WO2010032463A1 - 音響再生装置 - Google Patents
音響再生装置 Download PDFInfo
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- WO2010032463A1 WO2010032463A1 PCT/JP2009/004668 JP2009004668W WO2010032463A1 WO 2010032463 A1 WO2010032463 A1 WO 2010032463A1 JP 2009004668 W JP2009004668 W JP 2009004668W WO 2010032463 A1 WO2010032463 A1 WO 2010032463A1
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- piezoelectric body
- sound
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- ultrasonic
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- 238000006073 displacement reaction Methods 0.000 claims abstract description 76
- 230000008878 coupling Effects 0.000 abstract description 7
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- 229910010293 ceramic material Inorganic materials 0.000 description 1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R17/00—Piezoelectric transducers; Electrostrictive transducers
- H04R17/10—Resonant transducers, i.e. adapted to produce maximum output at a predetermined frequency
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R3/00—Circuits for transducers, loudspeakers or microphones
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R17/00—Piezoelectric transducers; Electrostrictive transducers
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
- H04R2217/00—Details of magnetostrictive, piezoelectric, or electrostrictive transducers covered by H04R15/00 or H04R17/00 but not provided for in any of their subgroups
- H04R2217/03—Parametric transducers where sound is generated or captured by the acoustic demodulation of amplitude modulated ultrasonic waves
Definitions
- the present invention relates to an acoustic reproduction apparatus having high directivity capable of reproducing an audible band sound wave in a specific spatial range by modulating and radiating an audible band signal using an ultrasonic band signal as a carrier wave.
- a normal sound reproducing device can emit sound waves in the audible band directly into a medium such as air through a diaphragm, and can propagate sound waves in the audible band in a relatively wide range by a diffraction effect.
- This sound reproducing apparatus is generally called a super-directional speaker or a parametric speaker.
- a signal in the audible band is modulated as a carrier wave with a signal in the ultrasonic band, and further amplified at a specific magnification, and then the modulated signal is input to a sound emitting unit including an ultrasonic transducer and the like, and a medium such as air It emits as a sound wave in the ultrasonic band.
- the sound wave radiated from the sound emitting part propagates through the medium with high directivity due to the propagation characteristics of the ultrasonic wave as a carrier wave. Furthermore, while the sound wave in the ultrasonic band propagates through the medium, the amplitude of the sound wave in the audible band increases cumulatively due to the nonlinearity of the medium, and the sound wave in the ultrasonic band attenuates due to absorption by the medium and spherical diffusion. To do. As a result, the sound wave in the audible band modulated in the ultrasonic band is self-demodulated into the sound wave in the audible band due to the nonlinearity of the medium, and the sound wave in the audible band can be reproduced only in a limited narrow space range.
- the super-directional speaker uses the nonlinearity of the medium through which the sound wave propagates and the high directivity of the ultrasonic wave. For example, if a super-directional speaker is used as a speaker for explaining an exhibition in a museum or a museum, sound waves in the audible band can be transmitted only to a person existing within a specific spatial range.
- the above-described sound reproducing device uses a frequency in the vicinity of a resonance frequency for exciting a resonance mode of an ultrasonic vibrator made of a piezoelectric body or the like. Used as a frequency.
- the mechanical quality factor Qm (a constant indicating the sharpness of mechanical vibration displacement in the vicinity of the resonance frequency when the piezoelectric body or the like causes resonance vibration) is high, and maximum for the applied AC electric field. The vibration displacement can be obtained.
- the resonance frequency of the ultrasonic transducer varies among individuals.
- the mechanical quality factor Qm is also affected by temperature changes of the ultrasonic transducer itself and load fluctuations caused by a medium such as air. Therefore, even if an electric field having the same frequency and the same amplitude is applied to a plurality of ultrasonic transducers.
- Non-Patent Document 1 is known as prior art document information relating to the above-described sound reproduction device.
- the present invention includes an audible band signal source that generates an audible band signal, a carrier wave generator that generates a carrier wave, a modulator that modulates an audible band signal with a carrier wave, and a signal output from the modulator. And at least a sound emitting unit for outputting the reproduced sound by the ultrasonic vibrator.
- the ultrasonic vibrator of the sound emitting unit has a plurality of resonance modes in which vibration displacement is maximized at different frequencies, and can excite mode-coupled vibration between frequencies for exciting the plurality of resonance modes.
- a part of a frequency band in which mode-coupled vibration can be excited is defined as a carrier frequency.
- the resonance frequency of the ultrasonic vibrator varies or fluctuates due to the manufacturing process of the ultrasonic vibrator or load fluctuation during operation, it is possible to excite mode-coupled vibration.
- the vibration amplitude fluctuation of the ultrasonic transducer is small and stable.
- the sound wave in the audible band is self-demodulated, a broadband and stable sound pressure is realized.
- FIG. 1 is a block diagram of a sound reproducing device according to Embodiment 1 of the present invention.
