JP4595117B2 - Ultrasound propagation imaging method and apparatus - Google Patents

Description

  The present invention relates to a technique related to nondestructive inspection by ultrasonic flaw detection used for health monitoring of a structure, and more particularly to an ultrasonic propagation imaging method and apparatus.

  As methods for imaging the state of propagation of ultrasonic waves, the Schlieren method and the photoelastic method are widely known, but these methods can be applied only to transparent objects.

  As a method for imaging an ultrasonic wave propagating through an opaque object, there is a reception laser scanning method (see Non-Patent Document 1) developed by the present inventors. However, in a practical method in terms of detection sensitivity and workability, There wasn't.

Furthermore, as a method of applying the reception laser scanning method, a method and an apparatus for visualizing the propagation of elastic waves by scanning a reception piezoelectric sensor have already been applied for a patent (see Patent Document 1). However, since this method requires scanning with the receiving sensor in contact with the subject, the workability is poor, and the received ultrasonic waves are strongly influenced by the sensor bonding conditions, so that the reproducible and highly accurate image is obtained. Hard to get.
Transactions of the Japan Society of Mechanical Engineers, volume C, 65, 639 4299-4304, November 1999 JP 2001-296282 A

The conventional ultrasonic wave propagation imaging method is as described above. The problems are summarized as follows.
(1) Reception laser scanning method a. Detection sensitivity is low.
B. The subject surface must be flat and smooth.
C. Laser light must be applied perpendicularly to the subject and a constant focal length must be maintained.
D. Receiving lasers are expensive.

(2) Receiving piezoelectric sensor scanning method a. The subject surface must be flat.
B. Because of contact scanning, workability is poor and it is easily affected by bonding conditions.
C. Since the diameter of the piezoelectric sensor is more than an order of magnitude larger than that of the laser light beam, an image with high resolution cannot be obtained.

In order to solve the above-mentioned problems, the present invention scans the surface of the subject and irradiates a plurality of measurement points on the scanning path of the pulsed laser beam to generate thermally excited ultrasonic waves, and is attached to the subject and is fixed, the thermal excitation ultrasonic waves generated by the plurality of measuring points and a receiving piezoelectric sensor that detect in synchronism with the pulse of the laser beam, the ultrasonic waves propagating on the subject An imaging device is provided.

In order to solve the above-mentioned problems, the present invention scans the surface of the subject and irradiates a plurality of measurement points on the scanning path of the pulsed laser beam to generate thermally excited ultrasonic waves, and is attached to the subject are to fixed, with the plurality of receiving piezoelectric sensor that detect in synchronism with the pulses of the thermal excitation ultrasonic waves generated at the measurement point the laser beam, and the a / D converter, and a computer An ultrasonic imaging apparatus for propagating on a subject , wherein the A / D converter performs A / D conversion on a signal related to the ultrasonic wave detected by the receiving piezoelectric sensor to obtain waveform string data. The personal computer records the waveform train data, and converts the amplitude value of the waveform train data into an image by luminance-modulating it, thereby imaging the ultrasonic wave propagating on the subject . Providing the device.

An oscillation laser scans the surface of the subject and irradiates a plurality of measurement points with pulsed laser light along a scanning path, generates thermally excited ultrasonic waves at the plurality of measurement points, and applies the ultrasonic waves to the subject. Detection is performed in synchronization with the pulse of the laser beam by a receiving piezoelectric sensor attached to a specimen, and the detected signal is used as waveform string data, and the amplitude value at each time of the waveform string data is intensity-modulated to generate an image. An imaging method for ultrasonic waves propagating on a subject is provided.

In order to solve the above problems, the present invention scans the surface of a subject with an oscillating laser, irradiates a plurality of measurement points with a pulse laser beam along a scanning path, and applies thermal excitation ultrasonic waves to the plurality of measurement points. The ultrasonic wave is detected in synchronization with the pulse of the laser beam by a receiving piezoelectric sensor mounted and fixed on the subject, and the detected signal is sent to a personal computer as waveform train data by an A / D converter. There is provided a method of imaging an ultrasonic wave propagating on a subject , characterized in that the recorded waveform train data is imaged by luminance modulation of amplitude values at each time by the personal computer.

  If the images obtained by imaging are continuously displayed in time series, an image of ultrasonic propagation can be obtained.

