JPH03231600A - Piezoelectric sounder - Google Patents

Abstract

PURPOSE:To attain a low frequency and broad band characteristic even with a thin profile by forming a front air chamber having a sounding hole and a rear chamber having a leakage hole to both sides of a diaphragm and arranging the sounding hole and the leakage hole so that a case itself integrated with the sounder acts like a buffle. CONSTITUTION:The piezoelectric sounder is provided with a stationary body 13 having a step 16 coincident with an outer shape of a diaphragm 12 and air chamber forming plates 14, 15 to fix the diaphragm 12. A rear air chamber 31 has a leakage hole 33, a front air chamber 32 has a sounding hole 34, at least one of the leakage hole 33 and the sounding hole 34 is placed at a right angle with respect to the vibrating direction of the diaphragm 12 and the direction of the two holes is selected to have an angle of 90 deg. or over with respect to the center of the diaphragm 12, the volume of the rear air chamber 31 is selected smaller than the front air chamber 32 and the opening area of the leakage hole 33 is selected to be 0.5mm<2> or over. Thus, the optimum shape is attained easily and the characteristic of low frequency and broad band is obtained even with thin profile.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric sounding body, and particularly to a piezoelectric sounding body that can be installed in a thin device such as a card type device.

[Technological environment]

In recent years, piezoelectric sounding bodies have been required to be smaller and thinner as communication equipment has become smaller and thinner.
As a card-type device, there is a need for performance that can be installed in card-type telephones and card-type pagers.

In addition to the piezoelectric type, there are electromagnetic types as sounding bodies, but while the electromagnetic type can achieve a high sound pressure level, it requires a large drive current and consumes a lot of power, and it is difficult to use small batteries such as those used in card-type devices. If it cannot be mounted, there is a problem with its use in terms of power consumption, and the use of a piezoelectric type is strongly desired.

In addition, for sounds that are not unpleasant for humans to hear, low frequency sounds are preferable to high frequency sounds, and moreover, it is preferable to generate melodies (not pseudo-sounds by chopping single frequency sounds) rather than single sounds. Low-frequency, wide-band sounding bodies have become desirable.

[Common technology]

In general, piezoelectric sounding bodies are made by bonding a piezoelectric material to a support plate such as a metal plate, and applying an electric field to the piezoelectric material to cause deflection deformation in relation to the support plate.The electric field is changed by alternating voltage. By applying this, the direction of deflection of the support plate changes alternately,
This becomes vibration and produces sound.

In such a piezoelectric sounding body, the resonant frequency increases as the diameter of the diaphragm decreases, and the resonant frequency can be lowered by reducing the thickness of the diaphragm.

However, even if the thickness of the diaphragm is reduced to 50 μm or less, the sound pressure level will inevitably decrease due to the relationship with the adhesive part, and the conventional simple structure will not be able to achieve the desired performance such as sound pressure level and frequency band. It was something that could not be obtained.

For this reason, Japanese Patent Applications No. 62-188194 and No. 188195. Japanese Patent Application No. 62-336046 and other publications disclose a groove-formed support in which grooves are formed on both sides alternately near the peripheral fixing part of a support plate constituting a diaphragm, and a groove is formed directly under the piezoelectric material bonding part to bond the piezoelectric material. A diaphragm is shown that has a structure in which the vibration occurs at two points: the center and the outer periphery.

[Conventional technology]

A conventional example will be explained with reference to the drawings.

Figure 6 shows the frequency characteristics of the sound pressure of a piezoelectric semitone whose diaphragm is thinned to 50 μm and the peripheral part of the diaphragm is fixed with elastic adhesive.The drive voltage is IV, 1M5, and the distance is 30c.
This is the characteristic when m.

As is clear from this characteristic, the sound pressure level in the low frequency range was low and the performance was far from suitable for mounting on a pager.

When using a diaphragm with a groove-formed support in which grooves are formed on the periphery of the support plate that constitutes the diaphragm, the grooves formed on the outer periphery of the diaphragm increase the degree of freedom of the support, and vibration As shown in FIG. 7, the resonant frequency of the plate was lowered to 1/2 or less when the depth of the groove was 315 mm, which was the thickness of the support plate, compared to the structure without grooves.

In addition, in the groove provided directly under the piezoelectric material, the main part that causes displacement of the piezoelectric material is not directly bonded to the support plate, so even if the piezoelectric material becomes thinner, the displacement will not decrease due to bonding.
Even with the thin diaphragm structure required for lower frequencies, there was no drop in sound pressure level.

[Problem to be solved by the invention]

It has been revealed that the above-mentioned diaphragm structure with grooved support can achieve a significantly lower frequency and higher sound pressure level than a diaphragm with a conventional structure without grooves. (with both sides open),
The frequency band that can be produced is narrow, making it impossible to generate melodies with good sound quality.