- FIG. 2 is a cross-sectional view of the ultrasonic transducer in the first embodiment of the present invention.
- FIG. 3 is a diagram showing frequency characteristics of admittance and vibration displacement in the thickness direction of a conventional piezoelectric body.
- FIG. 4 is a diagram showing frequency characteristics of admittance and vibration displacement of the piezoelectric body according to the first embodiment of the present invention.
- FIG. 5 is a diagram showing that a specific frequency band centered on the resonance frequency f m1 is a carrier frequency in the first embodiment of the present invention.
- FIG. 6 is a diagram showing the relationship between the resonance frequency of radial expansion vibration and the vibration displacement in the thickness direction in the piezoelectric body according to the first embodiment of the present invention.
- FIG. 7 is a diagram showing frequency characteristics of vibration displacement with respect to the mechanical quality factor Qm of the piezoelectric body in the first embodiment of the present invention.
- FIG. 8 is a diagram showing that a specific frequency band centered on the frequency f Lm at which the vibration displacement takes the minimum value ⁇ Lm is used as the frequency of the carrier wave in the first embodiment of the present invention.
- FIG. 9 is a diagram showing the relationship between the frequency at which the admittance takes a maximum value and the minimum value of vibration displacement in the thickness direction when the dimensional ratio is changed in the piezoelectric body according to the first embodiment of the present invention.
- FIG. 10 is a front view of the sound emitting unit in the second embodiment of the present invention.
- FIG. 11 is a diagram illustrating the frequency characteristics of the admittance and vibration displacement of the piezoelectric bodies of the three ultrasonic transducers according to the second embodiment of the present invention.
- FIG. 12 is a cross-sectional view of the ultrasonic transducer according to the third embodiment of the present invention.
- FIG. 1 is a block diagram of a sound reproducing device according to Embodiment 1 of the present invention.
- FIG. 1 illustrates a drive unit of the sound reproducing device 1 of the present invention.
- An audible band signal (approximately 20 Hz to 20 kHz as a frequency) generated by the audible band signal source 2 and a carrier wave (approximately 20 kHz or higher ultrasonic wave) generated by the carrier wave oscillator 3 are input to the modulator 4, and an audible band signal is input. Is modulated with a carrier wave. The modulated signal is amplified by the power amplifier 5 and input to the sound emitting unit 6.
- the signal from the modulator 4 input to the sound emitting unit 6 is radiated as an ultrasonic wave to a medium such as air, and after propagating a certain distance, the sound wave in the ultrasonic band as a carrier wave is attenuated, and Sound waves in the audible band self-demodulate due to nonlinearity.
- the sound reproducing device 1 can reproduce sound waves in the audible band only in a very narrow spatial range by using ultrasonic waves having high directivity as carrier waves. It has become.
- FIG. 2 is a cross-sectional view of the ultrasonic transducer 7 according to Embodiment 1 of the present invention.
- the ultrasonic vibrator 7 is a part that vibrates the piezoelectric body 8 and receives sound waves to a medium such as air when a signal from the modulator 4 is input.
- the piezoelectric body 8 is a cylindrical piezoelectric ceramic made of a composite perovskite piezoelectric material (for example, a ternary piezoelectric ceramic material such as PbTiO 3 —ZrTiO 3 —Pb (Mg 1/2 Nb 1/2 ) TiO 3 ).
- the acoustic matching layer 9 is disposed substantially at the center on one surface in the thickness direction.
- the piezoelectric body 8 has a dimensional ratio L / D of about 0.7, where L is the thickness and D is the diameter, and is polarized in the thickness L direction.
- L is the thickness and D is the diameter
- a piezoelectric ceramic such as PZT (PbTiO 3 —ZrTiO 3 ), barium titanate (BaTiO 3 ), or a piezoelectric single crystal may be used. Good.
- a cylindrical case 10 is fixed so as to surround the piezoelectric body 8, and the piezoelectric body 8 is protected from the outside.
- the case 10 is made of aluminum.
- a terminal block 11 is provided at the opening of the case 10 (the inner surface near the end opposite to the connection portion of the acoustic matching layer 9).
- the terminal block 11 and the piezoelectric body 8 are provided with a certain gap so that they do not come into contact with each other due to external impact, vibration of the piezoelectric body 8 or the like.
- the terminal block 11 is provided with two rod-like terminals 12, and these terminals 12 are electrically connected to the electrodes of the piezoelectric body 8 through lead wires 13, respectively. That is, an alternating electric field can be applied to the piezoelectric body 8 via the terminal 12.
- the ultrasonic vibrator 7 having such a configuration, when an alternating electric field having a specific frequency is applied to the electrodes provided on both main surfaces of the piezoelectric body 8, elastic vibration determined by the material constant, shape, dimensions, and the like is applied to the piezoelectric body 8. Can be excited. A sound wave generated by this elastic vibration is radiated to a medium such as air through the acoustic matching layer 9 and propagates in a specific direction (upward direction in FIG. 2).
