JP2012100040A - Oscillator and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a small size oscillator which achieves high sound quality.SOLUTION: An elastic member 20 restricting a piezoelectric element 10 is joined to a support medium 45 through a low rigid vibration member 30. A fundamental resonant frequency of an electro-acoustic transducer 50 is adjusted so as not to interfere with a resonant frequency of a body housing mounting the electro-acoustic transducer 50. Hence, fewer peaks or dips of acoustic characteristics occur and a wideband sound reproduction at large volume is achieved.

Description

  The present invention relates to an oscillating device including a piezoelectric vibrator, and more particularly to an oscillating device in which a piezoelectric vibrator is mounted on an elastic diaphragm, and an electronic apparatus having the oscillating device.

  In recent years, demand for portable electronic devices such as mobile phones and notebook computers has been increasing. In such an electronic device, development of a thin portable terminal whose commercial value is an acoustic function such as a videophone, a video playback, and a hands-free phone is being promoted. Under such development, there is an increasing demand for high-quality sound, small size, and thinness for electroacoustic transducers (speaker devices) that are oscillation devices.

  In order to reduce the thickness of electrodynamic electroacoustic transducers, it is necessary to reduce the thickness of the permanent magnets and voice coils, which are its components. is not. In the operation principle of the magnetic circuit, the driving force depends on the magnetic flux density and the current. When the permanent magnet is thinned, the magnetic flux is remarkably lowered, resulting in deterioration of acoustic characteristics. In addition, in a current-driven electrodynamic converter, when the voice coil is thinned, there is a possibility that the coil wire may burn out due to consumption of a large current.

  In addition, there is a method to increase the magnetic flux by changing the material of the magnet, but no magnetic material that can replace the current neodymium magnet has yet been developed. Even if a new material is developed, it is practical and reliable. There is a problem as a material for electronic device parts such as cost. While it is difficult to reduce the thickness of electrodynamic electroacoustic transducers, there is a piezoelectric electroacoustic transducer that converts electrical energy into mechanical energy by the piezoelectric effect as means for realizing a small and thin electroacoustic transducer. .

  Piezoelectric electroacoustic transducers generate vibration amplitude by electrostrictive action due to the input of an electrical signal, utilizing the piezoelectric effect of a ceramic material. The ceramic itself, whose upper and lower layers are constrained by the electrode material, vibrates and functions as a driving source. Therefore, a magnet and a voice coil are unnecessary, which is advantageous for thinning.

  For example, Patent Documents 1 and 2 describe using a piezoelectric vibrator as an electroacoustic transducer. As another example of an oscillation device using a piezoelectric vibrator, in addition to a speaker device, a sound wave sensor that detects a distance to an object using a sound wave oscillated from the piezoelectric vibrator (see Patent Document 3) Various electronic devices such as) are known.

No. 2007-026736 Table 2007-083497 JP-A-3-270282

  However, since the electroacoustic transducer of the piezoelectric vibrator uses a ceramic material having a low internal loss as a vibration source, the mechanical quality factor Q tends to be higher than that of an electrodynamic electroacoustic transducer that generates amplitude through an organic film. It is in. For example, the electrodynamic Q is about 3 to 5, while the piezoelectric Q is about 50. Since the mechanical quality factor Q indicates the sharpness at the time of resonance, the summary means that in the piezoelectric electroacoustic transducer, the sound pressure is high near the fundamental resonance frequency and the sound pressure is attenuated in other bands. . For example, in a piezoelectric electroacoustic transducer having a fundamental resonance frequency of 1 kHz, the sound pressure level is attenuated at a high-order resonance frequency where the next resonance mode is generated, for example, in a band of 3 to 5 kHz.

  The present invention has been made in view of the above-described problems, and provides an oscillation device that can output a large volume of sound in a wide band with few peaks and dips in acoustic characteristics.

The oscillation device according to the present invention includes a piezoelectric element that expands and contracts depending on the state of an electric field, an elastic member having a piezoelectric element bonded to at least a surface, and an elastic member having at least a lower rigidity than the elastic member and bonded to the surface. A basic resonance of an electroacoustic transducer having a vibration member and a support member that is rigid and more rigid than the vibration member and is bonded to the main body housing and includes a piezoelectric element, an elastic member, the vibration member, and the support member The frequency F (1), the third resonance frequency F (3), and the basic resonance frequency F (a) of the main body housing are:
0.7 × ((F (1) + F (3)) / 2) <2 × F (a) <1.3 × ((F (1) + F (3)) / 2)
Or
0.7 × ((F (1) + F (3)) / 2) <3 × F (a) <1.3 × ((F (1) + F (3)) / 2)
Satisfied.

  A first electronic device according to the present invention includes the oscillation device according to the present invention, a main body housing in which the oscillation device is mounted, and an oscillation driving unit that outputs an audible sound wave to the oscillation device mounted in the main body housing. .

  A second electronic device according to the present invention includes an oscillation device according to the present invention, a main body housing in which the oscillation device is mounted, an oscillation drive unit that drives the oscillation device mounted in the main body housing to output ultrasonic waves, and an oscillation Ultrasonic wave detection means for detecting ultrasonic waves oscillated from the apparatus and reflected by the measurement object, and distance calculation means for calculating the distance from the detected ultrasonic wave to the measurement object.

  In the oscillation device of the present invention, the elastic member that restrains the piezoelectric element is joined to the support via the low-rigidity vibration member. Since the sound wave of the electroacoustic transducer and the sound wave caused by the vibration of the main body housing on which the electroacoustic transducer is mounted are adjusted to interfere with each other, it is possible to output a loud sound with a wide band.