For this reason, it is necessary to improve the characteristics by adding a cavity to the diaphragm in addition to the diaphragm, or because it is not possible to widen the band with the generally known cavity structure, and due to the cavity. Since the overall height of the sounding body is high, a thin structure that can be built into a card device cannot be realized.

[Means to solve the problem]

The piezoelectric sounding body of the present invention includes a diaphragm made of a piezoelectric material having electrodes formed on both sides and a grooved support plate having alternating grooves on both sides in the vicinity of the peripheral fixed part, and a fixed body and a cavity formed from these both sides. This is a piezoelectric sounding body in which a front air chamber and a back air chamber are formed on both sides of a diaphragm that is sandwiched between air chamber forming plates, and includes a fixing body having a step that matches the outer shape of the diaphragm and an air chamber for fixing the diaphragm. The back air chamber has a leak hole, the front air chamber has a sound emission hole, and at least one of the sound emission holes of the leak hole is perpendicular to the vibration direction of the diaphragm. in,
In addition, these two directions are set at 90 degrees or more with respect to the center of the diaphragm, the volume of the back air chamber is smaller than that of the front air chamber, and the opening area of the leak hole is 0.5 mm2 or more.

[Example] Next, an example of the present invention will be described in detail with reference to the drawings.

FIGS. 1(a) to 1(d) are exploded perspective views of the piezoelectric sounding body of the present invention. It is composed of four parts: a fixed body 13 having a structure, a front air chamber forming plate 14 forming a cavity, and a back air chamber forming plate 15.

In the figure, the fixed body 13 passes through the top and bottom at the same diameter as the supporting diameter of the diaphragm, and has circular stepped portions 16 and 17 on both sides, each having a diameter larger than the length of one side of the fixed body. A diaphragm 12 is dropped onto the surface, and a back air chamber forming plate 15 with leakage hole slits 18 formed thereon is adhesively fixed thereon, and a step 17 is placed on the opposite surface of the fixed body 13.
A front air chamber forming plate 14 having a sound emitting hole slit 19 formed therein is adhesively fixed to the front air chamber forming plate 14 .

Next, the specific shape and characteristics of the present invention will be explained.

Figures 2 (a) and (b) are similar to Figures 1 (a) to (d).
The shape of the diaphragm is based on the grooved support shown in .

Alternate ring-shaped grooves 22 are formed on both sides in a portion surrounded by the outer periphery of the piezoelectric material 11 and the support fixing part 21, and are formed by etching so that the depth of the grooves is about 315 mm, which is the support plate thickness T1. So, the diameter of the piezoelectric material 11 is 9.3 dragons,
The diameter of the supporting and fixing part was 12 m+++, and four grooves were evenly arranged between the bindings.

Fig. 3 shows a cross-sectional shape designed to mount the piezoelectric sounding body of the present invention on a card-type pager with a thickness of 4 mm. The height of the back air chamber 31 was set to 0.5 m.
m, and the height of the front air chamber 32 was set to 1.9 mm (1.0 mm excluding the step forming part of the fixed body and the height of the front air chamber forming plate 9). Furthermore, the back air chamber forming plate 14 has a height of 0.5 and a width of 2.
．． A leak hole 33 of 3 mm is formed, and a sound emitting hole 34 of 0.9 mm in height and 1.6 mm in width is formed in the front air chamber forming plate 15.
This positional relationship was set at 180 degrees with respect to the center of the diaphragm 12. With this shape, the overall height of the sounding body is 3cm, making it possible to mount it on a card-type pager with a thickness of 4mm.

Figure 4 shows the sound pressure characteristics of the 13 aperture thickness 3cm shown in Figure 3 above, with the vertical axis representing the sound pressure level, the horizontal axis representing the frequency, the drive voltage in IVams, and the measurement distance. 30
This is the characteristic when fixed to a baffle plate.

In general, the sound pressure characteristics of a sounding body that is open on the back side of the diaphragm vary greatly depending on the presence or absence of a baffle. Sound will interfere and deteriorate the characteristics.

Therefore, when this sounding body is actually installed, as shown in Fig. 5, the sound emitting hole 32 is directed outward and the leakage hole is directed toward the component mounting direction inside the case, and a baffle is installed in the case itself. It has an effect. At this time, the required space when looking inside the case from the leak hole is more than three times the volume of the back air chamber (
In this example, if 170 in3>, there is no effect on the characteristics.
This can be sufficiently secured by the gaps between the parts mounted inside the card.

