JP6221135B2 - Ultrasonic sound generator, ultrasonic element, and parametric speaker using the same - Google Patents

Description

  The present invention relates to an ultrasonic sound generator, an ultrasonic element, and a parametric speaker using the same, which are used as an oscillation source.

  The ultrasonic sounding body includes a piezoelectric vibrator in which a metal plate and a piezoelectric element are bonded. The piezoelectric vibrator vibrates by applying an alternating voltage in the vicinity of the resonance frequency unique to the piezoelectric vibrator and emits ultrasonic waves. An ultrasonic sounding body is called an “ultrasonic” sounding body because its resonance frequency is in the ultrasonic band (above 20 kHz).

  In addition, by attaching a conical cylinder-shaped (including parabolic or funnel-shaped) resonator made of aluminum or an aluminum alloy to the piezoelectric vibrator, sound pressure can be increased and forward directivity can be provided. Can do.

  The ultrasonic sounding body is fixed by bonding a node that does not move in the bending vibration of the piezoelectric vibrator with a silicon adhesive or the like so as not to disturb the vibration as much as possible. Note that the ultrasonic sounding body has the same structure as the ultrasonic sensor, the ultrasonic sensor transmits and receives ultrasonic waves, and the ultrasonic sounding body transmits only ultrasonic waves.

  A parametric speaker is composed of a plurality of ultrasonic sound generators arranged side by side, and the parametric speaker can be used from an ultrasonic wave when the ultrasonic waves generated by the ultrasonic sound generators reach a sound pressure that is superposed in the air. The sound is demodulated and can be heard. In addition, since only the central portion where the ultrasonic waves overlap is an audible sound, the speaker has a sharp directivity.

  For example, the ultrasonic transmitter described in Patent Document 1 uses light magnesium or a magnesium alloy as a material in order to reduce the size and weight of the resonator and increase the transmission sound pressure. On the other hand, Patent Document 1 also describes that in order to prevent distortion of the resonator, the natural frequency of the resonator should be outside the use band centered on a specific resonance frequency of the ultrasonic transmitter. .

JP 2007-88886 A

  However, as described above, the method of increasing the vibration width of the piezoelectric vibrator while reducing the size and weight of the resonator cannot always transmit ultrasonic waves with high efficiency. In addition, the resonance frequency of the ultrasonic transmitter described in the above-mentioned Patent Document 1 that the natural frequency of the resonator should be out of the band is considered to be the resonance frequency on the high frequency side, The vicinity of the resonance frequency has not been verified.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultrasonic sound generator, an ultrasonic element, and a parametric speaker using the ultrasonic sound generator capable of efficiently obtaining a high sound pressure. .

  (1) In order to achieve the above object, the ultrasonic sounding body of the present invention is an ultrasonic sounding body used as an oscillation source of a parametric speaker, and the plate-like piezoelectric element and the piezoelectric element are one of the main elements. A piezoelectric vibrator formed by a diaphragm bonded to a surface, and a resonator provided on the other main surface of the diaphragm and generating an ultrasonic wave by resonating with vibration of the diaphragm, It is characterized in that the frequency of the natural vibration of only the resonator matches the frequency of its own primary resonance.

  As a result, not only the entire ultrasonic transducer but also the resonator can resonate to obtain a high sound pressure. Further, when the sound pressure increases, the number of ultrasonic sounding bodies necessary for the parametric speaker can be reduced, and the parametric speaker can be made small and inexpensive.

  (2) Further, an ultrasonic element of the present invention is characterized by including the above-described ultrasonic sounding body and a support member that supports the ultrasonic sounding body with a vibration node. Thereby, a large sound pressure can be obtained without inhibiting the vibration of the ultrasonic sounding body.

  (3) A parametric speaker according to the present invention is a parametric speaker that emits ultrasonic waves from a plurality of oscillation sources, and includes the ultrasonic element and a wiring pattern, and the ultrasonic element is provided on the wiring pattern. And a flat substrate provided. Thereby, a large sound pressure can be obtained with a plurality of oscillation sources.

