Patent Application
20080218031
The present invention relates to electroacoustic transducers used as sounders such as speakers, and, more particularly, to an electroacoustic transducer having a cantilever support structure in which a piezoelectric element is supported at one end portion thereof.
In recent years, electroacoustic transducers such as a speaker and a buzzer using a piezoelectric effect are widely used. For example, the following Patent Document 1 discloses a sounder 101 illustrated in an elevational cross-sectional view in
In the sounder 101, the piezoelectric vibrating element 103 is supported at one end portion thereof, and the other end portion of the piezoelectric vibrating element 103 is a free end portion. That is, since the piezoelectric vibrating element 103 is supported in the cantilever manner, the free end portion of the piezoelectric vibrating element 103 can be significantly displaced. Accordingly, a high sound pressure can be obtained.
On the other hand, the following Patent Document 2 discloses a piezoelectric ceramic speaker illustrated in
Patent Document 1: Japanese Unexamined Utility Model Application Publication No. 63-191800
Patent Document 2: Japanese Utility Model Registration No. 3068450
In the sounder 101, the peripheral portion of the piezoelectric vibrating element 103 excluding the portion coupled to the box 102 is exposed in the box 102. Accordingly, when the piezoelectric vibrating element 103 vibrates, the air pressure on the side of one surface of the piezoelectric vibrating element 103 and the air pressure on the side of the other surface of the piezoelectric vibrating element 103 cancel each other. As a result, sound in a low frequency range cannot be obtained. That is, a high sound pressure cannot be obtained over a wide range of frequencies.
On the other hand, in the piezoelectric ceramic speaker 111 disclosed in Patent Document 2, the cone-shaped diaphragm 114 capable of directly acting on the air generates an acoustic wave. Accordingly, in addition to the piezoelectric vibrating element 113, the large cone-shaped diaphragm 114 is required. As a result, the piezoelectric ceramic speaker 111 becomes larger in size. This makes it difficult to reduce the thickness of the piezoelectric ceramic speaker 111. Furthermore, the number of components is increased, and the number of manufacturing processes is therefore increased. This leads to the increase in cost.
Furthermore, natural in-plane vibration of the cone-shaped diaphragm 114 occurs. As a result, a frequency characteristic becomes deteriorated. Still furthermore, although the piezoelectric vibrating element 113 is supported at one end portion thereof in the cantilever manner, the free end portion thereof is coupled to the cone-shaped diaphragm 114. Accordingly, there is a vibration mode in which the free end portion of the piezoelectric vibrating element 113 is hardly displaced. As a result, a sharp dip occurs in a frequency characteristic.
It is an object of the present invention to provide an electroacoustic transducer capable of obtaining a high sound pressure over a comparatively wide range of frequencies with certainty and coming down in size, in particular, in thickness without increasing the number of components and the number of manufacturing processes.
According to the present invention, there is provided an electroacoustic transducer including a frame having an opening, a plurality of piezoelectric elements each placed in the opening of the frame and each having one end portion coupled to the frame, and a flexible thin film that is bonded to the frame and the piezoelectric elements so as to cover at least a gap between the frame and each of the piezoelectric elements in the opening of the frame. The other end portions opposite to the end portions of the piezoelectric elements are free end portions, and face each other across a gap in the opening of the frame.
In an aspect of an electroacoustic transducer according to the present invention, the flexible thin film is placed so that it covers an entire area of the opening of the frame, and an entire area of one of main surfaces of each of the piezoelectric elements is bonded to the flexible thin film.
In another aspect of an electroacoustic transducer according to the present invention, the piezoelectric elements each has a substantially trapezoidal shape having an upper base and a lower base corresponding to the end portion coupled to the frame.
In still another aspect of an electroacoustic transducer according to the present invention, a length of the end portion of each of the piezoelectric elements which is coupled to the frame is smaller than a width of the opening at the gap across which the piezoelectric elements face each other. The width of the opening is a dimension in the same direction as a direction of the length of the end portion.
In still another aspect of an electroacoustic transducer according to the present invention, a rigid plate that is bonded to the flexible thin film at the gap across which the piezoelectric elements face each other and has a higher rigidity than that of the flexible thin film is further included.
