JPH01176200A - Piezoelectric diaphragm - Google Patents

Abstract

PURPOSE:To improve low frequency characteristic by forming alternately a slot deviated from both faces of an adhered member with a piezoelectric member adhered thereto at the border between a free state part displaced as a diaphragm and a stationary part supporting the diaphragm. CONSTITUTION:A piezoelectric substance 12 formed with an electrode 11 on its both sides is adhered to the center of a metallic disk 13 and the circumference part is fixed by a stationary part 14 in the diaphragm. Plural slots 15 are formed alternately while their positions are deviated to the both sides from the part close to the inner circumferential part of the stationary part 14 between the outer peripheral part of the piezoelectric member on the metallic plate 13 and the inner peripheral part of the stationary part 14. The slots at the peripheral stationary part facilitate the flexure deformation caused in the application of an electric field to the piezoelectric member and the diaphragm is moved freely by utilizing the slots. Thus, the movement of the diaphragm due to the stationary body 14 is not hindered and the resonance frequency is far lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a piezoelectric diaphragm, and more particularly to a piezoelectric diaphragm that lowers the resonance frequency of the diaphragm to which a piezoelectric material and a support plate are attached.

(Prior art) A piezoelectric diaphragm obtained by pasting a piezoelectric material on which electrodes are formed on a support plate is made by applying an alternating voltage to the piezoelectric body, which causes the piezoelectric body to expand and contract in the plane direction. Since one surface of the piezoelectric material is fixed, expansion and contraction of the piezoelectric material causes warping in the vertical direction about the bonded surface of the support plate. Therefore, if the outer circumferential portion of the support plate is fixed, the center portion will be displaced up and down due to this warp, resulting in a vibrator that vibrates at the frequency of the applied alternating voltage.

If a signal with a frequency of several kHz is applied to such a diaphragm,
This vibration creates a compressional wave in the air, which becomes a sounding body that produces sound, and has been put into practical use as piezoelectric buzzers and piezoelectric speakers.

In addition, the shape of the diaphragm itself is rectangular, and by supporting and fixing one side of the diaphragm, the end opposite to the fixed end can be largely displaced, and by utilizing this displacement, it has been put into practical use as an actuator. There are fans, pumps, etc.

On the other hand, if the electrode leads from the piezoelectric material of the diaphragm are connected to the input of an amplifier, etc., the charge from the piezoelectric material generated by the external force applied to the diaphragm will be converted into voltage, so these characteristics can be used. It is also used as an acceleration sensor, pressure sensor, microphone, etc.

(Problems to be Solved by the Invention) In the application of the piezoelectric diaphragm as described above, the first piezoelectric sounding body is normally used near the resonance frequency where the amount of displacement (vibration amplitude) becomes large. However, this resonant frequency becomes higher as the diameter of the part to be supported and fixed becomes smaller, and it is not possible to generate low-frequency sound with a small size.

The first resonant frequency f1 of such a diaphragm is:
αm: Constant that differs depending on the support method (in case of peripheral fixed αm=
3.2) (In case of peripheral support αm=2.22) hl: Thickness of piezoelectric material (m) a: Radius of support part (m) p: Thickness of piezoelectric material h1/thickness of support plate h2E2: Young's modulus of support plate (N/m2) p2: Density of support plate (g/m3) 112: Poisson's ratio of support plate α: Can be determined by Young's modulus of piezoelectric material/Young's modulus of support plate, and peripheral support is Obtained as the lowest resonant frequency. However, although peripheral fixation can be achieved with a simple configuration of simply sandwiching the peripheral part between supports, peripheral support requires supporting the peripheral part with the end of the pin to facilitate vertical movement, so in reality this is not possible. Support is difficult, and a similar method of support involves fixing the peripheral portion with an elastic adhesive, so the actual resonant frequency is only higher than the calculated value.

As a result, it is difficult to generate sound of 2 kHz or less with a 13 mm opening, for example.

Also, in order to use an actuator obtained by supporting and fixing one end of the diaphragm in a resonant state, the lower the resonance frequency, the smaller the actuator can be and the same vibration amplitude can be obtained. The resonant frequency will be lower if the part is as close as possible to a point. However, when supporting one end, it is difficult to fix with an elastic adhesive from the viewpoint of reliability.

On the other hand, when used as a pressure sensor, acceleration sensor, or microphone that converts the electric charge induced from a piezoelectric material into voltage, peripheral support has a wider band and higher sensitivity than peripheral support. . In this case as well, it would be better to fix the bottle at the end of the bottle instead of fixing it with an elastic adhesive close to the peripheral support, but this is difficult.

