JP2011228881A - Electric sound converter and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric sound converter that has a wide directivity and a large sound pressure level and that is suitable for installation to electronic devices.SOLUTION: An electric sound converter 100 comprises a plurality of piezoelectric film diaphragms 1 in which an electrode is formed on both surfaces of a piezoelectric film vibrating in accordance with the state of an electric field. The plurality of piezoelectric film diaphragms 1 are disposed in the shape of a polyhedron. Each of the piezoelectric film diaphragms 1 is inserted into an opening formed on each surface of a polyhedron-shaped frame 2 and engaged therewith.

Description

  The present invention relates to a small electroacoustic transducer having a wide directivity and a high sound pressure level that can be mounted on an electronic device such as a mobile phone, and an electronic device including the electroacoustic transducer.

  With the advancement of the functionality of mobile phones, models that appeal AV (Audio / Visual) functions have been actively developed. In addition, miniaturization of mobile phones is progressing. With the advancement of AV functions, the demand for applications such as moving image playback is increased, and a small electroacoustic transducer having a large volume and wide directivity is required as an acoustic component.

As a technique for increasing the volume of an electroacoustic transducer, there is a technique for arranging a plurality of electrodynamic speakers as disclosed in Patent Document 1. However, in the technique disclosed in Patent Document 1, since a plurality of electrodynamic speakers are arranged, the size of the electroacoustic transducer is remarkably increased, so that it is not suitable for mounting on an electronic device such as a mobile phone. .
In Patent Document 2, a main speaker and a microphone are arranged on the same plane, and when the microphone does not collect sound, the microphone is used as a speaker, and the sound is amplified by interference between the sound emitted from the microphone and the sound emitted from the main speaker. Technology is disclosed. However, the technique disclosed in Patent Document 2 has a problem in that reproduction of a large volume is insufficient because the sound pressure generated from the microphone is very small compared to the sound pressure generated from the main speaker.

On the other hand, as a technique for achieving the wide directivity of the electroacoustic transducer, there is a technique in which a plurality of electrodynamic speakers are arranged in a multifaceted manner as disclosed in Patent Document 3. However, in the technique disclosed in Patent Document 3, since a plurality of electrodynamic speakers are arranged in the same manner as the technique disclosed in Patent Document 1, the size of the electroacoustic transducer is remarkably increased. It is not suitable for mounting on electronic equipment.
On the other hand, Patent Document 4 discloses a technique using a piezoelectric film diaphragm having a curved surface. According to Patent Document 4, it is said that reproduction of a high sound pressure level and a wide band is possible by using a piezoelectric film diaphragm.

JP 2009-1111836 A JP 2002-281135 A JP-A-10-341493 Japanese Patent Laid-Open No. 2003-259489

As described above, the technique of disposing a plurality of electrodynamic speakers disclosed in Patent Document 1 and Patent Document 3 has a problem that the size of the electroacoustic transducer increases.
Further, the technique disclosed in Patent Document 2 has a problem that the sound pressure level is insufficient.
On the other hand, the technique disclosed in Patent Document 4 has a problem in that the size of the electroacoustic transducer increases because a piezoelectric film diaphragm having a curved surface is used to obtain a high sound pressure level. In particular, in a small electronic device such as a mobile phone, since the vertical and horizontal sizes and thickness are severely limited, there is a possibility that the piezoelectric film diaphragm having a curved surface as disclosed in Patent Document 4 cannot be mounted.

  The present invention has been made to solve the above-described problems, and has an object to provide a small electroacoustic transducer having a wide directivity and a high sound pressure level and suitable for mounting on an electronic device such as a mobile phone. And

  The electroacoustic transducer of the present invention includes a plurality of piezoelectric film diaphragms in which electrodes are formed on both surfaces of a piezoelectric film that vibrates according to the state of an electric field, and the plurality of piezoelectric film diaphragms are arranged in a polyhedral shape. It is what.

