JPH028480Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to a directional microphone that utilizes the parametric effect of a sound field.

Figure 1 shows the configuration of the parametric directional sound reception system. 1 is an oscillator, 2 is a power amplifier, and 3 is a transmitter. The transmitter 3 emits ultrasonic waves with a frequency of ₁ in the direction of a receiver 4. Here, when a signal with a frequency of ₂ arrives from the direction of the transmitter, if the ultrasonic output is sufficiently large, an air nonlinear phenomenon occurs, and as a result, in addition to frequencies ₁ and ₂ , a signal with a frequency of ₁ ± ₂ is generated. A secondary wave is generated. These sound waves ₁ , ₁ ±
₂ is received by the receiver and sent to the demodulator 6 via the preamplifier 5.
If you perform PM or FM demodulation, signal wave ₂ can be obtained.
Also, the smaller the angle of incidence of the signal wave with respect to the transducer axis, the more the interference zone will be, so the detection output will be larger, and the larger the angle, the smaller the output will be.
Directional sound reception becomes possible. However, as can be seen in Figure 1, when a signal wave is incident from the 0° direction, the transmitter must be small enough to mask the signal wave, but in reality the transmitted wave power It is necessary to increase the size of the transmitter. Therefore, as a means to solve this problem, a wave transmitting/receiving system as shown in FIG. 2 has been proposed. In the figure, the transmitter 3 includes a plurality of piezoelectric elements 31 attached to a base 32. A through hole 33 is provided in the base. That is, by providing the through hole in the transmitter, the signal wave can reach the receiver 4 without being hindered by the transmitter. However, in this case, although the transmitter can be made larger, the detection sensitivity for signals having a large angle of incidence also increases. In particular, the disadvantage is that the output from the 180° direction becomes large.

The present invention was devised to solve this problem, and its key points are to provide an acoustic horn, place a transmitter in its mouth and a receiver in its throat, as well as attach a part of the inner surface of the acoustic horn. Another reason is that the entire structure is equipped with an ultrasonic absorbing substance. FIG. 3 shows an example of this. In the figure, the transmitter 3 has the same configuration as in FIG. 2, but the base 32 is curved.
The ultrasonic wave ₁ from the piezoelectric element 31 is better transmitted to the receiver 4.
It is beginning to converge in this area. signal wave ₂
is guided to the acoustic horn 7 through a through hole 33 provided in the transmitter and directed to the receiver 4. On the other hand, signals from unnecessary directions are blocked by the horn and cannot interfere with the ultrasonic waves, so no output is produced, and good directivity characteristics can therefore be obtained.

However, the problem here is the ultrasonic waves sent from the piezoelectric element 31. Acoustic horns are effective in efficiently converting the impedance of audio signals and increasing sound pressure, but when the wavelength becomes short like ultrasonic waves, they no longer function as a horn.
It becomes a mere sound wave reflecting object. Therefore, some of the ultrasonic waves emitted from the transmitter hit the walls of the horn, forming waves that travel in various directions and canceling out the sound waves coming from the transmitter. As a result, the sound pressure level of the ultrasonic waves decreases, making it impossible to obtain sufficient parametric effects. Therefore, in the present invention, in order to avoid this harm, an ultrasonic absorbing material 8 is added along the inner surface of the acoustic horn 7.
is pasted on all or part of the surface. As a result, the ultrasonic waves that hit the wall of the horn are absorbed without being reflected, and the receiver receives a direct wave from the transmitter and a signal wave whose sound pressure has been increased by this direct wave and the horn. Only secondary waves due to nonlinear interference will arrive. The material for the ultrasonic absorbing substance 8 is preferably a sheet of polyurethane foam with open cells.

As described above, in the present invention, an acoustic horn is provided in a parametric transducer, the transmitter is placed at the mouth of the horn, and the receiver is placed at the throat of the horn.
Additionally, an ultrasonic absorbing material is placed on the inner surface of the horn. For this reason, the signal wave passes through the transmitter and is guided to the horn, increasing the sound pressure.On the other hand, the ultrasonic waves emitted from the transmitter can reach the receiver without being diffusely reflected by the horn wall. Efficient generation of secondary waves becomes possible, and signal detection with an excellent signal-to-noise ratio is possible. Additionally, a directional microphone with sharp directional characteristics can be obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the configuration of parametric directional sound reception, Figure 2 is a longitudinal cross-sectional view of the main parts of the transmitting and receiving system, and Figure 3 is a diagram showing the configuration of parametric directional sound reception.
The figure is a longitudinal cross-sectional view of the essential parts of a transmitting/receiving system according to an embodiment of the present invention. 1 is an oscillator, 2 is a power amplifier, 3 is a transmitter,
4 is a receiver, 5 is a preamplifier, 6 is a demodulator, 7 is an acoustic horn, 8 is an ultrasonic absorption material, 31 is a piezoelectric element, 32 is a base, and 33 is a through hole.

Claims (1)

[Scope of utility model registration request] Nonlinear interference occurs between an acoustic horn, a transmitter that generates ultrasonic waves through the opening of the acoustic horn toward the throat of the acoustic horn, and the ultrasonic waves generated by the transmitter caused by the sound waves that enter through the opening of the acoustic horn. A parametric array microphone characterized in that it is equipped with a receiver that receives waves generated at the throat of an acoustic horn, and that an ultrasonic absorbing material is arranged along the inner surface of the acoustic horn.