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TECHNICAL FIELD The present invention relates to a directional micropon using paroc) II sock
fruit of a sound field. FIG. 1 shows the configuration of the parametric directional sound
reception system. A frequency of +1 is generated by the oscillator 1, and an ultrasonic wave of
frequency J 1 is emitted in the direction of the receiver 4 by the transmitter 3 through the power
amplifier 2. When a signal of frequency f2 arrives from the direction of the transmitter, if the
output of the ultrasonic wave is in a finite amplitude region, i / i7 is phase-modulated by the
signal wave f2 due to the nonlinear phenomenon of air. Therefore, a modulation wave having this
fl as a carrier and f1 ± f2 as a side band is received by the receiver 4 and is demodulated by the
demodulator 6 through the preamplifier 5 to obtain the signal wave f2. Moreover, as the angle θ
at which the signal wave is incident with respect to the axis of the transducer is smaller, the
interference distance is increased and the detection output is more dog-like, thus enabling
directional sound reception. Considering the level of the detection signal, this is limited to the
magnitude of the modulation index mf. The magnitude of this modulation index is proportional to
the frequency of the ultrasonic wave from the transmitter and the distance between the
transmitter and receiver, and is not related to the sound pressure level of the ultrasonic wave.
The sound pressure level of the ultrasonic wave is related to the signal to noise level of the
modulation wave, so the signal to noise level at the demodulator is improved since the
modulation index does not increase even if sufficient transmit power to cause parametric action
is obtained I will not. If you try to increase the modulation index by increasing the ultrasonic
frequency or increasing the distance between transmitters and receivers, the attenuation of air
works in either case, and the signal-to-noise level of the modulated wave is degraded. So there is
a limit. A specific example of this modulation index is m′′po, 02 when the ultrasonic
frequency is 300 KHz, the distance between transducers is 50 cm, and the signal sound pressure
is 90 c LBsPL. Practically as a microphone, a signal of about 30 dBspL should not be able to be
detected in practice, so the demodulator must be able to reproduce the modulation wave of rQ =
2 × 10− ′ ′ without being buried in noise, but it is currently difficult. Therefore, it is
conceivable to increase the apparent modulation index. That is, to lower the carrier level with
respect to the sideband level. One possible way of achieving this is to insert a carrier trap circuit
in front of the demodulator, but the transmitter uses a high resonance sharpness Q to increase
the conversion efficiency, There is a disadvantage that the trap circuit has to be variable because
the resonance point changes due to heat generation. The present invention was made to
eliminate this drawback.
The point is that a part of the output from the oscillator of the ultrasonic wave is subjected to
amplitude-two-phase adjustment to lead to the modulation wave from the transmitter and the
combination demodulator. A part of the output from the oscillator 1 whose amplitude is adjusted
by the amplifier 7 is shown in FIG. 2 according to one embodiment of the present invention, and
it is transmitted from the wave receiver 4 to the preamplifier 5 via the phase shifter 8. The added
modulation wave is added to the demodulator 6. The phase adjustment may be performed by
omitting the phase shifter 8 and finely adjusting the distance between the transducers. As
described above, in the present invention, part of the output of the oscillator for generating the
ultrasonic wave from the transmitter is amplituded. Since the phase is adjusted and added to the
modulated wave output from the receiver, the apparent modulation index of the modulated wave
can be easily raised. Therefore, the signal-to-noise ratio of the demodulator is not excessively
demanded, and the real-phase effect is thick in the parameter) + 1 directional directional sound
receiving system.
Brief description of the drawings
FIG. 1 shows the configuration of parametric directional reception. FIG. 2 shows the
configuration of parametric link directional reception according to 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 amplifier, and 8 is a phase shifter. Applicant: Nippon Columbia Ltd.
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