JPH0884396A - Piezoelectric speaker - Google Patents

Abstract

PURPOSE: To increase the sound volume by adhering the underside of a piezoelectric element to a middle part of the top surface of a diaphragm. CONSTITUTION: The underside 1b of a flat piezoelectric element 1b is adhered to the top surface 2a of a flat diaphragm 2 made of a conductor such as a metal via a conductive adhesives 3 and one end of each of conductors 4a, 4b is soldered to the top surface 1a of the piezoelectric element 1 and the underside 2b of the diaphragm 2 and led out. Innumerable very-small diameter through holes 5 are made to the piezoelectric speaker B1 over the middle part 2a1 of the top surface 2a of the diaphragm 2 with respect to the piezoelectric 1. It is equivalent to decrease the width of the diaphragm 2 macroscopically by making the through holes 5. Since the deflection displacement of the diaphragm is increased, the sound volume emitted from the piezoelectric speaker is increased and a higher electroacoustic transducing efficiency is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric speaker (crystal speaker) which is a relatively small electro-acoustic conversion element using a piezoelectric effect.

[0002]

2. Description of the Related Art Conventionally, there has been a piezoelectric speaker which is an electro-acoustic conversion element utilizing the piezoelectric effect of a piezoelectric element, and is smaller, thinner, lighter and cheaper than an electrodynamic speaker (dynamic speaker). It is widely used mainly as a sounding body for small electronic devices by taking advantage of many features such as no magnetic circuit required, high drive impedance, low drive power, and the ability to set resonance frequency arbitrarily.

A conventional piezoelectric speaker will be described with reference to the drawings. FIG. 5 (a) is an overall perspective view of a conventional piezoelectric speaker, FIG. 5 (b) is a conceptual diagram of the same structure, and FIG. 5 (c) is a front sectional view. FIG. 6A is a plan view showing a method of cutting out the evaluation model from the piezoelectric element, and FIG. 6B is an overall perspective view of the evaluation model. FIG. 7 is an explanatory diagram of dimensions of each part of the same evaluation model.

In the figure, A is a piezoelectric speaker, 1 is a piezoelectric element,
Reference numeral 1a is a piezoelectric element top surface, 1b is a piezoelectric element bottom surface, 2 is a diaphragm, 2a is a diaphragm top surface, 2b is a diaphragm bottom surface, 3 is a conductive adhesive, and 4a and 4b are conducting wires.

The conventional piezoelectric speaker A shown in FIGS. 5A to 5C has a structure in which BaTiO ₃ (barium titanate) or P, which is electrically polarized in advance in the vertical direction with respect to the element surface, is used.
A flat plate-shaped piezoelectric element 1 bottom surface 1b made of a material such as a solid solution of bZrO ₃ and PbTiO ₃ is attached to a flat plate-shaped diaphragm 2 upper surface 2a made of a conductor such as a metal via a conductive adhesive 3 to form a piezoelectric element. 1 top surface 1a and diaphragm 2 bottom surface 2b
And one end of each of the conductive wires 4a and 4b is soldered and connected to the and.

When the other ends of these conductors 4a and 4b are connected to an oscillator (not shown) and an AC drive voltage of an audible frequency is applied, the piezoelectric element 1 is caused to move between the upper surface 1a and the bottom surface 1b of the piezoelectric element 1 based on the piezoelectric effect. Complementarily, it periodically expands and contracts at the frequency. In response to the expansion and contraction of the piezoelectric element 1, the diaphragm 2 attached to the bottom surface 1b of the piezoelectric element 1 flexes and vibrates in the thickness direction, and the density of the air near the diaphragm 2 changes, which changes the air in the surrounding space. Sound waves are emitted by conduction.

With respect to such a piezoelectric speaker A, the relational expression between the size of each part and the emitted sound volume will be described. Here, in order to simplify the calculation, as shown in FIGS. 6 (a) and 6 (b),
A piece of minute width b is cut out from the piezoelectric speaker A, and an evaluation model placed in free space is assumed.

