JP6159984B2 - Ultrasonic sound generator and parametric speaker - Google Patents

Description

  The present invention relates to an ultrasonic sounding body that generates ultrasonic waves and a parametric speaker using the same.

  The ultrasonic sounding body includes a piezoelectric vibrator in which a diaphragm and a piezoelectric element are bonded. When an AC voltage near the resonance frequency inherent to the piezoelectric vibrator is applied to the piezoelectric element, the piezoelectric vibrator vibrates and emits ultrasonic waves. The resonance frequency is included in an ultrasonic band exceeding 20 kHz.

  Furthermore, by attaching a conical cylindrical resonator to the piezoelectric vibrator, it is possible to increase the sound pressure of the generated ultrasonic wave and to give the ultrasonic wave directivity forward. The ultrasonic sounding body is fixed by adhering a node that does not move in the bending vibration of the piezoelectric vibrator with a silicon adhesive or the like so as to prevent the vibration as much as possible. The ultrasonic sounding body has the same structure as the ultrasonic sensor, but the ultrasonic sensor transmits and receives ultrasonic waves, and the ultrasonic sounding body only transmits ultrasonic sensors. ing.

  The parametric speaker is configured by arranging a plurality of such ultrasonic sounding bodies (see, for example, Patent Documents 1 and 2). The ultrasonic waves generated by the ultrasonic sound generators of the parametric loudspeakers overlap in the air and are demodulated into audible sounds when they reach a certain sound pressure. In addition, since an audible sound is generated only at the central position where the ultrasonic waves overlap, the parametric speaker functions as a speaker having a sharp directivity.

On the other hand, a piezoelectric ceramic material having a high mechanical quality factor Qm and characteristics suitable for use of an ultrasonic vibrator or the like is disclosed (for example, see Patent Document 3). The piezoelectric material described in Patent Document 3 contains Bi, Na, Ti, Ba, Mn, Nb, and O, and has a general formula: (1-xy) (Bi _0.5 Na _0.5 ) TiO ₃ -xBaTiO ₃ This is a piezoelectric ceramic material represented by -yBa (Mn _1/3 Nb _2/3 ) O ₃ .

JP 60-167597 A Japanese Patent Laid-Open No. 62-296698 JP 2007-137704 A

  In the ultrasonic sounding body and ultrasonic sensor as described above, a high sound pressure can be obtained by setting the driving frequency to the resonance frequency at which the piezoelectric vibrator vibrates most. However, when driving at the resonance frequency, sound pressure can be obtained, but heat generation of the piezoelectric vibrator is large. Further, when the temperature of the piezoelectric vibrator rises, the resonance frequency is lowered as shown in FIG. 8, and the resonance frequency is separated from the set drive frequency, so that the sound pressure is lowered.

  Since the ultrasonic sensor alternately performs transmission and reception by intermittent driving, the temperature rise of the piezoelectric vibrator is small. On the other hand, since the ultrasonic sound generator constitutes a parametric speaker and is continuously driven, the temperature rise of the piezoelectric vibrator becomes large, and the sound pressure is lowered due to the above situation. Therefore, an ultrasonic sounding body for a parametric speaker that is continuously driven is desired to have a small temperature rise and prevent a decrease in sound pressure and to emit high sound pressure ultrasonic waves.

  The present invention has been made in view of such circumstances, and it is an object of the present invention to provide an ultrasonic sounding body and a parametric speaker that can suppress a temperature rise even when the applied voltage is increased to increase the sound pressure. And

  (1) In order to achieve the above object, an ultrasonic sounding body of the present invention is an ultrasonic sounding body for a parametric speaker that generates ultrasonic waves, and a piezoelectric material having a mechanical quality factor Qm of 100 or more is used. A piezoelectric vibrator formed by a piezoelectric element used and a diaphragm in which the piezoelectric element is bonded to one main surface, and an ultrasonic wave generated by vibration of the diaphragm provided on the other main surface of the diaphragm And a resonator to be provided.

  Thus, since the ultrasonic sounding body of the present invention uses a piezoelectric material having a mechanical quality factor Qm of 100 or more, even if the applied voltage is increased and the sound pressure is increased, the temperature rise can be suppressed. it can. In addition, since the ultrasonic sounding body of the present invention is for a parametric speaker, it is not necessary to receive ultrasonic waves, and it is not necessary to contain vibration in a short time, and a piezoelectric material having a large Qm can be used. Yes.

