JP2012015755A - Oscillation device and electronic equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an oscillation device that is capable of oscillating at a plurality of resonance frequencies with a simple structure.SOLUTION: A plurality of piezoelectric oscillators 110 and 120 obtained by forming electrode layers 112, 113, and 122 on front faces and rear faces of piezoelectric layers 111 and 121 are stacked in order on a front face of an elastic diaphragm 101 having elasticity, with resonance frequencies in a main mode of the plurality of the piezoelectric oscillators 110 and 120 differing each other at least partially. This enables oscillation at a plurality of resonance frequencies with a simple structure.

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 a vibrating member, 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 acoustic components.

  Conventionally, electrodynamic electroacoustic transducers have been used as electroacoustic transducers in electronic devices such as mobile phones. This electrodynamic electroacoustic transducer is composed of a permanent magnet, a voice coil, and a diaphragm.

  However, there is a limit to reducing the thickness of electrodynamic electroacoustic transducers due to their operating principles and structures. On the other hand, 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 oscillators and electronic devices are known.

  For example, there is a proposal for realizing a bimorph oscillation device by stacking two piezoelectric vibrators of the same shape and the same material on a vibrating member in two stages (Patent Document 4). There is also a proposal for realizing a bimorph oscillation device by arranging two piezoelectric vibrators having different planar shapes one on each side of a vibrating member (Patent Document 5).

No. 2007-026736 Table 2007-083497 Japanese Patent Laid-Open No. 03-270282 JP 2002-112391 A JP 2008-28593 A

  An oscillating device using a piezoelectric vibrator generates a vibration amplitude by an electrostrictive action by inputting an electric signal by using a piezoelectric effect of a piezoelectric layer. The electrodynamic electroacoustic transducer generates vibration by a piston-type forward / backward movement, whereas the oscillation device using the piezoelectric vibrator has a bending-type vibration state and thus has a small amplitude. For this reason, it is superior in reducing the thickness of the electrodynamic electroacoustic transducer described above.

  However, the resonance frequency of the main mode, which is one of the physical indices of the oscillation device, is determined as one depending on the shape and material of the piezoelectric vibrator. However, when the oscillation device is used as a speaker device, only a monotone sound can be output with a single resonance frequency.

  The present invention has been made in view of the above-described problems, and provides an oscillation device that can oscillate at a plurality of resonance frequencies with a simple structure, and an electronic apparatus using the oscillation device.

  An oscillation device according to the present invention includes a vibration member having elasticity, and a plurality of piezoelectric vibrators in which electrode layers are formed on a front surface and a back surface of a piezoelectric layer and are sequentially stacked on the surface of the vibration member. At least some of the plurality of piezoelectric vibrators have different main-mode resonance frequencies.

  A first electronic device of the present invention includes the oscillation device of the present invention and an oscillation drive unit that causes the oscillation device to output an audible sound wave.

  A second electronic device according to the present invention includes an oscillation device according to the present invention, an ultrasonic detection unit that detects an ultrasonic wave oscillated from the oscillation device and reflected by the measurement object, and from the detected ultrasonic wave to the measurement object. And a distance measuring unit for calculating the distance.

  In addition, the fact that the planar shape is different in the present invention includes that the shape is similar and the size is different.

  In the oscillation device of the present invention, since the resonance frequencies of the main modes of the plurality of piezoelectric vibrators stacked in order on the vibration member are different, the oscillation can be performed at a plurality of resonance frequencies with a simple structure.

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 top view which shows the structure of an electroacoustic transducer. It is a typical vertical front view which shows the polarization direction of two piezoelectric vibrators. It is a perspective view which shows the structure of the electroacoustic transducer of one modification. It is a perspective view which shows the structure of the electroacoustic transducer of another modification. It is a typical vertical front view which shows the structure of the electroacoustic transducer of another modification.

  A first embodiment of the present invention will be described below with reference to FIGS. As shown in FIG. 1, an electroacoustic transducer 100 that is an oscillation device according to the present embodiment includes an elastic diaphragm 101 that is a resilient vibration member, and electrodes on the front and back surfaces of the piezoelectric ceramics 111 and 121. Layers 112, 113, and 122 are formed, and a plurality of piezoelectric vibrators 110 and 120 are sequentially stacked on the surface of the elastic diaphragm 101.

