JPH02270500A - Piezoelectric electroacoustic transducer - Google Patents

Abstract

PURPOSE:To prevent change in the frequency characteristic due to environmental change by fringing a damping plate made of a high polymer foaming material into contact with a metallic diaphragm so as to use it an attenuation element and forming a skin layer to the surface at least at the diaphragm side of the damping plate. CONSTITUTION:A soft damping plate 8 whose outer diameter is equal to the inner diameter of a cup and whose inner diameter is sufficiently larger than a piezoelectric ceramic plate 1 is arranged in the inside of a metallic diaphragm 3 formed as a cup. In this embodiment, the soft damping plate 8 is made of a foaming rein (high polymer foaming material) such as polyethylene foam or polyurethane foam whose both surfaces are provided with surface skins 8a, 8b (that is, skin layers) in the thickness of nearly 10-100mum. Thus, when the soft damping plate 8 is interposed between the metallic diaphragm 3 and a rigid retainer 8, the soft damping plate 8 is compressed and a force in a direction of suppressing the vibrating motion of the metallic diaphragm 3 is exerted from the soft damping plate 8 to the bottom wall 3a of the metallic diaphragm 3.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a piezoelectric sound generator driven by a piezoelectric ceramic plate, and more particularly to a piezoelectric electroacoustic transducer with stable and flat frequency characteristics.

BACKGROUND ART Conventionally, a piezoelectric speaker as shown in FIG. 9 has been proposed for the purpose of audio reproduction in small electronic devices. That is, this piezoelectric electroacoustic transducer is equipped with a piezoelectric diaphragm constructed by bonding a piezoelectric ceramic plate B to the surface of a metal diaphragm A with a large area. The outer periphery is supported by frame D.

Therefore, in a piezoelectric electroacoustic transducer having such a structure, when an audio signal is applied between the external connection leads E connected to the metal diaphragm A and the piezoelectric ceramic plate B, the piezoelectric diaphragm vibrates and produces sound. Piezoelectric diaphragms have their own resonant frequencies, so when an audio signal is input to piezoelectric ceramic plate B, a large peak dip occurs near the resonant frequency and this higher-order frequency, so the frequency is flat. Unable to obtain properties.

For this reason, in the past, a soft damping plate F for suppressing the resonance motion of the piezoelectric diaphragm was attached to the surface of the metal damping plate A using an adhesive G.
A structure (shown in FIG. 10) in which the adhesive is bonded with the adhesive is proposed.

However, although this structure has the effect of attenuating the resonant motion of the piezoelectric diaphragm to some extent, as shown by the frequency curve α in FIG. It was not possible to obtain a flat frequency response. In other words, Fig. 11 shows the frequency characteristics when an audio input as shown by the frequency curve β is input to the piezoelectric electroacoustic transducer shown in Fig. 10, but the frequency curve β and the output of the piezoelectric electroacoustic transducer are As can be understood from the comparison with the frequency curve α, the 10th
In the illustrated piezoelectric electroacoustic transducer, a resonance peak dip is clearly observed.

In this structure, the rubber, sponge, etc. used as the brake plate F are dissolved by the solvent contained in the adhesive G, and the physical properties of the brake plate F change, and the amount of adhesive G applied and the hardness change over time. Therefore, it was not possible to obtain the expected frequency characteristics.

In addition, in each of the above-mentioned structures, external connection leads E must be connected to the metal diaphragm A and the piezoelectric ceramic plate B, respectively, which makes it difficult to mass-produce, and there is a limit to the reduction of manufacturing costs due to mass-production effects. There are some problems.

For this reason, the present applicant proposed a structure in which the expected wide band and flatter frequency characteristics can be easily obtained and a sufficient mass production effect can be expected, by filing Japanese Patent Application No. 63-295494. That is, FIG. 12 shows a piezoelectric electroacoustic transducer disclosed in the same application, in which a piezoelectric diaphragm is constructed by bonding a piezoelectric ceramic plate B and a metal diaphragm A1. A ring-shaped frame D surrounds the metal diaphragm of the piezoelectric diaphragm.

A holding plate H made of an electrically insulating material is fixed to the
is fixed to the frame D1 in a state in which the peripheral part of the metal diaphragm A1 is in close contact with the peripheral part of the metal diaphragm A1, and a brake plate Fl made of a polymeric foam material is provided between the holding plate H and the metal diaphragm A is inserted in a compressed state.

In other words, piezoelectric electroacoustic transducers with this structure do not use adhesive at all, which prevents the instability of frequency characteristics caused by the application of adhesive and the adverse effects of changes in the hardness of the adhesive over time. As a result, a flat frequency characteristic over a wide band such as the frequency curve β in FIG. 11 can be obtained.