  (2) Further, the ultrasonic sounding body of the present invention is characterized in that the piezoelectric material used for the piezoelectric element has a mechanical quality factor Qm of 600 or more. Thereby, even if the applied voltage is increased to increase the sound pressure, the temperature rise can be suppressed.

  (3) In addition, the ultrasonic sounding body of the present invention is characterized in that the ultrasonic sound pressure generated can be maintained at 122.5 dB or more even when the temperature rises by 20 ° C. Thereby, a sufficiently large sound pressure can be maintained when the allowable range of temperature rise is 20 ° C.

  (4) Moreover, the parametric speaker of the present invention includes a flat substrate provided with a wiring pattern, a support member provided on the substrate, and the ultrasonic sounding body supported by the support member, A plurality of the ultrasonic sounding bodies are provided, and by continuously driving the ultrasonic sounding body, an audible sound is caused to appear due to non-linear characteristics when ultrasonic waves propagate.

  In this way, by configuring a parametric speaker with an ultrasonic sound generator using a piezoelectric material having a large Qm, the individual sound pressure of the ultrasonic sound generator can be increased, and a sufficient number of sound pressures can be obtained with a small number. Can be obtained. As a result, the parametric speaker can be reduced in size.

  According to the present invention, even if the applied voltage is increased to increase the sound pressure, the temperature rise of the ultrasonic sounding body can be suppressed to a low level.

It is a front view which shows the parametric speaker of this invention. It is a side view which shows the structure of the ultrasonic sounding body of this invention. (A), (b) is a side view which shows one scene of operation | movement of the ultrasonic sounding body of this invention. It is a block diagram which shows the electric constitution of a parametric speaker. It is a graph which shows an experimental result by the relationship of the temperature rise with respect to a sound pressure. It is a graph which shows an experimental result by the temperature rise with respect to the mechanical quality factor Qm. It is a graph which shows an experimental result by the relationship of the sound pressure with respect to the mechanical quality factor Qm. It is a graph which shows the relationship between the resonant frequency and impedance in each temperature of a piezoelectric vibrator.

  Next, embodiments of the present invention will be described with reference to the drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same components in the respective drawings, and duplicate descriptions are omitted.

(Configuration of parametric speaker)
FIG. 1 is a front view showing the parametric speaker 100. The parametric speaker 100 generates an ultrasonic wave modulated with a strong sound pressure and causes an audible sound to appear due to nonlinear characteristics when the ultrasonic wave propagates through the air. In this way, it is possible to specify the direction and distance and give directivity to convey acoustic information.

  As shown in FIG. 1, the parametric speaker 100 is configured by providing a plurality of ultrasonic sounding bodies 110 on a substrate 120. The ultrasonic sounding body 110 generates ultrasonic waves based on the modulation signal. The substrate 120 fixes and supports the ultrasonic sounding body 110. In addition, in FIG. 1, the external appearance structure is shown and the electrical configuration is omitted.

  By forming the parametric speaker 100 with the ultrasonic sounding body 110 using a piezoelectric material having a large Qm, the individual sound pressure of the ultrasonic sounding body 110 can be increased, and sufficient sound pressure can be obtained with a small number. be able to. As a result, the parametric speaker 100 can be reduced in size.

(Configuration of ultrasonic sound generator)
FIG. 2 is a side view showing the configuration of the ultrasonic sounding body 110. The ultrasonic sounding body 110 is used for the parametric speaker 100 and generates ultrasonic waves. Since the ultrasonic sounding body 110 is for a parametric speaker, it is not necessary to receive ultrasonic waves, and it is not necessary to contain vibration in a short time, and a large Qm piezoelectric material can be used. The ultrasonic sounding body 110 generates a modulated ultrasonic signal by applying a voltage. The ultrasonic sounding body 110 includes a piezoelectric element 111, a diaphragm 112, lead wires 113a and 113b, and a resonator 114.

  The piezoelectric element 111 is formed in a plate shape using a piezoelectric material having a mechanical quality factor Qm of 100 or more, and expands and contracts by applying a voltage in the thickness direction. Thus, since the piezoelectric material having a mechanical quality factor Qm of 100 or more is used, even if the applied voltage is increased and the sound pressure is increased, the temperature rise can be suppressed.