- the acoustic matching layer 9 is for matching the acoustic impedance between the piezoelectric body 8 and a medium such as air, and attenuation of sound waves due to reflection at a boundary surface due to a difference in acoustic impedance between the piezoelectric body and the medium. Is reduced.
- the audible band signal source 2, the carrier wave oscillator 3, the modulator 4, and the power amplifier 5 are constituted by only one set.
- FIG. 3 is a diagram showing an example of frequency characteristics of admittance and frequency characteristics of vibration displacement in the thickness direction in a conventional piezoelectric body.
- a piezoelectric body has a plurality of resonance modes having different vibration directions and vibration modes (vibration modes) depending on the shape (size ratio), the direction of polarization (c-axis in the case of a single crystal) and the direction of an alternating electric field to be applied. Can be excited.
- FIG. 3 shows a cylindrical piezoelectric body.
- the piezoelectric body in the figure is a piezoelectric ceramic polarized in the thickness direction, and an AC electric field is applied in the thickness direction.
- the vibration displacement in the thickness direction is first near the frequency f L1 at which the admittance Y is maximized.
- a first resonance mode in which ⁇ L1 is maximum occurs. This resonance mode at the frequency f L1 is called longitudinal vibration in the thickness direction.
- a second resonance mode in which the radial vibration displacement is maximized is generated in the vicinity of the frequency f D1 at which the admittance Y is maximized.
- the resonance mode at this frequency f D1 is called radial expansion vibration. Note that the radial vibration displacement of the radial spreading vibration is not shown in FIG.
- the piezoelectric body is also an elastic body, vibration displacement occurs in the radial direction, and vibration displacement occurs also in the thickness direction due to Poisson coupling.
- the vibration displacement in the thickness direction in the vicinity of the frequency f D1 is very small compared to the vibration displacement ⁇ L1 in the vicinity of the frequency f L1 because the thickness L of the cylinder is larger than the diameter D.
- the vibration displacement in the thickness direction of the piezoelectric body decreases rapidly and is hardly obtained.
- the vibration displacement in the radial direction decreases and can hardly be obtained except in the vicinity of the frequency f L1 and the frequency f D1 . That is, the piezoelectric body hardly vibrates in the thickness direction and the radial direction at frequencies other than the vicinity of the frequency f L1 and the frequency f D1 .
- the two resonance modes ie, the longitudinal vibration in the thickness direction and the vibration in the radial direction, do not affect each other and vibrate independently in the vicinity of the respective resonance frequencies.
- each resonance mode does not affect each other and vibrates independently, and the mechanical quality factor Qm of each resonance mode increases.
- a cylindrical piezoelectric body 8 having a dimensional ratio L / D between the thickness L and the diameter D of about 0.7 is used. It was.
- a mode-coupled vibration is excited at a frequency between the resonance frequencies for exciting the two resonance modes of the thickness direction longitudinal vibration and the radial spread vibration, It is possible to obtain a vibration displacement ⁇ L of a certain level or more in the thickness direction.
- a part of the frequency band in which this mode-coupled vibration can be excited is used as a carrier frequency band.
- FIG. 4 is a diagram showing frequency characteristics of admittance and vibration displacement of the piezoelectric body according to the first embodiment of the present invention.
- FIG. 4 shows an example of the result of numerical calculation of the frequency characteristics of the admittance Y of the piezoelectric body 8 and the vibration displacement ⁇ L in the thickness direction in the first embodiment using the finite element method.
- the piezoelectric body 8 excites a resonance mode having a high mechanical quality factor Qm at two resonance frequencies, frequency f m1 and frequency f m2 . Furthermore, between the frequency f m1 and frequency f m @ 2, and exciting the vibration mode coupling, as compared with the vicinity of the two frequencies f m1 and frequency f m @ 2, the absolute vibration displacement xi] L of the thickness direction Although the value is small, it is possible to obtain a frequency band with a small amount of change with respect to frequency fluctuation. In particular, in the vicinity of the frequency f Lm where the vibration displacement in the thickness direction becomes the minimum value ⁇ Lm , a flat region in which the change amount of the vibration displacement ⁇ L is the smallest with respect to the frequency variation can be obtained.
- the frequency region based on the frequency f Lm that excites the above mode-coupled vibration and minimizes the vibration displacement ⁇ L in the thickness direction is used as the frequency of the carrier wave. Even when the resonance frequency of the longitudinal vibration in the thickness direction and the radial expansion vibration of the piezoelectric body 8 fluctuates due to variations in materials and shapes, etc., within the frequency range in which mode-coupled vibration can be excited, The vibration amplitude fluctuation of the sound wave vibrator is small and stable. As a result, when the signal in the audible band is self-demodulated, a wide band and a stable sound pressure can be realized.
- FIG. 5 is a diagram showing that a specific frequency band centered on the resonance frequency f m1 is a carrier frequency in the first embodiment of the present invention.
