JPS60233999A - Piezoelectric speaker - Google Patents

Abstract

PURPOSE:To improve the output sound pressure and the average output sound pressure in a reproduction band by increasing a Young's modulus distribution of a reinforcing plate for adhering a piezoelectric ceramic plate in the direction of the surface opposite to that adhered to the piezoelectric ceramic plate. CONSTITUTION:On both surfaces of a piezoelectric ceramic plate 23, silver electrodes 24 are formed, and said plate 23 is adhered to a reinforcing plate, which consists of a stainless steel layer 21 and a polyester resin layer 22, and the piezoelectric ceramic plate 23 is adhered to the surface of the polyester resin layer. With this constitution a distribution of a Young's modulus increases in the direction of the surface opposite to that adhered to the ceramic plate. The reinforcing plate can consist of a metallic layer 31 and a hony comb structure 32. Since an action neutral plate of bending moment can be taken deeply, output sound pressure between respective resonators can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a piezoelectric speaker used in, for example, radios, stereo devices, and the like.

(Conventional configuration and its problems) In recent years, piezoelectric speakers have been researched and developed in order to reduce the weight and power consumption of audio equipment, and are increasingly being used as high-frequency speakers such as tweeters, receiver units, etc. It has become. A conventional piezoelectric speaker will be described below.

FIG. 1 is a half-sectional view of a conventional piezoelectric speaker. 1 is a circular piezoelectric vibrator, and approximately at the center of the piezoelectric vibrator 1,
The center top of the diaphragm 2 made of paper, resin film, etc. was bonded together, and the periphery of the diaphragm 20 was further bonded to the periphery of the frame 3.

Figures 2 (a) and (b) are 1. Each shows a configuration diagram of a piezoelectric vibrator of a conventional piezoelectric speaker and a schematic diagram of its bent state, and the piezoelectric vibrator 1 has a reinforcing plate 11 made of brass or stainless steel as shown in FIG. 2(a). A piezoelectric ceramic plate 12 having silver electrodes 13 formed on both sides is bonded to the top.

In this piezoelectric vibrator 1, a piezoelectric ceramic plate 12 generates a stress that expands and contracts in the radial direction in proportion to an input voltage, and a moment force M is applied to a surface 15 on which a bending moment acts, which does not change the length in the radial direction. and reinforcing plate 11 as shown in Figure 2 (
As shown in b), it is bent to generate flexural vibration.

Figure 3 shows the equivalent circuit of a piezoelectric speaker, where ■ is the input voltage, Cd is the damping capacity, A is the force coefficient, zl is the mechanical impedance of the piezoelectric vibrator, Zo is the mechanical impedance of the diaphragm, and za is the radiation. Mechanical impedance, F indicates force.

The piezoelectric force is expressed as F-A by using the force coefficient A due to the moment force M in bending vibration due to the input voltage V as a proportional constant.
A driving force of V is generated from the piezoelectric vibrator 1, and the driving force moves the self-mechanical impedance z1 of the piezoelectric vibrator 1 and the mechanical impedance Z c% radiation impedance Za of the diaphragm 2 at a speed V to obtain an acoustic output. There is. Note that the force coefficient A1 of the piezoelectric vibrator 1 and the self-machine impedance zl can be approximated by the following equation.

However, T1: Thickness of the piezoelectric ceramic, ρ1: Density of the piezoelectric ceramic, El: Young's modulus of the piezoelectric ceramic, σl: Poisson's ratio of the piezoelectric ceramic, r,: Outer diameter of the piezoelectric vibrator, To: Neutral bending moment action T2: Thickness of the reinforcing plate, E2: Young's modulus of the reinforcing plate, ρ2: Density of the reinforcing plate, F(ra)' vibration mode function of the piezoelectric vibrator, ra: Connection between the piezoelectric vibrator 1 and the diaphragm Diameter.

Combining the driving force of the piezoelectric vibrator 1 and the self-mechanical impedance of the piezoelectric vibrator 1 using equation (2), and considering the output sound pressure characteristics of the speaker camera, we can find that the diaphragm 2 is attached near the center of the piezoelectric vibrator l. When this is done, the effect of anti-resonance between each resonance of the piezoelectric vibrator is small, resulting in a piezoelectric speaker that can reproduce sound pressure over a relatively wide band.

However, in the above conventional configuration, in order to increase the force coefficient A of the piezoelectric vibrator 1, the reinforcing plate 11 has a Young's modulus E2 so that the neutral surface To of the bending moment expressed by equation (3) can be increased. A large metal plate such as phosphor bronze or stainless steel is used. Therefore, the density ρ2 of the reinforcing plate 11 increases, and the self-mechanical impedance Z of the piezoelectric vibrator l expressed by equation (2) increases. In the equivalent circuit shown in FIG. 3, the force F' applied to the terminals of the mechanical impedance 2° of the diaphragm 2 and the radiation mechanical impedance za is reduced. This result was manifested as a decrease in the output sound pressure between each resonance in the output sound pressure frequency characteristics of the piezoelectric speaker, resulting in a speaker with a large sound pressure deviation within the reproduction band and a low average output sound pressure.