Here, for simplification of calculation, it is assumed that the thickness of the conductive adhesive 3 is negligible and not shown. As a result of applying a predetermined drive voltage to the piezoelectric element 1, the piezoelectric element 1 expands in the horizontal direction, a bending moment M is applied to the diaphragm 2, and the bottom surface 1b of the piezoelectric element 1 as shown in FIG.
Is bent by a displacement λ in the vertical direction with respect to the bottom surface 1b when no drive voltage is applied, the radius of curvature R of the bottom surface 1b is
From the Young's modulus E, the moment of inertia I of area and the bending moment M of the diaphragm 2, R = E · I / M (Equation 1) The moment of inertia I of area of the diaphragm 2 is the width b and the thickness h of the diaphragm 2. ^{from, I = b · h 3/} 12 ...... ( equation 2) relational expression is obtained.

In addition, the flexural displacement λ of the bottom surface 1b of the piezoelectric element 1
From the radius of curvature R and the angle θ, λ = R {1-cos (θ / 2)} (Equation 3) The total length L of the piezoelectric element 1 is calculated from the radius of curvature R and the angle θ: L = R · θ (Equation 4) (θ: Angle (rad) that faces both ends of the piezoelectric element 1 from the center point of the radius of curvature R) The above four equations (Equation 1) to (Equation 4) are obtained.

The sound volume P at a place separated from the piezoelectric speaker A by a predetermined distance and the bending displacement amount λ of the diaphragm 2 are in a proportional relationship with each other, and the proportional coefficient is defined as α. Solving for the sound volume P from equations approximating (equation 1), (equation 2), (equation 4) and (equation 3) by P = 3α · M · L ² / (2E · b · h ³ ). (Equation 5) is obtained.

In order to increase the sound volume P, the bending moment M and the total length L of the piezoelectric element 1 are increased or the Young's modulus E, width b, and thickness h of the diaphragm 2 are decreased from the equation (5). good.

[0012]

However, the conventional piezoelectric speaker A described above has the following problems when compared with the electrodynamic speaker.
Since the electrical and mechanical driving impedance is high, the sound pressure is low and the obtained volume is small.

Therefore, the piezoelectric speaker A is generally used.
Is attached to a device casing (not shown) to substantially increase the area of the diaphragm 2, or the piezoelectric speaker A is integrally built in a resonance box (not shown) to enhance frequency characteristics near a specific frequency. Although a means for increasing the volume is used, its use is limited to the extent that it can be used as a substitute part for the electrodynamic speaker in various small electronic devices whose installation space is limited.

Even if an attempt is made to increase the volume for expanding the application, the bending moment M depends on the material and shape of the piezoelectric element 1 as shown in the relational expressions of the piezoelectric speaker of the above (Equation 1) to (Equation 5). , The total length L is determined from the diameter of the piezoelectric element 1, the Young's modulus E is determined from the material of the diaphragm 2, the width b and the thickness h are determined from the diameter and thickness of the diaphragm 2, respectively.
There is a large dependence on the characteristic values peculiar to these materials, and even if an appropriate material is selected, a theoretical increase in volume could hardly be expected.

Further, the diaphragm 2 is made of a metal which is a conductor for electrically connecting the bottom surface 1b of the piezoelectric element 1 and the conductor wire 4b to apply a drive voltage. However, since metal has a high bending rigidity, the displacement of the piezoelectric element 1 in the expansion and contraction in the horizontal direction is small, the displacement due to the vertical bending of the diaphragm 2 is small, and as a result, the volume is low, which has not been overcome.

Here, the present invention provides a piezoelectric speaker capable of increasing the volume while being simple and inexpensive to construct.

[0017]

In order to solve the above problems, the present invention employs the specific technical means listed below.
In other words, the first feature of the present invention is to provide a flat plate-shaped piezoelectric element that is polarized in the thickness direction and a flat plate-shaped diaphragm made of metal in which a myriad of minute through holes are provided in the central portion of the upper surface. A piezoelectric speaker comprising the piezoelectric element and a bottom surface of the piezoelectric element attached to a central portion of an upper surface of the diaphragm.