It is a typical longitudinal section front view showing the structure of the electroacoustic transducer which is the oscillation device of the first embodiment of the present invention. It is a typical longitudinal section front view showing the structure of a piezoelectric element. It is a typical vertical front view which shows operation | movement of an electroacoustic transducer. It is a typical disassembled perspective view which shows the structure of the existing electroacoustic transducer. It is a characteristic view which shows the aspect of the vibration of the existing piezoelectric type electroacoustic transducer. It is a characteristic view which shows the aspect of the vibration of an electroacoustic transducer. It is a typical vertical front view which shows the structure of an electroacoustic transducer. It is a typical vertical front view which shows the internal structure of an electronic device. It is a characteristic view which shows the sound pressure level of a fundamental resonant frequency (primary resonant frequency) and a tertiary resonant frequency. FIG. 6 is a vibration state diagram showing a state in which higher-order vibration modes generated after the fundamental resonance frequency overlap each other. It is a vibration figure which shows a secondary vibration mode. It is a vibration figure which shows the state in which secondary vibration mode overlaps. It is a characteristic view which shows a vibration transfer function. It is a characteristic view which shows the acoustic characteristic of a main body housing. It is a typical vertical front view which shows the structure of the electroacoustic transducer of the 2nd form of implementation of this invention. It is a schematic diagram which shows operation | movement of an electroacoustic transducer. It is a disassembled perspective view which shows the structure of the piezoelectric element of the electroacoustic transducer of the 3rd embodiment of this invention. It is a typical front view which shows the external appearance of the mobile telephone which is an electronic device of embodiment of this invention. 1 is a schematic front view showing an external appearance of a personal computer that is an electronic apparatus according to an embodiment of the present invention.

[First embodiment]
A first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a longitudinal sectional view showing an electroacoustic transducer 50 according to the present embodiment. As shown in FIG. 1, a piezoelectric electroacoustic transducer 50 that is an oscillation device of the present embodiment includes a piezoelectric element 10 that expands and contracts according to the state of an electric field, and at least the surface of the piezoelectric element 10 is bonded. The elastic member 20, the vibration member 30 having a rigidity lower than that of the elastic member 20 and having the elastic member 20 bonded to at least the surface, and the support having a rigidity higher than that of the vibration member 30 and supporting the vibration member 30 and being bonded to the main body housing. And a body 45.

The basic resonance frequency F (1) and the third resonance frequency F (3) of the electroacoustic transducer 50 and the basic resonance frequency F (a) of the main body housing are as follows:
[Equation 1]
0.7 × ((F (1) + F (3)) / 2) <2 × F (a) <1.3 × ((F (1) + F (3)) / 2)
Or
0.7 × ((F (1) + F (3)) / 2) <3 × F (a) <1.3 × ((F (1) + F (3)) / 2)
Satisfied.

  More specifically, the electroacoustic transducer 50 of the present embodiment includes the piezoelectric element 10, the elastic member 20, the vibration member 30, the support body 45, and the lead wire 1-e. In the piezoelectric element 10, the principal surface on one side is constrained by the elastic member 20, and the elastic member 20 is joined to the support body 45 via the vibration member 30.

  In addition, the lead wire 1-e plays a role of inputting an electric signal to the piezoelectric element 10. The piezoelectric element 10 converts electrical energy into mechanical energy and serves as a vibration source for the electroacoustic transducer 50. As shown in FIG. 2, the upper and lower main surfaces of the piezoelectric ceramic 2-b are constrained by the upper / lower electrode layers 2-a and 2-c. The piezoelectric ceramic 2-b has a piezoelectric effect that is a phenomenon in which a voltage is generated in accordance with strain generated by applying pressure.

  As shown in FIG. 2, the piezoelectric element 10 configured in this manner is applied with an alternating voltage applied to the upper electrode layer 2-a and the lower electrode layer 2-c to apply an alternating electric field in FIG. As shown in the figure, a radial expansion / contraction motion (diameter expansion motion) is performed such that both main surfaces 11 and 12 expand or contract simultaneously. In other words, the piezoelectric ceramic 2-b performs a motion that repeats a first deformation mode in which the main surface is enlarged and a second deformation mode in which the main surface is reduced.

  The elastic member 20 has a function of converting the expansion / contraction motion of the piezoelectric element 10 into the vertical vibration shown in FIG. The elastic member 20 is composed of an elastic body (stretchable material), and as a material thereof, a metal material (for example, aluminum alloy, linseed copper, titanium, or titanium alloy) or a resin material (for example, epoxy, acrylic, polyimide, Alternatively, a material having a lower rigidity than the ceramic material constituting the piezoelectric element 10 such as polycarbonate) can be widely used.

  The vibration member 30 is a film member for increasing the vibration amplitude of the electroacoustic transducer 50, and has a lower rigidity than the elastic member 20. As a combination of materials of the elastic member 20 and the vibration member 30, for example, the elastic member 20 may be a metal material and the vibration member 30 may be a resin material (for example, urethane, PET, polyethylene, etc.). Alternatively, the elastic member 20 and the vibration member 30 may be made of the same material, and the vibration member 30 may have a relatively low rigidity by making the film thickness of the vibration member 30 relatively thin. In addition to the above, the vibration member 30 may be paper, polyethylene terephthalate, or the like. The thickness of the vibration member 30 may be, for example, 5 μm or more and 500 μm or less in the case of a resin material. In particular, when the vibration member 30 is a flat sheet material, the vibration member 30 may preferably be 30 μm or more and 180 μm or less.

