JPH09257756A - Ultrasonic detection apparatus and method therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To dispense with highly accurate adjustment inevitable to an interferometer and to enable even an unskilled person to easily handle an apparatus. SOLUTION: The laser beam 151 emitted from a laser beam source 11 is incident on the surface of an object 30 to be inspected at a predetermined angle θand reflected by the mirror surface of the specimen 30 at the angle equal to the incident angle to become reflected beam 152 . The reflected beam 152 is applied to the surface of a PSD 12 to be converted to an electrical signal and, when ultrasonic waves propagate along the surface of the specimen, the surface of the specimen is displaced and the normal line direction of the surface thereof a changed. Herein, if the beam diameter of laser beam 151 is made sufficiently smaller than the wavelength λ of ultrasonic waves propagation along the surface of the specimen, even if the incident beam 151 is incident on the same point, the incident angle and reflected angle thereof change and the reflecting direction of the reflected beam 152 changes and, therefore, ultrasonic waves can be detected as a change of the position of the spot on the PSD.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic wave detecting apparatus and an ultrasonic wave detecting method which can be applied when, for example, ultrasonic waves are used to detect a defect inside a steel material.

[0002]

2. Description of the Related Art As one of the methods for inspecting internal defects of various materials, there is a so-called laser ultrasonic method. Regarding this, for example, "Ultrasonic TECHNO
May issue ”(vol.5, No.5, p38 (1993) Nippon Kogyo Shuppan). This method is to detect ultrasonic waves generated by irradiating a subject with a laser beam for excitation, using a laser beam for another probe. Defects can be inspected. Therefore, it is expected to be applied to quality inspections in the steel making process, weld inspections in the steel frame processing process, quality inspections of ceramic materials, internal inspections of aircraft parts, and quality inspections of other metals and composite materials.

FIG. 8 is a block diagram showing the construction of an example of a laser ultrasonic inspection apparatus using this laser ultrasonic method. In the figure, the excitation laser 50 is a laser for exciting ultrasonic waves on the surface of the subject 55, and a Q-switch YAG laser or the like capable of emitting a pulsed laser beam having a relatively large output is used. The laser beam 51 emitted from the excitation laser 50 is
The beam splitter 52 partially splits the mirrors 53, 5
It is reflected by 4 and is irradiated onto the surface of the subject 55. When irradiated with the laser beam 51, ultrasonic waves are generated in the subject 55 due to thermal stress or evaporation reaction force. This ultrasonic wave propagates inside the subject, reaches the back surface of the subject, is reflected, and returns to the front surface of the subject again as an echo. A part of the laser beam 51 split by the beam splitter 52 is guided to a photodetector 56, detected there and used as a trigger signal of the oscilloscope 57.

On the other hand, a probe light source 60 provided separately from the excitation laser 50 is a laser for detecting ultrasonic echoes returning to the surface of the subject 55, and is a He-Ne laser having a stable frequency, for example. Are used. Laser beam 6 emitted from the probe light source 60
1 is a mirror 62, a polarization beam splitter 63, a quarter
The surface of the subject 55 is irradiated with the light through the wave plate 64.
This reflected light passes through the quarter-wave plate 64, the polarization beam splitter 63, and the lens 65, and is passed through the Fabry-Perot interferometer 6
It is incident on 6. The light transmitted through the Fabry-Perot interferometer 66 is converted into an electric signal by a photodetector 67 including a photodiode. This signal is amplified by an amplifier 68, passed through a high pass filter 69 for removing low frequency noise, and then supplied to an oscilloscope 57.