  The piezoelectric material used for the piezoelectric element 111 preferably has a mechanical quality factor Qm of 600 or more. Thereby, even if an ultrasonic wave having a sound pressure of 122.5 dB is generated, the temperature rise is 20 ° C. or less, and even if the applied voltage is increased to increase the sound pressure, the temperature rise can be suppressed. Further, it is more preferable that the piezoelectric material used for the piezoelectric element 111 has a mechanical quality factor Qm of 1000 or more. Thereby, even if an ultrasonic wave having a sound pressure of 123 dB is generated, the temperature rise is 20 ° C. or less.

  The piezoelectric element 111 is installed by being bonded to one main surface of the diaphragm 112. In the piezoelectric element 111, the other main surface of the vibration plate 112 is a vibration surface, and ultrasonic waves can be generated via the vibration surface.

  The resonator 114 is formed in a conical cylinder shape, and is made of, for example, aluminum or an aluminum alloy. The conical cylinder shape includes a parabolic shape or a funnel shape. The resonator 114 is provided on the other main surface of the diaphragm 112 and resonates with the vibration of the diaphragm 112 to generate an ultrasonic wave. Electrodes are formed on both principal surfaces of the piezoelectric element 111, and the piezoelectric body of the main body is polarized in the thickness direction. The diaphragm 112 has a piezoelectric element 111 bonded to one main surface. The diaphragm 112 is formed in a disk shape from a metal such as brass, SUS304, 42 alloy or aluminum. The piezoelectric element 111 and the diaphragm 112 form a piezoelectric vibrator 115.

  Even in the case of the ultrasonic sounding body 110, when a material having a large mechanical quality factor Qm is selected as in the case of the ultrasonic sensor, tailing of the ultrasonic pulse waveform increases. In the ultrasonic sensor, when the ultrasonic wave is reflected back to an obstacle or the like and the vibration of the vibrator is not settled, the timing at which the ultrasonic wave returns cannot be determined, and the sensor function cannot be performed. The tailing of the above pulse waveform is a problem. In the ultrasonic sensor, vibration is reduced in a short time by using a small Qm material.

  On the other hand, an ultrasonic sounding body for a parametric speaker is specialized for transmitting ultrasonic waves, and the above-described problems do not occur. Since the ultrasonic sounding body 110 does not receive ultrasonic waves unlike an ultrasonic sensor, it is not necessary to quickly receive vibration, but rather it is preferable to vibrate using a material having a large Qm.

(Operation of ultrasonic sound generator)
3 (a) and 3 (b) are side views showing one scene of the operation of the ultrasonic sounding body 110 of the present invention. As shown in FIGS. 3A and 3B, the ultrasonic sounding body 110 bends and vibrates when an AC voltage is applied to the electrodes on both principal surfaces of the piezoelectric element 111 polarized in the thickness direction. At that time, a voltage is applied using the resonance frequency of the piezoelectric vibrator 115 as a driving frequency. At this time, if the mechanical quality factor Qm of the piezoelectric material is high, it is difficult for electric energy to be consumed as heat, and even if the sound pressure is increased, the temperature rise can be suppressed small.

(Method for producing ultrasonic sound generator)
A method for producing the ultrasonic sounding body 110 will be described. First, a piezoelectric element 111 is formed by forming a plate-like piezoelectric body with a piezoelectric material having a Qm of 100 or more (more preferably 600 or more), and providing an electrode for polarization. The piezoelectric element 111 is bonded to one main surface of the diaphragm 112. Then, the lead wires 113a and 113b are connected to electrodes or the diaphragm 112 at predetermined positions. The resonator 114 is bonded to the other main surface of the diaphragm 112. In this way, the ultrasonic sounding body 100 can be produced.

(Electric configuration of parametric speaker)
FIG. 4 is a block diagram showing an electrical configuration of the parametric speaker 100. As shown in FIG. 4, the parametric speaker 100 includes an oscillator 101, a modulator 102, an amplifier 105, and an ultrasonic sounding body 110, and generates ultrasonic waves through these. The oscillator 101 oscillates a signal at a predetermined frequency in the ultrasonic band. The frequency to be oscillated is a drive frequency for driving the piezoelectric element 111 when the oscillation signal is transmitted to the ultrasonic sounding body 110, and is determined in advance according to the application of the parametric speaker 100.

  The modulator 102 AM modulates the oscillation signal with the audio signal. The modulation may be DSB modulation, SSB modulation, or FM modulation instead of AM modulation. The amplifier 105 amplifies the modulated oscillation signal and outputs it to the ultrasonic sounding body 110. The ultrasonic sounding body 110 converts the amplified oscillation signal into a sound wave.