(1) The detection sensitivity is improved 100 to 1000 times compared to the receiving laser scanning method.
(2) Since it is not necessary to match the incident angle and focal length of the laser beam, workability is very good.
(3) By using sector scan, it is possible to remotely measure ultrasound images traveling over a wide area.
(4) Ultrasound of a complex object having curved surfaces and steps can be visualized.
(5) Since an oscillation laser is cheaper than a receiving laser, a low-cost measurement system can be configured.

  The best mode of an ultrasonic propagation imaging method and apparatus for carrying out the present invention will be described below with reference to the drawings based on the embodiments.

(principle)
The point A is irradiated with laser light to generate thermally excited ultrasonic waves, and the wave detected by the piezoelectric sensor at point B is reversely irradiated with laser light to generate thermally excited ultrasonic waves. The ultrasonic wave is almost the same as the wave detected at point A.

  By utilizing the reversibility of this ultrasonic wave propagation, while scanning the oscillation laser, irradiate pulsed laser light at multiple measurement points along the scanning path to generate thermally excited ultrasonic waves, and fix the ultrasonic waves On the other hand, the waveform sequence (a set of waveforms corresponding to the number of measurement points) detected by the piezoelectric sensor is a waveform detected by scanning the piezoelectric sensor with ultrasonic waves generated when the laser beam is irradiated to the piezoelectric sensor position. Can be considered identical to a column.

  Then, the amplitude value at each time of the detected waveform sequence when the oscillation laser is scanned is brightness-modulated and imaged (a contour map is created), and when this imaged image is continuously displayed in time series, the image Becomes a propagation image of the ultrasonic wave transmitted at the receiving point. As described above, the present invention does not scan the reception laser or the reception sensor, but conversely scans the oscillation laser and receives it by the fixed piezoelectric element, so that non-contact and high-sensitivity measurement is possible. .

  Therefore, there are matters necessary when scanning a conventional reception laser or reception sensor, such as that the subject is flat, that the laser beam should be applied perpendicularly to the subject and a certain focal length must be maintained. In the present invention, it is not strictly required. Therefore, according to the present invention, the workability is good, and the accuracy is improved as compared with the prior art.

  FIG. 1 is a diagram for explaining an ultrasonic propagation imaging method and apparatus according to the present invention. An ultrasonic wave propagation imaging apparatus according to the present invention includes a biaxial stage, an oscillation laser, a receiving piezoelectric sensor, an amplifier, an A / D converter, and a personal computer. A digital oscilloscope is used as the A / D converter.

  For example, a YAG laser or the like is used as the oscillation laser, and is placed on a biaxial stage, and irradiates the subject with pulsed laser light at a cycle of about 10 Hz. The measurement points are irradiated with 100 × 100 vertical and horizontal measurement points in total along the scanning path while controlling the two-axis stage with a personal computer to scan in a grid pattern. When the subject is irradiated with the pulse laser beam, the measurement point of the subject undergoes rapid thermal expansion, and as a result, thermally excited ultrasonic waves are generated.

  The receiving piezoelectric sensor electrically detects thermally excited ultrasonic waves generated at each measurement point. The detected electrical signal detected by the receiving piezoelectric sensor is amplified by an amplifier, further converted into a digital signal by a digital oscilloscope, and sent to a personal computer as a waveform train for recording.

  With the above-described configuration, an image obtained by modulating the luminance of the waveform sequence data recorded in the personal computer is considered by regarding the amplitude value at each time (same time) as the ultrasonic displacement at the measurement point irradiated with the laser beam. If the images obtained in this way are continuously displayed (continuous drawing) in time series, it is possible to obtain a video as if the ultrasonic wave started at the reception point.

  This image is not an image of ultrasonic waves actually transmitted, but is based on actually measured data and is an ultrasonic image that may actually exist. Hereinafter, specific experimental examples of techniques for imaging an ultrasonic wave by the ultrasonic wave propagation apparatus and method of the present invention will be shown.

(Experimental example 1)
FIG. 2 is a diagram illustrating Experimental Example 1. This Experimental Example 1 is an experimental example demonstrating the imaging of ultrasonic waves propagating through a carbon fiber composite material by the ultrasonic propagation imaging method and apparatus according to the present invention.