In still another aspect of an electroacoustic transducer according to the present invention, a resonance frequency in a fundamental mode of at least one of the piezoelectric elements is different from that of the other piezoelectric elements.
In still another aspect of an electroacoustic transducer according to the present invention, a planer shape of at least one of the piezoelectric elements is different from that of the other piezoelectric elements.
In still another aspect of an electroacoustic transducer according to the present invention, a thickness of at least one of the piezoelectric elements is different from that of the other piezoelectric elements.
In still another aspect of an electroacoustic transducer according to the present invention, the frame and the piezoelectric elements are integrally formed using a single piezoelectric ceramic plate.
In an electroacoustic transducer according to the present invention, each of a plurality of piezoelectric elements is coupled to a frame at one end portion thereof. The other end portion of each of the piezoelectric elements is a free end portion. Thus, the piezoelectric elements are supported in the cantilever manner. Accordingly, the free end portions of the piezoelectric elements can be significantly displaced. A flexible thin film is bonded to the frame and the piezoelectric elements so that it covers at least a gap between each of the piezoelectric elements and the frame. Accordingly, the flexible thin film bonded to the piezoelectric elements capable of being significantly displaced can also be significantly displaced. Consequently, a very high sound pressure can be obtained.
By simply bonding the piezoelectric elements and the flexible thin film to the frame, the miniaturization of an electroacoustic transducer, in particular, the reduction in thickness of the electroacoustic transducer can be easily achieved. Furthermore, the increase in the number of components can be prevented, and the electroacoustic transducer can be easily assembled. This leads to cost reduction.
If the flexible thin film is placed so that it covers the entire area of the frame and the entire area of one of main surfaces of each of piezoelectric elements is bonded to the flexible thin film, the flexible thin film can be bonded to the frame so that it covers the entire area of the opening of the frame and the piezoelectric elements can be easily bonded to the flexible thin film. Accordingly, the electroacoustic transducer can be more easily manufactured, and a more inexpensive electroacoustic transducer can be provided.
If the piezoelectric elements each has a substantially trapezoidal shape having an upper base and a lower base corresponding to the end portion coupled to the frame, the free end portion corresponding to the upper base can be more easily displaced. Accordingly, a higher sound pressure can be obtained.
If the length of the end portion of each of the piezoelectric elements which is coupled to the frame is smaller than a width of the opening at the gap across which the piezoelectric elements face each other (the width of the opening is a dimension in the same direction as the length direction of the end portion), the piezoelectric elements can be easily displaced on the side of the gap across which the piezoelectric elements face each other. Accordingly, a higher sound pressure can be obtained.
If a rigid plate is bonded to the flexible thin film at the gap across which the piezoelectric elements face each other, the portion of the flexible thin film at the gap in which the rigid plate is disposed is displaced. As a result, a higher sound pressure can be obtained.
If a resonance frequency in a fundamental mode of at least one of the piezoelectric elements is different from that of the other piezoelectric elements, a high sound pressure can be obtained over a wider range of frequencies. If a planer shape of at least one of the piezoelectric elements is different from that of the other piezoelectric elements, a resonance frequency in a fundamental mode of the piezoelectric element can be easily made different from that of the other piezoelectric elements. If a thickness of at least one of the piezoelectric elements is different from that of the other piezoelectric elements, a resonance frequency in a fundamental mode of the piezoelectric element can be similarly easily made different from that of the other piezoelectric elements.
If the frame and the piezoelectric elements are integrally formed using a single piezoelectric ceramic plate, the number of components can be reduced and an electroacoustic transducer capable of easily coming down in size can be provided.
a) and 1(b) are an elevational cross-sectional view and a plan view of an electroacoustic transducer according to a first embodiment of the present invention, respectively.
a) is a plan view of an electroacoustic transducer according to an exemplary modification of the first embodiment of the present invention, and
a) and 5(b) are an elevational cross-sectional view and a plan view describing an electroacoustic transducer according to a fourth embodiment of the present invention, respectively.
a) and 10(b) are a plan view and a plan cross-al sectional view describing an electroacoustic transducer according to still another exemplary modification of the first embodiment of the present invention, respectively.
Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.
a) and 1(b) are an elevational cross-sectional view and a plan view of an electroacoustic transducer according to a first embodiment of the present invention, respectively. An electroacoustic transducer 1 is suitable for use as a piezoelectric speaker. The electroacoustic transducer 1 includes a frame 4 obtained by bonding a first frame member 2 and a second frame member 3 together. The frame members 2 and 3 are made of an appropriate rigid material such as metal or ceramic. In this embodiment, the frame members 2 and 3 are made of metal.
The frame 4 includes an opening 4a. In the opening 4a, a flexible thin film 5 is bonded to the frame 4 so that it covers the entire area of the opening 4a. More specifically, the peripheral portion of the flexible thin film 5 is sandwiched and fixed between the frame members 2 and 3 so that the flexible thin film 5 covers the entire area of the opening 4a.
The flexible thin film 5 is composed of a flexible thin film made of a material that is not particularly limited, but is preferably a deformable and elastic material having a large internal loss and an excellent environmental resistance such as synthetic rubber having rubber elasticity, natural rubber, or elastomer. Examples of such synthetic rubber include ethylene-butadiene rubber and styrene-butadiene rubber.
The thickness of the flexible thin film 5 is not particularly limited, but, in this embodiment, ranges from 30 to 100 μm. The flexible thin film 5 is required to have a certain degree of flexibility that does not restrict displacement caused by the bending vibration of a piezoelectric element that will be described later.
Each of a first piezoelectric element 6 and a second piezoelectric element 7 is bonded to the upper surface of the flexible thin film 5. In this embodiment, each of the piezoelectric elements 6 and 7 is a laminated piezoelectric element obtained by forming piezoelectric ceramic layers made of piezoelectric ceramic such as lead zirconate titanate on opposite sides of a single internal electrode layer. On opposite main surfaces of this laminated piezoelectric element, electrode films are formed (not illustrated in
In this embodiment, the above-described internal electrode is made of an Ag—Pt alloy. The electrode films formed on the opposite main surfaces of the laminated piezoelectric element are formed by sputtering an Ni—Cu alloy. On the end face of the piezoelectric element 6, the internal electrode thereof and the electrode films thereof are electrically connected to each other. On the end face of the piezoelectric element 7, the internal electrode thereof and the electrode films thereof are electrically connected to each other. As illustrated in
One end portion 6a of the laminated piezoelectric element 6 and one end portion 7a of the laminated piezoelectric element 7 are fixed to the frame 4, whereby the laminated piezoelectric elements 6 and 7 are supported. More specifically, as illustrated in
Each of the piezoelectric elements 6 and 7 and the flexible thin film 5, which are sandwiched between the frame members 2 and 3, are bonded and fixed to each other using a known adhesive. Such an adhesive is not particularly limited. In this embodiment, however, a thermosetting silicon adhesive is used. Another adhesive such as an epoxy adhesive may be used. Alternatively, a hardening adhesive may be used instead of a thermosetting adhesive.
In the electroacoustic transducer 1 according to this embodiment, the piezoelectric elements 6 and 7 are used in such a manner that the bending vibrations of the piezoelectric elements 6 and 7 are in-phase with each other. Accordingly, the terminal electrodes 10 and 11 are connected to one potential, the electrode films 8 and 9 and the electrode films on the undersurfaces are connected to the other potential, and an alternating voltage is applied between the terminal electrode and the electrode film. As a result, the bending vibrations of the piezoelectric elements 6 and 7 are in-phase with each other, and the flexible thin film 5 vibrates in synchronization with the vibrations of the piezoelectric elements 6 and 7. Accordingly, sound is produced in accordance with the difference between the air pressure on the side of the upper surface of the flexible thin film 5 and the air pressure on the side of the undersurface of the flexible thin film 5.
In the electroacoustic transducer 1 that is manufactured as described previously, since the movement of the air between the side of the upper surface and the side of the undersurface of the flexible thin film 5 is interrupted, the difference between the air pressure on the side of the upper surface and the air pressure on the side of the undersurface is not canceled. Accordingly, a high sound pressure can be obtained over a wide range of frequencies. Furthermore, since the piezoelectric elements 6 and 7 are supported in the cantilever manner, the end portions 6b and 7b can be easily displaced. The flexible thin film 5 is therefore significantly displaced at a center position thereof at which the gap A is provided. Accordingly, a high sound pressure can be obtained.