The piezoelectric sounding body obtained with this configuration has a leak hole on the back air chamber side, and the case itself, which incorporates this leak hole, is arranged so as to act as a baffle, thereby achieving a wide range of low frequencies. At this time, as a structure for fixing the diaphragm, the fixing body has a step and is sandwiched between the back air chamber forming plates, thereby reducing the overall height of the sounding body.

In the above embodiment, the diaphragm is fixed with the back air chamber forming plate, but the back air chamber forming plate is integrally formed on the fixed body itself, and the diaphragm is fixed with the front air chamber forming plate. Also, the direction of the sound emitting hole is not limited to one facing toward the edge of the card, but a card with the sound emitting hole facing toward the surface of the card and the leakage hole toward the internal space of the card can also be used. Since the case itself acts as a baffle, the sound from the sound emission hole and the sound from the leakage hole do not interfere with each other, and low frequency and wide band characteristics can be obtained. In this case as well, the overall height of the sounding body is low, resulting in a thin sounding body that can be mounted on a card.

On the other hand, the groove formation pattern of the diaphragm used here is also shown in Figure 2 (
It is not limited to just the four grooves shown in a) and (b), and the depth of the groove, width of the groove, and
By selecting the clear pitch, etc., and then changing the opening area of the leakage hole formed in the back air chamber forming plate and the opening area of the sound emission hole formed in the front air chamber without directly observing the change in characteristics, it is easy to optimize. It is possible to find the shape.

〔Effect of the invention〕

As explained above, according to the piezoelectric sounding body of the present invention, the resonant frequency can be lowered by using the diaphragm with grooved support, and the diaphragm has sound emitting holes on both sides. A back air chamber having an air chamber and a leakage hole is formed, and the positional relationship between the sound emission hole and the leakage hole is arranged so that the case itself in which the sounding body is incorporated serves as a baffle, which is different from the conventional method! R
Although it is smaller and thinner than other structures, it has the effect of providing low frequency and broadband characteristics.

For example, even a compact type with 13 apertures and a thickness of 3 mm has a broadband characteristic of about 1 octave from 2 to 3.8 kHz, and the conventional structure shown in Figure 6 (simply by reducing the thickness of the diaphragm to 50 μm) It is clear that a low frequency and wide band can be obtained compared to the characteristics of a commercially available product with a structure in which the peripheral part of the diaphragm is fixed with an elastic adhesive).

In addition, the air chamber formation structure has a step on the fixed body,
Since the diaphragm is fixed and the air chambers are formed at the same time, the overall thickness of the sounding body is thin, and the sounding body can be built into a card type device.

[Brief explanation of drawings]

FIGS. 1(a) to (d) are exploded perspective views showing an embodiment of the present invention, and FIGS. 2(a) and (b) are top views showing the structure of a diaphragm according to an embodiment of the present invention. A side view, FIG. 3 is a sectional view showing the air chamber structure of a piezoelectric sounding body in an embodiment of the present invention, and FIG. 4 is a graph showing the frequency characteristics of sound pressure in the air chamber structure of FIG. 3. Fig. 5 is a partially cutaway perspective view showing a structure in which the piezoelectric sounding body of the present invention is incorporated into a card device, and Fig. 6 shows a structure in which the thickness of the diaphragm is reduced to 50 μm and the peripheral part is fixed with an elastic adhesive. FIG. 7 is a graph showing the frequency characteristics of the sound pressure of a conventional piezoelectric sounding body. FIG. 7 is a graph showing the relationship between the depth of the grooves of the grooved support and the resonance frequency calculated by the finite element method. DESCRIPTION OF SYMBOLS 11... Piezoelectric material, 12... Vibration plate, 13... Fixed body, 14... Front air chamber forming plate, 15... Front air chamber forming plate, 16... Step, 17...・Step, 18...Leak hole slit, 19...Sound emission hole slit.

Claims (1)

[Claims] A diaphragm made of a piezoelectric material with electrodes formed on both sides and a grooved support plate having alternating grooves on both sides near the peripheral fixed part is sandwiched between the fixed body and the air chamber forming plate forming the cavity from both sides of the diaphragm. In a piezoelectric sounding body that has a front air chamber and a back air chamber, it consists of a fixed body with a step that matches the outer shape of the diaphragm and an air chamber forming plate for fixing the diaphragm, and there is no leakage in the back air chamber. The front air chamber has a sound emission hole, and at least one of the sound emission holes of the leakage hole is perpendicular to the vibration direction of the diaphragm, and these two directions are aligned with the diaphragm. The angle should be at least 90 degrees with respect to the center, the volume of the back air chamber should be smaller than the front air chamber, and the opening area of the leak hole should be 0.5 mm^
A piezoelectric sounding body characterized in that the piezoelectric sounding body is 2 or more.