JP2012217036A - Oscillation device and electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oscillation device that provides a flat sound pressure level in a wide frequency range while maintaining reliability.SOLUTION: An oscillation device 100 includes: a piezoelectric vibrator 10; a vibrating member 20 that restricts the piezoelectric vibrator 10 on a surface thereof; a support member 30 that holds an edge of the vibrating member 20; and an emitting film 40 that covers the surface of the vibrating member 20 and includes a porous material such as carbon fiber, graphite powder, or alumina powder.

Description

  The present invention relates to an oscillation device having a piezoelectric vibrator and an electronic apparatus.

As an electroacoustic transducer mounted on an electronic device, there is a piezoelectric electroacoustic transducer. Piezoelectric electroacoustic transducers generate vibration amplitude by utilizing the expansion and contraction generated by applying an electric field to a piezoelectric vibrator. Piezoelectric electroacoustic transducers do not require a large number of members in order to generate vibration amplitude, and are advantageous for thinning.
As a technique related to the piezoelectric electroacoustic transducer, for example, there is one described in Patent Document 1.

  As another technique related to the piezoelectric element, for example, as described in Patent Documents 2 to 5, there is a technique related to an ultrasonic transducer having a piezoelectric element. The technique described in Patent Document 2 is to form a suppression layer for controlling penetration of the joining means on an acoustic matching body made of a ceramic porous body. The technique described in Patent Document 3 is to provide a matching member case that holds an acoustic matching member made of dry gel inside. The technique described in Patent Document 4 is to form a matching layer made of a porous material on the ultrasonic radiation surface side of a piezoelectric body. The technique described in Patent Document 5 is to sequentially form a metal member and an acoustic matching member on a piezoelectric member.

Japanese Utility Model Publication No. 62-72000 JP 2009-88827 A JP 2009-5383 A JP-A-6-327098 JP 2007-295540 A

An oscillation device including a piezoelectric vibrator has a high mechanical quality factor due to the high rigidity of the piezoelectric vibrator. For this reason, an oscillating device including a piezoelectric vibrator has acoustic characteristics such that the sound pressure level is high near the resonance frequency and the sound pressure level is low in other frequency bands. Therefore, an oscillation device including a piezoelectric vibrator is required to achieve a flat sound pressure level in a wide frequency band.
On the other hand, it is also required to improve the reliability of the oscillation device.

  An object of the present invention is to provide an oscillation device capable of realizing a flat sound pressure level in a wide frequency band while maintaining reliability.

According to the present invention, a piezoelectric vibrator;
A vibration member that restrains the piezoelectric vibrator on one surface;
A support member for supporting an edge of the vibration member;
A radiation film covering the one surface of the vibration member and made of a porous material;
With
An oscillation device is provided in which the porous material is carbon fiber, graphite powder, or alumina powder.

  According to the present invention, an electronic apparatus equipped with the above-described oscillation device is provided.

  According to the present invention, it is possible to provide an oscillation device capable of realizing a flat sound pressure level in a wide frequency band while maintaining reliability.

It is sectional drawing which shows the oscillation apparatus which concerns on this embodiment. It is sectional drawing which shows the piezoelectric vibrator shown in FIG. It is sectional drawing which shows the oscillation apparatus which concerns on a comparative example. It is a graph which shows the frequency dependence of the vibration amplitude speed of the oscillation apparatus which concerns on this embodiment and a comparative example.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In all the drawings, the same reference numerals are given to the same components, and the description will be omitted as appropriate.

  FIG. 1 is a cross-sectional view showing an oscillation device 100 according to this embodiment. The oscillation device 100 according to this embodiment includes a piezoelectric vibrator 10, a vibration member 20, a support member 30, and a radiation film 40. The oscillation device 100 is mounted on an electronic device such as a mobile phone.

  The vibration member 20 restrains the piezoelectric vibrator 10 on one surface. The support member 30 holds the edge of the vibration member 20. The radiation film 40 covers one surface of the vibration member 20 and is made of a porous material. The porous material is carbon fiber, graphite powder, or alumina powder. Hereinafter, the configuration of the oscillation device 100 will be described in detail.

