JP2002108346A - Piezoelectric sounding body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric sounding body which has flattened excellent sound pressure frequency characteristics. SOLUTION: A piezoelectric sounding element 10 is formed in a disk shape on the whole and has a driving plate 14 stuck on a diaphragm 12, and is supported across a support 24 on a step 22 of a housing 20 which is sectioned nearly in an L shape and annular on the whole. On the reverse-surface side of the diaphragm 12, a vibration suppressing material 16 is formed. This vibration suppressing material 16 suppresses the vibration of the diaphragm 12 and mechanical resistance increases. Consequently, a quality factor Q decreases and the sound pressure of the piezoelectric sounding body is flattened over a wide frequency range.

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 in electronic audio equipment, communication equipment, electronic equipment and the like.

[0002]

2. Description of the Related Art Piezoelectric sounding bodies are widely used as simple electro-acoustic conversion means, and in recent years, in particular, have been widely used in fields such as mobile phones. In general, as shown in a cross section in FIG. 8A, the piezoelectric driving plate 900 is bonded to a metal vibration plate 910. As the piezoelectric material, for example, a piezoelectric ceramic {ceramics mainly containing lead zirconate titanate (abbreviated as PZT), barium titanate, lead zirconate, lead titanate, etc.} is used.
While such a piezoelectric material is formed into a disk shape, for example,
After firing and polarization, a piezoelectric driving plate 900 is obtained. Driving electrodes 902 are provided on the upper surface (or both front and back surfaces) of the piezoelectric driving plate 900. On the other hand, as a metal forming the metal diaphragm 910, for example, an Fe—Ni-based stainless material is used. The piezoelectric driving plate 900 is bonded to the metal vibration plate 910 using an adhesive, so that a piezoelectric sounding body (or a piezoelectric speaker or a piezoelectric buzzer) 920 is obtained.

[0003] The piezoelectric sounding body 920 thus obtained is obtained.
, A drive signal 922 is applied between the electrode 902 and the metal vibration plate 910, in other words, on the front and back surfaces of the piezoelectric drive plate 900. The metal diaphragm 910 side is usually grounded.
When an electric displacement is applied to the piezoelectric driving plate 900 in this manner, the piezoelectric driving plate 900 expands and contracts in the circumferential direction as indicated by an arrow FA in FIG. However, the metal diaphragm 9
Due to the presence of 10, the whole becomes curved, and as a result, vibrates in the vertical direction as shown by the arrow FB, and a sound is generated.

[0004]

By the way, an equivalent circuit of the above-mentioned piezoelectric sounding body is shown, as shown in FIG. 8C, as an inductance Lr, a capacitance Cr, and a resistance R.
This is a circuit in which a capacitor Co is connected to the series circuit o.
Among them, the series circuit of the inductance Lr, the capacitance Cr, and the resistance Ro is an element that affects the mechanical (or physical) displacement, and the motional current i flowing through them is
As m increases, so does the mechanical displacement. If they are represented by a mechanical equivalent circuit, inductance Lr is equivalent mass m, capacitance Cr is stiffness s (hardness),
The resistances Ro respectively correspond to the mechanical resistances Rm. Note that the current io is a steady current.

In such an equivalent circuit, the resonance frequency fr of the mechanical system is, as is well known, fr = (1 / 2π) √ (Cr / Lr) = (1 / 2π) √ (s / m )..., And Q (quality factor) of the mechanical system is represented by Q = (1 / Rm) √ (m × s).

When the level of Q changes, the impedance Z of the piezoelectric sounding body changes as shown in FIG. That is, when Q is increased as in GA, the impedance greatly changes near the resonance point. As for the sounding body, it is better that the fluctuation is small at least in the audible frequency range. According to the above-described formula, Q decreases as the equivalent mass m and the stiffness s decrease. That is, the equivalent mass m
Is larger, the resonance frequency is lower. The resonance frequency of the piezoelectric sounding body depends on the diameter of the vibrating body, and it is necessary to produce a vibrating body with a large diameter in order to produce a bass range. However, by adding an equivalent mass, even a small-sized piezoelectric sounding body having a small diameter can produce a bass range. From such a relationship, to obtain a small-sized piezoelectric sounding body having good characteristics, the smaller the Q is, the better the m is.