  However, the resonance frequencies of the main modes of the plurality of piezoelectric vibrators 110 and 120 are different. More specifically, in the electroacoustic transducer 100 of the present embodiment, as shown in FIGS. 1 and 2, the planar shapes of the plurality of piezoelectric vibrators 110 and 120 having different resonance frequencies are different.

  That is, the lower piezoelectric vibrator 110 has a planar shape formed in a large-diameter circle, whereas the upper piezoelectric vibrator 120 has a planar shape formed in a small-diameter circle. In the electroacoustic transducer 100 of the present embodiment, the electrode layer 113 on the upper surface of the lower piezoelectric vibrator 110 is also used as the electrode layer 113 on the lower face of the upper piezoelectric vibrator 120.

  The three electrode layers 112, 113, 122 of the two piezoelectric vibrators 110, 120 as described above are individually connected to the control unit 130 that is an oscillation drive unit. An electric field that causes each of the piezoelectric vibrators 110 and 120 to oscillate in an audible region or an ultrasonic region is individually output.

  Further, as the piezoelectric ceramics 111 and 121, lead zirconate titanate (PZT) or the like is used, but is not particularly limited. The thickness of the piezoelectric ceramics 111 and 121 is not particularly limited, but is preferably 10 μm or more and 500 μm or less.

  For example, when a thin film having a thickness of less than 10 μm is used as a ceramic material that is a brittle material, chipping or breakage occurs due to weak mechanical strength during handling, making handling difficult.

  Further, when the piezoelectric ceramics 111 and 121 having a thickness exceeding 500 μm are used, the conversion efficiency for converting electrical energy into mechanical energy is remarkably reduced, and sufficient performance as the electroacoustic transducer 100 cannot be obtained.

  In general, in the piezoelectric ceramics 111 and 121 that generate an electrostrictive effect by inputting an electric signal, the conversion efficiency depends on the electric field strength. Since the electric field strength is expressed by the thickness / input voltage with respect to the polarization direction, an increase in thickness inevitably causes a decrease in conversion efficiency.

  In the piezoelectric vibrator 110 of the present embodiment, electrode layers 112, 113, and 122 are formed on the front surface and the back surface in order to generate an electric field. As described above, since the central electrode layer 113 is shared by the two piezoelectric ceramics 111 and 121, it is used as, for example, a ground.

  The electrode layers 112, 113, and 122 are not particularly limited as long as they are electrically conductive materials, but it is preferable to use silver or silver / palladium. Silver is used as a general-purpose electrode layer with low resistance, and has advantages in manufacturing process and cost.

  Further, since silver / palladium is a low-resistance material excellent in oxidation resistance, there is an advantage from the viewpoint of reliability. The thickness of the electrode layers 112, 113, 122 is not particularly limited, but the thickness is preferably 1 μm or more and 50 μm or less.

  For example, when the thickness is less than 1 μm, since the film thickness is thin, it cannot be uniformly formed, and conversion efficiency may be reduced. As a technique for forming the thin-film electrode layers 112, 113, and 122, there is a method of applying the paste in a paste form.

  However, the polycrystal such as the piezoelectric ceramics 111 and 121 has a problem that the surface state is a textured surface, so that the wet state at the time of application is poor and a uniform electrode film cannot be formed without a certain thickness.

  On the other hand, when the film thickness of the electrode layers 112, 113, and 122 exceeds 100 μm, there is no particular problem in manufacturing, but the electrode layers 112, 113, and 122 serve as constraining surfaces for the piezoelectric ceramics 111 and 121, and energy conversion is performed. There is a problem that reduces efficiency.

  In the electroacoustic transducer 100 of this embodiment, the lower surface of the upper piezoelectric vibrator 120 is constrained by the upper surface of the lower piezoelectric vibrator 110, and the lower surface of the lower piezoelectric vibrator 110 is the elastic diaphragm 101. Restrained at the top.

  The elastic diaphragm 101 resonates due to vibrations generated directly and indirectly from the piezoelectric vibrators 110 and 120. At the same time, the elastic diaphragm 101 has a function of adjusting the basic resonance frequency of the piezoelectric vibrator 110.

  The elastic diaphragm 101 is supported by an annular support frame 102. The fundamental resonance frequency f of the mechanical electroacoustic transducer 100 of the elastic diaphragm 101 depends on the load weight and compliance, as shown by the following equation.

[Equation 1]
f = 1 / (2πL√ (mC))
“M” is mass and “C” is compliance.