Problems to be Solved by the Invention - However, according to subsequent research on the structure shown in Figure 12, environmental tests were conducted on the structure that initially had a frequency characteristic similar to the frequency curve β turtle in Figure 13. However,
It was found that the frequency characteristics change over time as shown by the frequency curve γ due to changes in the temperature and humidity of the environment. To explain in detail, the frequency curve β1 in FIG. 13 is between the frequency curve β in FIG. This is the frequency characteristic after the test. That is, the same piezoelectric electroacoustic transducer was placed in a sample chamber of a temperature/humidity cycle tester, and taken out after a total of 63 cycles of environmental changes, and its frequency characteristics were measured, and a frequency curve γ was obtained.

As is clear from the comparison between the frequency curve β and the frequency curve γ, in the case of the piezoelectric electroacoustic transducer shown in Fig. 12, the frequency curve γ has an abnormally high sound pressure level in the high range, so it cannot be used. As a result, it is expected that the sound quality will shift toward higher frequencies.
There are still points to be improved in terms of reliability of frequency characteristics.

In view of the conventional problems described above, an object of the present invention is to obtain a structure in which a piezoelectric electroacoustic transducer using a polymer foam material as a damper element does not undergo changes in frequency characteristics over time due to the environment. .

Means for Solving a Problem - In order to achieve this object, the present invention fixes the peripheral part of the metal diaphragm of a piezoelectric diaphragm consisting of a piezoelectric ceramic plate and a metal diaphragm bonded together to a ring-shaped frame or In the supported piezoelectric electroacoustic transducer, a damping plate made of a polymeric foam material is used as a damping element by contacting the metal diaphragm, and a skin layer is formed on at least the diaphragm side surface of the damping plate. It is something to do.

One Embodiment - Hereinafter, details of an embodiment of the present invention will be described with reference to FIGS. 1 to 8.

1 to 4 are cross-sectional views of a piezoelectric electroacoustic transducer according to a first embodiment of the present invention, and the reference numeral "1" indicates a piezoelectric ceramic plate having conductive layers 2a and 2b formed on both sides. There is. One side of this small piezoelectric ceramic plate 1 is the same as the conventional one in that it is integrally bonded to a conductive surface plate, that is, a metal diaphragm 3 to form a piezoelectric diaphragm 4.
In the illustrated embodiment, the metal pickup plate 3 is pressed into a cup shape, and the piezoelectric ceramic plate 1 is fixed to the surface of the bottom wall 3a using an adhesive 5.

Further, the flange 3b of the metal diaphragm 3 is fixed to the ring-shaped frame 7 in a state in which it is in close contact with a peripheral portion 6a of a rigid presser plate 6, the details of which will be described later. Specifically, inside the cup-shaped metal diaphragm 3, there are arranged soft damping plates 8 whose outer diameter is equal to the cup inner diameter and whose inner diameter is sufficiently larger than the piezoelectric ceramic plate 1. In the embodiment, this soft brake plate 8 has a thickness of approximately 10 x lOOu on both surfaces.
It is made of foamed resin (polymer foamed material) such as polyethylene foam or polyurethane foam, and has skins 8a and 8b (that is, skin layers) of s. In other words,
The soft brake plate 8 in the illustrated example has an internal density of, for example, 0.4 (
g/cm') and having skins 8a and 8b of 50 uI and 11 thickness, and as shown in FIG. 4, the overall thickness is sufficiently larger than the depth L2 of the metal pickup plate 3. (According to other test results, the foaming density of the soft brake plate 8 is O02~0,6 (g/ca+')
There were no particular problems within this range. ), Therefore, when the soft brake plate 8 is interposed between the metal diaphragm 3 and the rigid holding plate 6, the soft brake plate 8 is compressed, and the vibration is A force in the direction of suppressing the movement acts from the soft brake plate 8.

Further, as understood from FIG. 2, the rigid presser plate 6 has a plurality of centripetal protrusions 6a, and the surface of these centripetal protrusions 6a allows the soft brake plate 8 to press against the metal pickup plate 3. is placed in close contact with the surface of the bottom wall 3a. Therefore, by adjusting the relationship between the thickness Ll of the soft diaphragm 7 and the depth L2 of the metal diaphragm 3, the bottom wall 3a of the metal diaphragm 3 can be adjusted.
Since the pressure applied to the frequency changes, you can obtain the desired frequency characteristics simply by managing this value.

Furthermore, a pair of lead terminals 9A and 9B for external connection are attached to one of the centripetal projections 6a. These lead terminals 9A.