  The parametric speaker 100 configured as described above oscillates a signal having a frequency in the ultrasonic band, modulates the oscillation signal with a desired audio signal, amplifies the modulation signal, and converts it into a sound wave with the ultrasonic sound generator 110. Then radiate. In this way, ultrasonic waves with sharp directivity can be emitted. For example, since guidance can be selectively sent to people in a narrow area, it can be used for museums, aquariums, museums, amusement facilities, and the like. In the future, it can also be used for traffic information.

(Example)
An ultrasonic sounding body was produced with piezoelectric elements using piezoelectric materials of different Qm, and the sound pressure was changed by adjusting the applied voltage, and each was continuously driven to measure the temperature rise. 5 to 7 are graphs showing experimental results from different viewpoints.

  FIG. 5 is a graph showing experimental results with a temperature rise relative to the sound pressure. FIG. 5 shows the temperature rise with respect to the sound pressure when saturated. The higher the sound pressure and the lower the temperature rise, the better the characteristics. It can be seen that an ultrasonic sounding body (Qm500 sample) using a piezoelectric material of Qm500 has characteristics close to an ultrasonic sounding body (Qm1350 sample) using a piezoelectric material of Qm1350, and a sample having a higher Qm has better characteristics.

  FIG. 6 is a graph showing an experimental result with a temperature increase with respect to the mechanical quality factor Qm. FIG. 6 shows the sound pressure with respect to Qm at each temperature rise. According to FIG. 6, for example, when the sound pressure is 117 dB, the temperature rise of the ultrasonic sounding body (Qm60 sample) using the piezoelectric material of Qm60 is 10.9 ° C., the temperature rise of the Qm500 sample is 6.0 ° C., and Qm 1350. The temperature rise of the sample is 5.0 ° C. Therefore, it can be seen that the sample with a larger Qm suppresses the temperature rise.

  FIG. 7 is a graph showing experimental results with sound pressure with respect to the mechanical quality factor Qm. According to FIG. 7, the temperature increase of 10 ° C. is 116.3 dB for the Qm60 sample, 119.1 dB for the Qm500 sample, and 120.0 dB for the Qm1350 sample. Thus, under the same temperature rise condition, the higher the mechanical quality factor Qm, the higher the sound pressure is obtained.

  From the above results, assuming the time of practical use, a difference occurs in the maximum sound pressure that can be produced with respect to the allowable range of temperature rise. For example, when the allowable temperature rise is up to + 20 ° C., the maximum sound pressure is 120.5 dB for the Qm50 sample, 122.3 dB for the Qm500 sample, and 123.7 dB for the Qm1350 sample. When 3 dB is higher, one ultrasonic sounding body can emit ultrasonic waves corresponding to 1.4. Therefore, the larger the Qm of the material, the larger the sound pressure can be obtained with respect to the constant temperature rise allowable range. As a result, the number of ultrasonic sounding bodies can be reduced, and the parametric speaker can be miniaturized.

100 Parametric Speaker 101 Oscillator 102 Modulator 105 Amplifier 110 Ultrasonic Sound Generator 111 Piezoelectric Element 112 Diaphragm 113a, 113b Lead Wire 114 Resonator 115 Piezoelectric Vibrator 120 Substrate

Claims (4)

An ultrasonic sounding body for a parametric speaker that generates ultrasonic waves,
A piezoelectric element using a piezoelectric material having a mechanical quality factor Qm of 600 or more, and a piezoelectric vibrator formed by a diaphragm having the piezoelectric element bonded to one main surface;
A resonator that is provided on the other main surface of the diaphragm and generates ultrasonic waves by vibration of the diaphragm ;
Ultrasonic sounding body, characterized in Rukoto to maintain the ultrasonic sound pressure also generates when there is a temperature rise of 20 ° C. or more 122.5DB. The ultrasonic sounding body according to claim 1, wherein the piezoelectric material used for the piezoelectric element has a mechanical quality factor Qm of 1000 or more. The ultrasonic sounding body according to claim 1 or 2, wherein the piezoelectric material used for the piezoelectric element has a mechanical quality factor Qm of 1350 or less . A flat substrate provided with a wiring pattern;
A support member provided on the substrate;
The ultrasonic sounding body according to any one of claims 1 to 3, which is supported by the support member,
A parametric speaker, wherein a plurality of the ultrasonic sounding bodies are provided, and an audible sound is caused to appear by non-linear characteristics when ultrasonic waves propagate by continuously driving the ultrasonic sounding body.

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