- the resonance frequency f m1 In the vicinity, since the mechanical quality factor Qm of the resonance mode is high, the vibration displacement of the ultrasonic vibrator 7 is large, and the sound wave emitted from the ultrasonic vibrator 7 can also obtain a high sound pressure.
- the vibration displacement of the ultrasonic transducer 7 is smaller at a frequency away from the resonance frequency f m1 by a frequency variation width ⁇ f than at the vicinity of the resonance frequency f m1 .
- the ultrasonic vibrator 7 when the ultrasonic vibrator 7 is excited with a signal obtained by modulating a wideband audible band signal with the resonance frequency fm1 as the frequency of the carrier wave, the vibration displacement of the ultrasonic vibrator 7 is reduced within the frequency range of the applied electric field. Since the amount of change is large, the sound pressure fluctuation with respect to the frequency of the sound wave radiated from the ultrasonic transducer becomes large, and the demodulated sound wave in the audible band also has a large amplitude fluctuation range depending on the frequency, and it is difficult to obtain a stable sound pressure. Become.
- a part of the frequency band in which mode-coupled vibration in which the change amount of the vibration displacement ⁇ L with respect to the frequency variation is relatively small can be excited is defined as the carrier frequency. This makes it possible to reproduce an audible band signal with a wide band and a stable sound pressure.
- FIG. 6 is a diagram showing the relationship between the resonance frequency of radial expansion vibration and the vibration displacement in the thickness direction in the piezoelectric body according to the first embodiment of the present invention.
- FIG. 6 shows a numerical calculation of the vibration displacement ⁇ L in the thickness direction by using the finite element method by changing the resonance frequency f m2 of the radial expansion vibration in the piezoelectric body 8 formed using the composite perovskite piezoelectric material. It is an example of the result.
- the horizontal axis shows the normalized frequency of the alternating electric field applied to the piezoelectric body 8, and shows the value of the resonance frequency f m2 when the resonance frequency f m1 is 1.
- the vertical axis represents the vibration displacement ⁇ L.
- the minimum value ⁇ of the vibration displacement ⁇ L Lma and ⁇ Lmb are extremely small. That is, it can be understood that vibration displacement in the thickness direction of the piezoelectric body 8 is hardly obtained at the frequencies indicating the minimum values ⁇ Lma and ⁇ Lmb . Further, almost no vibration displacement in the radial direction could be obtained. Therefore, it can be seen that in the frequency characteristic a and the frequency characteristic b, the two resonance modes do not affect each other and vibrate independently.
- the minimum values ⁇ Lmc and ⁇ Lmd of the vibration displacement ⁇ L are larger than the minimum values ⁇ Lma and ⁇ Lmb . That is, by bringing the resonance frequency f m2 closer to the resonance frequency f m1 , the vibration displacement ⁇ L in the thickness direction shows a value greater than a certain value, and the piezoelectric body 8 under such conditions excites the resonance mode. Between the frequencies, vibration mode-coupled to the piezoelectric body 8 can be excited.
- the frequency characteristic shows a waveform such as the frequency characteristic c or the frequency characteristic d.
- mode coupling occurs in the piezoelectric body 8.
- the frequency indicating the first resonance mode of the piezoelectric body 8 is f m1 and the frequency indicating the second resonance mode is f m2 , the frequency indicating the first resonance mode and the frequency indicating the second resonance mode.
- the dimensional ratio L / D of the piezoelectric body 8 may be adjusted as appropriate. By adjusting the dimensional ratio L / D, it is possible to adjust the frequency f m1 indicating the first resonance mode and the frequency f m2 indicating the second resonance mode.
- FIG. 6 shows an example in which the piezoelectric body 8 is formed using a composite perovskite piezoelectric material.
- a piezoelectric ceramic such as a PZT ceramic
- the result of the same numerical calculation shows that f m1
- mode coupling occurs in the piezoelectric body 8 when / f m2 is 0.4 or more. Accordingly, it is considered that mode coupling occurs in the piezoelectric body 8 if f m1 / f m2 is at least 0.4 or more, not limited to the composite perovskite piezoelectric material.
- the impedance of the piezoelectric body 8 is low at the resonance frequency fm1 .
- the power source connected to the ultrasonic vibrator 7 tends to flow more current.
- the burden on the power source becomes large or no current flows.
- the impedance of the piezoelectric body 8 is relatively high in the frequency band in which mode-coupled vibration can be excited, the ultrasonic vibrator 7 can be stabilized without adversely affecting the power source as described above. It is possible to drive.
- the piezoelectric body 8 of the first embodiment it is possible to obtain the sound reproducing device 1 that can exhibit stable performance against stress received from the surroundings due to a disturbance such as a temperature change or vibration. Details thereof will be described below.
- FIG. 7 is a diagram showing frequency characteristics of vibration displacement with respect to the mechanical quality factor Qm of the piezoelectric body in the first embodiment of the present invention.