  According to the present invention, it is possible to realize a small electroacoustic transducer with wide directivity and high sound pressure level by arranging a plurality of piezoelectric film diaphragms in a polyhedral shape and emitting sound waves from the plurality of surfaces. . In the piezoelectric film diaphragm arranged in a polyhedral shape, the radiation surface vibrates by applying a voltage to the electrodes. In the present invention, since the piezoelectric film diaphragm is used, the mechanical quality factor (Qm) of the transducer is reduced, and the sound pressure frequency characteristics can be flattened. In the electroacoustic transducer of the present invention, since a piezoelectric film diaphragm is used, parts such as magnets are unnecessary and the miniaturization can be promoted as compared with a conventional electrodynamic speaker. Further, in the present invention, unlike the conventional electroacoustic transducer, it is not necessary to use a piezoelectric film diaphragm having a curved surface, and a casing of a polyhedral electronic device is used as a frame, and a plate-like piezoelectric element is formed on each surface of the frame. Since a film diaphragm should just be arrange | positioned, it is suitable for mounting to small electronic devices, such as a mobile telephone. In addition, the electroacoustic transducer of the present invention is excellent in manufacturability and has high impact stability when dropped, and thus is suitable for mounting on a small electronic device such as a mobile phone.

It is an external view of the electroacoustic transducer which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the structure of the piezoelectric film diaphragm which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the polarization direction of the piezoelectric film which concerns on the 1st Embodiment of this invention. It is a figure which shows the solid crystal ion arrangement | positioning of the piezoelectric material which concerns on the 1st Embodiment of this invention. It is sectional drawing which shows the structure of the flame | frame concerning the 1st Embodiment of this invention. It is a top view which shows the evaluation method of the electroacoustic transducer based on the 1st Embodiment of this invention.

[First Embodiment]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an external view of an electroacoustic transducer according to a first embodiment of the present invention.
As shown in FIG. 1, an electroacoustic transducer 100 according to the present embodiment includes a plurality of piezoelectric film diaphragms 1 that vibrate when voltage is applied, a frame 2 that fixes the piezoelectric film diaphragm 1, and a piezoelectric film diaphragm. 1 includes wirings 3a and 3b for supplying a voltage to 1 and terminals 4a and 4b.

FIG. 2 is a cross-sectional view showing the structure of the piezoelectric film diaphragm 1. The piezoelectric film diaphragm 1 is formed by forming an upper electrode layer 11 and a lower electrode layer 12 on each main surface of a piezoelectric film 10 as shown in FIG.
The piezoelectric film 10 is made of a polymer material having piezoelectric characteristics. When an electric signal is applied to the piezoelectric film 10, vibration is generated by the piezoelectric effect, and a sound wave can be generated. The material of the piezoelectric film 10 is not particularly limited as long as it is a polymer material having a piezoelectric effect, and examples thereof include polyvinylidene fluoride (PVDF).

As a material of the upper electrode layer 11 and the lower electrode layer 12, a conductive material such as a metal can be used, but a silver paste (silver, silver-palladium) is preferably used. The thickness of the upper electrode layer 11 and the lower electrode layer 12 is optimally 5 μm to 300 μm. If the thickness of the upper electrode layer 11 and the lower electrode layer 12 is less than 5 μm, since the film thickness is thin, the film thickness varies in the production process, and a sufficient function as an electrode material cannot be obtained. On the other hand, when the thickness of the upper electrode layer 11 and the lower electrode layer 12 exceeds 300 μm, the upper electrode layer 11 and the lower electrode layer 12 restrain the movement of the piezoelectric film 10, so that the amplitude of the piezoelectric film 10 is attenuated. Will end up.
In the present embodiment, as shown in FIG. 3, the upper electrode layer 11 on the acoustic radiation surface (upper surface in FIG. 3) side is the positive electrode (+), the lower electrode layer 12 on the opposite side is the negative electrode (−), and the polarization direction Is formed from the negative electrode toward the positive electrode.