FIG. 9 is a schematic diagram showing the result of measuring the transmitted light intensity of a He—Ne laser beam by sweeping the resonator length (horizontal axis) of the Fabry-Perot interferometer, and FIG.
FIG. 10 is a schematic view showing an enlarged horizontal axis of FIG. 9. That is, the resonator length at which the transmitted light intensity reaches a peak is He-Ne.
Optical frequency ν of laser beam (wavelength is 682.8 nm)
On the other hand, when the resonator length is changed, the optical frequency at which the transmitted light intensity of the interferometer reaches its peak also changes, so the transmitted light intensity at the optical frequency ν decreases. Utilizing this characteristic, the resonator length of the Fabry-Perot interferometer 66 is adjusted in advance so that the transmitted light intensity with respect to the optical frequency ν of the He—Ne laser beam becomes the value shown at the point A ′ in FIG. Then, the reflected light from the subject 55 is made incident on the Fabry-Perot interferometer 66.

When the surface of the subject 55 is ultrasonically vibrated by the ultrasonic echo reflected by the back surface of the subject, the spatial position of the subject surface is displaced in the cycle of this ultrasonic wave. Therefore, when the laser beam from the probe light source 60 is reflected by the surface of the subject, the laser beam undergoes a Doppler shift due to this displacement, and the wavelength changes. As shown in FIG. 10, the reflected light from the subject 55 is ± by the Doppler shift.
When the frequency changes by Δν ′, the transmitted light intensity changes by ± ΔI ′ as shown in the figure. Thus, the reflected light from the subject 55 can be converted into a change in intensity by passing through the Fabry-Perot interferometer.

Therefore, the output signal of the photodetector 67 changes greatly every time the ultrasonic echo repeatedly reflected on the front and back surfaces of the subject 55 returns to the front surface. When this signal is displayed on the oscilloscope 57 with time on the horizontal axis and signal intensity on the vertical axis, if there is no defect in the subject, a constant time interval determined by the sound velocity inside the subject and the thickness of the subject. Changes the signal strength. On the other hand, if there is a defect such as a cavity or an impurity inside the subject, the ultrasonic wave is reflected by this defective portion, and the signal intensity changes in a time shorter than the above time.
Therefore, by checking this time interval, it is possible to check whether or not there is a defect inside the subject.

[0008]

By the way, the Fabry-Perot interferometer 66 used in the apparatus of FIG. 8 is composed of a complicated optical system. When performing the alignment of
Accurate adjustment is required. For example, the resonator length needs to be adjusted on the order of μm, and skill is required for such adjustment. In addition to the Fabry-Perot interferometer described above, it is possible to use an interferometer such as a homodyne interferometer, a heterodyne interferometer, etc., but any of these methods still uses optical interference, and therefore the optical axis There is a common problem that highly accurate adjustment such as alignment is required.

The present invention has been made based on the above circumstances, and does not require inevitable high-precision adjustment of the interferometer, and even an unskilled person can easily handle the ultrasonic detector and the ultrasonic detector. An object is to provide a sound wave detection method.

[0010]

According to a first aspect of the invention for solving the above-mentioned problems, a laser light source for irradiating a surface of a subject with a laser beam at a predetermined incident angle, and a reflection of the laser beam. A light receiving unit provided at a position where the beam reaches, receiving the reflected beam, and outputting a displacement signal based on the displacement when the position of the beam spot of the reflected beam is displaced, and a displacement signal from the light receiving unit. Signal processing means for detecting the ultrasonic vibration of the portion of the subject irradiated with the laser beam.

According to a second aspect of the invention, in the first aspect of the invention, the beam diameter of the laser beam is about 10% of the wavelength of the ultrasonic wave in the subject to be detected, even if it is large. Characterize. The invention according to claim 3 is the invention according to claim 1 or 2, wherein the light receiving means is a PSD.
It is characterized by being.

According to a fourth aspect of the invention, in the first or second aspect of the invention, the light receiving means is a split type photodiode. According to a fifth aspect of the invention, in the first or second aspect of the invention, the light receiving means is a split type phototransistor. According to a sixth aspect of the present invention, by irradiating a subject with a laser beam at a predetermined incident angle, receiving the reflected beam with a light receiving means, and detecting a change in the position of the beam spot of the reflected beam, It is characterized in that ultrasonic vibrations at the laser beam irradiation position of the subject are detected.