  The vibration member 20 has, for example, a flat plate shape. The vibration member 20 is made of a material having a high elastic modulus with respect to a ceramic that is a brittle material, such as metal or resin, and is made of a general-purpose material such as phosphor bronze or stainless steel. The thickness of the vibration member 20 is preferably 5 to 500 μm. The longitudinal elastic modulus of the vibration member 20 is preferably 1 to 500 GPa. When the longitudinal elastic modulus of the vibration member 20 is excessively low or high, the vibration characteristics and reliability of the oscillation device may be impaired.

  As shown in FIG. 1, the oscillation device 100 includes an elastic member 22. The elastic member 22 is provided on the edge of the vibration member 20. Further, the elastic member 22 is provided, for example, on the entire circumference of the vibration member 20. The elastic member 22 is made of, for example, a resin material such as urethane, PET, or polyethylene. The support member 30 supports the vibration member 20 via the elastic member 22.

As shown in FIG. 1, the support member 30 is fixed on a substrate 32, for example. The support member 30 has, for example, a cylindrical shape with both ends open. One end located on one surface side of the vibration member 20 is covered with the radiation film 40, and the other end opposite to the one end is covered with the substrate 32. The radiation film 40 is fixed to, for example, the end of the support member 30.
The both open ends of the support member 30 may be covered with the radiation film 40.

  Since the radiation film 40 is made of a porous material, it has a large number of holes serving as radiation holes for radiating the sound waves 50 output from one surface. For this reason, the sound wave 50 output from one surface of the vibration member 20 is radiated to the outside through the radiation hole. When the sound wave 50 passes through the radiation hole of the radiation film 40 that is a porous material, internal friction occurs between the sound wave 50 and the radiation hole. Thereby, the sound wave 50 output from one surface of the vibration member 20 is attenuated. Therefore, the sound pressure level in the vicinity of the resonance frequency can be reduced.

As shown in FIG. 1, the oscillation device 100 has a bimorph structure including the piezoelectric vibrator 10 on one surface of the vibration member 20 and the other surface opposite to the one surface, for example.
In this case, the polarization directions of the piezoelectric vibrator 10 provided on one surface of the vibration member 20 and the piezoelectric vibrator 10 provided on the other surface of the vibration member 20 are opposite to each other. In addition, the piezoelectric vibrator 10 provided on one surface of the vibration member 20 and the piezoelectric vibrator 10 provided on the other surface of the vibration member 20 are provided so as to overlap in a plan view.
Since the oscillation device 100 has a bimorph structure, it is possible to increase the vibration amplitude.

  FIG. 2 is a cross-sectional view showing the piezoelectric vibrator 10 shown in FIG. As shown in FIG. 2, the piezoelectric vibrator 10 includes a piezoelectric body 70, an upper electrode 72, and a lower electrode 74. The piezoelectric body 70 is sandwiched between the upper electrode 72 and the lower electrode 74. The piezoelectric body 70 is polarized in the thickness direction (vertical direction in FIG. 2). The piezoelectric vibrator 10 has, for example, a circle or an ellipse in a plane direction parallel to one surface of the vibration member 20.

  The piezoelectric body 70 is made of a material having a piezoelectric effect, for example, lead zirconate titanate (PZT) or barium titanate (BaTiO3) as a material having high electromechanical conversion efficiency. The thickness of the piezoelectric body 70 is preferably 10 μm to 1 mm. When the thickness is less than 10 μm, the piezoelectric body 70 is made of a brittle material, and thus is easily damaged during handling. On the other hand, when the thickness exceeds 1 mm, the electric field strength of the piezoelectric body 70 is reduced. For this reason, the energy conversion efficiency is reduced.

  The upper electrode 72 and the lower electrode 74 are made of a material having electrical conductivity, for example, silver or a silver / palladium alloy. Silver is a low-resistance general-purpose material and is advantageous from the viewpoint of manufacturing cost and manufacturing process. Further, the silver / palladium alloy is a low resistance material excellent in oxidation resistance and excellent in reliability. The thickness of the upper electrode 72 and the lower electrode 74 is preferably 1 to 50 μm. When the thickness is less than 1 μm, it becomes difficult to form the film uniformly. On the other hand, when the thickness exceeds 50 μm, the upper electrode 72 or the lower electrode 74 serves as a restraint surface with respect to the piezoelectric body 70 and causes a decrease in energy conversion efficiency.