  By the way, when the electroacoustic transducer 50 is used as an acoustic element, a configuration is often adopted in which an organic film or the like is attached to the vibrating portion of the electroacoustic transducer 50 so that sound is emitted. On the other hand, in this embodiment, the vibration member 30 provided to increase the amplitude functions as a vibration film as it is. That is, the vibration member 30 has not only a function as a vibration film in an existing acoustic element but also a function of increasing the vibration amplitude of the electroacoustic transducer 50.

  The support 45 is, for example, a member that constitutes the main housing of the electroacoustic transducer 50, and the material thereof is not particularly limited, and may be a resin material or a metal material. For example, an epoxy adhesive can be used for joining the piezoelectric element 10 and the elastic member 20 and joining the elastic member 20 and the vibration member 30. The thickness of the adhesive layer is not particularly limited, but if it is too thick, vibration energy absorbed by the adhesive layer may increase and a sufficient vibration amplitude may not be obtained. Preferably there is.

  Hereinafter, the generation mechanism of vibration of the electroacoustic transducer 50 will be described with reference to FIG. First, when a predetermined voltage (electric field) is applied to the piezoelectric element 10 from a neutral state where no voltage is applied to the piezoelectric element 10, the area of the piezoelectric element 10 is as shown by an arrow p in FIG. Deforms in the direction of spreading.

  Here, since the lower surface (main surface 10b) of the piezoelectric element 10 is constrained by the elastic member 20, this constraining effect causes a difference in the amount of deformation between the upper surface and the lower surface of the piezoelectric element 10, and as a result. This is a convex deformation mode as shown. In this deformation mode, the piezoelectric element 10 and the elastic member 20 and further the vibration member 30 supporting the elastic member 20 are in a curved state so as to be convex upward in the figure.

  Subsequently, when an electric field opposite to the above is applied to the piezoelectric element 10, this time the piezoelectric element 10 is deformed in a direction in which the area decreases as shown in FIG. Due to the restraining effect of the elastic member 20, a difference in deformation occurs between the upper surface and the lower surface of the piezoelectric element 10, and as a result, a concave deformation mode as shown in FIG. In this deformation mode, contrary to the above, the piezoelectric element 10, the elastic member 20, and the vibration member 30 are in a curved state that protrudes downward in the figure.

  In the electroacoustic transducer 50 according to the present embodiment, the piezoelectric element 10, the restraining member 20, and the vibration member 30 vibrate in the vertical direction by alternately repeating the convex deformation mode and the concave deformation mode as described above. To do.

  When the electroacoustic transducer 50 of the present embodiment is compared with the existing piezoelectric electroacoustic transducer 550 (see FIG. 4), the motion of the piezoelectric elements 10 and 510 is transmitted to the elastic members 20 and 524, and the vertical direction Both are common in that the vibration of is excited. However, in terms of the configuration, the electroacoustic transducer 50 according to the present embodiment is configured such that the elastic member 20 and the piezoelectric element 10 are supported via the vibration member 30, and the two are different in this respect. Due to this difference, the following effects can be obtained.

  That is, since the vibration member 30 is composed of a member having a relatively low rigidity as compared with the elastic member 20, the vibration member 30 is more easily deformed. Therefore, according to the electroacoustic transducer 50 of the present embodiment, a larger vibration amplitude can be obtained compared to the existing configuration in which the outer peripheral portion of the elastic member 524 is directly supported by the support body 527. In the electroacoustic transducer 50 according to the present embodiment, the vibration member 30 is provided so as to extend in the horizontal direction (that is, parallel to the main surface of the piezoelectric element 10). Therefore, the problem that the electroacoustic transducer 50 as a whole is enlarged due to the addition of the vibration member 30 is less likely to occur.

  In the present embodiment, the circular piezoelectric element 10 is used. Since the energy efficiency when the circular piezoelectric element 10 expands and moves is higher than that of the rectangular element, when the same voltage is applied, a greater driving force can be obtained with this configuration.

  Then, when such a large driving force propagates to the vibrating member 30, the amount of vibration of the piezoelectric electroacoustic transducer 50 increases. In the case of a circular element, since the distance from the center to the peripheral portion is uniform, the stress generated when propagating vibration to the beam is evenly distributed, energy efficiency is increased, and the amplitude is increased. is there. In addition, since the piezoelectric element 10, the elastic member 20, and the vibration member 30 are arranged concentrically, vibration undulation and the like are unlikely to occur.

  Next, the relationship between the vibration mode of the electroacoustic transducer 50 and the frequency characteristics will be described. The use of the piezoelectric electroacoustic transducer 50 as an acoustic element is also disclosed in Patent Documents 1 to 3 described above. However, the acoustic elements in these documents are intended for buzzers and vibrators. If it is used only as a vibrator, it is only necessary to improve the sound pressure. However, when used as a speaker, it is necessary to consider the vibration mode of the piezoelectric electroacoustic transducer 50 in consideration of its frequency characteristics. is there.

  FIG. 5A shows a vibration mode of the existing piezoelectric electroacoustic transducer 550 as shown in FIG. 4, and FIG. 5B shows an electromagnetic electroacoustic transducer. The mode of vibration (not shown) is shown.