[0013]

According to the present invention, with the above structure, when the surface of the subject is irradiated with a laser beam having a beam diameter sufficiently smaller than the wavelength of the ultrasonic wave to be detected, When the ultrasonic wave propagates, if the ultrasonic wave is an ultrasonic wave that propagates on the surface, the incident angle and the reflection angle of the laser beam change, and if the ultrasonic wave is a longitudinal wave that propagates inside the subject, the reflected beam The path translates. Therefore, in any case, when the portion of the subject irradiated with the laser beam is ultrasonically vibrated, the spot of the reflected beam which is the light receiving means is displaced. By appropriately processing the signal indicating this displacement by the signal processing means, the ultrasonic wave propagating through the subject can be detected.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a schematic arrangement of an ultrasonic detection device of the present embodiment and its periphery,
FIG. 2 is an exaggerated view showing how ultrasonic waves propagate on the surface of the subject, and FIG. 3 is an enlarged view showing how the direction of the reflected laser beam changes.

In FIG. 1, the ultrasonic detecting device 10 includes
Laser light source 11, PSD (Position S)
A positive detector 12) and a signal processing unit 13 are provided. The laser light source 11 is, for example, He-Ne.
A laser can be used. The light receiving means may be any one that can detect the change in the position of the spot of the incident light beam, and other than PSD, for example, a split type photodiode or a split type phototransistor can be used.

The ultrasonic wave generation source 20 provided separately from the ultrasonic wave detection device 10 generates ultrasonic waves on the surface of the subject 30. As the ultrasonic wave generation source, a well-known one such as a laser ultrasonic wave device which irradiates a laser beam to generate an ultrasonic wave or an electromagnetic ultrasonic wave device which generates an ultrasonic wave by electromagnetic means can be used. In this embodiment, steel (iron) is used as the subject 30, and the surface of the subject to be irradiated with the laser beam is a mirror surface.

As shown in FIG. 1, the laser beam 15 ₁ emitted from the laser light source 11 is incident on the surface of the subject 30 at a predetermined angle θ. This laser beam is reflected on the mirror surface of the subject surface at an angle θ equal to the incident angle, and becomes a reflected beam 15 ₂ . At this time, the incident beam 1
5 ₁ , the normal n, and the reflected beam 15 ₂ are on the same plane. The reflected beam 15 ₂ is applied to the surface of the PSD 12, it is converted into an electrical signal. This signal is sent to the signal processing unit 13, where necessary processing, calculation, data storage, and the like are performed.

If the object is in a steady state in which ultrasonic waves do not propagate, the position of the spot of the reflected beam 15 _{2 on} the photodetector does not change. When the ultrasonic wave propagates on the surface of the subject, the surface of the subject undergoes periodic and spatial displacements as shown in FIG. 2, and this displacement causes the normal line of the subject surface shown in FIG. The direction changes. Here, it is assumed that the beam diameter (beam diameter) of the laser beam 15 ₁ is sufficiently smaller than the wavelength λ of the ultrasonic wave propagating on the surface of the subject. At this time, if the displacement state of the surface of the subject is changed from the state of FIG. 3A to the state of FIG. 3B by the propagation of ultrasonic waves, even if the incident beam 15 ₁ is incident on the same point, The incident and reflected angles change and the reflected wave 15 ₂
The injection direction of changes.

As a result, the reflected beam 15 ₂ is reflected by the photodetector 1
The light spot formed on the second surface also moves according to the displacement of the surface based on the ultrasonic vibration of the surface of the subject. FIG. 4 is a diagram showing a state (S ′) in which the spot S of the reflected beam 15 ₁ moves by the distance l _{0 on} the light receiving surface of the PSD 12. The signal processing unit 13 receives the output signal from each optical sensor of the PSD 12 and calculates the position of the center of gravity of the spot at high speed. Then, the ultrasonic vibration at the position where the laser beam 15 ₁ is irradiated is detected from the movement of the position of the center of gravity.