  In other words, since the compliance is the mechanical rigidity of the electroacoustic transducer 100, this means that the fundamental resonance frequency can be controlled by controlling the rigidity of the piezoelectric vibrators 110 and 120.

  For example, it is possible to shift the fundamental resonance frequency to a low range by selecting a material having a high elastic modulus or reducing the thickness of the elastic diaphragm 101. 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 diaphragm 101.

  The elastic diaphragm 101 is not particularly limited as long as it is a material having a high elastic modulus with respect to a ceramic that is a brittle material such as a metal or a resin, but a general-purpose material such as phosphor bronze or stainless steel from the viewpoint of workability and cost. Is used.

  The thickness of the elastic diaphragm 101 is preferably 5 μm or more and 1000 μm or less. When the thickness is less than 5 μm, there is a problem that mechanical strength is weak, the function as a restraining member is impaired, and the mechanical vibration characteristics of the piezoelectric vibrator 110 are varied between production lots due to a decrease in processing accuracy.

  Further, when the thickness exceeds 1000 μm, there is a problem that the restraint on the piezoelectric vibrator 110 due to the increase in rigidity is strengthened and the vibration displacement amount is attenuated. The elastic diaphragm 101 of the present embodiment preferably has a longitudinal elastic modulus, which is an index indicating the rigidity of the material, of 1 GPa or more and 500 GPa or less. As described above, when the rigidity of the elastic diaphragm 101 is excessively low or excessively high, there is a problem that characteristics and reliability are impaired as a mechanical vibrator.

  Here, the manufacturing method of the electroacoustic transducer 100 of this Embodiment is demonstrated below. First, in the piezoelectric vibrators 110 and 120, for example, piezoelectric ceramics 111 and 121 having an outer diameter = φ3 mm, φ2 mm, and thickness = 200 μm are formed, and an electrode layer 112 having a thickness of 8 μm is formed on both surfaces of each of the piezoelectric ceramics 111 and 121. , 113, 122 are formed.

  For the piezoelectric ceramics 111 and 121, lead zirconate titanate ceramic is used, and for the electrode layers 112, 113 and 122, a silver / palladium alloy (weight ratio 70%: 30%) is used.

  The piezoelectric ceramics 111 and 121 are manufactured by a green sheet method, fired in the atmosphere at 1100 ° C. for 2 hours, and then the piezoelectric ceramics 111 and 121 are subjected to polarization treatment. An epoxy-based adhesive is used for bonding the piezoelectric vibrators 110 and 120 and bonding the piezoelectric vibrator 110 and the elastic diaphragm 101.

  Further, in this configuration, ultrasonic waves are oscillated in order to realize sound reproduction that can protect privacy. Here, the principle of a parametric speaker that demodulates modulated ultrasonic waves into audible sounds is used. The piezoelectric vibrators 110 and 120 oscillate ultrasonic waves having a frequency of 20 kHz or more.

  Here, AM (Amplitude Modulation) modulation, DSB (Double Sideband) modulation, SSB (Single-Sideband modulation) modulation, FM (Frequency Modulation) modulated ultrasonic waves are emitted into the air, and the ultrasonic waves enter the air. Sound reproduction is performed on the principle that audible sound appears due to nonlinear characteristics when propagating.

  Non-linearity includes a phenomenon in which the flow changes from laminar flow to turbulent flow when the Reynolds number indicated by the ratio between the inertial action and viscous action of the flow increases. That is, since the sound wave is slightly disturbed in the fluid, the sound wave propagates nonlinearly.

  However, the amplitude of the sound wave in the low frequency band is nonlinear, but the amplitude difference is very small, and is usually handled as a phenomenon of linear theory. On the other hand, nonlinearity can be easily observed with ultrasonic waves, and when radiated into the air, harmonics accompanying the nonlinearity are remarkably generated.

  In summary, sound waves are a dense state where molecular groups are mixed in the air, and if it takes time for the air molecules to recover rather than compress, the air that cannot be recovered after compression is continuously propagated air. This is the principle that an audible sound is generated by colliding with a molecule and generating a shock wave.

  Next, the operation principle of the piezoelectric vibrators 110 and 120 will be described. The piezoelectric ceramics 111 and 121 are made of a piezoelectric plate having two main surfaces as described above, and electrode layers 112, 113, and 122 are formed on the main surfaces of the piezoelectric ceramics 111 and 121, respectively.

