JPS6025200Y2 - piezoelectric buzzer - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a piezoelectric buzzer, and its purpose is to increase the sound pressure and to make the shape thinner.

A piezoelectric buzzer has a structure in which a thin piezoelectric ceramic plate is bonded to a diaphragm such as a thin metal plate, and it generates sound by the flexural vibration generated by the expansion and contraction of the piezoelectric ceramic plate when an alternating current signal is applied to the piezoelectric ceramic plate. Because the diaphragm acts as a direct sound transducer, it is highly efficient, and because it is thin, it is often used as a buzzer that does not consume current.

This piezoelectric buzzer is generally used for external excitation, in which the outer periphery of a diaphragm such as a metal plate is fixed and sound is generated by an external signal.

However, in this type of usage, the input impedance of the piezoelectric buzzer is large, making it difficult to receive large inputs, making it unsuitable for usage that generates large sound pressures.

In general, for generating large sound pressure or for automatic vibration, a piezoelectric buzzer is used with its nodes fixed during free vibration.

This will be explained based on the diagram.

Figure 1A9 shows a piezoelectric buzzer. In the figure, 1 is a thin piezoelectric ceramic plate, and 2 is a diaphragm such as a thin metal plate, which are bonded to the piezoelectric ceramic plate 1 and integrated.

FIG. 2 shows the vibration characteristics at fundamental resonance when an alternating current signal is applied to the piezoelectric ceramic plate 1, and 3 indicates a node.

In this case, since the piezoelectric buzzer is disk-shaped, the joint portion 3 is also circular.

FIG. 3 shows an example of a conventional piezoelectric buzzer in which the above-mentioned joints are fixed in a casing. It is elastically fixed by an elastic body 7.

A sound emitting hole 5 is provided in the case 4a on the side of the diaphragm 2 on which the piezoelectric ceramic plate 1 is not attached, and sound is emitted through the sound emitting hole 5.

Further, electrical connection with the electrodes of the piezoelectric ceramic plate 1 is made by soldering lead wires or the like to a terminal 9, and at this time, one of the electrodes of the piezoelectric ceramic plate 1 is taken out via the diaphragm 2.

Furthermore, in order to increase the sound pressure, the sound emission hole 5 and the protrusion 6 are
This is often achieved by acoustic resonance between the diaphragm 2 and the space 8 surrounded by the diaphragm 2.

Here, as is clear from FIG. 2, the front and back of the diaphragm 2,
That is, the phases of the sounds emitted from the bonded surface and the other surface of the piezoelectric ceramic plate 1 are 180 degrees out of phase.

Therefore, although it depends on the shape and frequency of the piezoelectric buzzer,
The sound is attenuated by the loop.

For this reason, in FIG. 3, the projection 6 prevents the back side (piezoelectric ceramic plate 1 side) from going around, and the space 8 on the sound emission hole 5 side is separated from the opposite side.

However, in this case, the sound emitted from the sound emitting hole 5 is only due to the vibration of the diaphragm 2 within the space 8, and the vibrations of other parts are not effectively utilized as sound.

Also, if the sound emitting hole is placed opposite to that shown in Fig. 3, that is, placed on the terminal 9 side, the effective vibration area of the diaphragm 2 will increase, but the back side (
Attenuation of sound pressure occurs due to wraparound from the side to which the piezoelectric ceramic plate 1 is not attached.

In order to reduce this as much as possible, we set a distance of λ/4 of the buzzer as the distance between the sound emission hole and the bottom of the case that opposes the diaphragm, and used the bottom of the case as a reflector.
The phase of the sound coming from the bottom of the case is shifted by 180 degrees to ensure the sound pressure.

As described above, the conventional structure has problems such as a reduction in the effective vibration area or an increase in the size due to the inclusion of the 1/4 reflector.

The present invention was devised to eliminate such problems, and an embodiment thereof will be described below with reference to FIG. 4, with the same numbers assigned to the same parts as above.

As shown in FIG. 4, in the present invention, a thin coating 10 made of vinyl chloride or the like is provided in the gap between the edge portion of the diaphragm 2 and the case 4a so as not to clamp vibrations, thereby forming a sealed space 11.

In FIG. 4, the sound emitting hole 5 may be provided on the terminal 9 side.

Therefore, in the present invention, one of the front and back sides of the diaphragm 2 is made into a closed space 11 (or 12).

The piezoelectric buzzer of the present invention is constructed in this way, and according to the present invention, the effective area from which sound can be extracted is all over the area, and the sound does not go around from the back side, so the sound pressure is attenuated. It is something that can be used without any problems, and is extremely useful.

[Brief explanation of the drawing]

Figure 1 (a) is a top view and front view showing an example of a piezoelectric buzzer, Figure 2 is a diagram explaining the vibration state of the buzzer, Figure 3 is a cross-sectional view of a conventional piezoelectric buzzer, and Figure 4 is a book. FIG. 2 is a sectional view showing an embodiment of the piezoelectric buzzer sounding body according to the invention. 1... Piezoelectric ceramic plate, 2... Vibration plate, 3
...Knot, 7...Elastic body, 11, 12
...closed space.

Claims (1)

[Scope of utility model registration request] In a piezoelectric buzzer having a structure in which the vicinity of a node of a piezoelectric sounding body in which a piezoelectric ceramic plate is bonded to a diaphragm such as a metal plate is supported in a case by an elastic body during free vibration, an end of the diaphragm and the case are connected. A piezoelectric buzzer, characterized in that the piezoelectric buzzer is connected by a film, and a sealed space is formed between the portion of the case where the sound emitting hole is not formed and the diaphragm.