  As shown in FIG. 5B, the existing piezoelectric electroacoustic transducer 550 has a flexural vibration mode in which the central amplitude is maximized. On the other hand, in the electromagnetic electroacoustic transducer 550, as an example, a piston-type vibration in which the central area A20 reciprocates in the vertical direction in the figure while maintaining the central area indicated by reference numeral A20 substantially flat. It is an aspect. In order to improve the frequency characteristics as an acoustic element, it is known that it is desirable to make the vibration mode as close as possible to the piston type.

  Next, characteristics of the bending type motion and the piston type motion will be described. The bending mode of vibration generated by existing piezoelectric electroacoustic transducers is a mountain shape where the central part of the piezoelectric ceramic is the maximum displacement bending point, and a large amplitude can be obtained in the central part, but in the vicinity of the fixed end. The closer it is, the more the displacement is attenuated.

  On the other hand, as shown in FIG. 6, the vibration state of the piston motion is a trapezoidal shape having a maximum displacement bending point in the vicinity of the fixed end, and has a feature that the vibration in the vicinity of the fixed end rises greatly. Comparing the amount of vibration displacement in these two vibration modes, the maximum vibration amount in the acoustic radiation surface is superior to the bending motion in the bending motion, but the average vibration amount in the acoustic radiation surface is The displacement amount at the fixed end is large, and the piston type motion is superior to the bending type motion.

  Normally, the sound pressure is defined by the volume exclusion amount to the radiation surface, so that the larger the average vibration amount is higher, and it is preferable to promote the piston-type vibration state in order to improve the sound pressure level. Piston-type motion and flexion-type motion can be defined by the ratio of average displacement and maximum displacement. The closer to 1 in the equation (average vibration) / (maximum vibration), the more piston The mold appearance was promoted.

  According to the electroacoustic transducer 50 of the present embodiment, as shown in FIG. 7, the region where the elastic member 20 is attached is a region corresponding to A20, and the outer side is apparently the region A20. The connection region A30 is less rigid (that is, more easily deformed). For this reason, since this connection part area | region A30 will show a comparatively big deformation | transformation, it becomes possible to make the aspect of vibration as a whole closer to a piston type | mold.

  Further, the fact that the region A30, which is the peripheral portion of the region where the elastic member 20 is pasted, is composed of a low-rigidity member, compared to the existing configuration in which the elastic member 20 is directly connected to the support body 45. This means that the resonance frequency of the diaphragm (referring to a laminate of the elastic member 20 and the vibration member 30) is lowered. And that the resonant frequency falls leads to the improvement of the frequency characteristic of an acoustic element as follows.

  In an acoustic element, it is usually relatively difficult to produce a sound with a sufficient frequency at a frequency lower than the basic resonance frequency. Therefore, only a frequency band higher than the basic resonance frequency can be reproduced. In many cases, a configuration to be used is adopted. Specifically, when the resonance frequency of the piezoelectric electroacoustic transducer 50 is in a high frequency band (for example, 2 kHz), simply speaking, the acoustic element can only generate sound in a band of 2 kHz or higher. .

  On the other hand, the fundamental frequency band required for playing music or the like on a mobile phone or the like is preferably 1 k to 10 kHz. Therefore, the piezoelectric electroacoustic transducer 50 having a fundamental resonance frequency of 1 kHz or less is suitable for a mobile phone or the like. In particular, if the electroacoustic transducer 50 is advantageous for downsizing as in the present embodiment. Its utility value is very high.

  However, since the piezoelectric electroacoustic transducer 50 uses a ceramic having high rigidity as the piezoelectric element 10, the resonance frequency of the vibration part is high, and there is a property that it is difficult to produce a low sound. It is also conceivable to increase the element size to reduce the apparent rigidity of the piezoelectric element 10 and lower the resonance frequency. However, as described above, since the piezoelectric electroacoustic transducer 50 is often mounted on a small electronic device such as a mobile phone, the element size can be reduced from the viewpoint of preventing the device from becoming large. It is preferable to configure so that a bass sound can be easily produced without changing.

  In summary, it can be said that it is important to set the basic resonance frequency of the piezoelectric electroacoustic transducer 50 at a lower position in order to reproduce music in a wider frequency band in a mobile phone or the like. In order to lower the fundamental resonance frequency, it is effective to reduce the rigidity of the diaphragm.

  According to the electroacoustic transducer 50 of the present embodiment, as shown in FIG. 3, the member that connects the elastic member 20 and the support body 45 is the vibration member 30 that is less rigid than the elastic member 20. The resonance frequency is reduced as compared with the existing configuration. As a result, the electroacoustic transducer 50 according to the present embodiment can obtain a sufficient vibration amplitude in a wide frequency band, and can achieve good frequency characteristics.

  In addition to the above, the piezoelectric electroacoustic transducer 50 of the present embodiment has the following advantages. First, the vibration characteristics of the electroacoustic transducer 50 can be easily adjusted by appropriately changing the material characteristics and shape of the elastic member 20 and the material characteristics and shape of the vibration member 30. In particular, since the shape of the elastic member 20 and the thickness of the vibration member 30 can be adjusted without changing the size of the main body housing (the size of the support 45), the support 45 can be used as a common component. It is also advantageous for reducing the manufacturing cost.

  Subsequently, as shown in FIG. 8, problems when the electroacoustic transducer 50 is mounted on the main body housing 100 of the electric device will be described below. In portable electronic devices such as cellular phones, there is a high demand for miniaturization and thinning. For this reason, in order to promote thinning of the device, the space volume inside the main body housing 100 decreases and the rigidity of the main body housing 100 tends to decrease. Normally, as shown in FIG. 8, in an electronic device, since the electroacoustic transducer 50 is directly joined to the main body housing 100 in order to radiate a sound wave from the sound hole, a sound wave is generated by vibration of the main body housing.