Since the main part including the flexible thin film 5 and the piezoelectric elements 6 and 7 is obtained by simply bonding the piezoelectric elements 6 and 7 to the flexible thin film 5, these components are on the substantially same surface. Accordingly, the thickness can be reduced. Furthermore, since it is not required to couple a cone-shaped diaphragm to the piezoelectric elements 6 and 7, the number of components can be reduced and the manufacturing process can be simplified. Consequently, the cost of an electroacoustic transducer can be effectively reduced.
Since the piezoelectric elements 6 and 7 function as diaphragms, it is not required to take a natural vibration other than the natural vibrations of the piezoelectric elements 6 and 7 into consideration. Furthermore, since not only the displacements of the end portions 6b and 7b of the piezoelectric elements 6 and 7 but also the displacements of the entire surfaces of the piezoelectric elements 6 and 7 are used, a sharp dip cannot be easily occurred in a frequency characteristic. Accordingly, a flat and high sound pressure characteristic can be obtained over a wide range of frequencies.
In this embodiment, the flexible thin film 5 covers the entire area of the opening 4a, but may cover at least the gap between each of the piezoelectric elements 6 and 7 and the frame 4. That is, the peripheral portions of the piezoelectric elements 6 and 7 may be coupled to the flexible thin film 5. The entire area of one of the main surfaces of each of the piezoelectric elements 6 and 7 may not necessarily be bonded to the flexible thin film 5 as described previously. The number of piezoelectric layers included in each of the piezoelectric elements 6 and 7 is not limited to two. Each of the piezoelectric elements 6 and 7 may include a large number of piezoelectric layers, for example, three or four piezoelectric layers.
a) is a plan view describing an exemplary modification of the electroacoustic transducer 1 according to this embodiment. In an electroacoustic transducer 12 according to this exemplary modification, each of piezoelectric elements 6A and 7A is composed of a trapezoidal piezoelectric ceramic plate having an upper base and a lower base whose length is larger than that of the upper base. That is, on the sides of the lower bases of the piezoelectric elements 6A and 7A, the piezoelectric elements 6A and 7A are supported by the frame 4, respectively. The upper bases of the piezoelectric elements 6A and 7A on the sides of tip portions thereof face each other with a gap therebetween. Except for this point, the electroacoustic transducer 12 has the same configuration as that of the electroacoustic transducer 1.
As described previously, the upper base whose width is smaller than that of the lower base is on the side of tip portion of each of the piezoelectric elements 6A and 7A. Accordingly, on the side of the upper base, a wide gap between each of the piezoelectric elements 6A and 7A and the frame 4 can be obtained. Each of the piezoelectric elements 6A and 7A can therefore be freely and significantly displaced. Accordingly, the electroacoustic transducer 12 can easily obtain a higher sound pressure than the electroacoustic transducer 1.
b) is a plan view of another exemplary modification of the electroacoustic transducer 1. An electroacoustic transducer 13 according to another exemplary modification has the same configuration as that of the electroacoustic transducer 1 except that the shape of an opening 4b of the frame 4 is different from that of the opening 4a illustrated in
From the viewpoint of capable of obtaining a high sound pressure, the electroacoustic transducers 12 and 13 are superior to the electroacoustic transducer 1 according to the first embodiment. However, in point of the simplification of a manufacturing process and the mechanical strength of the frame 4, the electroacoustic transducer 1 is superior to the electroacoustic transducers 12 and 13.
The rigid plate 22 is bonded to the flexible thin film 5. Accordingly, when the piezoelectric elements 6 and 7 are displaced, the rigid plate 22 is significantly displaced in a portion of the flexible thin film 5 in which the gap A is placed. As compared with a case in which only the flexible thin film 5 is displaced at the gap A, a higher sound pressure can be obtained since the rigid plate 22 is bonded to the flexible thin film 5. The reason for this is that the area in which vibration is performed with the maximum displacement is increased.