The second feature of the present invention is to provide a flat plate-shaped piezoelectric element polarized in the thickness direction, an infinite number of through holes having a minute diameter in the central portion of the upper surface, and innumerable portions other than the central portion of the upper surface. And a flat plate-shaped diaphragm made of metal provided with a hole having a small diameter which does not penetrate, and a bottom surface of the piezoelectric element is attached to a central portion of an upper surface of the diaphragm.

A third feature of the present invention is that a flat plate-shaped piezoelectric element polarized in the thickness direction and a flat plate-shaped diaphragm made of metal provided with innumerable penetrating holes over the entire upper surface. And a central portion of the upper surface of the diaphragm,
The piezoelectric speaker is configured such that a bottom surface of the piezoelectric element is adhered and a non-breathable film is adhered to a portion other than a central portion of an upper surface of the diaphragm.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention has the specific embodiment as described above, and then the embodiments of the present invention will be described with reference to the drawings. FIG.
(A) is an overall perspective view of the piezoelectric speaker of 1st Example of this invention, (b) is a conceptual diagram of a structure, (c) is a front sectional view. FIG. 2A is a plan view of the principle model of the same piezoelectric speaker,
(B) is the same whole perspective view.

In the figure, B1 is a piezoelectric speaker, 1 is a piezoelectric element, 1a is a piezoelectric speaker top surface, 1b is a piezoelectric speaker bottom surface, 2 is a diaphragm, 2a is a diaphragm top surface, and 2b.
Is a diaphragm bottom surface, 3 is a conductive adhesive, 4a and 4b are conducting wires, and 5 is a through hole. In the following description, a through hole means a hole penetrating between the front and back surfaces, and a drilling hole means a so-called blind hole that does not penetrate between the front and back surfaces.
The definition of the term "drilling" also follows these definitions.

The structure of the piezoelectric speaker B1 of the first embodiment shown in FIGS. 1 (a) to 1 (c) and the piezoelectric speaker A of the prior art is similar in structure to the element surface in the vertical direction. The bottom surface 1b of the flat plate-shaped piezoelectric element 1 made by sintering and polishing BaTiO ₃ (barium titanate) or a solid solution of PbZrO ₃ and PbTiO ₃ to which electric polarization has been applied, through the conductive adhesive 3 It is attached to the upper surface 2a of the flat plate-shaped diaphragm 2 made of a conductor such as metal, and the lead wires 4a and 4b are soldered and connected to the upper surface 1a of the piezoelectric element 1 and the bottom surface 2b of the diaphragm 2 so as to be drawn out. .

The structural difference between the piezoelectric speaker B1 of this embodiment and the piezoelectric speaker A of the conventional example is that the piezoelectric speaker B1 of this embodiment is different from the piezoelectric element 1 in the diaphragm 2 and the upper surface 2 thereof.
a Through-hole 5 of innumerable minute diameter over the entire central portion 2a1
This is because the piezoelectric speaker A of the conventional example does not have the through hole 5 formed therethrough. From the macroscopic point of view, the fact that the through hole 5 is provided means that the diaphragm 2 is substantially
It is equivalent to reducing the width b of.

For example, as shown in FIG. 2 which shows an arbitrary cross section of the diaphragm 2a, when n through holes 5 having a diameter D are provided so as to penetrate, the force for bending the diaphragm 2a is the same. In the above, since it works only in the portion where the through-hole 5 is not provided, it can be considered that the width (b−D · n) of the diaphragm 2a is substantially reduced.

The sound volume Px in this case is given by the above (formula 5) as follows: Px = 3α · M · L ² / {2E (b−D · n) h ³ } (formula 6)

From the equations (5) to (6), the ratio of the sound volume radiated when the through hole 5 is provided and when not provided is Px / P = b / (b−D · n). (Equation 7) is calculated.