The present invention has been made in view of the above points, and an object of the present invention is to provide a piezoelectric sounding body which can obtain a flattened and good sound pressure frequency characteristic.

[0008]

In order to achieve the above object, the present invention provides a piezoelectric sounding element in which a vibration plate supported by a housing and a driving plate constituted by a piezoelectric body having electrodes are attached. In the piezoelectric sounding body supported by the housing, the piezoelectric sounding element is provided with means for reducing a quality factor.

The main mode is characterized in that the means for reducing the quality factor is provided with any one of means for increasing the mechanical resistance, means for reducing the stiffness, and means for providing a plurality of resonance frequencies for the piezoelectric sounding element. And
The above and other objects, features and advantages of the present invention will be apparent from the following detailed description and the accompanying drawings.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS <First Embodiment> FIG. 1 shows an appearance and a main cross section of a first embodiment. In FIG. 1, the piezoelectric sounding element 10 is entirely formed in a disk shape, and has a configuration in which a driving plate 14 is adhered to a vibration plate 12. On the other hand, the casing 20 which is a support frame of the piezoelectric sounding element 10 has a substantially L-shaped cross section in the radial direction, and is formed in an entire annular shape. The step 22 of the housing 20
2 made of an adhesive or the like provided over the entire circumference
4, the piezoelectric sounding element 10 is supported.

A vibration suppressing member 16 is provided on the back side (lower side in the figure) of the diaphragm 12. The drive plate 14
Internal electrode 18 inside with a laminated structure of piezoelectric body (piezoelectric sheet)
Are embedded in parallel, and electrodes 32 and 34 are formed on the surface. The internal electrode 18 has a through-hole conductor 36
Are alternately connected to the electrodes 32 and 34. The electrode 32 is connected to the extraction terminal 38, and the electrode 34 is connected to the extraction terminal 4.
0. As the lead terminals 38 and 40, known terminals such as metal terminals and lead wires are used. When the diaphragm 12 and the housing 20 are made of metal,
One terminal may be drawn from them.

Next, each component will be further described.
As the diaphragm 12 of the piezoelectric sounding element 10, a known one can be used. For example, a metal plate such as stainless steel having a thickness of about 10 μm to 100 μm may be used. The vibration suppressing member 16 is formed of an elastic material such as a rubber paint. As a specific example, it is formed by a method such as applying and curing a soft liquid silicone rubber.

The driving plate 14 of the piezoelectric sounding element 10 is formed of a piezoelectric ceramic laminate using a known piezoelectric ceramic material such as PZT. As described above, the electrodes 32 and 34 on the surface and the internal electrodes 18 are alternately connected by the through-hole conductors 36, so that the adjacent electrodes have alternate polarities. The through-hole conductor 36 is formed by providing a through-hole land and filling the through-hole with a conductive paste.
The amount of displacement of the diaphragm 12 can be adjusted by increasing the number of laminated piezoelectric sheets on the driving plate 14, and the amount of displacement can be easily increased by increasing the number of laminated sheets. Various structures other than those shown in the figure can be applied as the laminated structure.

The housing 20 is preferably made of metal. By using metal, the housing 20 with high strength and high accuracy can be obtained even if the opening 26 is provided on the lower side. In particular,
A metal that is not easily oxidized and has a small coefficient of thermal expansion, such as a magnesium alloy, or a lightweight metal such as aluminum is desirable. The sound pressure can be adjusted by the shape, size, and number of the openings 26 (one in the illustrated example). The shape of the housing 20 is preferably annular, and the diaphragm 1 has a step 22 as shown in the figure.
(2) The size shall be able to receive. Such a housing 2
0 can be obtained by cutting or punching a flat plate.

The piezoelectric sounding element 10 may be mechanically fixed to the housing 20 by fitting or the like. However, in consideration of productivity, a method of fixing the piezoelectric sounding element 10 with an adhesive is desirable. Here, when the diaphragm 12 is a metal, a material that has good adhesion to the metal and does not hinder vibration is preferable, and a soft material such as a silicon-based adhesive is preferable. . Specifically, an elastic silicone adhesive or the like is used.