In the above, the beam diameter is proportional to the wavelength λ of the ultrasonic wave.
I assumed that they were all small enough, but here
To evaluate. Incident beam 15 for irradiating the subject₁Diameter of
Is about the same as the wavelength of the ultrasonic wave propagating on the surface of the subject or
Is larger than this, the reflected beam 15_TwoChange of direction
Can not be detected sufficiently. Reflected beam 15 _Two
In order to be able to fully detect changes in the traveling direction of
Is the incident beam 15₁The diameter of is at most 10 of the wavelength λ
It is necessary to keep it to about%. Now, the subject 30 is steel
(Iron), its speed of sound is 5000 m / sec, the frequency of ultrasonic waves
If the number is 10 MHz, the wavelength of ultrasonic waves is 0.5 mm
(500 μm). Therefore, the incident beam 15₁
It is necessary to make the diameter of 50 μm or less. On the other hand, the incident
Form 15₁The lower limit of the diameter is detected by PSD12
There is no particular limitation, provided that you can
It can be thin.

Up to this point, the detection of the ultrasonic waves propagating on the surface of the subject has been described, but the ultrasonic detection apparatus 1 of FIG.
With 0, longitudinal ultrasonic waves traveling from the inside of the subject to the surface can also be detected. FIG. 5 is a diagram showing how the path of the reflected beam 15 ₂ changes due to the ultrasonic waves propagating from the inside to the surface. When the surface of the subject 30 is displaced by the distance d due to ultrasonic vibration, the path of the reflected beam 15 ₂ moves in parallel. If the incident angle of the incident beam 15 ₁ is θ, this movement amount l ₁ is l ₁ = 2d si
nθ.

FIG. 6 shows the relationship between the incident angle θ and l ₁ l ₁ = 2
6 is a graph showing the relationship between d sin θ, the incident angle θ, and the spot size a ′ of the beam irradiated on the surface of the subject. If the angle θ is made larger than the curve of l ₁ , l ₁ becomes larger accordingly, and a slight displacement on the surface of the object is PS.
Since it appears as a large displacement of the spot position on D12, the sensitivity is improved. However, when the diameter of the incident beam 15 ₁ is a, the beam spot diameter a which is irradiated onto the subject surface 'is, a' is represented by = a / cos [theta], a 'also increases as θ increases. If a'is too large, the sensitivity decreases, so it is desirable to control a'to 50 μm or less. Therefore, if the incident angle θ of the incident beam 15 ₁ is maximized within the range where this condition is satisfied, the maximum sensitivity can be obtained.

FIG. 7 is a diagram showing how the spot of the reflected beam is displaced when the split type photodiode 40 is used as the light receiving means. In this example, the split photodiode is composed of four photodiodes 40a, 40b,
40c and 40d, and the amount of received light can be detected from the magnitude of each output signal. As long as the spot of the reflected beam from the subject is at the center of the split photodiode, as in S ₁ , the reflected beams evenly strike the left and right photodiodes 40b and 40d, and the output signals have the same magnitude. From this, it can be seen that S ₁ is almost at the center. On the other hand, when the spot of the reflected beam shifts to the right as in S ₂ , the output signal of the photodiode 40b becomes smaller and the output signal of the photodiode 40d becomes larger. By processing these signals with the signal processing unit, it can be detected that the spot of the reflected beam has moved to the right. The vertical movement of the spot can be detected from the ratio of the outputs of 40a and 50c. When such a split type photodiode is used as the light receiving means, it is necessary to appropriately arrange the laser light source, the subject, and the photodiode so that the movement range of the spot does not deviate from each photodiode.
Note that a phototransistor can be used instead of the photodiode.