- FIG. 7 shows only the frequency characteristics of the vibration displacement ⁇ L in FIG. 5, and the horizontal and vertical axes indicate the minimum value ⁇ Lm of the vibration displacement in the frequency band in which mode-coupled vibration can be excited, Each is shown normalized based on the frequency f Lm at that time.
- the solid line indicates the frequency characteristics when the piezoelectric body 8 is unloaded without disturbance, and the dotted line indicates the frequency characteristics when stress is applied to the piezoelectric body 8 from the outside.
- the frequency f m1 and the frequency f m2 In the vicinity of the respective resonance frequencies for exciting the first and second resonance modes, the frequency f m1 and the frequency f m2 , the mechanical quality factor Qm of the resonance mode varies and the vibration displacement ⁇ L varies greatly depending on the presence or absence of stress. I understand that.
- the mechanical quality factor Qm becomes low and the vibration displacement ⁇ L is unloaded. It is reduced to about 1/5 of the case.
- the vibration displacement ⁇ L is hardly reduced even when the same stress is applied.
- FIG. 7 shows that the susceptibility to the vibration displacement of the ultrasonic vibrator 7 due to the load fluctuation from the outside varies depending on the frequency of the AC electric field applied to the ultrasonic vibrator 7.
- FIG. 7 shows that in a frequency band in which mode-coupled vibration can be excited, it is difficult to be affected by vibration displacement due to load fluctuations.
- the piezoelectric body 8 is affected by disturbance such as temperature change, vibration, and support fixing conditions. Even when stress is applied, the change in the vibration displacement ⁇ L is small. As a result, it is possible to obtain the sound reproducing device 1 that can reproduce sound waves in a wide band and an audible band having a stable sound pressure.
- the ultrasonic vibrator 7 may be affected by heat generated when the sound reproducing device 1 of the first embodiment is driven. That is, when the temperature of the ultrasonic vibrator 7 changes, the sound velocity of the piezoelectric body 8 changes, and this change affects the resonance frequency of the ultrasonic vibrator 7.
- the piezoelectric ceramic used as the piezoelectric body 8 has a high temperature dependency of the resonance frequency and low stability of the resonance frequency with respect to a temperature change. Therefore, when a frequency in the vicinity of the resonance frequency is used as the frequency of the carrier wave, it is considered that a desired sound pressure cannot be obtained if the resonance frequency changes due to a temperature change.
- the frequency of the carrier wave a part of the frequency band that can excite mode-coupled vibration that is not easily affected by temperature change is used as the frequency of the carrier wave. Even if the temperature of the ultrasonic vibrator 7 changes due to heat, sound waves in the audible band having a stable sound pressure can be reproduced.
- the frequency of the carrier wave is preferably selected in a frequency band in which mode-coupled vibration can be excited, in particular, based on the frequency at which the vibration displacement ⁇ L of the ultrasonic transducer 7 is minimized.
- FIG. 8 is a diagram showing that a specific frequency band centered on the frequency f Lm at which the vibration displacement takes the minimum value ⁇ Lm is used as the frequency of the carrier wave in the first embodiment of the present invention.
- the frequency band including the frequency f Lm for example, the constant frequency band f Lm ⁇ ⁇ f centered on the frequency f Lm is used as the carrier frequency, so that the sound pressure of the sound wave in the audible band to be reproduced is further stabilized.
- Bandwidth can be expanded.
- FIG. 9 is a diagram showing the relationship between the frequency at which the admittance takes a maximum value and the minimum value of vibration displacement in the thickness direction when the dimensional ratio is changed in the piezoelectric body according to the first embodiment of the present invention.
- FIG. 9 shows a resonance frequency f m1 of longitudinal vibration in the thickness direction, a resonance frequency f m2 of radial expansion vibration, and excitation between these two resonance modes in the piezoelectric body 8 formed using the composite perovskite piezoelectric material.
- the maximum displacement ⁇ Lm in the mode-coupled vibration that can be performed is obtained by numerical calculation by the finite element method by changing the dimensional ratio L / D of the piezoelectric body 8.
- the horizontal axis is a standardized dimension ratio L / D of the piezoelectric body 8.
- the left axis of the vertical axis is a frequency normalized based on the frequency f Lm when the dimensional ratio L / D is 1.
- the axis on the right side of the vertical axis is the vibration displacement normalized based on the vibration displacement ⁇ Lm in the thickness direction when the dimension ratio L / D is 1.
- the frequency f m1 is a solid line
- the frequency f m2 is a one-dot chain line
- the vibration displacement ⁇ Lm is a wavy line.
- the vibration displacement ⁇ Lm in the mode-coupled vibration increases as the size ratio L / D of the piezoelectric body 8 increases, and when the size ratio L / D is around 0.7 and the size ratio L / D is 1. It can be seen that the maximum value is about 1.7 times the value of, and then decreases. For this reason, in the first embodiment, the dimension ratio L / D is set to 0.7 at which the vibration displacement ⁇ Lm is maximized.
