JPH0110080Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an electroacoustic transducer suitable for use in piezoelectric buzzers and the like.

Figure 1 shows a conventional electroacoustic transducer of this type.
Give an example. In this figure, a main electrode 2 and a return electrode 3 are formed on one surface of the piezoelectric ceramic vibrator 1, separated by a gap 4, and a counter electrode is formed on the other surface of the piezoelectric ceramic vibrator 1. A three-terminal electroacoustic transducer is constructed. In this case, each electrode is generally formed by printing, and the gap 4 has a dimension of about 500 to 800 μ to ensure that the main electrode 2 and the return electrode 3 do not come into contact with each other.

FIG. 2 shows an example of an oscillation circuit using such a three-terminal electroacoustic transducer. In this case, the main electrode 2 and counter electrode 5 of the three-terminal electroacoustic transducer are connected between the collector and emitter of the oscillating transistor Q, and the feedback electrode 3 is connected to the base of the transistor Q.
is connected.

By the way, the oscillation conditions of conventional electroacoustic transducers are very critical, and there are cases where the oscillation circuit does not produce sound. One of the reasons for this is that in the conventional case, the gap 4 is relatively wide at 500μ to 800μ, and the capacitance C between the main electrode 2 and the return electrode 3 is
The present inventor found that the value is as small as 40 pF to 70 pF.

In the electroacoustic transducer shown in FIG.
The relationship between the length L of the main electrode 2A in contact with the main electrode 2A and the capacitance C between the main electrode 2A and the return electrode 3A is expressed as the fourth
As shown in the figure. As can be seen from this figure, it can be seen that the capacitance can be increased by increasing the dimension L. Further, the relationship between the dimension 1 of the gap 4A and the capacitance C is shown in FIG. It can be seen from this figure that the capacitance increases as the dimension l decreases.

When a main electrode, a return electrode, and a counter electrode are provided on a disc-shaped piezoelectric ceramic vibrator with a diameter of 20 mm and a thickness of 0.25 mm,
When the distance between the main electrode and the return electrode is 500μ, the capacitance is 60pF, 100pF at 300μ, 180pF at 200μ, and 100μ
It turned out to be about 350pF.

In view of the above points, the present invention has been developed by setting a large capacitance between the main electrode and the return electrode, easing the oscillation conditions, and making it possible to obtain stable sound for various circuits. The present invention aims to provide an acoustic transducer.

Examples of the electroacoustic transducer according to the present invention will be described below along with comparative examples.

FIG. 6 shows a comparative example of piezoelectric ceramic vibrator 1B.
A three-terminal electroacoustic device is shown in which a main electrode 2B and a return electrode 3B are separately provided on one side of the screen. Shows a structure set large enough. However, since the feedback electrode 3B is provided only on the periphery of the piezoelectric ceramic vibrator 1 near the vibration nodes, a sufficient feedback voltage cannot be obtained when used in an oscillation circuit, making it impractical. It can be seen from FIG. 6 that consideration must be given not only to the capacitance but also to the shape of the return electrode.

FIG. 7 shows the first electroacoustic transducer according to the present invention.
An example is shown. In this figure, a main electrode 2C and a return electrode 3C are provided on one surface of a piezoelectric ceramic vibrator 1C, separated by a gap 4C.
A counter electrode is provided on the other surface of C. In this case, the distance between 4C and 4C is very small, preferably 50μ~
The main electrode 2C and the return electrode 3 are formed with a thickness of about 400μ.
The capacitance between the capacitance and the capacitance should be about 80 pF to 220 pF. Further, the shape of the feedback electrode 3C is separated so as to include a portion near the center of the vibrator 1C so that a sufficient feedback voltage can be obtained.

According to the configuration of the first embodiment, since the distance 4C is made very small, the capacitance between the main electrode 2C and the return electrode 3C can be increased, and the oscillation conditions can be made gentle. Therefore, it is possible to stably operate various oscillation circuits and generate buzzer sounds and the like.

FIG. 8 shows a second embodiment of the present invention. In this figure, one surface of the piezoelectric ceramic vibrator 1D includes a main electrode 2D, a first feedback electrode part 3D separated from the main electrode 2D by a small distance 4D, and a wide space 4D.
A second return electrode section 3E is formed which is separated from the oscillator 1D via the oscillator 1D, and a counter electrode is formed on the other surface of the vibrator 1D. In this case, the return electrode is the main electrode 2
It is composed of a first return electrode section 3D and a second return electrode section 3E, which are separated from each other by D.
In actual use, as shown in FIG. 9 or 10, the first return electrode part 3D is connected to the main electrode 2D side with conductive paint 10, or both electrode parts 3D and 3E are connected with conductive paint 11. Connect and use. That is, if the structure is as shown in FIG. 9, a three-terminal electroacoustic transducer having return electrodes separated by a wide space 4E can be realized, and if the structure is as shown in FIG. A three-terminal electroacoustic transducer having a separated return electrode can be obtained, and the capacitance between the main electrode and the return electrode can be adjusted over a wide range depending on the oscillation conditions of the oscillation circuit used. . As a result, the range of application of the electroacoustic transducer can be greatly expanded.

As explained above, according to the present invention, at least a portion of the gap between the main electrode and the return electrode is 50 μm or more.
By forming it in an extremely small space of 400μ,
Reduce the capacitance between the main electrode and the return electrode to 80 pF or more.
It is possible to obtain an electroacoustic transducer that can operate stably under various oscillation conditions with a large value of 220 pF.
It is particularly effective when used in piezoelectric buzzers and the like.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing a conventional electroacoustic transducer, Fig. 2 is a circuit diagram showing an example of an oscillation circuit using the electroacoustic transducer, and Fig. 3 is a dimension L and a dimension l in the electroacoustic transducer. 4th plan view for explaining the relationship between the main electrode and the capacitance between the main electrode and the return electrode.
The figure is a graph showing the relationship between dimension L and capacitance C.
Fig. 5 is a graph showing the relationship between dimension l and capacitance C, and Fig. 6 is a comparative example of the embodiment of the present invention, in which a return electrode is provided along the periphery of the piezoelectric ceramic vibrator. 7 is a plan view showing the first embodiment of the electroacoustic transducer according to the present invention, FIG. 8 is a plan view showing the second embodiment of the present invention, and FIGS. 9 and 10 are FIG. 9 is a plan view showing an example of use of the electroacoustic transducer of FIG. 8; 1,1B to 1D...piezoelectric ceramic vibrator, 2,2
A to 2D...main electrode, 3,3A to 3C...return electrode, 3D,3E...return electrode part, 4,4A to 4E...between, 10,11...conductive paint.

Claims (1)

[Claims for Utility Model Registration] (1) In a three-terminal electroacoustic transducer in which a main electrode and a return electrode are separately provided on one surface of a piezoelectric ceramic vibrator, An electroacoustic transducer characterized in that at least a part of the main electrode and the return electrode are formed in an extremely small range of 50μ to 400μ, and the capacitance between the main electrode and the return electrode is set to 80pF to 220pF. (2) The return electrode has a first return electrode part with a small gap to the main electrode, and a second return electrode part with a wide gap, and the connection between the two return electrode parts makes it possible to connect the main electrode to the main electrode. The electroacoustic transducer according to claim 1, which is configured to adjust the capacitance between the return electrodes.