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JPH04274753

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DESCRIPTION JPH04274753
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
apparatus and method for generating ultrasonic waves using an ultrasonic conversion method
using a laser beam applied to an ultrasonic flaw testing apparatus, an ultrasonic cleaner, and the
like.
[0002]
2. Description of the Related Art A conventional ultrasonic transmitter applies an electric pulse to
a ceramic or polymer material having a piezoelectric effect, and utilizes deformation (strain) of
the material generated thereby to generate an ultrasonic wave. The
[0003]
7, 8 and 9 show the basic configuration of the conventional system. In this configuration, the
ultrasonic waves 14 oscillated from the piezoelectric vibrator 12 are made of a piezoelectric
material. Even if a pulse wave drive signal C as shown in FIG. 8 is applied through the optical
waveguide 13 from the pulsar 11 that generates an electrical pulse according to the physical
property value and the shape etc., the emitted ultrasonic wave is shown in FIG. As shown in FIG.
4, the resonance and damping shape D are obtained.
This is determined by the Q value or the like of the piezoelectric vibration 12 (piezoelectric
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element) as described above. As shown in FIG. 9, the ultrasonic form D is oscillatory, that is, when
the position of the defect is close to the piezoelectric element in ultrasonic flaw detection, the
reflected echo wave is included in the attenuated oscillation wave of the emission wave. Since it
is buried, problems such as the inability to accurately detect the reflected wave sometimes occur.
In the present application, in order to solve such a problem, the configuration is such that if the
applied pulse is a single pulse without attenuating vibration, the generated ultrasonic wave also
becomes a pulse wave of one pulse (one cycle). .
[0004]
SUMMARY OF THE INVENTION The present invention has been proposed in view of the above
circumstances, and the target is irradiated with laser light emitted from a pulse laser and the
target is subjected to thermal stress. To transmit the stress to the outside to generate an
ultrasonic wave. That is, according to the present invention, there are provided a pulse laser, an
optical waveguide for guiding laser light emitted from the pulse laser, an optical system for
causing laser light to be incident on the optical waveguide, and a laser emitted from the optical
waveguide. A lens system for collecting light and a target for irradiating the collected laser light,
the target is a cylindrical tube closed at one end, and the laser light is irradiated toward the
closed end face. Providing an ultrasonic wave generating apparatus characterized in that stress is
generated inside the cylinder through a thermal phenomenon of laser light and ultrasonic waves
are transmitted to the outside by propagation of the stress, and pulse light is emitted from a
pulse laser The laser beam is emitted and irradiated so as to condense the emitted laser light on
the surface or inside of the target made of a metal plate to generate a strain due to thermal stress
in the target and propagate the strain to the outside as a vibration wave. According to the
ultrasonic wave generating method characterized in that a wave is generated, pulse light is
further emitted from a pulse laser, and the emitted laser light is cylindrical in which one end is
closed by a metal plate and gas is Irradiating so as to condense in the enclosed target, the gas
component inside the cylindrical target causes pressure fluctuation due to thermal expansion to
vibrate the metal plate, thereby generating an ultrasonic wave. The present invention provides a
method of generating ultrasonic waves.
[0005]
Since the present invention is configured as described above, the laser beam generated from the
pulse laser is irradiated to the target through the optical waveguide portion, and heat is
generated inside the cylindrical shape to generate thermal stress in the target. The thermal stress
generated in the kegget is propagated to the outside to generate an ultrasonic wave. Further, the
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gas component enclosed in the inside of a cylindrical target whose one end is closed by a metal
plate is thermally expanded by the heat generated by the condensing of the laser beam, causing
pressure fluctuation in the inside of the cylinder. The pressure fluctuation vibrates the target
metal plate to generate ultrasonic waves.
[0006]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to FIG. 1, an
ultrasonic wave generator according to an embodiment of the present invention will be
described. Reference numeral 1 denotes a pulse laser, such as a YAG laser, a CO2 laser or an
excimer laser. The pulse may be of the order of 10 ns and the energy may be of the order of 100
mJ to 1 J. Reference numeral 2 denotes a drive power supply unit of the laser, which emits a
pulse S in response to an external trigger signal T. The pulse laser 1 emits a laser pulse R in
response to the pulse S. An incident optical system 3 is coupled to a monitor device 32 in which
light of the laser pulse R is efficiently incident on the next optical waveguide 4 or a mirror 31 for
monitoring a part of the outgoing light is disposed. To monitor the waveform. The optical
waveguide 4 is used in such a case because it is general that the place where the pulse laser 1
and the ultrasonic wave are desired to be generated is far apart. As the optical waveguide 4, an
optical fiber is effective if it is a laser up to a near infrared wavelength. In the case of an optical
fiber, when the instantaneous incident power is high and there is a risk of damage, a fiber with a
thick core diameter or a bundle type fiber is used. In the case where there is no optical fiber
passing through the far infrared (10.6 .mu.m) wavelength like a CO2 laser, the optical waveguide
3 may be a relay lens, that is, a guide in which the lenses are sequentially arranged. In this case,
the optical waveguide 4 is fixed. An emission optical system 6 is a lens group assembled to
condense the laser light emitted from the optical waveguide 4 and appropriately irradiate the
target 71. Reference numeral 7 denotes a cylindrical casing, which serves as a lens barrel of the
optical system 6 and a portion of the closed end face of the tip serves as a target 71 to which the
laser is irradiated. 2 and 3 show portions where laser light is converted into ultrasonic waves 8.