When the relative level of the volume is displayed in decibels, it is calculated as follows: D (dB) = 10log (Px / P) = 10log {b / (b−Dn)} (Equation 8) From the equation (8), it is shown in principle that the volume increases as the diameter D of the through holes 5 increases and the total number n of the through holes 5 increases.

However, if only the diameter D of the through hole 5 is simply increased, the drive voltage is not applied to the central portion of the through hole 5, resulting in a decrease in drive efficiency.
In order to avoid this problem, this embodiment employs a structure in which an infinite number of through holes 5 having a minute diameter D are provided.

As a result of exhibiting such a specific embodiment, the present embodiment increases the flexural displacement amount of the diaphragm as compared with the above-mentioned conventional example, so that it is possible to increase the sound volume emitted from the piezoelectric speaker. Become.

A second embodiment of the present invention will be described with reference to the drawings. 3 (a) is an overall perspective view of the piezoelectric speaker of the present embodiment, FIG. 3 (b) is the same conceptual drawing, and FIG. 3 (c) is the same front sectional view. In the figure, B2 is a piezoelectric speaker, and 6 is a hole. The same members as those in the first embodiment are designated by the same reference numerals.

The structure of the piezoelectric speaker B2 of this embodiment will be described with respect to the differences from the piezoelectric speaker B1 of the first embodiment. The piezoelectric speaker B2 of this embodiment has a central portion 2a1 that is attached to the bottom surface 1b of the piezoelectric element 1 on the upper surface 2a of the diaphragm 2 of the piezoelectric speaker B1 of the first embodiment.
Innumerable minute through holes 5 are attached to the upper surface 2a
The diaphragm 2 is attached to the peripheral portion 2a2 other than the central portion 2a1.
A myriad of small-diameter holes 6 are formed which do not penetrate from the upper surface 2a to the bottom surface 2b.

Unlike the through hole 5, the perforation hole 6 does not penetrate between the upper surface 2a and the bottom surface 2b of the diaphragm 2 to prevent air flow.

The perforation holes 6 may be perforated from either the front or back surface of the diaphragm 2b. Further, it is preferable that the drilling depth of the drilling hole 6 is as deep as possible because the flexural displacement amount λ of the diaphragm 2b increases, but there is also a balance with the strength of the diaphragm 2b, and both are taken into consideration. However, it is desirable to select an appropriate drilling depth.

As a result of exhibiting such a specific embodiment, the present embodiment increases the flexural displacement amount of the diaphragm as compared with the conventional example, and therefore is shown in the first embodiment (Equation 6).
Through (Equation 8), it is possible to increase the volume emitted from the piezoelectric speaker.

A third embodiment of the present invention will be described with reference to the drawings. 4A is an overall perspective view of the piezoelectric speaker of the present embodiment, FIG. 4B is a conceptual view of the same, and FIG. 4C is a sectional view of the same. In the figure, B3 is a piezoelectric speaker, 7 is a film, and 8 is an adhesive. The same members as those in the first and second embodiments are designated by the same symbols.

The structure of the piezoelectric speaker B3 of this embodiment will be described with respect to the differences from the piezoelectric speaker B1 of the first embodiment. The diaphragm 2c has an infinite number of through-holes 5 with a small diameter and is provided over the entire surface between the front and back surfaces, and is adhered to the piezoelectric element 1 via a conductive adhesive 3.
Is not attached to the piezoelectric element 1, the central portion 2a of the upper surface 2a
A substantially donut-shaped non-breathable film 7 is attached to the peripheral portion 2a2 other than 1, and the upper surface 2a of the diaphragm 2 is
Air does not flow between the bottom surfaces 2b.

Since the material of the film 7 is required to be non-breathable and lightweight, polyethylene,
PVC (polyvinyl chloride), mylar, etc. can be used. Here, the material of the adhesive 8 used for adhering the diaphragm 2 and the film 7 may be conductive or non-conductive.

As a result of exhibiting such a specific embodiment, the present embodiment increases the flexural displacement of the diaphragm as compared with the conventional example, and therefore is shown in the first embodiment (Equation 6).
Through (Equation 8), it is possible to increase the volume emitted from the piezoelectric speaker.

