JPH04274753A - Apparatus and method for generating ultrasonic wave - Google Patents

Abstract

PURPOSE:To obtain an apparatus and a method for generating supersonic waves using an ultrasonic conversion method due to laser beams applicable to an ultrasonic flaw detecting tester, an ultrasonic cleaner or the like. CONSTITUTION:An ultrasonic wave generator applies laser light generated from a pulse laser 1 via a light waveguide 4 and an optical system 6 to a target 71 comprising a cylinder whose end is closed by a metallic plate, generates change due to thermal expansion of gas inside the cylindrical body or thermal stress of the metallic plate, and transmits this pressure or change in the stress to outside so as to generate ultrasonic waves. Resonance and attenuated waveforms are reduced, permitting accurate measurement wherein signals of reflection echoes are not buried in the attenuated waveforms.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic generation device and method using an ultrasonic conversion method using a laser beam, which is applied to ultrasonic flaw detection testing equipment, ultrasonic cleaners, and the like.

0002

2. Description of the Related Art Conventional ultrasonic transmitters generate ultrasonic waves by applying electric pulses to ceramics or polymeric materials having a piezoelectric effect, and utilizing the resulting deformation (strain) of the material.

0003

[Problems to be Solved by the Invention] The basic configuration of the conventional system is shown in FIGS. A pulsar 11 that generates electrical pulses depending on its shape etc.
Therefore, even if a pulse wave-like drive signal C as shown in FIG. 8 is applied through the optical waveguide 13, the emitted ultrasonic wave will have a resonance and attenuation shape D as shown in FIG. As mentioned above, this is determined by the Q value of the piezoelectric vibration 12 (piezoelectric element). As shown in Figure 9, the ultrasonic waveform D is vibratory, which means that when the defect is located close to the piezoelectric element in ultrasonic flaw detection, reflected echo waves are present in the attenuated vibration waves of the emitted waves. Problems sometimes occur, such as the reflected waves not being able to be detected accurately because they are buried. In order to solve this problem, the present application has a structure in which, without damping vibration, if the applied pulse is one pulse, the generated ultrasonic wave will also be a pulse wave of one pulse (one period). .

0004

[Means for Solving the Problems] The present invention has been proposed in view of the above circumstances, and involves irradiating a target with laser light emitted from a pulsed laser to generate thermal stress in the target due to the laser light. The stress is propagated to the outside to generate ultrasonic waves. That is, the present invention provides a pulsed laser, an optical waveguide that guides laser light emitted from the pulsed laser, an optical system that allows the laser light to enter the optical waveguide, and a laser emitted from the optical waveguide. It consists of a lens system that focuses light and a target that irradiates the focused laser beam, and the target has a cylindrical shape with one end closed, and the laser beam irradiates toward the closed end surface. , provides an ultrasonic generator characterized in that stress is generated inside a cylinder through thermal phenomena of laser light, and ultrasonic waves are transmitted to the outside by propagation of the stress, and pulsed light is emitted from a pulsed laser. The emitted laser beam is focused on the surface or inside of a target made of a metal plate to generate distortion due to thermal stress on the target, and the distortion is propagated to the outside as a vibration wave to generate ultrasonic waves. The ultrasonic generation method is further characterized by emitting pulsed light from a pulsed laser,
The emitted laser beam is focused in a cylindrical target with one end closed by a metal plate and gas is sealed inside the cylindrical target, and the gas component is collected inside the cylindrical target. The present invention provides an ultrasonic generation method characterized in that ultrasonic waves are generated by vibrating a metal plate by generating pressure fluctuations due to thermal expansion.

[0005]

[Operation] Since the present invention has such a structure, the laser light generated from the pulsed laser is irradiated onto the target via the optical waveguide, and heat is generated inside the cylindrical part, causing thermal stress in the target. The thermal stress generated in this cage is propagated to the outside, generating ultrasonic waves. Further, a gas component sealed inside the cylindrical target whose one end is closed with a metal plate is thermally expanded by the heat generated by the condensation of the laser beam, causing pressure fluctuations within the cylindrical interior. This pressure fluctuation causes the target metal plate to vibrate, generating ultrasonic waves.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An ultrasonic generator according to an embodiment of the present invention will be described below with reference to FIG. 1 is a pulse laser, such as a YAG laser, a CO2 laser, or an excimer laser. The pulse may be on the order of 10 ns, and the energy may be on the order of 100 mJ to 1 J. Reference numeral 2 denotes a laser drive power supply unit, which emits a pulse S in response to an external trigger signal T. Pulsed laser 1
emits a laser pulse R in response to the pulse S. 3 is
The input optical system efficiently inputs the laser pulse R light into the next optical waveguide 4, and couples the output light to a monitor device 32 equipped with a mirror 31 for monitoring a portion of the output light to monitor the waveform. I am making it possible to monitor. The optical waveguide 4 is used in such a case because the pulse laser 1 and the place where the ultrasonic waves are to be generated are generally far apart. As the optical waveguide 4, an optical fiber is effective as long as it uses a laser up to a near-infrared wavelength. In the case of optical fibers, the instantaneous incident power is high, so if there is a risk of damage, use fibers with a large core diameter or bundled fibers. Far infrared (10
．． If there is no optical fiber that passes a wavelength of 6μm),
The optical waveguide 3 may be a relay lens, that is, a guide in which lenses are sequentially arranged. In this case, the optical waveguide 4 becomes fixed. Reference numeral 6 denotes an output optical system, which is a group of lenses assembled to condense the laser light emitted from the optical waveguide 4 and appropriately irradiate the target 71. Reference numeral 7 designates a cylindrical housing, which serves as a lens barrel for the optical system 6, and a closed end face portion of the cylindrical housing 7 serves as a target 71 to which a laser beam is irradiated. 2 and 3 show a portion where laser light is converted into ultrasonic waves 8. FIG. A target surface 71 is irradiated with the laser light. The target 71 is made of thin metal, and the laser beam is irradiated to approximately the center position A thereof. When the laser beam hits the target 71, the energy of the laser beam is converted into heat over the entire layer surface of the target 71. Due to rapid thermal expansion on the surface of 71, thermal stress is generated inside. Strain caused by thermal stress propagates as longitudinal waves, and the generated ultrasonic waves8
becomes. 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 this steam blows up from the surface is the target 7
Join 1. At the trailing edge of the laser pulse, the heat input to the target 71 suddenly stops, so thermal contraction occurs inside. The longitudinal waves transmitted inside the target 71 exit from the outer surface and become generated ultrasonic waves 8. However, the outside of the cylindrical housing 7 or the target 71 is as shown in FIG.
As shown in FIG. 2, unless the device is immersed in water 72, the ultrasonic waves 8 cannot go outside due to acoustic impedance. Further, regarding the thickness of the target 71, in relation to the pulse width, if the thickness is set so that internal reflected waves do not occur, the accuracy will be better. Through the above process, it is possible to generate a single sharp ultrasonic wave as shown in FIG. 4 (b) in response to the laser pulse (a) shown in FIG. In addition,
Laser irradiation to the target 71 may be performed by focusing the focus A on the surface of the target 71 to create a point sound source as shown in FIG. 2, or by shifting the focus from point A as shown in FIG. 3 or FIG. 71 surface may be irradiated with a circular beam. Furthermore, if the focal point B is focused inside the tube of the cylindrical housing 7 as shown in FIG. 6, the beam can be irradiated in a circular manner in front of the target 71 as in the example shown in FIG. In this case, in the vicinity of point B, by injecting a gas having an absorption band at the laser wavelength into the cylinder and sealing the cylindrical housing 7,
The internal pressure increases due to rapid thermal expansion of the gas component, and if the target 71 is made thinner than the side surface of the cylindrical housing 7, the target 71 becomes a diaphragm, and ultrasonic waves can be generated by the vibration of this surface.