Below, the mechanism of vibration generation of the piezoelectric film diaphragm 1 will be described. In the piezoelectric film diaphragm 1 of the present embodiment, vibration is generated in the piezoelectric film 10 by inputting an electric signal to the pair of upper electrode layer 11 and lower electrode layer 12. The piezoelectric material has an effect that a voltage is generated by strain generated by applying pressure, that is, a piezoelectric effect. Since the piezoelectric effect is a reversible phenomenon, distortion occurs when a voltage is applied to the piezoelectric material. The piezoelectric effect is caused by the solid crystal ion arrangement of the piezoelectric material shown in FIG. 4, and the displacement of the ions arranged in the atomic lattice crystal is increased by applying pressure. A phenomenon in which one end is positive and the other end of the crystal is negative, that is, electric polarization occurs, and a voltage is generated. In FIG. 4, 40 is an ion such as Ba ²⁺ , Pb ²⁺ , La ³⁺ , 41 is an ion such as Ti ⁴⁺ , Zr ⁴⁺ , and 42 is an oxygen ion. In addition, since the piezoelectric effect is generated reversibly as described above, when voltage is applied to the piezoelectric material, an expansion / contraction motion is generated and vibration is generated. The electroacoustic transducer 100 according to the present embodiment uses this piezoelectric effect to generate vibrations in the piezoelectric film 10 to generate sound waves.

  In the present embodiment, the piezoelectric film diaphragm 1 is fixed to the frame 2. The frame 2 has a polyhedral shape having a plurality of faces, for example, a regular dodecahedron shape in which 12 regular pentagons are arranged. The piezoelectric film diaphragm 1 is disposed on each surface of the regular dodecahedron. As shown in FIG. 5A, an opening 20 is formed on each surface of the frame 2, and a recess 21 for attaching the piezoelectric film diaphragm 1 is formed around the opening 20 of the frame 2. Is formed. The piezoelectric film diaphragm 1 is inserted into the opening 20 of the frame 2 as shown in FIG. 5B, and the edge of the piezoelectric film diaphragm 1 is bonded to the recess 21 of the frame 2. Thereby, the edge of the piezoelectric film diaphragm 1 is fixed to the frame 2 so as not to cause displacement.

  When the diaphragm is constituted by conventional piezoelectric ceramics, since the piezoelectric ceramics is a brittle material, damage is likely to occur during the pasting operation and the assembly is difficult. Manufacturing costs also increase because the piezoelectric ceramics are easily damaged. Furthermore, since piezoelectric ceramics are easily damaged, there is a problem that the place of use is limited. On the other hand, since the piezoelectric film 10 is made of a resin material, it can absorb an impact at the time of dropping, and the drop strength of the electroacoustic transducer 100 can be improved. Moreover, since the piezoelectric film 10 is a resin material, it has good workability and can be processed into an arbitrary shape.

  The material of the frame 2 used in the electroacoustic transducer 100 of the present embodiment is not particularly limited, such as a metal or a resin material, but it is preferable to use aluminum or stainless steel. By using a stainless steel or aluminum metal material having high rigidity for the frame 2, the strength of the frame 2 is increased, so that the portability of the electroacoustic transducer 100 can be improved. Further, the vibration of the frame 2 generated when the piezoelectric film is driven can be attenuated by attaching the piezoelectric film diaphragm 1 to the highly rigid frame 2. That is, loss of vibration energy can be suppressed, and conversion efficiency from electric energy to vibration energy can be improved.

  The thickness of the frame 2 is preferably 30 μm to 1000 μm. When the thickness of the frame 2 is less than 30 μm, the rigidity of the frame 2 becomes weak and the bonding area of the piezoelectric film diaphragm 1 becomes small. Further, if the thickness of the frame 2 exceeds 1000 μm, the size of the electroacoustic transducer increases, which is not suitable for mounting on an electronic device such as a mobile phone.

