JP2001008291A - Piezoelectric sound producing body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To turn sound volume high, without increase in inputted voltage by incurvating a diaphragm from the circumference of a rim to the center of the diaphragm in unloaded state. SOLUTION: A piezoelectric unit to be constituted of a piezoelectric element film 21, formed by depositing electrodes on its main surfaces on both sides and the diaphragm 22 consisting of metal foil formed by sticking the piezoelectric element film 21, is incurvated so as to be recessed from the circumference of the rim to the center of the diaphragm 22. When the piezoelectric unit is set in a casing 1, the rim of the diaphragm 22 is mounted on a step part 11, fixed by adhesive agent, after that, adhered, welded to a casing 3 by ultrasonic waves and AC voltage is impressed on led wire 21a, 21b, the piezoelectric element film 21 and the diaphragm 22 are vibrated in a direction perpendicular to the surface in proportion to an electric field of an AC signal and a sound is produced. Thus, since compression stress is generated in the diaphragm when the diaphragm is vibrated in the direction to return incurvature and pulling stress is generated after vibration disappears, when the diaphragm is further vibrated when the diaphragm 22 is incurvated at the unloaded state, vibration quantity until the pulling stress becomes a prescribed value is increased, without increase in the inputted voltage to the piezoelectric element film 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric sounding body used for a portable telephone or the like.

[0002]

2. Description of the Related Art As a conventional piezoelectric sounding body of this type, for example, Japanese Patent Application Laid-Open No. 6-86389 has a diaphragm on which a thin plate-like piezoelectric element is adhered. Fixed in a casing over a period of time.
In this device, a step is formed on the inner peripheral surface of a bottomed cylindrical casing, a circular diaphragm on which a thin disk-shaped piezoelectric element is adhered is placed on the step of the casing, and a silicon resin is further formed. The peripheral edge of the diaphragm is fixed to the inner peripheral surface of the casing over the entire periphery by an adhesive such as. When an AC voltage such as an audio signal is applied to the piezoelectric element attached to the diaphragm, the piezoelectric element vibrates, and the vibration is transmitted to the diaphragm to generate sound.

[0003]

In the above-mentioned conventional piezoelectric sounding body, since the peripheral edge of the diaphragm is fixed over the entire circumference, a radial tensile stress is generated in the diaphragm as the amplitude of the diaphragm increases. However, the tensile stress acts in a direction to suppress vibration of the diaphragm. Therefore, in order to increase the sound volume in the above-mentioned conventional piezoelectric sounding body, it is necessary to increase the value of the AC voltage applied so as to be able to resist the tensile stress of the diaphragm. However, in order to increase the applied voltage, a special boosting circuit must be provided, and the circuit is inevitably complicated and large.

[0004] In view of the above problems, an object of the present invention is to provide a piezoelectric sounding body that can increase the volume without increasing the input voltage.

[0005]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention has a diaphragm on which a thin plate-like piezoelectric element is adhered, and a peripheral edge of the diaphragm is formed in a casing around the entire circumference. Is characterized in that the diaphragm is curved from the entire periphery to the center of the diaphragm in a no-load state.