(Objective of the Invention) The present invention solves the above conventional problems, and provides a piezoelectric speaker that can improve the output sound pressure in the frequency band between each resonance and improve the average output sound pressure in the reproduction band. The purpose is to

(Structure of the Invention) In order to achieve the above object, the present invention has a piezoelectric ceramic plate having conductive electrodes formed on both sides, bonded to a reinforcing plate having a distribution of Young's modulus in the thickness direction. By using a piezoelectric vibrator configured so that the Young's modulus distribution of the reinforcing plate increases in the direction of the surface facing the bonding surface with the piezoelectric ceramic plate as the drive source of the piezoelectric speaker, piezoelectric vibration can be achieved. The objective is to improve the force coefficient of the child, reduce the self-mechanical impedance, improve the output sound pressure in the frequency band between each resonance, and improve the average output sound pressure within the reproduction band.

(Description of Embodiment) FIGS. 4(a) and 4(b) show the structure of an embodiment of the piezoelectric vibrator in the piezoelectric speaker of the present invention and its bent state.
This is a schematic diagram, in which a single piezoelectric ceramic plate 23 with silver electrodes 24 formed on both sides is made of polyamide.

The first
The piezoelectric vibrator 1 shown in the figure is composed of a diaphragm 2 made of paper, resin film, etc., which is connected to the approximate center of the piezoelectric vibrator 1, and the periphery of the diaphragm 2 is connected to the periphery of a frame 3. They are glued together to form a piezoelectric speaker.

The entire operation of the piezoelectric speaker of the present invention constructed as described above will be explained below.

The piezoelectric vibrator 1 generates stress due to the expansion and contraction of the piezoelectric ceramic plate 23, has a neutral surface 25 on which a bending moment acts and whose length does not change in the radial direction, and applies a moment force M' to the surface 26. The polyester resin layer 22 and the stainless steel layer 21 of the reinforcing plate are bent to generate a flexural vibration.At that time, the acting neutral surface 25 of the bending moment is...(4) However, L, To'' bend is the moment Neutral surface of action, T2'I
It is expressed as: the thickness of the ester resin layer, the Young's modulus of the E2' grade ester resin layer, the thickness of the T3 stainless steel layer, and the Young's modulus of the E3 stainless steel layer. When the thickness of the polyester resin layer 22 of the reinforcing plate is 50 μm, the thickness of the stainless steel layer is 50 μm, and the thickness of the piezoelectric ceramic plate 23 is 100 μm, compared to the case where the reinforcing plate is composed of a single layer of stainless steel of 100 μm,
The neutral surface T on which the bending moment acts becomes deeper by about 17%, and the force coefficient A due to the moment force M' improves by 5%.

Furthermore, the self-mechanical impedance 21' of the piezoelectric vibrator 1
By making a part of the reinforcing plate resin, it can be reduced to 75% of that of a single stainless steel plate. By reducing the force coefficient A' and the self-mechanical I/P/S2, /, the piezoelectric speaker can improve the output sound pressure between each resonance by approximately 3 dBO compared to the conventional configuration. . These show that E3+73 expressed in equation (4), that is, the position of the neutral plane 25 on which the bending moment acts can be arbitrarily changed in a metal layer with a high Young's modulus.

FIG. 5 shows the structure of another embodiment of the piezoelectric vibrator according to the present invention, in which 3] is a metal layer, 32 is a -.nicum structure, 33 is a piezoelectric ceramic plate, and 34 is a silver electrode.

In this example, a Nicum structure 32 is used instead of the polyester resin layer 22 in FIG. Effects of the Invention) As explained above, the present invention improves the output sound pressure between each resonance by giving the reinforcing plate of the piezoelectric vibrator a distribution of Young's modulus, and increases the average output sound pressure within the reproduction band. This makes it possible to realize an excellent piezoelectric speaker with improved performance.

[Brief explanation of drawings]

Figure 1 is a half-sectional view of a conventional piezoelectric speaker, and Figure 2 (a
) and (b) are the configuration diagram of a piezoelectric vibrator of a conventional piezoelectric speaker and a schematic diagram of its bent state, FIG. 3 is a diagram showing an equivalent circuit of a piezoelectric speaker, and FIG. 4 (a) and (b) 5 is a schematic diagram showing the structure of one embodiment of the piezoelectric vibrator in the piezoelectric speaker of the present invention and its bent state, and FIG. 5 is a diagram showing the structure of another embodiment of the piezoelectric vibrator in the present invention. ■...Piezoelectric vibrator, 2...Vibration plate, 3...Frame, 2
1... Stainless steel layer, 22... Polyester fat-using layer, 2!3, 33... Piezoelectric ceramic plate, 24, 3
4... Silver electrode, 25... Neutral surface on which bending moment acts, 26... Surface on which bending moment acts, 31... Metal layer, : 32. Honeycomb structure. Figure 1

Claims (4)

[Claims] (1) A piezoelectric ceramic plate with conductive electrodes formed on both sides is bonded to a reinforcing plate with a Young's modulus distribution in the thickness direction, and the Young's modulus distribution of the reinforcing plate is 1. A piezoelectric speaker characterized in that it uses a piezoelectric vibrator configured such that the number of vibrators increases in the direction of the surface facing the adhesive surface. (2) A piezoelectric speaker according to claim (1), wherein the complementary plate is constructed by laminating a resin film and a metal plate. (3) The piezoelectric speaker according to claim (1), wherein the reinforcing plate is constructed by joining a nicam-shaped core to a single metal plate. (4) Claim No. (1) characterized in that the reinforcing plate also serves as one electrical input terminal to the piezoelectric ceramic plate.
The piezoelectric speaker described in Section 1.