  In the electroacoustic transducer 100 of the present embodiment, in order to apply an electrical signal to the piezoelectric film 10, a pair of wirings 3a and 3b and a pair of terminals 4a and 4b are used. One end of the wiring 3a is connected to the upper electrode layer 11 of each piezoelectric film diaphragm 1 via solder, and the other end of the wiring 3a is connected to the terminal 4a. One end of the wiring 3b is connected to the lower electrode layer 12 of each piezoelectric film diaphragm 1 via solder, and the other end of the wiring 3b is connected to the terminal 4b. The material of the wirings 3a and 3b is not particularly limited as long as it is a conductive material having electrical conductivity, but it is preferable to use copper wires with polyurethane film as the wirings 3a and 3b. The material of the terminals 4a and 4b is not particularly limited as long as it is a conductive material having electrical conductivity, but it is preferable that the portion other than the connection portion with the outside is covered with an insulating material. As the terminals 4a and 4b, for example, it is desirable to use a flexible substrate.

The operation of the electroacoustic transducer 100 of the present embodiment will be described below. By inputting electric signals to the upper electrode layer 11 and the lower electrode layer 12 of each piezoelectric film diaphragm 1 via the terminals 4a and 4b, the piezoelectric film 10 of each piezoelectric film diaphragm 1 vibrates and generates sound waves. .
In the electroacoustic transducer 100 of the present embodiment, since the piezoelectric film diaphragm 1 is disposed on multiple surfaces, sound waves are generated from a plurality of radiation surfaces, and the sound pressure level increases. Usually, the sound pressure level is determined by the pressure change to the air medium, and therefore depends on the radiation area and the vibration amplitude. In other words, in the present embodiment, an apparent radiation area can be increased by arranging a plurality of radiation surfaces in three dimensions, which is useful for improving the sound pressure level.

  Moreover, in the electroacoustic transducer 100 of the present embodiment, the sound pressure level can be increased, and at the same time, the sound pressure frequency characteristics can be flattened. That is, in this embodiment, since the diaphragm is composed of the piezoelectric film 10 having a large mechanical loss, the mechanical quality factor (Qm) is small compared to the conventional ceramic material, and the sound pressure peak generated near the resonance point is low. Since it attenuates, a flatter acoustic characteristic can be realized.

  Moreover, in the electroacoustic transducer 100 of this Embodiment, the frequency band to reproduce | regenerate can be expanded. In a normal acoustic element, the sound pressure level rises after the fundamental resonance frequency, and thus it is necessary to reduce the fundamental resonance frequency of the acoustic element in order to realize low-frequency sound reproduction. For example, in a cellular phone, the sound reproduction band is from 100 Hz to 20 kHz, and in order to realize good sound reproduction within this band, the basic resonance frequency of the acoustic element has to be 800 Hz or less. However, as shown in the equation (1), the basic resonance frequency f0 is determined by the load weight m, the diaphragm rigidity c, and the diaphragm length l. It was difficult to adjust to the basic resonance frequency f0.

In this embodiment, since the piezoelectric film 10 is used as the diaphragm, the diaphragm has low rigidity, and the fundamental resonance frequency f0 can be reduced, which is optimal for low-frequency reproduction.
In addition, since the flexible piezoelectric film 10 is used, the impact at the time of dropping is absorbed by the resin material, which is suitable for mounting on a small electronic device such as a mobile phone.

  Moreover, in the electroacoustic transducer 100 of this Embodiment, since a sound wave is radiated | emitted in many directions, wide directivity can be implement | achieved. In the conventional acoustic component, since the radiation direction is one direction, the directivity greatly varies depending on the frequency to be reproduced. For example, since the sound wave circulates in the low frequency band, a wide directivity can be obtained, but the directivity becomes narrow in the high frequency band where the straightness of the sound wave is strong. On the other hand, in the present embodiment, a wide directivity can be obtained at any frequency without being affected by the directivity characteristic of the sound wave in the multi-plane direction.

  In summary, according to the present embodiment, it is possible to realize a small electroacoustic transducer 100 with wide directivity and large volume. In the present embodiment, it is not necessary to use a piezoelectric film diaphragm having a curved surface as in the electroacoustic transducer disclosed in Patent Document 4, and the housing of the polyhedral electronic device is used as the frame 2, and the frame 2 Since the flat piezoelectric film diaphragm 1 may be disposed on each surface, it is suitable for mounting on a small electronic device such as a mobile phone. Further, the electroacoustic transducer 100 according to the present embodiment is excellent in manufacturability and has high impact stability when dropped, and thus is suitable for mounting on a small electronic device such as a mobile phone.