The piezoelectric sounding body 50 constructed as described above
Is, for example, the piezoelectric sounding element 1
It is attached to the electronic device so that the drive plate 14 side of the zero is the device side, that is, the vibration generated by the diaphragm 12 is output to the outside through the openings 26 and 53. For example, the upper side of FIG. 1 is the inside of the mobile phone,
The lower side of FIG. 1 is the outside of the mobile phone. As described above, if the piezoelectric sounding body 50 is directly attached to the electronic device housing 52, it is possible to realize a high-density electronic device, particularly, a low profile. Instead of being directly attached to the electronic device housing 52, a shield plate having an opening may be simply put on the drive plate 14 side as a case.

Next, as the lead terminals 38 and 40, various known design forms can be applied. First, the lead wires may be directly electrically connected to the electrodes 32 and 34 of the driving plate 14. Next, in the example shown in FIG. 2A, metal terminals 60 and 62 are attached at appropriate positions around the piezoelectric sounding element 10, respectively. In this example, the diaphragm 12 is conductive, and is connected to one electrode of the driving plate 14.

In FIG. 2A, one metal terminal 60 is shown.
Are electrically connected to the electrodes 32 on the upper surface of the driving plate 14 and are led out as terminals 61 to the outside. The other metal terminal 62 is electrically connected to the diaphragm 12 made of a conductive metal, and is drawn out as a terminal 63 to the outside. The vibration plate 12 is electrically connected to the electrode 34 on the back surface of the driving plate 14 by a conductive adhesive. Metal terminal 6
0,62 is a metal piece bent into a crank shape,
It is exposed at the outer peripheral portion of the housing 20. When the housing 20 is made of metal, the insulating terminals 6 and 62 are provided between the metal terminals 60 and 62 so that the metal terminals 60 and 62 do not make electrical contact with the housing 20.
4, 66 are provided.

FIG. 2B shows a configuration in which the diaphragm 12 and the housing 20 are conductive and connected to one electrode of the driving plate 14. That is, the vibration plate 12 electrically connected to the back electrode 34 of the driving plate 14 is connected to the housing 20 by the lead wire 68. Terminal 63
Is taken out from an appropriate part of the housing 20. The one metal terminal 60 side is the same as the example of FIG. 2A. As shown in FIG. 2 described above, a surface-mountable piezoelectric sounding body can be obtained by pulling out from the housing using a terminal made of a metal piece. Of course, the metal piece (or the conductive pattern) may be drawn further to the outer peripheral side of the housing 20.

FIG. 3 shows an opening 71 for adjusting the sound pressure.
The flat plates 70 and 72 each having a corresponding one of the
0 is provided on the back side or the front surface of the housing 20. Thus, the flat plate 70 or 7 for adjusting the sound pressure is used.
By providing 2, even if the piezoelectric sounding bodies 50 have the same structure, different sound pressure characteristics can be obtained, and manufacturing costs such as mold costs can be reduced.

Next, the main manufacturing steps of the above-described piezoelectric sounding body 50 will be described with reference to FIG. First, drive plate 1
Explaining from the laminate to be No. 4, a slurry is prepared by adding a binder to a ceramic powder having a PZT-based composition,
From this, a green sheet is obtained by a method such as a doctor blade.

The green sheet thus obtained is cut, and a conductive paste such as Ag or Ag / Pd is printed by a method such as screen printing to form laminated sheets 14A to 14C shown in FIG. I do. It should be noted that through holes 14D to 14F are formed at the corresponding locations. Thereafter, as shown in FIG. 3B, the respective laminated sheets 14A to 14C are laminated and pressed. And
As shown in FIG. 3C, the inside of the through hole is filled with a conductive paste. Thereafter, the laminate is cut into a predetermined shape and fired at a temperature of about 1100 to 1300 degrees to obtain a laminate having an outer diameter of 15 mm and a thickness of 60 μm (20 μm × 3 layers).