(Means for Solving the Problems) In a piezoelectric diaphragm in which a piezoelectric material having electrodes formed on both sides is attached to a support plate and a part or all of the peripheral portion of the support plate is fixed, the support plate is At least one groove is provided on both surfaces along the fixing part between the peripheral fixing part and the place where the piezoelectric material is attached. Further, it is preferable that the grooves, which are parallel or concentric with the peripheral fixing portion of the support plate, are provided alternately at different positions on both surfaces.

(Function) The piezoelectric diaphragm of the present invention is constituted by a bimorph or unimorph diaphragm in which a piezoelectric material is attached to both or one side of a support plate. The piezoelectric material is placed around the support plate to which it is attached or near the fixed part on one side in a state parallel to the fixed part (in the case of a circular diaphragm, in a ring state concentric with the fixed part),
A groove is formed that is shifted from the screen of this support plate in the direction of the piezoelectric material.

When a plurality of grooves (preferably 2 to 3 grooves) are formed on both sides of the support plate, the grooves on both sides are formed alternately. The depth of the groove is about 172 to 2/3 of the thickness of the support plate, and the width of the groove is also about the same as the depth of the groove, and the groove position on the opposite side is about 0.1 to 2/3.
Form with a 2 mm offset. By using a support plate with such grooves, if a piezoelectric material is attached to this support plate and the area near the groove is fixed, any warping that occurs on the surface of the piezoelectric material will cause warping of the support plate. occurs. At this time, since the groove is formed near the peripheral fixed part, the support plate is free to warp in the groove part, and the resonance frequency as a diaphragm becomes low, and the displacement of the center part (in the case of a circular shape) becomes large. . Such grooves can be easily obtained using normal etching techniques,
Since the grooves create a free state, a piezoelectric diaphragm with a simple configuration in which the periphery is fixed is capable of low-frequency vibration, has a wide band, and has a large vibration amplitude can be obtained.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a cross-sectional structural diagram of a piezoelectric sounding body according to an embodiment of the present invention. The diaphragm has a piezoelectric body 12 with electrodes 11 formed on both sides attached to the center of a circular metal plate 13, and the peripheral part is fixed with a fixing body 14. Between the outer periphery of the piezoelectric material 12 on the metal plate 13 and the inner periphery of the fixing part 14, a plurality of grooves 15 are arranged alternately on both sides with their positions sequentially shifted from the side closer to the inner periphery of the fixing body 14. is formed. Here, electrode 1
The thickness of the piezoelectric body 12 including 1 is tl, the thickness of the metal plate 13 is t2, and the remaining thickness of the groove forming portion is t3. or,
With respect to the diameter d0 of the piezoelectric material 12, a groove having a width g1 is formed by changing the diameter from the inner peripheral diameter d2 of the fixed body 14 on both sides. At this time, adjacent grooves 15 on the same surface of the metal plate 13
The mutual spacing g2 is such that the groove 15 on the opposite side is located exactly between them.

For example, when making an ultra-small piezoelectric buzzer with an external dimension of 13 mm, the space available for the fixed body is 1 m on the outer circumference.
m, the inner peripheral diameter d2 of the fixed body is 11 mm. At this time, if the diameter d1 of the piezoelectric material is 7.6 mm, a groove may be formed between the outer circumference of the piezoelectric material and the inner circumference of the fixed body. Here, the thickness t2 of the metal plate used as the diaphragm is 50 pm, and the thickness to of the piezoelectric material to be pasted is 70 pm.
m, as the remaining part of the groove, t3 is 20 pm, and the first groove is 11 mm to 10.52 mm in diameter on the back side, and the second groove is 10.4 mm to 9.56 mm in diameter.
mm on the surface, the third groove is 9.08 mm to 8
．． A 6 mm groove is formed on the back side, and a fourth groove from 8.12 mm to 7.6 mm is formed on the front side. A diaphragm for an ultra-small piezoelectric buzzer can be obtained by using stainless steel for the metal plate (steel or brass has the lowest resonant frequency) and by using a conductive adhesive to bond it to the piezoelectric material.

This movement will be observed by focusing on the groove near the peripheral fixed part of the diaphragm for the ultra-small piezoelectric buzzer obtained with the above configuration.

Figures 2 (a) and (b) show cross-sections of the four grooves in the peripheral fixing part, where (a) shows no deflection due to the piezoelectric material, and (b) shows the case where the piezoelectric material is not bent. This figure shows the deformed state when deflection occurs.

As can be seen from these figures, the grooves in the peripheral fixed portion facilitate the deflection deformation that occurs when an electric field is applied to the piezoelectric material, allowing the groove portion to move in a free state. Therefore, the motion of the diaphragm is no longer inhibited by the fixed body 14, and the resonance frequency is lower than that of a conventional peripheral fixed diaphragm having the same shape.