  Next, the results of evaluating the acoustic characteristics and directivity characteristics of the electroacoustic transducer 100 of the present embodiment are shown below. As a result of measuring the sound pressure level of 1 kHz with a microphone 10 cm away from the electroacoustic transducer 100, the 1 kHz sound pressure level of the electroacoustic transducer 100 was 93 dB. The directivity was measured by arranging the electroacoustic transducer 100 and the microphones 101-1, 101-2, 101-3, and 101-4 as shown in FIG. The distance between the electroacoustic transducer 100 and the microphones 101-1, 101-2, 101-3, and 101-4 is 10 cm. The measurement frequency was set to three types of 1 kHz, 3 kHz, and 5 kHz, three types of frequencies were measured in each direction, and a total of 12 points of data were acquired. Table 1 shows the measurement results of the directivity characteristics.

  The criterion for wide directivity is that the difference between the maximum value and the minimum value of each measurement result is within 3 dB. According to the measurement results in Table 1, since the difference between the maximum value 93 dB and the minimum value 91 dB of each measurement result was within 3 dB, it was determined that wide directivity was obtained.

[Second Embodiment]
In the second embodiment, the electroacoustic transducer was manufactured by setting the thickness of the piezoelectric film 10 of the first embodiment to 30 μm. As a result of measuring the characteristics of this electroacoustic transducer, the sound pressure level of 1 kHz was 93 dB, and good wide directivity similar to that of the first embodiment was obtained.

[Third Embodiment]
In the third embodiment, an electroacoustic transducer was manufactured by setting the thickness of the piezoelectric film 10 of the first embodiment to 100 μm. As a result of measuring the characteristics of this electroacoustic transducer, the sound pressure level at 1 kHz was 90 dB, and good wide directivity similar to that of the first embodiment was obtained.

[Fourth Embodiment]
In the fourth embodiment, the electroacoustic transducer was manufactured by changing the shape of the frame 2 of the first embodiment to a cubic shape. As a result of measuring the characteristics of this electroacoustic transducer, the sound pressure level of 1 kHz was 93 dB, and good wide directivity similar to that of the first embodiment was obtained.

[Fifth Embodiment]
In the fifth embodiment, the shape of the frame 2 of the first embodiment is changed to a triangular pyramid to produce an electroacoustic transducer. As a result of measuring the characteristics of this electroacoustic transducer, the sound pressure level of 1 kHz was 93 dB, and good wide directivity similar to that of the first embodiment was obtained.

[Sixth Embodiment]
In the sixth embodiment, an electroacoustic transducer was manufactured by setting the thicknesses of the upper electrode layer 11 and the lower electrode layer 12 of the first embodiment to 100 μm. As a result of measuring the characteristics of this electroacoustic transducer, the sound pressure level of 1 kHz was 93 dB, and good wide directivity similar to that of the first embodiment was obtained.

[Seventh Embodiment]
In the seventh embodiment, the electroacoustic transducer was manufactured by setting the thicknesses of the upper electrode layer 11 and the lower electrode layer 12 of the first embodiment to 50 μm. As a result of measuring the characteristics of this electroacoustic transducer, the sound pressure level of 1 kHz was 93 dB, and good wide directivity similar to that of the first embodiment was obtained.

[Eighth Embodiment]
In the eighth embodiment, stainless steel is used as the material of the frame 2 of the first embodiment to produce an electroacoustic transducer. As a result of measuring the characteristics of this electroacoustic transducer, the sound pressure level of 1 kHz was 93 dB, and good wide directivity similar to that of the first embodiment was obtained.