If the ultrasonic waves propagating through the subject can be detected as described above, for example, the ultrasonic waves generated in the subject can be easily detected by a laser ultrasonic device or an electromagnetic ultrasonic device. can do. The ultrasonic waves propagating through the subject are reflected or scattered there when there is a defect inside. Therefore, the defect in the subject can be inspected by examining the time from the generation of the ultrasonic wave in the subject to the detection and the state of attenuation of the ultrasonic wave.

The present invention is not limited to the above embodiment, and various modifications can be made within the scope of the gist thereof.

[0026]

As described above, according to the present invention,
The reflected beam of the laser beam applied to the subject is
By detecting with light receiving means such as D,
Compared with conventional ultrasonic inspection equipment that used laser interferometers such as the Perot interferometer, complicated adjustments such as optical axis alignment are not required, and even an unskilled person can easily handle the equipment. Since the configuration is simplified, it is possible to provide a simple and inexpensive ultrasonic inspection apparatus and ultrasonic inspection method.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic arrangement of an ultrasonic detection device according to an embodiment of the present invention and its periphery.

FIG. 2 is an exaggerated view showing how ultrasonic waves propagate on the surface of a subject.

FIG. 3 is an enlarged view of FIG. 2 showing how the direction of a reflected laser beam changes.

FIG. 4 is a diagram showing a state where a spot on a light receiving surface of PSD 12 moves.

FIG. 5 is a diagram showing how the path of a reflected beam 15 ₂ is changed by an ultrasonic wave propagating from the inside to the surface.

FIG. 6 is a graph showing the relationship between the incident angle θ and l ₁ , l ₁ = 2d sin θ, and the relationship between the incident angle θ and the spot size a ′ of the beam irradiated on the surface of the subject.

FIG. 7 is a diagram showing how spot changes are detected when a split photodiode is used as a light receiving unit.

FIG. 8 is a block diagram showing a configuration of an example of a conventional laser ultrasonic inspection apparatus.

FIG. 9 is a schematic diagram showing a result of measuring an optical frequency of a He—Ne laser beam by sweeping a resonator length (horizontal axis) of a Fabry-Perot interferometer.

FIG. 10 is an enlarged schematic view of the horizontal axis of FIG.

[Explanation of symbols]

10 Ultrasonic wave detector 11 Laser light source 12 PSD (Position Sensitive Detector) 13 Signal processing part 15 ₁ Incident beam 15 ₂ Reflected beam 20 Ultrasonic wave source 30,55 Subject 40 Split photodiode 40a, 40b, 40c, 40d Photo Diode 50 Excitation laser 52 Beam splitter 53, 54, 62 Mirror 60 Probe light source 63 Polarization beam splitter 64 Quarter wave plate 65 Lens 66 Fabry-Perot interferometer 67 Photodetector 68 Amplifier 69 High-pass filter

Claims (6)

[Claims] 1. A laser light source that irradiates a surface of a subject with a laser beam at a predetermined incident angle, and a position where a reflected beam of the laser beam arrives, receives the reflected beam, and receives the reflected beam. When the beam spot of the object is displaced, a light receiving means for outputting a displacement signal based on the displacement, and a displacement signal from the light receiving means are subjected to signal processing to detect ultrasonic vibrations of a portion of the subject irradiated with the laser beam. An ultrasonic detecting device comprising: a signal processing unit. 2. Even if the beam diameter of the laser beam is large, it is about 10% of the wavelength of the ultrasonic wave in the subject to be detected.
The ultrasonic detection device according to claim 1, wherein 3. The ultrasonic detecting device according to claim 1, wherein the light receiving unit is a PSD. 4. The ultrasonic detecting device according to claim 1, wherein the light receiving unit is a split type photodiode. 5. The ultrasonic detecting device according to claim 1, wherein the light receiving means is a split phototransistor. 6. The subject is irradiated with a laser beam at a predetermined incident angle, the reflected beam is received by a light receiving means, and the change in the position of the beam spot of the reflected beam is detected to detect the subject. An ultrasonic wave detection method, which comprises detecting ultrasonic vibrations at a laser beam irradiation position.