Reference numeral 9B denotes a pair of lead terminal foils 10A formed in a laminated manner on the surface of the rigid holding plate 6, which are soldered to one end of the IOB. It faces the surface of the flange 3b of the plate 3. That is, on the inner surface of the metal diaphragm 3 corresponding to the lead terminal foil 10^, a conductor foil 12 insulated from the metal diaphragm 3 by an insulating layer 11 is formed by a printed wiring method, and one end 12a a conductive foil 11 connected to the conductive layer 2a
The other end 12b is exposed on the surface of the flange 3b of the metal diaphragm 3, as shown in FIG. On the other hand, since one end of the lead terminal foil 10B faces the surface of the flange 3b of the metal diaphragm 3, as shown in FIG. By caulking the peripheral portion 6a of the rigid holding plate 6, the lead terminal 9A
can be electrically connected to the piezoelectric ceramic plate 1, and the lead terminal 9B can be electrically connected to the metal diaphragm 3.

As described above, the piezoelectric electroacoustic transducer according to the first embodiment has a soft damping plate 8 inserted inside the metal diaphragm 3, and a rigid holding plate 6 applied to the surface of the soft damping plate 8. Then, while compressing the soft damping plate 8, the peripheral portion 6a of the rigid holding plate 6 is attached to the flange 3b of the metal diaphragm 3 using the frame 7.
It can be completed by simply caulking. In other words, by fixing with the frame 7, the conductor foil 11 is attached to the lead terminal foil 10^,
The flange 3b of the metal diaphragm 3 is attached to the lead terminal foil 10B,
Since they are electrically conductive, it is not necessary to solder the lead terminal wires one by one as in the conventional case, and the structure can be easily mass-produced.

In addition, the illustrated structure not only makes it possible to omit the gluing process that is difficult to manage, but also provides a piezoelectric electroacoustic transducer with stable quality, without the risk of frequency characteristics changing over time due to variations in the amount of adhesive applied, etc. can be provided. In fact, according to the prototype example of the illustrated structure, an initial frequency characteristic as shown in frequency curve β2 in Fig. 5 was obtained, but the frequency characteristic after the temperature/humidity cycle test of the same prototype was as shown in Fig. 5. It was found that the frequency curve changes like δ.

Explaining this fact in detail in relation to the frequency curve β1 in FIG. The curve β2 can be considered to be between the frequency curve βl and the path.The piezoelectric electroacoustic transducer with such initial characteristics was placed in the sample chamber of the temperature/humidity cycle tester, and a total of 63 cycles were performed. removed after an environmental change.

In other words, Figure 6 shows the temperature and humidity cycle in the sample chamber, and this cycle test consisted of 1 cycle of 28 hours and a hold time of 1.
．． It is a span of 5 hours, first the temperature in the sample chamber is kept at 2 o 0 c1 humidity = 60% for 1.5 hours, then 7 o
This is a cycle in which the temperature is raised to 0C and 90% RH, the environment in the sample chamber is returned to the initial temperature and humidity, and then cooled to -30C to return to the initial environment. Therefore, a total of 6
3 cycles of environmental change is - 3 cycles per day 21
After the environmental test, which lasted several days, the frequency characteristics of the prototype were measured and a frequency curve δ was obtained. As can be understood from the comparison between the frequency curve δ and the frequency curve β2, in the structure of the first embodiment, the frequency characteristics hardly change even with environmental changes, in other words, stable frequency characteristics can be obtained.

The reason for this is that, in the case of the structure shown in FIG.
Moisture penetrates into the interior due to the breathability of the soft brake plate F, which causes early deterioration of the entire brake plate F, especially its surface layer. This is because changes in the material of the soft brake plate 8 itself due to changes in temperature and humidity are sufficiently suppressed due to the presence of dense skins 8a and 8b (i.e., skin layers) that have no heat insulating properties and are highly insulating. I think that the. Of course, in the structure of the first embodiment, early deterioration of the skinned soft brake plate 8 is prevented, so that the frequency characteristic in which the resonant frequency and the resonant peak dip at its higher-order frequencies are clearly reduced can be maintained for a long period of time. In the structure of the first embodiment, when we measured the frequency characteristics by changing the riveting mechanism of the frame 7, we found that the amplitude in the usable band and at various frequencies, that is, the sound quality, varied depending on the selection of the clamping pressure. I know it's going to change a lot. Further, in the above embodiments, a metal diaphragm press-formed into a cup shape was exemplified, but the present invention is not limited to this structure, and the centripetal protrusion of the rigid presser plate is not necessarily limited to this structure. Alternatively, conduction with the piezoelectric ceramic plate and the metal diaphragm may be achieved by an "L"-shaped contact member extending from the rigid holding plate without forming a lead terminal foil on the rigid holding plate.