[Ninth Embodiment]
In the ninth embodiment, aluminum is adopted as the material of the frame 2 of the first embodiment, and an electroacoustic transducer is manufactured. As a result of measuring the characteristics of this electroacoustic transducer, the sound pressure level of 1 kHz was 93 dB, and good wide directivity similar to that of the first embodiment was obtained.

[Tenth embodiment]
In the tenth embodiment, the piezoelectric film diaphragm 1 of the first embodiment is increased to a double number to produce an electroacoustic transducer. As a result of measuring the characteristics of this electroacoustic transducer, the sound pressure level of 1 kHz was 110 dB, and good wide directivity similar to that of the first embodiment was obtained.

  In the first to tenth embodiments, a common electric signal is applied to all the piezoelectric film diaphragms 1 of the electroacoustic transducer. However, the present invention is not limited to this. Another electric signal may be applied to the upper electrode layer 11 and the lower electrode layer 12 of the film diaphragm 1. Thereby, multiple types of sound waves can be radiated from one electroacoustic transducer. In order to radiate a plurality of types of sound waves from one electroacoustic transducer, the wirings 3 a and 3 b and the terminals 4 a and 4 b may be provided for each group of the piezoelectric film diaphragm 1. If different electrical signals for each group are input to the terminals 4a and 4b of the group, the piezoelectric film diaphragm 1 of each group emits a different sound wave for each group. In terms of securing the sound pressure level, it is preferable to provide a plurality of piezoelectric film diaphragms 1 for each group.

  In the first to tenth embodiments, a mobile phone is described as an example of an electronic device on which an electroacoustic transducer is mounted. However, the present invention is not limited to this, and other electronic devices may be used. Needless to say, an electroacoustic transducer can be mounted.

  A part or all of the above embodiments can be described as in the following supplementary notes, but is not limited thereto.

  (Appendix 1) Electroacoustic conversion comprising a plurality of piezoelectric film diaphragms having electrodes formed on both sides of a piezoelectric film that vibrates according to the state of an electric field, and the plurality of piezoelectric film diaphragms arranged in a polyhedral shape vessel.

  (Additional remark 2) The electroacoustic transducer of Additional remark 1 WHEREIN: The said piezoelectric film consists of piezoelectric polymer materials, The electroacoustic transducer characterized by the above-mentioned.

  (Appendix 3) The electroacoustic transducer according to appendix 1 or 2, wherein each piezoelectric film diaphragm is inserted into an opening formed in each surface of a polyhedral frame. .

  (Appendix 4) In the electroacoustic transducer according to any one of appendices 1 to 3, the piezoelectric film diaphragms are divided into a plurality of groups, and different electric signals can be input to the electrodes for each group. An electroacoustic transducer characterized by.

  (Appendix 5) An electronic apparatus comprising the electroacoustic transducer according to any one of appendices 1 to 4.

  The present invention can be applied to a small electroacoustic transducer.

  DESCRIPTION OF SYMBOLS 1 ... Piezoelectric film diaphragm, 2 ... Frame, 3a, 3b ... Wiring, 4a, 4b ... Terminal, 10 ... Piezoelectric film, 11 ... Upper electrode layer, 12 ... Lower electrode layer, 20 ... Opening, 21 ... Recess, 100 ... electroacoustic transducer.

Claims (5)

A plurality of piezoelectric film diaphragms having electrodes formed on both sides of a piezoelectric film that vibrates according to the state of the electric field,
An electroacoustic transducer in which the plurality of piezoelectric film diaphragms are arranged in a polyhedral shape. The electroacoustic transducer according to claim 1, wherein
The electroacoustic transducer, wherein the piezoelectric film is made of a piezoelectric polymer material. The electroacoustic transducer according to claim 1 or 2,
Each piezoelectric film diaphragm is fitted into an opening formed on each surface of a polyhedral frame, and the electroacoustic transducer is characterized in that The electroacoustic transducer according to any one of claims 1 to 3,
Each piezoelectric film diaphragm is divided into a plurality of groups, and an electric signal different for each group can be input to the electrode.   An electronic apparatus comprising the electroacoustic transducer according to claim 1.

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