According to the embodiment described above, the pulse laser 1 emits the laser pulse R in response to the pulse S from the laser drive power supply section in response to the trigger signal, and this laser light enters the cylindrical housing and hits the target 71. irradiated. Because the target 71 emits sharp ultrasonic waves corresponding to laser light pulses, unlike conventional ultrasonic waves with resonance and attenuation waveforms, the defect location was close to the contact part of the ultrasonic oscillator. Even in cases where there is no damped oscillation in the emitted wave,
This prevents the reflected echo from being buried in these vibration waveforms and allows the reflected wave to be detected with high accuracy. Furthermore, unlike conventional ultrasonic oscillators, the transducer can be made smaller because it uses light, and there is no influence of electrical noise, contributing to highly accurate measurements.

[0008]

[Effects of the Invention] According to the ultrasonic generator and method of the present invention described above, sharp ultrasonic waves corresponding to laser pulses can be emitted by irradiating a target with a laser beam, which is different from conventional methods. Unlike ultrasonic waves, which have strong resonance and damped waveforms, even if the position of the defect is close to the contact part of the ultrasonic oscillator, there will be no damped vibration in the emitted wave, and as a result, reflected echoes will be buried in those vibration waveforms. Therefore, the reflected waves can be detected with high accuracy. Furthermore, unlike conventional ultrasonic oscillators, the transducer can be made smaller because it uses light, and there is no influence of electrical noise, contributing to highly accurate measurements.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an ultrasonic generator and method according to an embodiment of the present invention.

FIG. 2 is a conceptual diagram of a portion that converts laser into ultrasonic waves in an embodiment of the present invention.

FIG. 3 is another conceptual diagram of the part that converts laser into ultrasonic waves in the embodiment of the present invention.

FIG. 4 In this example, (a) is a laser light pulse, (b)
) is a waveform diagram of the transmitted ultrasound pulse.

FIG. 5 is another conceptual diagram showing the convergence state of laser light in the embodiment of the present invention.

FIG. 6 is a conceptual diagram when gas is used in the cylinder in another embodiment of the present invention.

FIG. 7 is a diagram showing the configuration of a conventional ultrasonic generator.

FIG. 8 is a waveform diagram of a conventional pulser.

FIG. 9 is a waveform diagram of conventionally generated ultrasonic waves.

[Explanation of symbols]

1 Pulse laser 3 Input optical system 4 Optical waveguide 6 Output optical system 7 Cylindrical housing 71 Target

Claims (3)

[Claims] 1. A pulsed laser, an optical waveguide that guides the laser beam emitted from the pulsed laser, an optical system that makes the laser beam enter the optical waveguide, and an optical system that guides the laser beam emitted from the optical waveguide. It consists of a lens system that focuses light and a target that irradiates the focused laser beam.The target is cylindrical with one end closed. 1. An ultrasonic generator that generates stress through thermal phenomena of laser light, and transmits ultrasonic waves to the outside by propagation of the stress. [Claim 2] Light is emitted from a palace laser, and the emitted laser light is focused on the surface or inside of a target made of a metal plate to generate distortion due to thermal stress on the target, and the distortion is removed by vibration. An ultrasonic generation method characterized by generating ultrasonic waves by propagating them to the outside as waves. [Claim 3] Pulse light is emitted from a pulse laser, and the emitted laser light is focused in a cylindrical target with one end closed with a metal plate and a gas sealed inside the cylindrical shape. An ultrasonic generation method characterized in that upon irradiation, a gas component causes pressure fluctuations due to thermal expansion inside the cylindrical target, causing a metal plate to vibrate, thereby generating ultrasonic waves.