  Although the polarization direction of the piezoelectric ceramics 111 and 121 is not particularly limited, in the electroacoustic transducer 100 of the present embodiment, as shown in FIG. 3, the vertical direction (thickness direction of the piezoelectric vibrators 110 and 120). The lower piezoelectric vibrator 110 faces downward, and the upper piezoelectric vibrator 120 faces upward.

  In the piezoelectric vibrators 110 and 120 configured in this way, when an alternating voltage is applied to the electrode layers 112, 113, and 122 and an alternating electric field is applied, both main surfaces are expanded or contracted simultaneously. , Perform radial expansion and contraction (diameter expansion).

  In other words, the piezoelectric vibrators 110 and 120 perform a bimorph motion that repeats a first deformation mode in which the main surface expands and a second deformation mode in which the main surface contracts.

  When the piezoelectric vibrators 110 and 120 repeat such a bimorph motion, the elastic diaphragm 101 uses the elastic effect to generate vertical vibrations due to the inertial action and the restoring action, using both ends as fulcrums, thereby generating sound waves. .

  In the configuration of the present invention, the piezoelectric vibrators 110 and 120 oscillate ultrasonic waves having a frequency of 20 kHz or more. Sound reproduction is performed based on the principle of a so-called parametric speaker that oscillates FM or AM-modulated ultrasonic waves and demodulates the modulated wave to reproduce audible sound using the nonlinear state (dense / dense state) of air. This propagates sound waves using the high directivity that is characteristic of ultrasonic waves, and it is possible to realize a privacy sound source that can only be heard by the user.

  In the electroacoustic transducer 100 according to the present embodiment, the resonance frequencies of the main modes of the plurality of piezoelectric vibrators 110 and 120 that are sequentially stacked on the elastic diaphragm 101 are different, and thus the plurality of resonance frequencies. Can oscillate.

  Nevertheless, since the plurality of piezoelectric vibrators 110 and 120 are sequentially laminated on the surface of the elastic diaphragm 101, the structure is simple and the manufacture is easy. In addition, since the two piezoelectric vibrators 110 and 120 are shared by the electrode layer 113, the structure is simpler and the manufacture is easier.

  As described above, the electroacoustic transducer 100 according to the present embodiment is small and can reproduce a large volume. Further, since ultrasonic waves are used, directivity is narrow, and industrial value is great in terms of protecting user privacy.

  That is, the electroacoustic transducer 100 according to the present embodiment has higher rectilinearity of the sound wave than the conventional electroacoustic transducer, and can selectively propagate the sound wave to a position to be transmitted to the user. In summary, the electroacoustic transducer 100 according to the present embodiment can be used as a sound source of an electronic device (for example, a mobile phone, a notebook personal computer, a small game device, etc.). In addition, since the electroacoustic transducer 100 can be prevented from being enlarged and the acoustic characteristics are improved, the electroacoustic transducer 100 can be suitably used for portable electronic devices.

  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 this embodiment, the piezoelectric ceramics 111 and 121 such as lead zirconate titanate (PZT) are used as the piezoelectric elements of the piezoelectric vibrators 110 and 120.

  However, the piezoelectric element is not particularly limited as long as it has a piezoelectric effect, and a material having high electromechanical conversion efficiency, for example, a material such as barium titanate (BaTiO 3) can be used.

  In the above embodiment, as the piezoelectric vibrators 110 and 220 having different main-mode resonance frequencies, the piezoelectric vibrators 110 and 120 having the same thickness and material and the same diameter are stacked on the elastic diaphragm 101 in order. Exemplified that

  However, like the electroacoustic transducer 200 which is an oscillation device illustrated in FIG. 4, a large-diameter circular piezoelectric vibrator 210 and a small rectangular piezoelectric vibrator 220 are sequentially stacked on the elastic diaphragm 101. May be.

  Conversely, a large polygonal piezoelectric vibrator and a small-diameter circular piezoelectric vibrator or the like may be sequentially stacked on the elastic diaphragm 101, and the elastic diaphragm 101 may have a large polygonal piezoelectric vibrator. Small-diameter polygonal piezoelectric vibrators may be stacked in order (both not shown).

  Further, three or more stages of piezoelectric vibrators may be loaded on the elastic diaphragm 101. Further, like an electroacoustic transducer 300 which is an oscillation device illustrated in FIG. 5, a small-diameter semicircular planar shape is formed on the upper surface of a large-diameter circular piezoelectric vibrator 210 mounted on the elastic diaphragm 101. Two piezoelectric vibrators 320 may be stacked in parallel.

