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JPH11196493

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DESCRIPTION JPH11196493
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
cavitation detection method and a microphone with an acoustic filter for detecting whether
cavitation has occurred in a liquid in a container during ultrasonic cleaning.
[0002]
2. Description of the Related Art Conventionally, an ultrasonic transducer is mounted on the
bottom of a container, and the ultrasonic transducer is driven to irradiate the liquid in the
container with ultrasonic waves, and the ultrasonic waves irradiated to the liquid are detected. An
underwater microphone is used to detect.
[0003]
However, cavitation generated by the irradiation of ultrasonic waves is the growth of surface
wave vibration of bubbles, and this surface wave has a large attenuation in distance in the liquid
compared to the longitudinal wave. Since energy is not emitted much in water, there is a problem
that the microphone can not be detected unless the air bubble is directly touched or in the
vicinity.
[0004]
According to the present invention, a piezoelectric element coated with an acoustic filter and a
piezoelectric element not coated with an acoustic filter are immersed in a liquid in a container
irradiated with ultrasonic waves by an ultrasonic transducer, The output of the piezoelectric
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element coated with the acoustic filter is compared with the output of the piezoelectric element
not coated with the acoustic filter to detect that cavitation is generated in the liquid when there is
a difference in the output, Also, the piezoelectric element is enclosed in a polyethylene film
container or bag, and an acoustic filter such as silicon, degassed water or oil is sealed around the
piezoelectric element.
[0005]
In the present invention, the cavitation generated by the irradiation of the ultrasonic wave is the
surface wave of the bubble, and the surface wave has a greater attenuation in distance in the
liquid compared to the longitudinal wave of the ultrasonic wave, and it is mostly in the liquid. If
liquid that does not generate cavitation is intervened between the microphone and cavitation
taking advantage of the fact that it is not emitted, the microphone intervened by this liquid can
receive longitudinal waves, but it has an acoustic filter for surface waves Since a microphone can
be used, a cavitation surface wave can be distinguished and detected by a microphone having an
acoustic filter and a microphone having no acoustic filter.
[0006]
1 is a plan view of a microphone with an acoustic filter according to an embodiment of the
present invention, and FIG. 2 is a side view of the microphone of FIG. 1, in which lead wires 2 are
connected to a PZT ceramic microphone 1; The microphone 1 is sealed together with an acoustic
filter 4 such as silicon, deaerated water or oil in a polyethylene film container 3 provided around
the periphery, and a microphone 5 with an acoustic filter is configured.
[0007]
In the microphone 5 with an acoustic filter of this embodiment configured as described above,
the longitudinal wave of the ultrasonic wave generated from the ultrasonic transducer passes
through the acoustic filter 4 but the surface wave of the bubble generated by the irradiation of
the ultrasonic wave is This acoustic filter 4 can not be propagated.
[0008]
Therefore, as shown in FIG. 3, the liquid 8 is put into the container 7 having the ultrasonic
transducer 6 mounted on the bottom, and the microphone 5 with an acoustic filter and the
microphone 9 without an acoustic filter are inserted into the liquid 8 When an ultrasonic wave is
irradiated into the liquid 8 from the ultrasonic transducer 6, the longitudinal wave by the
ultrasonic wave is transmitted to the microphone 5 with an acoustic filter and the microphone 9
without an acoustic filter, and the ultrasonic wave detected by the microphone 5 with an acoustic
filter In the waveform A of the spectrum, as shown in FIG. 4, in the waveform B of the spectrum
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of the ultrasonic wave detected only by the longitudinal wave and detected by the microphone 9
without the acoustic filter, as shown in FIG. In addition, 1⁄2 subharmonic C is detected.
[0009]
Therefore, the 1⁄2 sub-harmonic (frequency component of the basic longitudinal wave / 2) C
detected by the microphone 9 without an acoustic filter is a component generated by cavitation,
and thus two microphones 5 and 9 are generated. If there is a difference in the output of, it
indicates that cavitation has occurred.
[0010]
In addition, since the 1⁄2 sub harmonic occurs even in the other than cavitation, in order to
accurately detect cavitation, as in the present invention, using the microphone 5 with an acoustic
filter and the microphone 9 without an acoustic filter, It is important to confirm from the signals
of the two microphones 5 and 9 that the component due to cavitation is surface wave vibration.
[0011]
As described above, according to the cavitation detection method of the present invention, using
the microphone with an acoustic filter and the microphone without an acoustic filter, the surface
waves generated by cavitation are compared by the outputs of the two microphones. Cavitation
can be reliably detected for detection, and the microphone with an acoustic filter can reduce the
influence of surface waves, and thus has an advantage of being very advantageous for detection
of cavitation.
[0012]
Brief description of the drawings
[0013]
1 is a plan view of a microphone with an acoustic filter according to an embodiment of the
present invention.
[0014]
2 is a side view of the microphone with acoustic filter of FIG.
[0015]
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3 is a diagram for explaining a method of detecting cavitation according to an embodiment of the
present invention.
[0016]
4 is a diagram showing the waveform of the spectrum of the ultrasonic wave detected by the
microphone with an acoustic filter of FIG.
[0017]
5 is a diagram showing the waveform of the spectrum of the ultrasonic wave detected by the
microphone without the acoustic filter.
[0018]
Explanation of sign
[0019]
Reference Signs List 1 PZT ceramic microphone 2 lead wire 3 polyethylene film container or bag
4 acoustic filter 5 microphone with acoustic filter 6 ultrasonic transducer 7 container 8 liquid 9
microphone without acoustic filter
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