FIGS. 3(a) and 3(b) compare the resonance frequencies of the same shapes, and show the frequency characteristics of vibration amplitude using a photonic sensor, which is an optical non-contact displacement meter. As can be seen from this figure, the resonant frequency of the grooved diaphragm is much lower than that of a conventional diaphragm, and it can be seen that the resonant frequency is almost close to the calculated value for the peripheral support. .

FIG. 4 shows another embodiment of the piezoelectric fan, which is one of the applications as an actuator. In this case as well, grooves 45 are provided alternately from above and below near the fixing part 44 which is the end of the metal plate 43 to which the piezoelectric material 42 having the electrodes 41 formed on both sides is attached. Further, the other end of the metal plate 43 is provided with wings 46 for generating wind.

When an alternating voltage is applied to the piezoelectric material of the diaphragm constructed in this way, the diaphragm bends and vibrates in accordance with the frequency of the applied alternating current voltage due to the relationship between the piezoelectric material and the metal plate. As a result,
The blades 46 provided at the tip of the diaphragm also vibrate, which generates wind. In this case as well, since grooves are simply formed in the fixed part of the metal plate, these grooves facilitate vertical movement and the resonance frequency is much lower than that of conventional diaphragms of the same shape. The air volume as a fan can be increased.

In yet another embodiment, the sounding body shown in FIG. 1 may be used as a microphone, but in this case as well, the grooves provided near the fixed part facilitate the movement of the diaphragm. The diaphragm is easily deformed even in response to a small external force, that is, a small sound input, and as a result, a microphone with high sensitivity can be obtained. In addition, a diaphragm with such a structure can be used as a pressure sensor or an acceleration sensor, rather than a microphone, with improved performance compared to a diaphragm whose peripheral portion is simply fixed.

In addition, for application as a sensor, in addition to pasting piezoelectric ceramics, a piezoelectric material/thin film may be formed on a metal plate by means such as sputtering, and the grooves formed near the supporting and fixed parts will act as a vibration plate. It is possible to improve performance by making it easier.

Further, the material of the metal plate is not limited to any material, and is not limited to plastic, glass, or other materials as long as it is possible to form grooves as a support plate.

Furthermore, as shown in FIG. 5, the groove-formed supporting and fixing method of the present invention allows the formation of a plurality of vibrators 51 on a plane, so that the resonance of each vibrating part can be achieved even when using vibration over a wide area. frequency becomes lower.

(Effects of the Invention) As explained above, according to the present invention, the piezoelectric material can be pasted from both sides of the member at the boundary between the free state portion that is displaced as a diaphragm and the fixed body portion that supports the diaphragm. Because the grooves are alternately formed at different positions, the groove forming part can be supported in a nearly free state, and as a sounding element, the resonance frequency is much lower than that of conventional peripheral fixed support of the same shape, and it is effective in the low frequency range. characteristics are improved. Furthermore, when applied as an actuator, forming grooves in the part to be supported and fixed can lower the resonant frequency as a diaphragm, and when applied as a fan, the air volume can be increased by lowering the frequency. Furthermore, in applications such as microphones, pressure sensors, or acceleration sensors, the formation of grooves in the parts that are supported and fixed can improve sensitivity and band performance.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a sounding body showing one embodiment of the present invention. FIGS. 2(a) and 2(b) are cross-sectional views of the grooves in the portion to be supported and fixed in a deformed state. Figure 3(a). (b) is a frequency characteristic diagram of vibration amplitude compared with conventional peripheral fixation. FIG. 4 is a perspective view showing an embodiment as a piezoelectric fan, which is one of the applications as an actuator. FIG. 5 is a perspective view showing an embodiment in which a plurality of diaphragms are arranged on a plane. In the figure, 11...electrode, 12...piezoelectric material, 13...metal plate, 14...fixing part, 15...groove, dl...diameter of piezoelectric material, d2...fixing diameter of the section, tl...thickness of the piezoelectric material, t2...thickness of the support plate, t3. ...Remaining thickness of the groove, 41... Electrode, 42... Piezoelectric material, 43...
Metal plate, 44...fixing part, 45...groove, 46...
Feather 51... is a diaphragm.

Claims (2)

[Claims] (1) In a piezoelectric diaphragm in which a piezoelectric material having electrodes formed on both sides is attached to a support plate, and a part or all of the peripheral part of the support plate is fixed, the peripheral fixed part of the support plate and the piezoelectric 1. A piezoelectric diaphragm characterized in that at least one groove is provided on both sides along a fixing part between the area to which a product is attached and the fixing part. (2) The piezoelectric diaphragm according to claim 1, wherein the grooves which are parallel or concentric with the peripheral fixing portion of the support plate are provided at different positions on both surfaces.