[0039]

As described above, the piezoelectric speaker of the present invention is higher than the conventional piezoelectric speaker when the same driving voltage is applied by using the piezoelectric element and the diaphragm having the same external dimensions. It is possible to obtain electro-acoustic conversion efficiency, high sound pressure, and high volume.

Comparing the structure with the conventional piezoelectric speaker,
It can be realized mainly by processing the diaphragm, and it can be realized without increasing the initial cost, thus exhibiting high economic efficiency.

[Brief description of drawings]

1A is an overall perspective view of a piezoelectric speaker according to a first embodiment of the present invention, FIG. 1B is a conceptual view of the same structure, and FIG. 1C is a sectional view of the same.

2A is a plan view of a principle model of a piezoelectric speaker, and FIG. 2B is a perspective view of the same.

3A is an overall perspective view of a piezoelectric speaker according to a second embodiment of the present invention, FIG. 3B is a conceptual view of the same structure, and FIG. 3C is a sectional view of the same.

4A is an overall perspective view of a piezoelectric speaker of a third embodiment of the present invention, FIG. 4B is a conceptual view of the same structure, and FIG. 4C is a sectional view of the same.

5A is an overall perspective view of a conventional piezoelectric speaker, FIG.
(B) is a conceptual diagram of the same structure, and (c) is a sectional view of the same structure.

6A is a plan view showing a method of cutting out an evaluation model from a piezoelectric element, and FIG. 6B is an overall perspective view of the evaluation model.

FIG. 7 is a diagram for explaining the dimensions of each part of the above-mentioned evaluation model.

[Explanation of symbols]

R Curvature radius of the bottom surface 1b of the piezoelectric element 1 M Bending moment applied to both ends of the bottom surface 1b of the piezoelectric element 1 λ Deflection displacement of the bottom surface 1b of the piezoelectric element 1 L Total length of the piezoelectric element 1 b Width of the diaphragm 2 h Thickness of the diaphragm 2 θ Curvature radius The angle n which faces both ends of the piezoelectric element 1 from the center point of R n The total number of the through holes 5 and the drilled holes 6 in the arbitrary section of the diaphragm 2 D The diameter of the through hole 5 and the drilled hole 6 P The volume of sound emitted from the piezoelectric speaker A Px Piezoelectric loudspeaker B1 to B3 radiated sound volume α Proportional constant between deflection displacement λ and sound volume P, Px A, B1 to B3 Piezoelectric speaker 1 Piezoelectric element 1a Piezoelectric element upper surface 1b Piezoelectric element bottom surface 2 Diaphragm 2a Diaphragm upper surface 2a1 Diaphragm Upper surface central portion 2a2 Diaphragm upper surface peripheral portion 2b Diaphragm bottom surface 3 Conductive adhesive 4a, 4b Conductor wire 5 Through hole 6設孔 7 film 8 adhesive

Claims (3)

[Claims] 1. A flat plate-shaped piezoelectric element polarized in the thickness direction, and a flat plate-shaped diaphragm made of metal having an infinite number of holes penetrating a minute diameter formed in the central portion of the upper surface, and the upper surface of the diaphragm. A piezoelectric speaker characterized in that the bottom surface of the piezoelectric element is attached to the central portion. 2. A flat plate-shaped piezoelectric element polarized in the thickness direction, and an infinite number of small holes penetrating in the center of the upper surface, and innumerable holes not penetrating in the small area other than the central part of the upper surface. And a flat plate-shaped diaphragm made of metal, the bottom surface of the piezoelectric element being attached to the central portion of the upper surface of the diaphragm. 3. A flat plate-shaped piezoelectric element polarized in the thickness direction, and a flat plate-shaped diaphragm made of metal provided with innumerable small-diameter through-holes over the entire upper surface thereof. The piezoelectric speaker is configured such that a bottom surface of the piezoelectric element is attached to a central portion of an upper surface of the diaphragm, and a non-breathable film is attached to a portion other than a central portion of the upper surface of the diaphragm.