- the dimensional ratio L / D of the piezoelectric body 8 is not limited to 0.7, but within a range of ⁇ 0.3 centered on 0.7 where the vibration displacement ⁇ Lm takes the maximum value, that is, the dimensional ratio.
- L / D should just be a value of 0.4-1.0. If the dimensional ratio L / D is a value of 0.4 or more and 1.0 or less, the piezoelectric body 8 can efficiently vibrate with respect to the applied AC electric field, and sound waves can be emitted from the ultrasonic transducer 7. As an acoustic reproduction device, it is possible to output sound waves in the audible band efficiently.
- the vibration loss of the piezoelectric body 8 increases, and therefore the vibration amplitude with respect to the applied AC electric field. Becomes smaller.
- the sound wave radiated from the ultrasonic vibrator 7 becomes small, and the heat generated by the vibration loss adversely affects the material characteristics of the piezoelectric body 8, which increases the possibility of deteriorating the operation reliability of the ultrasonic vibrator 7. .
- the piezoelectric body 8 is formed using a composite perovskite piezoelectric material
- the same numerical calculation and prototyping are performed even when the piezoelectric ceramic such as PZT ceramic or the material such as the piezoelectric single crystal is different.
- the examination it is possible to determine the optimum dimensional ratio L / D of the cylindrical piezoelectric body 8.
- the sound emitting unit 6 is configured by one ultrasonic transducer.
- the sound emitting unit is configured by a plurality of ultrasonic transducers 7 will be described below.
- FIG. 10 is a front view of the sound emitting unit in the second embodiment of the present invention.
- the sound emitting unit 14 in the second embodiment is configured by arranging a plurality of ultrasonic transducers 7 in a plane.
- FIG. 11 is a diagram illustrating the frequency characteristics of the admittance and vibration displacement of the piezoelectric bodies of the three ultrasonic transducers according to the second embodiment of the present invention.
- FIG. 11 shows the frequency characteristics of the admittances and the frequency characteristics of the vibration displacement of the piezoelectric bodies 8 constituting the three ultrasonic vibrators 7 among the ultrasonic vibrators 7 constituting the sound emitting unit 14 of FIG.
- the admittance Y 1 and the vibration displacement ⁇ L1 , the admittance Y 2 and the vibration displacement ⁇ L2 , and the admittance Y 3 and the vibration displacement ⁇ L3 indicate the admittance of the same piezoelectric body 8 and the frequency characteristics of the vibration displacement, respectively. ing.
- the admittance Y 1 , admittance Y 2 , admittance Y 3 , vibration displacement ⁇ L1 , vibration displacement ⁇ L2 , and vibration displacement ⁇ L3 of the three piezoelectric bodies 8 do not have exactly the same frequency characteristics. Cause misalignment. This is due to variations in manufacturing conditions, material characteristics, and shape dimensions when the piezoelectric body 8 is manufactured. Furthermore, since variations in assembling the ultrasonic vibrator 7 by supporting and fixing the piezoelectric body 8 are also affected, in the admittance of a plurality of ultrasonic vibrators 7 constituting the sound emitting unit 14 or the frequency characteristics of vibration displacement, The resonance frequency that can excite the resonance mode also varies.
- each ultrasonic vibrator 7 When a plurality of ultrasonic vibrators 7 having the same resonance frequency are used and the frequency of the carrier wave is fixed near the frequency f m1 or the frequency f m2 and the sound reproducing apparatus is configured, each ultrasonic vibrator 7 The sound pressure level of the sound wave emitted from the sound source varies, and as a result, it may be difficult to obtain a stable sound pressure when the sound wave in the audible band is demodulated.
- the frequency of the carrier wave is not a resonance frequency that excites the resonance mode, but a frequency that can excite mode-coupled vibration excited between the resonance modes. A part of the band is used.
- the piezoelectric body 8 in the second embodiment is the same as the piezoelectric body 8 in the first embodiment, and has a cylindrical shape with a dimensional ratio L / D between the thickness L and the diameter D of 0.7. It is a piezoelectric body. With such a dimensional ratio, a part of a frequency band in which the sound emitting unit 14 is configured by a plurality of piezoelectric bodies 8 as shown in FIG. 10 and vibrations mode-coupled to the piezoelectric bodies 8 can be excited. Is the frequency of the carrier wave, electric fields having the same amplitude and the same frequency are applied to the respective piezoelectric bodies 8.
- the sound emitting unit 14 is an example in the case where there is an individual difference in the resonance frequency of the piezoelectric body 8 constituting the ultrasonic vibrator 7, but in the case where the sound emitting unit 14 is configured by the piezoelectric body 8 having the same resonance frequency. Even if it exists, it is effective. That is, the frequency characteristics of the vibration amplitude of the ultrasonic transducer 14 may change due to a temperature change of the ultrasonic transducer 14 during operation or stress applied to the piezoelectric body 8 when the ultrasonic transducer 14 is assembled. Even in such a case, the configuration of the second embodiment can be applied.