[0006] When the diaphragm is curved in a no-load state as described above, a compressive stress is once generated in the diaphragm when the diaphragm vibrates in the direction to return to the curved state, and when the diaphragm further vibrates, the compressive stress disappears and thereafter. Tensile stress occurs. Therefore, even if the input voltage at the piezoelectric element is not increased, the amount of vibration, that is, the amplitude until the tensile stress reaches a predetermined value becomes larger than that of the conventional one in which the diaphragm is not bent.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, reference numeral 1 denotes a casing formed by injection molding of a resin, which is formed in a bottomed cylindrical shape. The inner peripheral surface of the casing 1 has a stepped portion 1 over substantially the entire circumference.
1 is formed. Further, a part of the peripheral wall of the casing 1 was cut off to form a cutout groove 12 communicating the inside and outside of the casing 1. A large number of pores 14 functioning as dampers are provided through the bottom 13 of the casing 1. 2
Denotes a piezoelectric unit, which includes a piezoelectric element film 21 having electrodes deposited on both main surfaces thereof, and a diaphragm 22 made of metal foil to which the piezoelectric element film 21 is adhered. In the posture shown in FIG. 1, the piezoelectric unit 2 is curved so as to be recessed from the entire periphery to the center of the diaphragm 22 toward the center from the periphery. As shown in FIG. 1, the piezoelectric unit 2 was set in the casing 1 with the upper surface of the piezoelectric unit 2 depressed, and the peripheral edge of the diaphragm was placed on the step portion 11. By the way, lead wires 21a and 21b are respectively provided on an electrode on the main surface of the main surface of the piezoelectric element film 21 opposite to the vibration plate 22 and on the vibration plate 22 electrically connected to the other electrode. When the piezoelectric unit 2 is set in the casing 1 by soldering, the lead wires 21 a and 21 b pass through the cutout groove 12.
When the peripheral edge of the diaphragm 22 is placed on the step 11, the peripheral edge of the diaphragm 22 is fixed to the inner peripheral surface of the casing 1 with an adhesive made of a silicon-based resin. The adhesive is filled in the notch groove 12 to fix the lead wires 21a and 21b and to close the notch groove 12. After the adhesive is cured, the casing 1 is turned upside down from the state shown in FIG. 1 to be in the state shown in FIG. 2 and fixed to the housing 3 such as a mobile phone by an ultrasonic bonding method. Lead wires 21a and 21b
When an AC voltage is applied to the piezoelectric element film 21, the piezoelectric element film 21 vibrates in a direction perpendicular to the plane in proportion to the electric field of the AC signal.
Is pronounced by vibrating in the direction perpendicular to the plane. By the way, in the present embodiment, a flat portion that is not curved is left in the peripheral portion of the diaphragm 22 in an annular shape so that the diaphragm 22 can be easily mounted on the step portion 11.

Referring to FIG. 3, a description will be given of the tensile stress P generated in the diaphragm 22 due to the vibration of the diaphragm 22. In a no-load state where the diaphragm 22 is not vibrating, the center of the diaphragm 22 is at the position indicated by a. At this time, no tensile stress is generated in the diaphragm 22. When the diaphragm 22 vibrates upward, the tensile stress P increases as the amplitude increases. When the center point of the diaphragm 22 shifts to the position b, the tensile stress becomes Pp and the piezoelectric element film 21
No further displacement occurs in balance with the distortion force generated in the step. On the other hand, when the diaphragm 22 shifts downward from the neutral state, since the diaphragm 22 is curved, a compressive stress is generated instead of a tensile stress until the center point of the diaphragm 22 reaches the position c. When the center point of the diaphragm 22 exceeds the point c, the compressive stress is relaxed, and when the diaphragm 22 moves further downward, a tensile stress is generated. When the center point of the diaphragm 22 reaches the position of d, the tensile stress becomes Pp, and the diaphragm 22 can no longer be shifted downward. When the compressive stress becomes Pc, the diaphragm 22 cannot shift in the direction in which the compressive stress further increases. However, since the compressive stress at the position c where the compressive stress becomes maximum is smaller than Pc, The points can shift beyond c to d. By the way, in the description of FIG. 3, only the tensile stress has been described.
Is subjected to shear stress and bending moment. Therefore, particularly in the downward shift, the shift cannot be made to the position of d, but since the diaphragm 22 is extremely thin, the shear stress and the bending moment are extremely small and can be ignored.

In the above embodiment, metal foil is used as the diaphragm, but the diaphragm may be formed of a resin film. In this case, the lead wire 21b is connected to the piezoelectric element film 21.
Solder to the electrodes.

[0010]

As is apparent from the above description, according to the present invention, since the vibration plate of the piezoelectric sounding body is curved in advance, the AC signal applied to the vibration plate is greater than that of a conventional piezoelectric sounding body having a flat plate shape. Can be increased.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing a configuration of a sounding body.

FIG. 2 is a cross-sectional view showing a curved state of the diaphragm.

FIG. 3 is a diagram showing the magnitude of tensile stress with respect to displacement of a diaphragm.

[Explanation of symbols]

 Reference Signs List 1 casing 2 piezoelectric unit 21 piezoelectric element film 22 diaphragm

Claims (1)

[Claims] 1. A piezoelectric sounding body having a diaphragm on which a thin plate-shaped piezoelectric element is adhered, wherein a peripheral edge of the diaphragm is fixed in a casing over the entire circumference, wherein the diaphragm is in a no-load state. Wherein the piezoelectric sounding body is curved from the entire periphery to the center of the diaphragm.