JPH02213300A - Composite piezoelectric vibrating element - Google Patents

Abstract

PURPOSE:To obtain a satisfactory output sound pressure response characteristic over a wide band by matching the center of gravity in a symmetrical star weight, which is composed of two parts of a central part and a protruding part, with the center of a piezoelectric vibrating element, interposing a braking piece composed of an elastic layer in an interval between the weight and vibrating element and elastically coupling the both weight and vibrating element. CONSTITUTION:For a weight 4, a back surface is wholly made flat and the center of gravity 9, which is the center of the weight, is matched with a center 1a of a vibrator 1 through a braking piece 7. Then, the weight and vibrator 1 are elastically coupled. For the braking piece 7, a pressure sensitive elastic adhesive agent or an elastic silicone adhesive agent is applied to the both surfaces of the piece, which normally has thickness in the measure of 1mm. Then, one surface is attached to the weight 4 and the, other surface is attached to the vibrator 1 with attention as much as possible so that bend distortion can not be applied. Then, the weight and vibrator are elastically coupled. Thus, a central part 5 of the weight 4 mainly restricts the central part of the vibrator 1 and a convex lens-shaped reference vibration mode is generated. Three protruding parts 6 suppress and block the generation of periodic circular vibration. As a result, the periodic circular vibration is removed and the almost plane characteristic can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric vibrating element that uses a piezoelectric element as an electro-acoustic transducer.

[Prior art] A piezoelectric vibrator is a so-called unimorph (2 A bimorph (layer type) or bimorph (three layer type) is common, and is attracting attention in the field of electronics as a reversible electro-mechanical conversion element. However, piezoelectric ceramics are hard, have a high elastic modulus, and are brittle, so it is difficult to process them into thin films. Its application has been limited to narrow ranges such as buzzers, and has hardly been used in transducers such as speakers that require a wideband output sound pressure response.

Regarding electro-acoustic transducers using piezoelectric vibrating elements, U.S. Pat.
It is disclosed in Japanese Patent No. 1-65600.

FIG. 10 is a side view showing a conventional single-type piezoelectric vibrating element disclosed in the above-mentioned patent. In FIG. , 2 is the piezoelectric ceramic, 3 is the edge of the vibrator 1, 10 is a small cylindrical weight, and 11 is a damping piece made of a viscoelastic layer. A weight 10 is coupled to the vicinity of the center 1a of the vibrator 1 via a brake piece 11, and this is used as a constraint impedance Z1 that acts in conjunction with the frequency.
The degrees of freedom of a are constrained and controlled to generate a concave lens-shaped curved deformation vibration as shown in the figure.At the same time, the radius of curvature of the curved deformation is changed by the frequency-related restraint of the restraint impedance Z1, and the edge of the vibrator 1 is The excitation force F, which has been speeded up, is taken out from the section 3. The excitation force F is transmitted from the edge portion 3 to a separate diaphragm for sound pressure radiation, and this can be driven at a constant speed to produce a useful acoustic product such as a speaker.

[Problems to be Solved by the Invention] In the conventional piezoelectric vibrating element described above, as the vibrator 1 becomes thinner, the surface rigidity decreases and bending changes easily. This induces harmful nodal vibrations in existing waves and impedes the conversion function, but the conventional method of configuring a single type constraint impedance according to the above patent has surprisingly little ability to prevent nodal vibrations. found.

On the other hand, with the diversification of requirements for speakers and the increase in the size of the radiating diaphragm, load inbeaters 1. There is a problem in that as the noise increases, nodal circular vibrations of the standing waves appear due to reflection phenomena, leading to a deterioration in sound quality, and therefore an improved means is required to suppress and prevent this.

-m, the nodal circular vibration parasitic on the vibrator has a negative effect on the reproduced sound quality as it has lower dimensions such as first order and second order.The following describes the situation in which this occurs.

Fig. 11 is a sectional view showing a piezoelectric speaker using the piezoelectric vibrating element shown in Fig. 10, Fig. 12 is an equivalent circuit diagram showing the operating principle of the piezoelectric speaker shown in Fig. 11, and Fig. 13 is a cross-sectional view of a piezoelectric speaker using the piezoelectric vibrating element shown in Fig. 10. FIG. 3 is an output sound pressure response characteristic diagram of a certain piezoelectric speaker. A weight 10 (m+) and a damping piece 11 (C+, rl) made of a viscoelastic layer are coupled to the center of the vibrator 1 to form a constraint impedance Z1. The edge portion 3 is coupled to a driving point 14 of a sound pressure radiation diaphragm 12 (m2.C2, r3) via a coupling ring 13 (Z2) which is a coupling damper. Now, when input signal voltage e is applied, the corresponding primary velocity ■1 flows through the coupling ring 13 (Z2), and along with it, the secondary velocity V2 flows into the diaphragm 12 and excites it. Drive the required acoustic output P. radiate. At this time, V, , V2 must flow smoothly and in a well-balanced manner over the entire operating band into the two branches on the left and right with the driving point 14 as the boundary, but the first condition is to first configure the vibration circuit. It is necessary to harmonize the impedance of each part. If this condition is not met, a standing wave will be generated in the vibrator 1, and nodal circular vibrations of fl and f2 will appear as shown by the dotted line, Vl will be out of tune, and this will have an adverse effect on V2. Eventually, an abnormal portion will appear in the output sound pressure Po.