FIG. 7 shows a piezoelectric electroacoustic transducer according to a second embodiment of the present invention. This is an example in which a soft brake plate 8A is attached with an adhesive 13. That is, the piezoelectric diaphragm 4A is constructed by bonding a piezoelectric ceramic plate IA to the bare surface of a metal diaphragm 3A with a large area, and the outer circumference of the piezoelectric diaphragm 4A is attached to a frame frame A via a soft holding member 14. I support it. In the illustrated example, the soft brake plate 8A has an internal density of o, 4 (g/
cm3) It is made of polyurethane foam with a large 50ual thickness skin 8C and AD, and a metal diaphragm 3A.
An audio signal is applied between the external connection leads 15 and 16 connected to the piezoelectric ceramic plate IA and the piezoelectric ceramic plate IA.

Since the piezoelectric electroacoustic transducer according to the second embodiment has the structure as described above, the prototype with the illustrated structure has the frequency curve α1 shown in FIG.

As can be understood from the comparison between the frequency curve α1 in FIG. 8 and the frequency curve α in FIG. 11, the structures in FIGS. 7 and 10 are the same except for the soft brake plate 8A.
The frequency curve α in FIG. 8 and the frequency curve α in FIG. 11 are very similar curves. When a total of 63 cycles of temperature/humidity cycle tests were conducted as described in detail in the first example, the frequency characteristics of the prototype, which initially had a frequency curve α, were as shown in Figure 8 after the temperature/humidity cycle test. The frequency curve has changed to α2. As can be understood from the comparison between the frequency curve α2 and the frequency curve α1, the frequency characteristics of the prototype do not change much even after the temperature/humidity cycle test. This is due to the fact that the adhesive 13 does not penetrate into the inside of the soft brake plate 8A due to the presence of the tough skin 8c, and therefore the soft brake plate 8A does not change in quality. 0 epidermis 8c, 8 judged to be
In order to confirm the effect of d, the frequency curve α3 obtained when a soft brake plate 8A without a skin is fixed with adhesive instead of the soft brake plate 8A with a skin is also shown in FIG. 8 as a 0 frequency curve α.

As can be understood from the comparison between It is obvious that the effectiveness of the brake plate is lost.

In addition, it is soft! Although the deterioration prevention effect of the IdJ plate is somewhat reduced, it is effective just to form a skin on the surface of the soft brake plate facing the metal diaphragm.

-Effects of the Invention- As is clear from the above description, according to the present invention, a skin is formed on at least the metal diaphragm side surface of the soft damping plate supported or fixed to the metal diaphragm constituting the piezoelectric diaphragm. By simply keeping it in place, it is possible to obtain a piezoelectric electroacoustic transducer that prevents changes in frequency characteristics due to environmental changes.

[Brief explanation of drawings]

1 is a sectional view taken along line I-1 in FIG. 2 of a piezoelectric electroacoustic transducer according to a first embodiment of the present invention; FIG. Figure 3 shows the In of Figure 2.
- A cross-sectional view along the river edge; Figure 4 is a cross-sectional view showing the relationship between the metal diaphragm and damping plate of the piezoelectric electroacoustic transducer; Figure 5 is a frequency characteristic diagram of the piezoelectric electroacoustic transducer; Figure 6 is a temperature and humidity cycle diagram, Figure 7 is a sectional view of a piezoelectric electroacoustic transducer according to the second embodiment of the present invention, Figure 8 is a frequency characteristic diagram of the same piezoelectric type electroacoustic transducer, and Figure 9 is a conventional diagram. 10 is a sectional view of another conventional piezoelectric electroacoustic transducer, FIG. 11 is a frequency characteristic diagram of a conventional piezoelectric electroacoustic transducer, and FIG. 12 is a sectional view of another conventional piezoelectric electroacoustic transducer. A cross-sectional view of the piezoelectric electroacoustic transducer of the prior application, and FIG. 13 is a frequency characteristic diagram of the same piezoelectric electroacoustic transducer. 1. IA...Piezoelectric ceramic plate, 3.3A...Metal diaphragm, 4.4A...Piezoelectric diaphragm, 6...Rigidity holding plate, 7.7A...Frame, 8.8A. ...Soft brake plate, 88-8d...Skin, 9A, 9B...Lead terminal. Patent applicant Iwasaki Tsushinki Co., Ltd. Figure 3 Figure 4 Frequency (KHzl Figure 6 Time Figure 7 Figure 8 Frequency (KHzl Figure 9 Figure 10 Frequency (KHzl

Claims (1)

[Claims] 1) In a piezoelectric electroacoustic transducer in which the peripheral part of a piezoelectric diaphragm consisting of a piezoelectric ceramic plate and a metal diaphragm bonded together is fixed or supported on a ring-shaped frame, a damping plate made of a polymer foam material is used. A piezoelectric electroacoustic transducer, characterized in that it is used as a damping element in contact with the metal diaphragm, and a skin layer is formed on at least the surface of the diaphragm side of the damping plate.