 0.85 (dimension ratio at which the voltage sensitivity of the sounding element is maximized in Figure 4). plate clamp diameter) and
An example of the relationship with sound receptor sensitivity is shown. The curve is electrode 4
When a is used, the curve shows the relative sensitivity of the sound receiver when the entire surface electrode is used and the ratio of the diameter of the ceramic piezoelectric plate to the diameter of the metal plate is changed (same as in FIG. 4). However, the resonant frequency is assumed to be constant.

From FIG. 6, it is clear that the diameter of the ceramic piezoelectric plate 2 is selected so that the sensitivity of the sounding body is maximized, and when used as a sound receiver, the diameter of the ceramic piezoelectric plate 2 is selected so that the sensitivity of the sounding body is maximized. It can be seen that when only the diameter of 4a is reduced, for example, when it is 30% or less of the clamp diameter of metal plate 1, the sensitivity is about 2 dB higher.
Furthermore, compared to the case where the sound generating body which maximizes the sensitivity is used as the sound receiving body with the entire surface electrode 3' as it is, a sound receiving body having a sensitivity higher by approximately 5 dB can be realized. Furthermore, the diameter of the electrode 4a should be 60% or less of the clamp diameter of the metal plate 1, that is, the diameter of the electrode 4a should be 70% or more of the diameter of the ceramic piezoelectric plate 2, and the area should be 1/2 or less of the area of the ceramic piezoelectric plate 2. In this way, it is possible to realize a sound receiving body with higher sensitivity than before without reducing the sensitivity as a sounding body. In this case, metal plate 1,
The same ceramic piezoelectric plate 2 can be used, and simply changing the electrode diameter on one side of the ceramic piezoelectric plate 2 is advantageous in terms of mass production efficiency and parts management, and even when used as a diaphragm.
Since they are mechanically and acoustically the same, transducer design is easy.

The electrode on the side to be attached to the metal plate 1 may be the entire surface electrode 3', the same size as the electrode 4a on the side to which it is not attached, or an intermediate size between these.

Further, although the ceramic piezoelectric plate 2 is used in the above embodiment, it may be any other piezoelectric plate, and another substrate such as a non-conductive plate may be used in place of the metal plate 1. Further, the shape of the electrode 4a is not limited to a circular shape, and a rectangular shape, a polygonal shape, or the like can also be used.

As explained in detail above, the present invention provides electrodes on the surface of the piezoelectric plate that are not attached to the substrate of the piezoelectric plate.
Since this is made into a piezoelectric electroacoustic transducer by forming it in the center of the piezoelectric plate, it is possible to obtain a sound receiving body with higher sensitivity than conventional ones, and the S/N ratio can be improved. Furthermore, since this invention only changes the shape of the electrodes of the piezoelectric plate, it is possible to use substrates and piezoelectric plates of the same size for the sound receiving body and the sounding body, thereby achieving mass production effects and simplifying component management. It has the advantage of being able to be quantified.

[Brief explanation of the drawing]

Figure 1 shows a conventional diaphragm for a sounding body, and Figures 2 and 3 show diaphragms for a sounding body used in combination with a conventional self-excited oscillation circuit. A perspective view of the plate, each figure B is a plan view of the electrode pattern on the side that is not bonded to the metal plate, each figure C is a plan view of the electrode pattern on the side that is bonded to the metal plate, and Figure 4 is a plan view of the electrode pattern on the side that is bonded to the metal plate. (Metal plate thickness)/
Relative voltage sensitivity of the converter when (ceramic piezoelectric plate thickness) = 1 and (diameter of ceramic piezoelectric plate) /
Figures 5a, b, and c are perspective views of a diaphragm for a sound receiver showing an embodiment of the present invention, and electrode patterns on the surface not bonded to the metal plate. Figure 6 shows the relationship between the electrode diameter and sensitivity when the ceramic diameter is set to a value that maximizes the sensitivity of the sounding element. It is a diagram. In the figure, 1 is a metal plate, 2 is a ceramic piezoelectric plate,
3 and 3' are full surface electrodes, and 4a is an electrode.

Claims (1)

[Claims] 1. In a piezoelectric electroacoustic transducer using a piezoelectric bimorph diaphragm formed by pasting a piezoelectric plate on a substrate, the electrode on the side of the piezoelectric plate that is not pasted on the substrate is 1/2 or less of the area of the piezoelectric plate. , and a piezoelectric electroacoustic transducer characterized in that this is formed in the center of a piezoelectric plate.