  Further, the materials of the piezoelectric ceramics 111 and 121 of the plurality of piezoelectric vibrators 110 and 120 having different resonance frequencies may be different, and the materials of the electrode layers 112, 113, and 122 may be different (not shown). )

  Further, like the electroacoustic transducer 400 exemplified as the oscillation device in FIG. 6, the piezoelectric vibrators 410 and 420 having different resonance frequencies may have different plate thicknesses, and the piezoelectric ceramics 111 and 121 and the electrode layers 112, 113, and 122 may have different layer thicknesses.

  Furthermore, in the said form, the mobile telephone etc. which output an audio | voice with the electroacoustic transducer 100 grade | etc., Were assumed as an electric equipment. However, as an electronic device, an electroacoustic transducer 100 that is an oscillation device, an ultrasonic detection unit that detects an ultrasonic wave oscillated from the electroacoustic transducer 100 and reflected by a measurement object, and a detected ultrasonic wave A sonar (not shown) having a distance measuring unit that calculates the distance from the sound wave to the measurement object can also be implemented.

  In the above embodiment, the two piezoelectric vibrators 110 and 120 stacked in order on the elastic diaphragm 101 are polarized in the upside down direction and operate as a bimorph. However, the two piezoelectric vibrators 110 and 120 may be polarized in the same direction and driven individually.

  Further, in the above embodiment, the two piezoelectric vibrators 110 and 120 share the intermediate electrode layer 113 as an example. However, dedicated electrode layers may be formed on the upper surface of the lower piezoelectric vibrator 110 and the lower surface of the upper piezoelectric vibrator 120, respectively (not shown).

  In such a case, by forming an insulating layer between the electrode layers of the upper surface of the lower piezoelectric vibrator 110 and the lower surface of the upper piezoelectric vibrator 120, the two piezoelectric vibrators 110 and 120 can be individually connected more reliably. It becomes possible to drive.

  Needless to say, the above-described plurality of embodiments and the plurality of modifications 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.

DESCRIPTION OF SYMBOLS 100 Electroacoustic transducer 101 Elastic diaphragm 102 Support frame 110 Piezoelectric vibrator 111,121 Piezoelectric ceramic 112,113,122 Electrode layer 120 Piezoelectric vibrator 130 Control part 200 Electroacoustic transducer 210 Piezoelectric vibrator 220 Piezoelectric vibrator 300 Electricity Acoustic transducer 320 Piezoelectric vibrator

Claims (11)

A vibration member having elasticity,
A plurality of piezoelectric vibrators in which electrode layers are formed on the front and back surfaces of the piezoelectric layer and are sequentially stacked on the surface of the vibrating member;
An oscillation device in which at least some of the plurality of piezoelectric vibrators have different main-mode resonance frequencies.   The oscillation device according to claim 1, wherein the plurality of piezoelectric vibrators having different resonance frequencies have different planar shapes.   The oscillation device according to claim 1 or 2, wherein plate thicknesses of the plurality of piezoelectric vibrators having different resonance frequencies are different.   4. The oscillation device according to claim 1, wherein the piezoelectric layers of the plurality of piezoelectric vibrators having different resonance frequencies have different layer thicknesses.   5. The oscillation device according to claim 1, wherein the electrode layers of the plurality of piezoelectric vibrators having different resonance frequencies have different layer thicknesses.   The oscillation device according to claim 1, wherein materials of the piezoelectric layers of the plurality of piezoelectric vibrators having different resonance frequencies are different.   The oscillation device according to any one of claims 1 to 6, wherein materials of the electrode layers of the plurality of piezoelectric vibrators having different resonance frequencies are different.   The oscillation device according to any one of claims 1 to 7, wherein a frequency of an ultrasonic wave generated by at least one of the plurality of piezoelectric vibrators having different resonance frequencies exceeds 20 kHz.   The oscillation device according to any one of claims 1 to 8, wherein at least one of the plurality of piezoelectric vibrators oscillates an audible ultrasonic modulated wave. The oscillation device according to any one of claims 1 to 9,
An oscillation drive unit for outputting an audible sound wave to the oscillation device;
Electronic equipment having The oscillation device according to any one of claims 1 to 9,
An ultrasonic detector for detecting the ultrasonic wave oscillated from the oscillation device and reflected by the measurement object;
A distance measuring unit for calculating a distance from the detected ultrasonic wave to the measurement object;
Electronic equipment having

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