- the sound reproducing device 1 according to the second embodiment in FIG. 10 is illustrated as a configuration in which the ultrasonic transducers 7 in the sound emitting unit 14 are densely arranged in a honeycomb shape, but the arrangement method is not limited thereto. However, the same effect can be obtained as long as the sound wave emitted from the sound emitting unit can be efficiently collected at a predetermined position.
- FIG. 12 is a cross-sectional view of the ultrasonic transducer 15 according to the third embodiment.
- the configuration of the ultrasonic transducer 7 shown in the first embodiment is partially different. Since the configuration other than this is the same as that of the first embodiment, the same portions are denoted by the same reference numerals, detailed description thereof is omitted, and only different portions will be described.
- the case 16 has a bottomed cylindrical shape, and the piezoelectric body 8 is placed at the center of the inner bottom surface of the case 16.
- Two rod-shaped terminals 12 are provided on the inner bottom surface of the case 16, and these terminals 12 are electrically connected to the electrodes of the piezoelectric body 8 through lead wires 13 as in the first embodiment.
- the case 16 is made of aluminum.
- a conical resonator 17 is fixed to the central portion of the upper end surface of the piezoelectric body 8 with an adhesive.
- the material of the resonator 17 is preferably light and has a sound velocity of about 3,000 to 10,000 m / s.
- the resonator 17 capable of following the amplitude of the piezoelectric body 8 can be configured, and the vibration mode remains unchanged without changing the vibration mode shape.
- the amplitude can be amplified by That is, the resonator 17 according to the third embodiment exhibits resonance characteristics corresponding to the vibration of the piezoelectric body 8 and can emit a stable ultrasonic wave to a medium such as air with respect to the amplitude of the piezoelectric body 8.
- the resonator 17 is also surrounded by the case 16 as shown in FIG.
- the resonator 17 is provided so that the diameter of the sound source can be increased and the sound pressure output can be improved.
- the sound reproduction device 1 according to Embodiment 1 since the sound reproduction device 1 according to Embodiment 1 outputs ultrasonic waves having high directivity, it is possible to reproduce sound waves in the audible band only in a very narrow spatial range.
- the resonator 17 is provided like the ultrasonic transducer 15 of the third embodiment, and the directivity of the sound reproducing device 1 is expanded. Can be supported.
- each ultrasonic transducer 15 is formed by the resonator 17 as described above. It has the characteristic that directivity is expanded to some extent. For this reason, the radiation range of the ultrasonic wave output from each ultrasonic transducer 15 is likely to overlap with the ultrasonic radiation range of the ultrasonic transducer 15 disposed in the vicinity thereof. That is, at the positions where the radiation ranges overlap, the ultrasonic waves output from the ultrasonic transducers 15 are added together, so that the sound waves in the audible band to be reproduced can be heard with a higher sound pressure. It becomes possible.
- the directivity by the resonator 17 can be adjusted by appropriately changing the angle of the conical portion of the resonator 17.
- the circular part of the cone is not limited to a perfect circle and may be an ellipse.
- the shape of the piezoelectric body 8 constituting the ultrasonic vibrator 7 is a cylindrical shape, and the vibration excited by the piezoelectric body 8 is the resonance vibration of the thickness direction longitudinal vibration and the radial expansion.
- the case where the vibration in which the resonance vibration of the vibration is mode-coupled has been described.
- the present invention is not limited to a specific shape or a specific resonance mode with respect to the shape of the piezoelectric body and the vibration mode excited in the piezoelectric body.
- the same effect can be obtained even when the piezoelectric body 8 is formed in a prismatic shape and vibration in which the thickness direction longitudinal vibration and the resonance vibration of the diagonal direction or side direction vibration are mode-coupled is used.
- the sound reproducing apparatus of the present invention can stabilize the sound pressure of sound waves in the audible band to be reproduced in a wide band by setting a part of the frequency band capable of exciting mode-coupled vibration as the frequency of the carrier wave. .
- it is useful as a sound reproducing device that reproduces sound waves in the audible band only in a limited spatial range.