Like the piezoelectric elements 6A and 7A used in the electroacoustic transducer 12, the piezoelectric elements 32 to 35 each has a substantially trapezoidal shape. Each of the piezoelectric elements 32 to 35 has an upper base at a tip portion thereof, and is fixed to the frame 4 at a lower base thereof. In this embodiment, the flexible thin film 5 is similarly fixed to the frame 4 so that it covers the entire area of the opening 4a. In a gap region A on the side of the tip portion of each of the piezoelectric elements 32 to 35 having a substantially trapezoidal shape, a rectangular rigid plate 30 is bonded to the flexible thin film 5. Accordingly, in this embodiment, using the rigid plate 30, the area in which vibration is performed with the maximum displacement can also be increased and a higher sound pressure can also be obtained.
Furthermore, in this embodiment, a larger number of piezoelectric elements (the piezoelectric elements 32 to 35) are provided. Accordingly, a larger or heavier rigid plate can be disposed. As a result, the level of sound pressure can be increased.
In
a) and 5(b) are an elevational cross-sectional view and a plan view describing an electroacoustic transducer according to a fourth embodiment of the present invention, respectively. In an electroacoustic transducer 41 according to this embodiment, a first piezoelectric element 42 and a second piezoelectric element 43 each having a planer rectangular shape are used. The piezoelectric elements 42 and 43 are fixed to the frame 4 at one end portions 42a and 43a thereof, respectively, and the other end portions 42b and 43b face each other with a gap therebetween. That is, the piezoelectric elements 42 and 43 are also supported in the cantilever manner.
The plane area of the first piezoelectric element 42 is different from that of the second piezoelectric element 43, and is larger than that of the second piezoelectric element 43. Except for this point, the electroacoustic transducer 41 has the same configuration as that of the electroacoustic transducer 1.
Since the area of the piezoelectric element 42 is larger than that of the piezoelectric element 43, the resonance frequency of the fundamental wave of the piezoelectric element 42 is different from that of the piezoelectric element 43. Accordingly, in this embodiment, a high sound pressure can be obtained over a wide range of frequencies.
The reason why a high sound pressure can be obtained over a wide range of frequencies when the resonance frequencies of the first piezoelectric element 42 and the second piezoelectric element 43 are different from each other will be described below.
The larger number of resonance points are illustrated in
In the electroacoustic transducer 41 illustrated in
Although the manufacturing method of the electroacoustic transducers 1, 21, 31, 41, and 51 is not particularly limited, a method of fixing a single piezoelectric element and cutting the fixed piezoelectric element is preferably used. That is, as illustrated in a plan view in
In the case of the above-described method of fixing the piezoelectric element 61 and then cutting the piezoelectric element 61, only a single piezoelectric element is required so as to obtain the electroacoustic transducer 1. Accordingly, the manufacturing process can be simplified. In a case where a piezoelectric element is fixed to the frame 4 and is then cut, misalignment of the piezoelectric elements 6 and 7 rarely occurs as compared with a case where two piezoelectric elements are prepared in advance. Accordingly, the accuracy of an electroacoustic transducer including a plurality of piezoelectric elements can be increased.
In an electroacoustic transducer according to the present invention, a frame and piezoelectric element may be integrated using a piezoelectric ceramic plate.
As illustrated in
On the undersurface of the ceramic plate 71, an electrode film is formed using the same method as that used for the formation of the electrode film 74. An internal electrode 75 illustrated in
For connection to an external portion, the electrode film 74 and the electrode film formed on the undersurface of the ceramic plate 71 are electrically connected to each other and are then connected to the external portion on the side of the side face 71b. When electrically connecting the internal electrode 75 to an external portion, an external electrode is formed on the side of the other side face 71c and is then connected to the external portion. Accordingly, for example, electrical connection portions with an external portion can be integrated on the side of a supported portion of one of the first and second piezoelectric elements, and wiring of a lead wire can be simplified.
That is, in the electroacoustic transducer 1, an electrical connection portion with an external portion is provided in both of the first piezoelectric elements 6 and the second piezoelectric element 7. On the other hand, according to this embodiment, the electrical connection configuration can be simplified and design flexibility can be increased.
| Number | Date | Country | Kind |
|---|---|---|---|
| JP 2005-339033 | Nov 2005 | JP | national |
The present application is a continuation of International Application No. PCT/JP2006/315587, filed Aug. 7, 2006, which claims priority to Japanese Patent Application No. JP2005-339033, filed Nov. 24, 2005, the entire contents of each of these applications being incorporated herein by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2006/315587 | Aug 2006 | US |
| Child | 12126022 | US |