  According to the present invention, not only the entire ultrasonic transducer but also the resonator can resonate to obtain a high sound pressure.

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 the parametric speaker of this invention. It is a figure which shows the impedance characteristic of the ultrasonic sounding body of this invention. (A)-(c) It is a figure which shows the result of having simulated the vibration of the ultrasonic sounding body by the finite element method (FEM).

  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 is provided with a wiring pattern, is formed in a flat plate shape, and fixes and supports the ultrasonic sounding body 110. The support member is formed of a rubber material and is provided on the substrate, and supports the ultrasonic sounding body 110 with a vibration node. Thereby, since the movement of the ultrasonic sounding body 110 is not hindered, a large sound pressure can be obtained with a small number of oscillation sources. In addition, in FIG. 1, the external appearance structure is shown and the electrical configuration is omitted. The support member may be a resin terminal block provided with a ring-shaped protrusion. The ultrasonic sounding body 110 and the support member constitute an ultrasonic element.

(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 in the parametric speaker 100 as an oscillation source and generates ultrasonic waves. 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 such as PZT, and expands and contracts by applying a voltage in the thickness direction. The piezoelectric material preferably has a mechanical quality factor Qm100 or more. The diameter of the piezoelectric element 111 is preferably equal to or smaller than the diameter of the diaphragm 112. 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, has a diameter equal to or smaller than the diameter of the diaphragm 112, and is made of, for example, aluminum or an aluminum alloy. The height of the resonator 114 is preferably 0.5 to 1.5 mm. 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. Since the frequency of the natural vibration of only the resonator matches the frequency of the primary resonance, the frequency becomes about 1/10 of the frequency of the secondary resonance, so that the resonator 114 is hardly distorted and is damaged. It is difficult to do.

  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 disc 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. The diameter of the diaphragm 112 is preferably 5 to 15 mm, but is not limited thereto.

  The resonator 114 and the piezoelectric vibrator 115 are designed so that the frequency of the natural vibration of only the resonator 114 matches the frequency of the primary resonance of the ultrasonic sounding body 110. Thereby, not only the piezoelectric vibrator 115 but also the resonator 114 can resonate to obtain a high sound pressure. Further, when the sound pressure increases, the number of ultrasonic sounding bodies 110 necessary for the parametric speaker can be reduced, and the parametric speaker 100 can be made small and inexpensive. In addition, when the frequency is within 1 kHz, it can be said that “match”.

  It is preferable that the piezoelectric vibrator 115 has a small thickness and a large diameter. Thereby, the fluctuation range of the piezoelectric vibrator 115 can be increased and the sound pressure can be increased. Since the sound pressure is obtained as the vibration width of the piezoelectric vibrator 115 is large and the displacement is large, the thin shape is better for obtaining the displacement.

(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.

(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 from a piezoelectric material, 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 art museums, aquariums, museums, amusement facilities, and the like. In the future, it can also be used for traffic information.

(Impedance characteristics)
FIG. 5 is a diagram showing impedance characteristics of the ultrasonic sounding body. As shown in FIG. 5, in the ultrasonic sound generator, two resonances appear in the impedance characteristic: primary resonance (resonance mainly composed of piezoelectric vibrators) and secondary resonance (resonance mainly composed of resonators). In the primary resonance and the secondary resonance, both the piezoelectric vibrator and the resonator vibrate.

  FIGS. 6A to 6C are diagrams showing the results of simulating the vibration of the ultrasonic sounding body by the finite element method (FEM). The shading in the figure indicates the magnitude of vibration. 6A shows the time of primary resonance, FIG. 6B shows the time of secondary resonance, and FIG. 6C shows the time of natural vibration of only the resonator.