The laminate is polarized by applying a DC voltage with electrode terminals connected to both sides, and becomes a piezoelectric driving plate. With such a laminated structure, a higher electric field can be formed inside the piezoelectric material than in the case of a single-layer structure. The driving plate 14 thus obtained is bonded to the vibration plate 12 on which the vibration suppressing member 16 is formed, as shown in FIG. The bonding between the vibration plate 12 and the driving plate 14 is performed by, for example, uniformly printing the adhesive 12A on the main surface of the vibration plate 12 by a method such as screen printing and affixing the driving plate 14 thereto. At this time, a conductive adhesive may be used as the adhesive 12A. Thus, the piezoelectric sounding element 10 is obtained.

On the other hand, after a silicon-based adhesive is applied as a support 24 to the step 22 in the housing 20 provided with the opening 26 in a ring shape, the above-described piezoelectric sounding element 10 is removed as shown in FIG. Glue. When the adhesive 24 cures, the diaphragm 12 is fixedly supported. Conversely, diaphragm 12
After applying silicone adhesive 24 in a ring shape on the side,
Although it may be bonded to the step 22 of 0, it is better to apply the adhesive 24 to the housing 20 side in consideration of workability. In this case, since the vibration environment of the piezoelectric sounding element 10 changes according to the hardness of the adhesive 24, the mass and / or the thickness of the laminate are adjusted according to the application conditions such as the hardness of the adhesive 24. For example, when the adhesive 24 is hard, the laminate is made heavy and thick.

Next, the operation of the present embodiment will be described. First, the basic operation is the same as that of a conventional piezoelectric sounding body. That is, when an audio signal voltage is applied to the driving plate 14,
Expands and contracts. Then, the diaphragm 12 bends based on the expansion and contraction, and vibrates according to the audio signal. As a result, a sound corresponding to the sound signal is output.

In the first embodiment, the diaphragm 12
Is provided with a vibration suppressing member 16. By doing so, the vibration of the diaphragm 12 is suppressed, and the mechanical resistance Rm increases. Then, the quality factor Q decreases from the above equation. When the quality factor Q decreases, the impedance characteristics of the piezoelectric sounding body are flattened in a wide frequency band, as shown by GB in FIG. That is, the sound pressure vibration is flattened in a wide frequency band. As is clear from the above equation, the resonance frequency fr does not depend on the mechanical resistance Rm. Therefore, there is no possibility that the resonance frequency fr fluctuates by providing the vibration suppressing member 16.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, the stiffness s is reduced. As shown in the figure, in the present embodiment, a low-rigidity material 100 is provided instead of the vibration material 16 described above. That is, the low-rigidity material 100 has a ring shape that fits inside the step 22 of the housing 20, and the piezoelectric sounding element 10 is supported at the center thereof. A bellows-like elastic portion 102 is provided between the contact portion with the diaphragm 12 and the contact portion with the step 22.

The low-rigidity material 100 is made of the diaphragm 1
2, formed of a material having lower rigidity than any of the drive plate 14 and the housing 20. For example, a material such as foamable rubber is used. The stretchable portion 102 is formed on such a low-rigidity material by, for example, a method such as injection molding. In addition,
Low rigidity material 100 and step 22 between diaphragm 12 and housing 20
Are joined by, for example, a silicone adhesive.

Next, the operation of the present embodiment will be described. The piezoelectric sounding element 10 is supported by the housing 20 via the low-rigidity material 100. The low-rigid material 100 is provided with a telescopic part 102. Therefore, the stiffness s of the whole sounding body is reduced. Then, the quality factor Q also decreases from the above equation, and the sound pressure vibration is flattened in a wide frequency range.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIGS. In the third embodiment, sound pressure frequency characteristics are flattened by providing a plurality of resonance points. First, in the example shown in FIG. 6, a weight 200 is attached to the diaphragm 12.
However, as shown in FIG. 7A, the weight 200
It is provided at a position shifted from the center of the piezoelectric sounding element 10.

According to this example, the provision of the weight 200 first increases the mechanical resistance Rm of the above equation. Then, the quality factor Q decreases, and the first and second embodiments described above.
Similarly, the frequency characteristics of the sound pressure are flattened.
Furthermore, since the center of mass of the piezoelectric sounding element 10 and the center of mass of the weight 200 are shifted, a plurality of resonance points appear as a whole, and the frequency characteristics of the sound pressure are also flattened.