There are various possible causes for the generation of standing waves, but first, it largely depends on the diameter of the diaphragm 12. That is, D≦50
Even if there is no abnormality in the dragon, when D≧60 to 70 dragon, the load impedance of the driving point 14 suddenly increases and primary and secondary nodal circular vibrations f+ and f2 appear in the vibrator 1.
As shown in the characteristic diagram of FIG. 12, the output sound pressure response has a deep dip at fl (approximately 2 kHz) and a sharp peak at f2 (approximately 3 kHz), resulting in a significant deterioration of the reproduced sound quality. The thickness t and diameter d of the vibrator 1 are also related to the cause of this nodal circular vibration. For example, d=30Il1m,
Even if there is almost no abnormality in the vibrator 1 with t = 200 μm, if the thickness t is as thin as 150 μm or less, or if the external dimension d is 400 μm or more, nodal circular motion is likely to occur. Measures are needed to prevent this.

This invention was made to solve such pressure points, and when the drive impedance of the load terminal is large or when the surface rigidity of the vibrator is insufficient, the harmful nodal circular vibration parasitic to the vibrator can be suppressed. The purpose of this invention is to obtain a composite piezoelectric vibrating element that suppresses absorption and realizes a high-quality piezoelectric acoustic device.

[Means for Solving the Problem] A composite piezoelectric element according to the present invention aligns the center of gravity of a symmetrical star-shaped weight consisting of three parts, a center part and a protruding part, with the center of a piezoelectric vibrator, and A braking piece made of a viscoelastic layer is sandwiched between the two to viscoelastically connect them.

In the first invention, the symmetrical star-shaped weight is integrated.

In the second invention, the symmetrical star-shaped weight and the brake piece are separated into two parts, a center part and a protruding part, and are coupled to both or one side of the piezoelectric vibrator.

[Function] In the composite piezoelectric vibrating element of the present invention, the symmetrical star-shaped weight, together with the action of the damping piece of the viscoelastic layer that connects the weight and the vibrator, causes the center of the weight to , mainly constrains the center of the vibrator to generate a concave lens-shaped vibration mode, and its protruding portion acts to absorb and remove parasitic nodal circular motion of the vibrator.

[Example] FIG. 1 is a plan view showing a composite piezoelectric vibrating element as an example of the present invention, and FIG. 2 is a side view of FIG. 1. The same or equivalent parts as in FIG. 10 are indicated using the same reference numerals, and detailed explanation thereof will be omitted. In FIG. The center portion 5 of the weight made of a star-shaped metal piece may be made spherical if necessary to enable weight adjustment. 7 is a brake piece of a viscoelastic layer made by cutting a foamed butyl rubber sheet with skins on both sides into a shape similar to the outer shape of the weight 4; 9 is the center of gravity of the weight 4;

The composite piezoelectric vibrating element shown in FIGS. 1 and 2 is
Transducer 1 has outer diameter d=25~30I1m, thickness t=200
It is most suitable for a 2R type or three layer type with a thickness of about 300 μm. The weight 4 has an outer radius rl of the protrusion 6 which is 30 to 40 of the outer radius r of the vibrator 1.
%, thickness is about 1.0 to 21 mII, weight is about 1.5 to 3 g, and the material is preferably lead or a soft alloy made of its alloy.

The weight 4 has a flat back surface, and its center of gravity 9 is aligned with the center 1a of the vibrator 1 via the brake piece 7.
It is viscoelastically coupled to the vibrator 1.

The brake piece 7 is an important circuit element in the configuration, and is usually one strand thick and coated with pressure-sensitive adhesive or viscoelastic silicone adhesive on both sides. The surfaces are bonded and viscoelastically bonded with care as much as possible so as not to give any bending distortion to the vibrator 1. With the above configuration, the center part 5 of the weight 4 mainly restrains the center part of the vibrator 1, as in the conventional single weight 10, and forms a concave lens shape as shown by the dotted line in FIG. Generate a reference vibration mode. In addition, the 31-piece protrusion 6 suppresses and prevents the occurrence of nodal vibration by applying the viscous resistance of the brake piece 7 to the part corresponding to the "antinode" of the nodal vibration where the standing wave is predicted to occur. do. In this case, when applying excessive suppression, it not only causes a decrease in the degree of variation and an increase in nonlinear distortion, but also results in a deterioration of the sound quality, so be careful to keep it within the appropriate limit. There is a need. As a result, as shown in the output sound pressure response characteristic diagram of FIG. 9, nodal vibrations were eliminated and a generally flat characteristic was obtained, resulting in a marked improvement in the reproduced sound quality.