  As described above, according to the analysis by the finite element method (FEM), there is a frequency at which only the resonator vibrates in addition to the primary resonance and the secondary resonance. The impedance characteristic is measured by connecting the piezoelectric element side and the diaphragm side of the piezoelectric vibrator, but the natural vibration of the resonator does not appear because the piezoelectric vibrator does not vibrate. By matching the primary resonance with the natural vibration frequency of the resonator that does not appear in the impedance characteristics, the resonator can vibrate and a higher sound pressure can be obtained. Further, when the sound pressure increases, the number of ultrasonic sounding bodies necessary for the parametric speaker can be reduced, and the size and cost can be reduced.

(Example)
By changing the thickness of the piezoelectric vibrator of the ultrasonic sounder composed of the resonator (aluminum alloy, outer diameter φ6.5 mm, height 1.0 mm, thickness 0.1 mm) and piezoelectric vibrator (φ9 mm), Analyzed.

  Table 1 shows the relationship of the frequency of each vibration to the thickness of the piezoelectric vibrator. When the thickness of the piezoelectric vibrator is changed, the primary resonance and the secondary resonance change, but the frequency of the natural vibration of the resonator hardly changes and remains at 44.50 kHz. When the thickness of the piezoelectric vibrator was set to 0.6 mm, the frequency of the primary resonance and the natural vibration of the resonator became close.

  Based on such analysis results, an ultrasonic sounding body having the same dimensions as the analyzed one was actually produced, and the resonance frequency and sound pressure were measured. The sound pressure was measured at an applied voltage of 30 Vp-p and a distance between the ultrasonic sounding body and the microphone of 30 cm.

  Table 2 shows the measurement results of the resonance frequency and the sound pressure with respect to the thickness of the piezoelectric vibrator. As a result of analysis, a high sound pressure was obtained at a thickness of 0.6 mm of the piezoelectric vibrator in which the resonance frequency of the primary resonance was close to the natural vibration of the resonator. As a result, it was confirmed that a high sound pressure was obtained when the primary resonance was close to the natural vibration of the resonator. In addition, an ultrasonic sounding body having a high sound pressure of 45 kHz was obtained.

  In this way, the shape and dimensions of the resonator are designed by analysis so that the natural frequency of the resonator matches the frequency of the ultrasonic sounding body to be manufactured, and then the shape and dimensions of the piezoelectric vibrator are adjusted. An ultrasonic sounding body in which the frequencies of the primary resonance and the natural vibration were combined was actually manufactured. The produced ultrasonic sounding body was able to obtain a high sound pressure with a design in which the primary resonance frequency of the piezoelectric vibrator and the natural vibration frequency of the resonator coincided with each other at frequencies other than those described above.

  In addition, the thickness of the piezoelectric vibrator was fixed to 0.6 mm, and the diameter was changed for analysis. Table 3 shows the relationship of the frequency of each vibration to the diameter of the piezoelectric vibrator. Although the natural vibration slightly changed compared with the case of changing the thickness, it was confirmed that the natural vibration of the resonator did not change even when the diameter was changed.

  Further, the displacement (maximum value) of a piezoelectric vibrator in which a disc-shaped diaphragm having a diameter of 9 mm and a piezoelectric element were combined was analyzed. Table 4 shows the displacement (μm) with respect to the combination of the thickness of the diaphragm and the thickness of the piezoelectric element. The sound pressure is obtained as the vibration width of the piezoelectric vibrator increases, that is, as the displacement increases. From the results shown in Table 4, it can be seen that the thinner is better for obtaining the displacement.

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 (3)

An ultrasonic sound generator used as an oscillation source of a parametric speaker,
A piezoelectric vibrator formed by a plate-like piezoelectric element and 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 that generates ultrasonic waves by resonating with vibration of the diaphragm;
The ultrasonic sounding body, wherein the natural vibration frequency of only the resonator coincides with the frequency of its own primary resonance. An ultrasonic sounding body according to claim 1;
An ultrasonic element comprising: a support member that supports the ultrasonic sounding body with a vibration node. A parametric speaker that emits ultrasonic waves from a plurality of oscillation sources,
The ultrasonic element according to claim 2;
A parametric speaker comprising: a wiring board, and a flat substrate on which the ultrasonic element is provided on the wiring pattern.