  The oscillation device 100 includes a control unit 90 and a signal generation unit 92. The signal generator 92 is connected to the piezoelectric vibrator 10 and generates an electric signal input to the piezoelectric vibrator 10. The control unit 90 is connected to the signal generation unit 92 and controls signal generation by the signal generation unit 92. The control unit 90 controls the generation of the signal of the signal generation unit 92 based on information input from the outside, whereby the output of the oscillation device 100 can be controlled.

When the oscillation device 100 is used as a parametric speaker, the control unit 90 inputs a modulation signal as a parametric speaker via the signal generation unit 92. In this case, the piezoelectric vibrator 10 uses a sound wave of 20 kHz or more, for example, 100 kHz, as a signal transport wave.
When the oscillation device 100 is used as a normal speaker, the control unit 90 may input the audio signal as it is to the piezoelectric vibrator 10 via the signal generation unit 92.
When the oscillation device 100 is used as a sound wave sensor, the signal input to the control unit 90 is a command signal for oscillating sound waves. When the oscillation device 100 is used as a sound wave sensor, the signal generation unit 92 causes the piezoelectric vibrator 10 to generate a sound wave having a resonance frequency of the piezoelectric vibrator 10.

Next, the effect of this embodiment will be described. According to the present embodiment, the radiation film 40 that covers one surface of the vibration member 20 and is made of a porous material is provided. The porous material is carbon fiber, graphite powder, or alumina powder.
With the above configuration, the sound wave 50 output from the vibration member 20 is radiated to the outside through the numerous radiation holes of the porous material. When the sound wave 50 passes through the radiation hole of the porous material, internal friction occurs between the sound wave 50 and the radiation hole. For this reason, the sound wave 50 output from one surface of the vibration member 20 is attenuated. As a result, the sound pressure level in the vicinity of the resonance frequency can be reduced. Therefore, an oscillation device having a flat sound pressure level in a wide frequency band can be realized.
The porous material is carbon fiber, graphite powder, or alumina powder. Thus, by forming the radiation film 40 with a material having high thermal conductivity, it becomes easy to diffuse the heat generated by the internal friction generated between the sound wave and the radiation hole to the outside. Therefore, a highly reliable oscillation device can also be realized.

FIG. 3 is a cross-sectional view showing an oscillation device 102 according to a comparative example. The oscillation device 102 according to the comparative example has the same configuration as that of the oscillation device 100 according to the present embodiment, except that the radiation film 40 is not provided.
FIG. 4 is a graph showing the frequency dependence of the vibration amplitude speed of the oscillation devices according to the present embodiment and the comparative example. FIG. 4 shows each of cases where the radiation film 40 is made of carbon fiber, graphite powder, and alumina powder in the oscillation device 100 according to the present embodiment. FIG. 4 shows the measurement result of the vibration amplitude velocity (m / s) of the demodulated audible sound wave when the oscillation device according to this embodiment and the comparative example is used as a parametric speaker.

As shown in FIG. 4, in the oscillation device 102 according to the comparative example, a peak with a high vibration amplitude speed is seen in the vicinity of 40 Hz. On the other hand, in the oscillation device 100 according to the present embodiment, the peak in the vicinity of 40 Hz is smaller than that in the comparative example. In particular, when alumina powder is used as the radiation film 40, the peak of the vibration amplitude speed is the smallest.
Thus, according to this embodiment, it can be seen that an oscillation device having a flat sound pressure level in a wide frequency band is realized.

  As mentioned above, although embodiment of this invention was described with reference to drawings, these are the illustrations of this invention, Various structures other than the above are also employable.

DESCRIPTION OF SYMBOLS 10 Piezoelectric vibrator 20 Vibration member 22 Elastic member 30 Support member 32 Substrate 40 Radiation film 50 Sound wave 70 Piezoelectric body 72 Upper electrode 74 Lower electrode 90 Control unit 92 Signal generation unit 100 Oscillation device 102 Oscillation device

Claims (3)

A piezoelectric vibrator;
A vibration member that restrains the piezoelectric vibrator on one surface;
A support member for holding an edge of the vibration member;
A radiation film covering the one surface of the vibration member and made of a porous material;
With
The oscillation device, wherein the porous material is carbon fiber, graphite powder, or alumina powder. The oscillation device according to claim 1,
An elastic member provided at an edge of the vibration member;
The oscillation device in which the support member supports the vibration member via the elastic member.   An electronic device on which the oscillation device according to any one of claims 1 to 3 is mounted.

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