JP6186622B2 - 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. In particular, with respect to the resonator, the use of magnesium or a magnesium alloy as a material reduces the weight while increasing the rigidity of the resonator, and improves the durability of the resonator when transmitting broadband ultrasonic waves. It is proposed to 3rd.

JP 60-167597 A Japanese Patent Laid-Open No. 62-296698 JP 2007-88886 A

    FIG. 6 is a graph showing the relationship between drive frequency and impedance for a conventional ultrasonic sounding body. The resonance of the ultrasonic sounding body includes a primary resonance mainly including a piezoelectric vibrator and a secondary resonance mainly including a resonator. FIG. 6 shows a case where an audio signal having a maximum width of 20 kHz is input to the ultrasonic sounding body.

  Usually, when driving the ultrasonic sounding body, an AC voltage having a frequency of primary resonance which is resonance of the piezoelectric vibrator is applied. When driven by secondary resonance, the resonator vibrates strongly, so that the resonator can be easily broken or broken.

  When a constant ultrasonic wave is emitted, the ultrasonic sounding body is driven at the frequency of the primary resonance and is not driven at the secondary resonance. However, in the case of modulation like a parametric speaker, the ultrasonic sounding body is driven in the frequency range of primary resonance ± sound signal, so that the secondary resonance is changed from the primary resonance to the sound signal as shown in FIG. If it is within the frequency, it is driven at the frequency of the secondary resonance. The driving at the secondary resonance is not preferable as described above.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ultrasonic sounding body and a parametric speaker that can prevent vibration of a resonator that is too strong due to excitation of secondary resonance.

  (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 by application of a voltage, and includes a plate-like piezoelectric element and the piezoelectric element A piezoelectric vibrator formed by a diaphragm bonded to one main surface, and a resonator that is provided on the other main surface of the diaphragm and generates ultrasonic waves by vibration of the diaphragm, The difference between the frequency of the primary resonance mainly consisting of the vibration of the piezoelectric vibrator and the frequency of the secondary resonance mainly consisting of the vibration of the resonator exceeds the maximum frequency of the audio signal having the primary resonance as a carrier wave. It is characterized by being. As a result, when the ultrasonic sounding body is driven by the primary resonance ± sound signal with the primary resonance as the carrier wave, the vibration of the resonator that is too strong caused by the excitation of the secondary resonance can be prevented, and the resonator can be removed. Can be prevented.

  (2) In the ultrasonic sound generator of the present invention, the resonator is formed in a conical cylinder shape having a flat bottom, and the flat bottom causes the difference between the frequency of the primary resonance and the frequency of the secondary resonance to be It is characterized by exceeding the maximum frequency of an audio signal having a primary resonance as a carrier wave. Thus, by forming a flat bottom in the conical cylindrical resonator, the frequency of the secondary resonance can be shifted to the larger side.

  (3) Moreover, the parametric speaker of the present invention includes a flat board provided with a wiring pattern, a support member provided on the board, 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. Thereby, a parametric speaker that can be driven stably can be realized.

  According to the present invention, when the ultrasonic sounding body is driven by the primary resonance ± sound signal using the primary resonance as a carrier wave, the secondary resonance is not excited, and the resonator can be removed by vibration of the resonator that is too strong. Damage can be prevented.

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. It is a graph which shows the relationship between the drive frequency and impedance about 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 the relationship between the drive frequency and impedance about the conventional ultrasonic sounding body.

  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. Then, by continuously driving the ultrasonic sounding body 110, an audible sound is caused to appear by nonlinear characteristics when the ultrasonic wave propagates. The substrate 120 is provided with a wiring pattern and is formed in a flat plate shape. In addition, in FIG. 1, the external appearance structure is shown and the electrical configuration is omitted.

(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. The ultrasonic sounding body 110 is driven by applying a voltage modulated for the parametric speaker 100.

  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, and expands and contracts by applying a voltage in the thickness direction. 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.

  The difference between the frequency of the primary resonance mainly including the vibration of the piezoelectric vibrator 115 and the frequency of the secondary resonance mainly including the vibration of the resonator 114 exceeds the maximum frequency of the audio signal. As a result, when the ultrasonic sounding body is driven by the primary resonance ± sound signal using the primary resonance as a carrier wave, the secondary resonance is not excited, and damage such as removal of the resonator due to strong vibration of the resonator can be prevented. .

  When the maximum frequency of the audio signal is 10 kHz, the ultrasonic sounding body 110 is designed so that the difference between the primary resonance frequency and the secondary resonance frequency exceeds 10 kHz. Further, when the maximum frequency of the audio signal is 30 kHz, the ultrasonic sounding body 110 is designed so that the difference between the primary resonance and the secondary resonance exceeds 30 kHz. That is, the frequency to be separated is determined by the maximum frequency of the audio signal, and the ultrasonic sound generator 110 is designed so that (primary resonance frequency + maximum frequency of the audio signal) <(secondary resonance frequency).