  Therefore, while the design conditions for increasing the volume are restricted, such as downsizing the electroacoustic transducer 50 or reducing the mounting space, a means for increasing the volume by using sound waves from the vibration of the main body housing 100 is considered promising. It is done. However, in the piezoelectric electroacoustic transducer 50 having a higher machine Q than the electrodynamic type, the sound pressure level in the vicinity of the resonance frequency is significantly higher than in other bands, and the sound from the vibration of the main body housing 100 can be reduced. There is a problem that the sound pressure peak further expands due to interference.

  For this reason, when the piezoelectric electroacoustic transducer 50 is mounted on a portable device, how to suppress the vibration of the main body housing 100 has been the key to development. By the way, the relationship between the vibration mode and acoustic characteristics of the piezoelectric electroacoustic transducer 100 will be described with reference to FIGS. 9, 10, 11, and 12.

  As shown in FIG. 9, the sound pressure level is greatly attenuated in a band between the fundamental resonance frequency (first resonance frequency) and the third resonance frequency. This will be described with reference to FIG. 10, FIG. 11, and FIG. The vibration state of the piezoelectric electroacoustic transducer 50 is formed by overlapping high-order vibration modes generated after the fundamental resonance frequency shown in FIG. Vibration mode is mixed.

  For example, in the secondary vibration mode shown in FIG. 11, since a seesaw-like vibration is performed, the sound wave is canceled in the radiation plane. And in the tertiary vibration mode as shown in FIG. 12 where the secondary vibration modes overlap, the radiation amount of the sound wave increases again. For this reason, the sound pressure level is significantly attenuated in a band between the first resonance frequency and the third resonance frequency. Therefore, in the electroacoustic transducer 50 according to the present embodiment, the first resonance frequency and the third resonance frequency are obtained by using the vibration of the main body housing 100 due to the second harmonic and the third harmonic of the main housing 100 to be mounted. Sound pressure level in a band between and can be improved.

  That is, the vibration when the electroacoustic transducer 50 rings is propagated to the main body housing 100, and vibration is generated in the main body housing 100. The sound pressure generated by the vibration of the main body housing 100 having a large area with respect to the electroacoustic transducer 50 is larger than the sound pressure generated from the electroacoustic transducer 50. This is because the sound pressure level is increased by causing the sound pressure from the electroacoustic transducer 50 to interfere. As shown by the vibration transfer function in FIG. 13, in the main body housing 100 having a basic resonance frequency of 500 Hz, vibrations having a second harmonic at 1000 Hz and a third harmonic at 1500 Hz are generated.

Therefore, the basic resonance frequency F (1) and the third resonance frequency F (3) of the electroacoustic transducer 50 and the basic resonance frequency F (a) of the main body housing 100 are as follows.
[Equation 2]
0.7 × ((F (1) + F (3)) / 2) <2 × F (a) <1.3 × ((F (1) + F (3)) / 2)
Or
0.7 × ((F (1) + F (3)) / 2) <3 × F (a) <1.3 × ((F (1) + F (3)) / 2)
Adjust to satisfy.

  That is, as shown in FIG. 14, the acoustic characteristics are improved by interfering with sound waves from the vibration of the main body housing 100 caused by the harmonics of the main body housing 100. In the electroacoustic transducer 50 of the present embodiment, the basic resonance frequency can be easily adjusted by the material / thickness of the vibration member and the distance between the support and the elastic member.

The basic resonance frequency f of the mechanical vibrator is expressed by the following mathematical formula.
[Equation 3]
f = 1 / (2πL√ (mC))
“M” is mass and “C” is compliance.

  Thus, the fundamental resonance frequency of the mechanical vibrator depends on the load weight and compliance. In other words, since the compliance is the mechanical rigidity of the vibrator, this means that the fundamental resonance frequency can be controlled by controlling the rigidity of the vibration member. For example, the fundamental resonance frequency can be shifted to a low range by selecting a material having a high elastic modulus and reducing the thickness of the material. On the other hand, the fundamental resonance frequency can be shifted to a high range by selecting a material having a high elastic modulus or increasing the thickness of the elastic material.

  In the conventional piezoelectric electroacoustic transducer, it is necessary to change the shape of the piezoelectric material, the area of the transducer, and the like in order to adjust the fundamental resonance frequency. However, the electroacoustic transducer of the present embodiment is superior in design restrictions and cost without changing the basic structure. As in the present invention, by changing the elastic material as a constituent member, it can be easily adjusted to a desired fundamental resonance frequency, and sound quality deterioration due to vibration of the main body housing can be avoided, so that the industrial value is great.

  The electroacoustic transducer according to the present invention can also be used as a sound source of an electronic device (for example, a mobile phone, a laptop personal computer, a small game device, etc.). Compared to conventional electroacoustic transducers, the fundamental resonance frequency can be adjusted only with the material of the vibrating member, so the overall shape of the electroacoustic transducer does not increase and the acoustic characteristics are improved. Also, it can be suitably used.

[Second embodiment]
A second embodiment of the present invention will be described with reference to FIG. The present embodiment is characterized in that the elastic member 20 is constrained by two piezoelectric elements 10a and 10b with respect to the first embodiment.