The shape of the weight 4 is not limited to that shown in FIG. 1, but may also be shaped as shown in FIGS. 3 to 5, for example.

3 to 5 are plan views showing examples in which the weight 4 of the composite piezoelectric vibrating element shown in FIG. 1 is deformed. Third
The composite piezoelectric vibrator shown in the figure has two protrusions 6 on the weight 4a, and has the slowest suppressing effect on nodal vibration, making it suitable for a small-diameter vibrator 1.The one shown in FIG. The weight 4b has four protruding parts 6, and the above-mentioned suppressing effect is large.
Adapt to. In addition, the weight 4C shown in Fig. 5 is an equilateral triangle suitable for simple shape action, and its outer diameter is usually 25mm.
Suitable for small objects smaller than Maro.

FIG. 6 is a plan view showing a composite piezoelectric vibrating element which is an example of a pond according to the present invention, FIG. 7 is a sectional view taken along line AA in FIG. 6, and FIG.
The figure is a back view of FIG. 6 above.

In this embodiment, the integrated weight 4 of the embodiment shown in FIG. Brake piece 7
is similarly separated into 7a and 7b. And the center weight 5a
The center of gravity 9 of the vibrator 1 is aligned with the center 1a of one side of the vibrator 1, and the center of gravity 9 of the protrusion 6a is aligned with the center 1a of the other side, and the brake piece 7a is aligned.

They are separately installed on both sides of the vibrator 1 via 7b. In this embodiment, since the brake pieces 7a and 7b are separated, the viscoelastic constant of each material can be freely selected depending on the application purpose, and precise adjustment is possible.

Although not shown, for the same purpose, a central weight 5
It is also possible to provide one side of the protrusion a in the center opening 8 of the protrusion 6a.

[Effects of the Invention] As described above, the composite piezoelectric vibrating element according to the present invention has a structure in which the center of gravity of a symmetrical star-shaped weight consisting of three parts, a center part and a protruding part, is aligned with the center of the piezoelectric vibrator. A damping piece made of a viscoelastic layer is sandwiched in the gap, and the two are viscoelastically coupled, so it can be used when the drive impedance of the load terminal is large or when the surface rigidity of the vibrator is insufficient. The present invention also has excellent effects such as being able to absorb and suppress the harmful nodal vibrations parasitic on the vibrator and realize a piezoelectric acoustic product having high quality output sound pressure response characteristics over a wide band.

In addition, in the case where the weight and brake piece are separated into two parts, the center part and the protruding part, there is an advantage that the viscoelastic constant of the material can be freely selected depending on the application purpose, and precise adjustment is possible. It has excellent effects such as making it possible to realize piezoelectric acoustic products of better quality.

[Brief explanation of the drawing]

Fig. 1 is a plan view showing a composite piezoelectric vibrating element which is an embodiment of the present invention, Fig. 2 is a side view of Fig. 1 above, and Figs.
FIG. 5 is a plan view showing an example of a modified weight of the composite piezoelectric vibrating element shown in FIG. 1, and FIG. 6 is a plan view showing a composite piezoelectric vibrating element as another example of the present invention. 7 is a sectional view taken along the line A-A in FIG. 6 above, FIG. 8 is a rear view of FIG. 6 above, and FIG. 9 is an output sound pressure of a piezoelectric speaker using the composite vibration element of the present invention. Response characteristic diagram, Figure 10 is a side view showing a conventional single type piezoelectric vibrating element, Figure 11 is a
Figure 12 is an equivalent circuit diagram showing the operating principle of the piezoelectric speaker shown in Figure 11, and Figure 13 is the output of a piezoelectric speaker with nodal vibration. FIG. 3 is a sound pressure response characteristic diagram. In the figure, 1...piezoelectric vibrator (vibrator), 1a...
Center, 2... Piezoelectric ceramic, 3... Edge, 4° 4a, 4b, 4c, 10... Weight, 5... Center, 5
a...Central weight, 6,6a...Protrusion, 7.7a,
7b, 11... Braking piece, 8... Center opening, 9... Center of gravity, 12... Vibration plate, 13... Coupling ring, 14...
...is a driving point. Note that in each figure, the same reference numerals indicate the same or equivalent parts.

Claims (2)

[Claims] (1) The center of gravity of a symmetrical star-shaped weight with protruding parts radially protruding from the center is aligned with the center of the piezoelectric vibrator, and a damping piece made of a viscoelastic layer is sandwiched in the gap, so that both of them are made viscoelastic. 1. A composite piezoelectric vibrating element characterized in that it is configured to be coupled with each other. (2) Individual symmetrical star-shaped weights with separate center and protruding parts are arranged with their centers of gravity aligned with the center of both sides or one side of the piezoelectric vibrator, and independent viscoelastic properties are created in the gaps between them. A composite piezoelectric vibrating element characterized in that it is configured such that a damping piece consisting of layers is sandwiched between the two and the two are viscoelastically coupled.