Next, in the example shown in FIG. 7B, the piezoelectric sounding element 300 itself is formed in an elliptical shape. Also in this example, a plurality of resonance points similarly appear, and the frequency characteristics of the sound pressure are similarly flattened.

<Other Embodiments> The present invention has many embodiments, and various modifications can be made based on the above disclosure. For example, the materials, shapes, and dimensions described in the above embodiments are merely examples, and the design can be changed so as to achieve the same operation. The same applies to the number of stacked sheets and the pattern of the internal electrodes. Further, the above embodiments may be combined.

[0034]

As described above, according to the present invention,
Since the mechanical resistance of the piezoelectric sounding element is increased, the stiffness is reduced, and a plurality of resonance points are provided, the quality factor is reduced, the frequency characteristics of sound pressure are flattened, and a piezoelectric sounding body having good characteristics is obtained. The effect that it can be obtained is obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing an appearance and a main cross section of a first embodiment of the present invention.

FIG. 2 is a main cross-sectional view illustrating an example of an electrode structure according to the first embodiment.

FIG. 3 is a main cross-sectional view showing a modification of the first embodiment.

FIG. 4 is a view showing main manufacturing steps of the first embodiment.

FIG. 5 is a diagram showing an appearance and a main cross section of a second embodiment of the present invention.

FIG. 6 is a diagram showing an appearance and a main cross section of a third embodiment of the present invention.

FIG. 7 is a diagram showing a plan configuration of a third embodiment.

FIG. 8 is a diagram showing a basic configuration of a piezoelectric sounding body.

FIG. 9 is a diagram showing basic characteristics of a piezoelectric sounding body.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Piezoelectric sound-generating element 12 ... Vibration plate 12A ... Adhesive 14 ... Driving plate 14A-14C ... Laminated sheet 14D-14F ... Through hole 16 ... Vibration suppressor 18 ... Internal electrode 20 ... Housing 22 ... Step 24 ... Support 26 ... Openings 32, 34 ... Electrodes 36 ... Through-hole conductors 38, 40 ... Lead-out terminals 50 ... Piezoelectric sound generators 52 ... Electronic equipment housings 53 ... Openings 60, 62 ... Metallic terminals 61, 63 ... Terminals 64, 66 ... Insulating coat 68 ... Lead wires 70 and 72 .. Flat plates 71 and 73.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Yasuyuki Inomata 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Induction Co., Ltd. (72) Inventor Hiroshi Kishi 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Induction Co., Ltd.

Claims (11)

[Claims] 1. A piezoelectric sounding element in which a piezoelectric sounding element in which a vibration plate supported by a housing and a driving plate formed of a piezoelectric body having electrodes are bonded is supported by the housing. And a quality factor reducing means. 2. The quality factor reducing means includes:
2. The piezoelectric sounding body according to claim 1, wherein the piezoelectric sounding element is means for increasing the mechanical resistance of the piezoelectric sounding element. 3. The piezoelectric sounding body according to claim 2, wherein the means for increasing the mechanical resistance is a vibration suppressing means formed on the diaphragm. 4. The power generating sounding body according to claim 2, wherein said vibration suppressing means is a coating of an elastic body. 5. The quality factor reducing means includes:
2. The piezoelectric sounding body according to claim 1, wherein the piezoelectric sounding element is means for reducing the stiffness of the piezoelectric sounding element. 6. The piezoelectric sounding body according to claim 5, wherein said stiffness reducing means is low rigidity supporting means formed between said piezoelectric sounding body and said housing. 7. The piezoelectric sounding body according to claim 6, wherein said low-rigidity support means is formed of a foamed rubber material. 8. The piezoelectric sounding body according to claim 7, wherein a stretchable portion is formed in said low-rigidity support means. 9. The quality factor reducing means includes:
2. The piezoelectric sounding body according to claim 1, wherein the means for providing a plurality of resonance frequencies of the piezoelectric sounding element. 10. The means for providing a plurality of resonance frequencies,
The piezoelectric sounding body according to claim 9, wherein the weight is provided at a position shifted from a center of the diaphragm. 11. The means for providing a plurality of resonance frequencies,
10. The piezoelectric sounding body according to claim 9, wherein the piezoelectric sounding body has an elliptical diaphragm shape.