  That is, a bimorph structure using two piezoelectric elements 10a and 10b. As shown in FIG. 16, the bimorph type piezoelectric elements 10a and 10b are formed by bonding two piezoelectric ceramics whose polarization directions are opposite to each other, bending one by extending in the longitudinal direction, and shrinking the other. Compared to a unimorph structure composed of a single piezoelectric element 10 according to the first embodiment, a larger displacement can be obtained.

  For the two piezoelectric elements 10a and 10b, the same piezoelectric material as in the first embodiment can be used. Further, the two piezoelectric elements 10a and 10b may have the same shape or different shapes. In the case where the piezoelectric elements 10a and 10b have different shapes, two resonances resulting from the piezoelectric shape can be generated, and a wide band of acoustic characteristics can be realized. It is also possible to realize a parametric speaker by applying a high frequency electric field to one of the two piezoelectric elements 10a and 10b and a low frequency electric field to the other.

  As described above, the electroacoustic transducer according to the present embodiment can also be used as a sound source of an electronic device (for example, a mobile phone, a laptop personal computer, a small game device, etc., as shown in FIGS. 15 and 16). is there. Since the overall shape of the electroacoustic transducer does not increase and the acoustic characteristics are improved, the electroacoustic transducer can be suitably used for a portable electronic device.

[Third embodiment]
Furthermore, a third embodiment of the present invention will be described with reference to FIG. In this embodiment, it is composed of a laminated piezoelectric element. As shown in FIG. 17, the piezoelectric element has a multilayer structure in which piezoelectric plates 13a to 13e made of a piezoelectric material are laminated in five layers. Between the piezoelectric plates, electrode layers (conductor layers) 14a to 14d are formed one by one. The polarization directions of the piezoelectric plates 13a to 13e are opposite to each other, and the direction of the electric field is also alternately opposite. According to the piezoelectric element having such a laminated structure, since the electric field strength generated between the electrode layers is high, the driving force of the entire piezoelectric element is improved by an amount corresponding to the number of laminated piezoelectric plates.

[Fourth embodiment]
A fourth embodiment of the present invention will be described below. In this embodiment, as shown in FIG. 3, the piezoelectric element 10 has a square shape. Thus, even if the piezoelectric element 10 is rectangular, the effect obtained by connecting the elastic member 20 to the support 45 via the vibration member 30 can be obtained in the same manner as described above. By using the rectangular piezoelectric element 10, the manufacturing stability and cost are superior to the circular piezoelectric element 10. That is, it is only necessary to cut on a line at the time of processing, and since there is no dead space compared to a circle, the material can be reduced.

[Other embodiments of the invention]
The characteristic evaluation of the electroacoustic transducer of the present invention was performed using evaluation items 1 to 5 below.

  (Evaluation 1) Measurement of resonance frequency: The basic resonance frequency at the time of AC voltage 1V input was measured. Further, the third resonance frequency was measured from the acoustic characteristics.

  (Evaluation 2) Measurement of sound pressure level frequency characteristics: The sound pressure level when an AC voltage of 1 V was input was measured with a microphone placed at a position away from the element by a predetermined distance. The predetermined distance is 10 cm unless otherwise specified, and the frequency measurement range is 10 Hz to 10 kHz.

  (Evaluation 3) Measurement of flatness of sound pressure level frequency characteristics: The sound pressure level when an AC voltage of 1 V was input was measured with a microphone placed at a position away from the element by a predetermined distance. The frequency measurement range was 10 Hz to 10 kHz, and in the measurement range of 2 kHz to 10 kHz, the flatness of the sound pressure level frequency characteristic was measured by the sound pressure level difference between the maximum sound pressure level Pmax and the minimum sound pressure level Pmin. As a result, the sound pressure level difference (referring to the difference between the maximum sound pressure level Pmax and the minimum sound pressure level Pmin) was within 20 dB, and x was over 20 dB. This predetermined distance is 10 cm unless otherwise specified.

  (Evaluation 4) Drop impact test: A mobile phone equipped with an electroacoustic transducer was naturally dropped 5 times from directly above 50 cm, and a drop impact stability test was performed. Specifically, breakage such as cracks after the drop impact test was visually confirmed, and the sound pressure characteristics after the test were further measured. As a result, the sound pressure level difference (referring to the difference between the sound pressure level before the test and the sound pressure level after the test) was 3 dB or less, and 3 dB or more was evaluated as x.

  (Evaluation 5) Resonance frequency characteristics of main body housing: An impulse hammer method was used to apply vibration to the center of the main body housing, and an acceleration sensor was used to measure a vibration transfer function. The transfer function was analyzed, and the frequency showing the maximum vibration speed was defined as the basic resonance frequency of the main body housing.

[Example 1]
The electroacoustic transducer described in the first embodiment of the present invention was mounted on the mobile phone shown in FIG. 18, and the characteristics were evaluated. The evaluation results are as follows.
Basic resonance frequency of electroacoustic transducer: 1120Hz
Basic resonance frequency of electroacoustic transducer: 3460 Hz
Basic resonance frequency of main body housing of mobile phone: 650Hz
Sound pressure level (1 kHz): 90 dB
Sound pressure level (3 kHz): 92 dB
Sound pressure level (5 kHz): 95 dB
Sound pressure level (10 kHz): 86 dB
Flatness of sound pressure level frequency characteristics: ○
Drop impact stability: ○
As is clear from the above results, according to the electroacoustic transducer of this embodiment, the sound pressure level frequency characteristic is flat. It was also demonstrated that the sound pressure level exceeds 80 dB in a wide frequency band.