The laser light is emitted to the 71 target surface. The target 71 is a thin metal, and the laser
beam is irradiated approximately at its center position A. When the laser beam hits the target 71,
the energy of the laser beam is converted as heat over the entire surface of the layer 71. Thermal
stress is generated inside the surface 71 due to rapid thermal expansion. The strain generated by
the thermal stress travels as a longitudinal wave and becomes an ultrasonic wave 8 generated.
Further, as shown in FIG. 3, when the laser energy is high, the surface of the target 71 is partially
evaporated. The reaction force 9 of the force F when the steam blows up is applied to the target
71 from the surface. At the falling edge of the laser pulse, the heat input to the target 71 rapidly
disappears, so thermal contraction occurs this time.
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The longitudinal waves transmitted through the inside of the target 71 become ultrasonic waves
8 generated from the outer surface and generated outside. However, if the outside of the
cylindrical housing 7 or the target 71 is not caught in the water 72 as shown in FIG. 3, the
ultrasonic wave 8 can not go outside due to the relationship of the acoustic impedance. Further,
the thickness of the target 71 is more accurate if the thickness is set so as not to generate an
internal reflected wave in relation to the pulse width. In the above process, it is possible to
generate a sharp one-wave ultrasonic wave as shown in (b) for the laser pulse (a) shown in FIG.
The laser irradiation to the target 71 may be focused on the surface of the target 71 as shown in
FIG. 2 to make a point sound source, or the focal point may be shifted from the point A as shown
in FIG. The surface of the target 71 may be irradiated with a circular beam. Further, as shown in
FIG. 6, when the focal point B is formed inside the cylinder of the cylindrical casing 7, the beam
can be irradiated in a circle in front of the target 71 as in the example shown in FIG. In this case,
a gas having an absorption band at the laser wavelength is injected into the cylinder, and by
sealing the cylindrical casing 7, the gas component is thermally expanded rapidly at point B and
the internal pressure rises, and the target 71 is If it is made thinner than the side surface of the
form body 7, the target 71 becomes a diaphragm, and it is possible to generate an ultrasonic
wave by the vibration of this surface.
[0007]
According to the embodiment described above, the pulse laser 1 emits the laser pulse R by the
pulse S from the laser drive power source unit according to the trigger signal, and the laser light
enters the cylindrical housing and is applied to the target 71. It is irradiated. Since the target 71
emits a sharp ultrasonic wave corresponding to the pulse of the laser light, it differs from the
conventional ultrasonic wave of resonance and attenuation waveform, and the position of the
defect was at a point close to the contact portion of the ultrasonic oscillator In this case as well,
the emitted wave has no damped vibration, and the reflected echo is not buried in these vibration
waveforms, so that the reflected wave can be detected accurately. Further, unlike the
conventional ultrasonic oscillation apparatus, the use of light enables the vibrator to be
miniaturized, and contributes to high-precision measurement since there is no influence of
electrical noise.
[0008]
According to the ultrasonic wave generating apparatus and method of the present invention
described above, it is possible to emit a sharp ultrasonic wave corresponding to a laser pulse by
irradiating the target with a laser beam. Unlike ultrasonic waves with conventional resonance and
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attenuation waveforms, even when the defect is located at a point close to the contact point of
the ultrasonic oscillator, there is no attenuation oscillation in the emitted wave, and as a result,
the reflected echoes become these oscillation waveforms It is possible to accurately detect the
reflected wave without being buried. Further, unlike the conventional ultrasonic oscillation
apparatus, the use of light enables the vibrator to be miniaturized, and contributes to highprecision measurement since there is no influence of electrical noise.
[0009]
Brief description of the drawings
[0010]
1 is a diagram showing the configuration of an ultrasonic wave generating apparatus and method
according to an embodiment of the present invention.
[0011]
2 is a conceptual diagram of a portion for converting the laser to ultrasonic waves in the
embodiment of the present invention.
[0012]
3 is another conceptual diagram of the portion of the same as in the embodiment of the present
invention to convert the laser to ultrasound.
[0013]
In the present embodiment, (a) is a laser light pulse, and (b) is a waveform diagram of a
transmission ultrasonic pulse.
[0014]
5 is another conceptual view showing a state of focusing of laser light in the embodiment of the
present invention.
[0015]
6 is a conceptual diagram in the case of using a gas in the cylinder in another embodiment of the
present invention.
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[0016]
7 is a diagram showing the configuration of a conventional ultrasonic wave generator.
[0017]
8 is a waveform diagram of a conventional pulser.
[0018]
9 is a waveform diagram of the conventional generated ultrasound.
[0019]
Explanation of sign
[0020]
Reference Signs List 1 pulse laser 3 incidence optical system 4 optical waveguide 6 emission
optical system 7 cylindrical housing 71 target
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