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- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Acoustics & Sound (AREA)
- Signal Processing (AREA)
- Transducers For Ultrasonic Waves (AREA)
- Circuit For Audible Band Transducer (AREA)
- Piezo-Electric Transducers For Audible Bands (AREA)
Abstract
Description
以下、図を用いて、本実施の形態1における音響再生装置の構成について説明する。図1は、本発明の実施の形態1における音響再生装置のブロック図である。図1は、本発明の音響再生装置1の駆動部を説明する。
実施の形態1は、放音部6を1つの超音波振動子で構成したが、本実施の形態2では、複数の超音波振動子7で放音部を構成する一例について以下に説明する。
以下、図12を用いて、実施の形態3における超音波振動子15の構成について説明する。図12は本実施の形態3における超音波振動子15の断面図である。
2 可聴帯域信号源
3 搬送波発振器
4 変調器
5 パワーアンプ
6 放音部
7 超音波振動子
8 圧電体
9 音響整合層
10 ケース
11 端子台
12 端子
13 リード線
14 放音部
15 超音波振動子
16 ケース
17 共振子
Claims (6)
- 可聴帯域の信号を生成する可聴帯域信号源と、
搬送波を生成する搬送波発振器と、
前記可聴帯域の信号と前記搬送波とを変調する変調器と、
前記変調器から出力された信号を超音波振動子により音波として出力する放音部とを備え、
前記超音波振動子は、異なる周波数で振動変位が極大となる複数の共振モードを有し、前記複数の共振モードを励振する周波数の間でモード結合した振動を励振し、
前記モード結合した振動を励振することができる周波数帯域の一部を前記搬送波の周波数とする音響再生装置。 - 前記複数の共振モードを励振する周波数のうち、隣接し合う周波数を小さい周波数からfm1、fm2とした時、これら周波数の比fm1/fm2を0.4以上とした請求項1に記載の音響再生装置。
- 前記モード結合した振動を励振することができる周波数帯域の一部が、前記超音波振動子の振動変位が極小となる周波数を基準として選択された請求項1に記載の音響再生装置。
- 前記超音波振動子は円柱形状の圧電体を有し、前記圧電体の厚さをL、直径をDとした時、前記円柱形状の圧電体の寸法比L/Dを0.4~1.0とした請求項1に記載の音響再生装置。
- 前記超音波振動子は圧電体を有し、前記圧電体の中央部上面に略円錐形状の共振子が固定されている請求項1に記載の音響再生装置。
- 前記放音部は、複数の超音波振動子から成る請求項1に記載の音響再生装置。
Priority Applications (4)
Application Number | Priority Date | Filing Date | Title |
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EP09814308.4A EP2328359B1 (en) | 2008-09-18 | 2009-09-17 | Sound reproducing apparatus |
KR1020117006151A KR101181188B1 (ko) | 2008-09-18 | 2009-09-17 | 음향 재생 장치 |
CN2009801366008A CN102160399B (zh) | 2008-09-18 | 2009-09-17 | 声音再生装置 |
US13/061,762 US9100755B2 (en) | 2008-09-18 | 2009-09-17 | Sound reproducing apparatus for sound reproduction using an ultrasonic transducer via mode-coupled vibration |
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JP2008239129A JP5444670B2 (ja) | 2008-09-18 | 2008-09-18 | 音響再生装置 |
JP2008-239129 | 2008-09-18 |
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US (1) | US9100755B2 (ja) |
EP (1) | EP2328359B1 (ja) |
JP (1) | JP5444670B2 (ja) |
KR (1) | KR101181188B1 (ja) |
CN (1) | CN102160399B (ja) |
WO (1) | WO2010032463A1 (ja) |
Cited By (1)
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JP2014064204A (ja) * | 2012-09-21 | 2014-04-10 | Taiheiyo Cement Corp | 超音波発音体およびパラメトリックスピーカ |
Families Citing this family (7)
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JP5444670B2 (ja) | 2008-09-18 | 2014-03-19 | パナソニック株式会社 | 音響再生装置 |
JP5609384B2 (ja) * | 2010-07-29 | 2014-10-22 | 日本電気株式会社 | 携帯端末装置 |
US9402137B2 (en) * | 2011-11-14 | 2016-07-26 | Infineon Technologies Ag | Sound transducer with interdigitated first and second sets of comb fingers |
ES2375857B1 (es) * | 2012-01-13 | 2012-09-12 | Universitat Ramón Llull Fundació Privada | Fuente sonora omnidireccional y procedimiento para generar sonidos omnidireccionales. |
CN103237279A (zh) * | 2012-08-07 | 2013-08-07 | 瑞声声学科技(深圳)有限公司 | 指向性扬声器装置及其使用方法 |
JP6221135B2 (ja) * | 2013-06-27 | 2017-11-01 | 日本特殊陶業株式会社 | 超音波発音体、超音波素子およびこれを用いたパラメトリックスピーカ |
CN108924277A (zh) * | 2018-05-31 | 2018-11-30 | 业成科技(成都)有限公司 | 面板结构 |
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US9100755B2 (en) | 2015-08-04 |
JP5444670B2 (ja) | 2014-03-19 |
CN102160399A (zh) | 2011-08-17 |
KR20110054018A (ko) | 2011-05-24 |
KR101181188B1 (ko) | 2012-09-18 |
EP2328359A1 (en) | 2011-06-01 |
EP2328359A4 (en) | 2013-06-05 |
EP2328359B1 (en) | 2015-12-23 |
CN102160399B (zh) | 2013-11-27 |
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