[Comparative Example 1]
As Comparative Example 1, an existing voice coil type electroacoustic transducer (not shown) was fabricated and mounted on the mobile phone of FIG. The evaluation results are as follows.
〔result〕
Basic resonance frequency of electroacoustic transducer: 854Hz
Basic resonance frequency of main body housing of mobile phone: 650Hz
Sound pressure level (1 kHz): 77 dB
Sound pressure level (3 kHz): 75 dB
Sound pressure level (5 kHz): 76 dB
Sound pressure level (10 kHz): 97 dB
Flatness of sound pressure level frequency characteristics: ×
Drop impact stability: ×
As is clear from the above results, according to the electroacoustic transducer of Comparative Example 1, it was proved that the sound pressure level frequency characteristics are not good and the sound pressure level exceeding 80 dB is not obtained in a wide frequency band.

[Example 2]
The electroacoustic transducer described in the second embodiment of the present invention was mounted on the mobile phone shown in FIG. 18, and the characteristics were evaluated. The evaluation results are as follows.
Basic resonance frequency of electroacoustic transducer: 1180Hz
Basic resonance frequency of main body housing of mobile phone: 650Hz
Sound pressure level (1 kHz): 97 dB
Sound pressure level (3 kHz): 97 dB
Sound pressure level (5 kHz): 92 dB
Sound pressure level (10 kHz): 88 dB
Flatness of sound pressure level frequency characteristics: ○
Drop impact stability: ○
As is clear from the above results, according to the electroacoustic transducer of this embodiment, the sound pressure level frequency characteristic is flat. It was also demonstrated that the sound pressure level exceeds 80 dB in a wide frequency band.

[Example 3]
The electroacoustic transducer described in the third embodiment of the present invention was mounted on the mobile phone shown in FIG. 18, and the characteristics were evaluated. The evaluation results are as follows.
Basic resonance frequency of electroacoustic transducer: 1180Hz
Basic resonance frequency of main body housing of mobile phone: 530Hz
Sound pressure level (1 kHz): 91 dB
Sound pressure level (3 kHz): 94 dB
Sound pressure level (5 kHz): 90 dB
Sound pressure level (10 kHz): 87 dB
Flatness of sound pressure level frequency characteristics: ○
Drop impact stability: ○
As is clear from the above results, according to the electroacoustic transducer of this embodiment, the sound pressure level frequency characteristic is flat. It was also demonstrated that the sound pressure level exceeds 80 dB in a wide frequency band.

[Example 4]
The electroacoustic transducer described in the fourth embodiment of the present invention was mounted on the mobile phone shown in FIG. 18, and the characteristics were evaluated. The evaluation results are as follows.
Basic resonance frequency of electroacoustic transducer: 1080Hz
Basic resonance frequency of main body housing of mobile phone: 650Hz
Sound pressure level (1 kHz): 90 dB
Sound pressure level (3 kHz): 88 dB
Sound pressure level (5 kHz): 85 dB
Sound pressure level (10 kHz): 88 dB
Flatness of sound pressure level frequency characteristics: ○
Drop impact stability: ○
As is clear from the above results, according to the electroacoustic transducer of this embodiment, the sound pressure level frequency characteristic is flat. It was also demonstrated that the sound pressure level exceeds 80 dB in a wide frequency band.

[Example 5]
The electroacoustic transducer described in the first embodiment of the present invention was mounted on the laptop PC of FIG. 19, and the characteristics were evaluated. The evaluation results are as follows.
Basic resonance frequency of electroacoustic transducer: 1120Hz
Basic resonance frequency of PC body housing: 650Hz
Sound pressure level (1 kHz): 93 dB
Sound pressure level (3 kHz): 90 dB
Sound pressure level (5 kHz): 90 dB
Sound pressure level (10 kHz): 88 dB
Flatness of sound pressure level frequency characteristics: ○
Drop impact stability: ○
As is clear from the above results, according to the electroacoustic transducer of this embodiment, the sound pressure level frequency characteristic is flat. It was also demonstrated that the sound pressure level exceeds 80 dB in a wide frequency band.

[Comparative Example 2]
As Comparative Example 2, the electroacoustic transducer shown in FIG. 17 was manufactured and mounted on the laptop PC of FIG. The evaluation results are as follows.
〔result〕
Basic resonance frequency of electroacoustic transducer: 854Hz
Basic resonance frequency of main body housing of mobile phone: 730Hz
Sound pressure level (1 kHz): 75 dB
Sound pressure level (3 kHz): 74 dB
Sound pressure level (5 kHz): 77 dB
Sound pressure level (10 kHz): 91 dB
Flatness of sound pressure level frequency characteristics: ×
Drop impact stability: ×
As is clear from the above results, according to the electroacoustic transducer of Comparative Example 2, it was proved that the sound pressure level frequency characteristics were not good and the sound pressure level exceeding 80 dB was not obtained in a wide frequency band.

[Example 6]
The electroacoustic transducer described in the second embodiment of the present invention was mounted on the laptop PC of FIG. 19, and the characteristics were evaluated. The evaluation results are as follows.
Basic resonance frequency of electroacoustic transducer: 1180Hz
Basic resonance frequency of main body housing of mobile phone: 730Hz
Sound pressure level (1 kHz): 91 dB
Sound pressure level (3 kHz): 94 dB
Sound pressure level (5 kHz): 90 dB
Sound pressure level (10 kHz): 99 dB
Flatness of sound pressure level frequency characteristics: ○
Drop impact stability: ○
As is clear from the above results, according to the electroacoustic transducer of this embodiment, the sound pressure level frequency characteristic is flat. It was also demonstrated that the sound pressure level exceeds 80 dB in a wide frequency band.