  For example, if the ultrasonic sounding body 110 designed so that the difference between the primary resonance frequency and the secondary resonance frequency exceeds 20 kHz, 20 Hz to 20 kHz generally recognized as an audible sound range with the primary resonance as a carrier wave. The secondary resonance is not excited even when the audio signal is driven.

  The secondary resonance frequency can be determined according to the primary resonance frequency determined by the structure of the piezoelectric vibrator and the audio signal. Conversely, the primary resonance frequency can be determined according to the secondary resonance determined by the resonator structure and the audio signal. Therefore, the piezoelectric vibrator and the resonator can take various configurations depending on the adjustment.

  For example, by forming the resonator 114 in the shape of a conical cylinder having a flat bottom, the frequency of the secondary resonance is shifted to the larger side, and the difference between the frequency of the primary resonance and the frequency of the secondary resonance is the maximum of the audio signal. It can be larger than the frequency. By increasing the diameter of the flat bottom, it is possible to sufficiently increase the frequency of the secondary resonance (see examples described later). As described above, the frequency of the secondary resonance can be changed by the shape of the resonator 114, but can also be changed by the material. The shape includes the thickness of the resonator. By controlling the frequency of the secondary resonance, the ultrasonic transducer 110 and the parametric speaker 100 that can be driven stably can be realized.

  As described above, the piezoelectric resonator 115 and the resonator 114 may be designed so that the difference between the primary resonance frequency and the secondary resonance frequency can be made. For example, when the primary resonance frequency is 40 kHz and the maximum frequency of the audio signal is 25 kHz, the secondary resonance frequency may be designed to exceed 65 kHz. Further, when the secondary resonance frequency is 70 kHz and the maximum frequency of the audio signal is 25 kHz, the primary resonance frequency may be designed to be less than 45 kHz.

  FIG. 3 is a graph showing the relationship between the drive frequency and impedance for the ultrasonic sounding body 110. In order not to drive by secondary resonance, the parametric speaker 100 should use an ultrasonic sounding body in which the difference between the primary resonance and the secondary resonance exceeds the frequency of the audio signal used for modulation as shown in FIG. preferable. In addition, the ultrasonic sounding body 110 may take measures such as increasing the secondary resonance when the primary resonance is increased, and may provide a difference between the resonance frequency of the primary resonance and the resonance frequency of the secondary resonance. preferable.

(Operation of ultrasonic sound generator)
4A and 4B are side views showing a scene of the operation of the ultrasonic sounding body 110 of the present invention. As shown in FIGS. 4A and 4B, 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. On the other hand, the shape of the resonator 114 is designed so that the difference between the resonance frequency of the primary resonance and the resonance frequency of the secondary resonance is sufficient, and the resonator 114 is manufactured. Then, 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. 5 is a block diagram showing an electrical configuration of the parametric speaker 100. As shown in FIG. 5, 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)
Next, the ultrasonic sounding body 110 having the above-described configuration was produced, and the relationship between the shape of the resonator 114 and the secondary resonance frequency was verified. The resonator 114 was formed in a conical cylinder shape, and the frequency of secondary resonance was measured by changing the size of the bottom surface with the outer diameter and height fixed. The following table shows the relationship between the shape of the resonator 114 and the frequency of the secondary resonance.

  As shown in Table 1, it was confirmed that the frequency of the secondary resonance can be increased by increasing the diameter of the bottom surface, and that the difference from the frequency of the primary resonance can be widened.

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 sounding body for a parametric speaker that generates ultrasonic waves by applying a voltage,
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 generates ultrasonic waves by vibration of the diaphragm;
The difference between the frequency of primary resonance mainly consisting of vibration of the piezoelectric vibrator and the frequency of secondary resonance mainly consisting of vibration of the resonator exceeds the maximum frequency of the audio signal to be conveyed ,
An ultrasonic sounding body using only primary resonance as a carrier wave of the audio signal .   The resonator is formed in a conical cylinder shape having a flat bottom, and the flat bottom causes a difference between the frequency of the primary resonance and the frequency of the secondary resonance to be a maximum frequency of an audio signal having the primary resonance as a carrier wave. The ultrasonic sounding body according to claim 1, wherein the ultrasonic sounding body exceeds. A flat substrate provided with a wiring pattern;
A support member provided on the substrate;
The ultrasonic sounding body according to claim 1 or 2, 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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