[Example 7]
The electroacoustic transducer described in the third embodiment of the present invention was mounted on the laptop PC of FIG. 19, and the characteristics were evaluated. The evaluation results are as follows.
Basic resonance frequency of electroacoustic transducer: 1180Hz
Basic resonance frequency of main body housing of mobile phone: 730Hz
Sound pressure level (1 kHz): 90 dB
Sound pressure level (3 kHz): 87 dB
Sound pressure level (5 kHz): 91 dB
Sound pressure level (10 kHz): 89 dB
Flatness of sound pressure level frequency characteristics: ○
Drop impact stability: ○
As is clear from the above results, according to the electroacoustic transducer of this embodiment, the sound pressure level frequency characteristic is flat. It was also demonstrated that the sound pressure level exceeds 80 dB in a wide frequency band.

[Example 8]
The electroacoustic transducer described in the fourth embodiment of the present invention was mounted on the laptop PC of FIG. 19, and the characteristics were evaluated. The evaluation results are as follows.
Basic resonance frequency of electroacoustic transducer: 1080Hz
Basic resonance frequency of main body housing of mobile phone: 730Hz
Sound pressure level (1 kHz): 88 dB
Sound pressure level (3 kHz): 91 dB
Sound pressure level (5 kHz): 95 dB
Sound pressure level (10 kHz): 82 dB
Flatness of sound pressure level frequency characteristics: ○
Drop impact stability: ○
As is clear from the above results, according to the electroacoustic transducer of this embodiment, the sound pressure level frequency characteristic is flat. It was also demonstrated that the sound pressure level exceeds 80 dB in a wide frequency band.

  The present invention is not limited to the present embodiment, and various modifications are allowed without departing from the scope of the present invention. For example, in the electroacoustic transducer of the above embodiment, as shown in FIGS. 18 and 19, a cellular phone or a personal computer that outputs sound with the electroacoustic transducer is illustrated as an electrical device. However, as an electronic device, an electroacoustic transducer that is an oscillation device, an oscillation drive unit that drives the electroacoustic transducer to output ultrasonic waves, and an ultrasonic wave that is oscillated from the electroacoustic transducer and reflected by the measurement object A sonar (not shown) having an ultrasonic detection unit that detects a sound wave and a distance calculation unit that calculates a distance from the detected ultrasonic wave to the measurement target can also be implemented.

  Needless to say, the above-described embodiments and examples can be combined within a range in which the contents do not conflict with each other. In the above-described embodiment, the structure of each part has been specifically described. However, the structure and the like can be variously changed within a range that satisfies the present invention.

1-e Lead wire 2-a Upper electrode layer 2-b Piezoelectric ceramic 2-c Lower electrode layer 10 Piezoelectric element 11 Main surface 12 Main surface 20 Elastic member 30 Vibration member 45 Support body 50 Electroacoustic transducer 100 Main body housing 550 Electricity Acoustic transducer

Claims (10)

A piezoelectric element that expands and contracts according to the state of the electric field;
An elastic member having at least the piezoelectric element bonded to the surface;
A vibration member having a lower rigidity than the elastic member and having the elastic member bonded to at least the surface;
A support body that is more rigid than the vibration member and supports the vibration member and is joined to a main body housing,
A basic resonance frequency F (1) and a third resonance frequency F (3) of an electroacoustic transducer including the piezoelectric element, the elastic member, the vibration member, and the support, and a basic resonance frequency F ( a)
0.7 × ((F (1) + F (3)) / 2) <2 × F (a) <1.3 × ((F (1) + F (3)) / 2)
Or
0.7 × ((F (1) + F (3)) / 2) <3 × F (a) <1.3 × ((F (1) + F (3)) / 2)
An oscillation device characterized by satisfying   The oscillation device according to claim 1, wherein the vibration member has a smaller elastic modulus than the elastic member.   The oscillation device according to claim 1, wherein the vibration member is made of a resin mainly composed of any one of urethane, PET (Polyethylene Terephthalate), and polyethylene film.   4. The oscillation device according to claim 1, wherein a basic resonance frequency of the electroacoustic transducer is adjusted by a shape change of the vibration member. 5.   5. The oscillation device according to claim 1, wherein the oscillation device is formed in a bimorph type in which a pair of the elastic members and a pair of the piezoelectric elements are individually joined to both surfaces of the vibration member in order.   6. The oscillation device according to claim 1, wherein the piezoelectric element is formed in a stacked structure in which piezoelectric material layers and electrode layers are alternately stacked.   The oscillation device according to any one of claims 1 to 6, wherein a frequency of an ultrasonic wave oscillated by the piezoelectric vibrator exceeds 20 kHz.   The oscillation device according to any one of claims 1 to 7, wherein the piezoelectric vibrator oscillates an ultrasonically modulated ultrasonic wave. An oscillation device according to any one of claims 1 to 8,
The body housing to which the oscillation device is mounted;
Oscillation drive means for outputting sound waves in the audible range to the oscillation device mounted on the main body housing;
Electronic equipment having An oscillation device according to any one of claims 1 to 8,
The body housing to which the oscillation device is mounted;
Oscillation drive means for driving the oscillation device mounted on the main body housing to output ultrasonic waves;
Ultrasonic detection means for detecting the ultrasonic wave oscillated from the oscillation device and reflected by the measurement object;
Distance calculating means for calculating a distance from the detected ultrasonic wave to the measurement object;
Electronic equipment having

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