  In this experimental example 1, specifically, a device as shown in FIG. 2 is used, a receiving AE (Acoustic Emission) sensor is attached as a receiving piezoelectric sensor on the back side of the subject, and the front side is a pulse laser by laser scanning. The state of ultrasonic waves transmitted through light was visualized. Also, in order to see how the transmission of ultrasonic waves changes due to damage, impact damage was done with a hammer, and the ultrasonic waves transmitted through the damaged part were also visualized.

  The results are shown in FIG. 3 over time (2 μs, 6 μs, 10 μs, 14 μs, 18 μs) comparing the intact material (upper diagram) with the damaged material (lower diagram). As for the damaged material, the state in which the waveform is disturbed after the ultrasonic wave passes through the damaged portion is visualized (see the 18 μs diagram in the lower part of FIG. 3).

In addition, the sound velocity anisotropy ( _So wave) peculiar to the carbon fiber composite material used as the specimen has been clearly observed. Since this carbon fiber composite material has a large wave attenuation, it has been difficult to visualize ultrasonic waves by conventional means, but the present invention makes it possible to realize highly sensitive imaging.

(Experimental example 2)
FIG. 4 is a diagram showing Experimental Example 2 of the ultrasonic wave propagation imaging method and apparatus according to the present invention. In Experimental Example 2, as in Experimental Example 1, the ultrasonic wave propagation imaging method and apparatus (see FIG. 2) according to the present invention (see FIG. 2) is used to propagate around a fatigue crack generated in a stainless steel weld. An example in which sound waves are visualized is shown.

  The test piece used as the test object in Experimental Example 2 is shown in the lower diagram of FIG. This test piece was prepared by welding two stainless steel flat plates (plate thickness 8 mm). Two types of test pieces are prepared: a test piece that does not create a fatigue crack in this test piece (an intact material), and a test piece that produces a fatigue crack in this test piece (a crack material).

  The cracked material is one in which a fatigue crack is created by repeatedly applying a load to an intact specimen. The fatigue crack is generated from the inside of the weld interface and is generated with a surface length of 20 mm toward the side surface of the test piece.

  An imaging image obtained by scanning these two types of test pieces (an intact material and a cracking material) using the ultrasonic wave propagation imaging method and apparatus according to the present invention is shown in the upper part of FIG. Shown in comparison with a single figure.

  As for the cracked material (the left figure in the upper part of FIG. 4), the ultrasonic wave is in a state of proceeding without any problem. However, with regard to the crack material (the upper right diagram in FIG. 4), it has been observed that the ultrasonic wave advances as it wraps around the crack. As a result, it is possible to detect the presence or absence of a crack in the welded portion of the test piece prepared by welding, and check the soundness of the welded portion.

(Experimental example 3)
FIG. 5 is a diagram showing Experimental Example 3 in which the ultrasonic wave propagation imaging method and apparatus according to the present invention are applied to a curved object. In Experimental Example 3, as in Experimental Example 1, an example of imaging ultrasonic waves transmitted through a teacup by the ultrasonic propagation imaging method and apparatus according to the present invention (see FIG. 2) is shown.

  In Experimental Example 3, as shown in the lower diagram of FIG. 5, an image obtained by attaching a receiving AE sensor to the inside of a teacup that is a curved object and irradiating the back surface with a pulsed laser beam by laser scanning is obtained. The upper diagram of FIG. 5 shows the results over time (4 μs, 8 μs, 12 μs, 16 μs). As described above, it has been proved that it is possible to visualize ultrasonic propagation of a curved object, which has been difficult to visualize.

  Conventionally, the imaging technology of ultrasonic propagation has been used only as a means of ultrasonic research in university laboratories and the like because measurement requires advanced equipment adjustment, but the image of ultrasonic propagation according to the present invention has been used. The method and equipment are easy to adjust the equipment, have good workability, and can perform high-sensitivity measurement without contact, so that it is easy to visualize ultrasonic images in the field such as manufacturing and inspection. is there.

  The present invention can be used as an auxiliary tool in nondestructive inspection of structures and products and development of ultrasonic equipment. In particular, the present invention is capable of inspecting a wide range of areas remotely without contact by sector scanning with a laser, and inspecting high places such as bridges or in radioactive or high temperature environments such as nuclear facilities. Powerful for remote inspections in special environments where people cannot approach, such as inspections in the field.

  Recent ultrasonic diagnostic techniques are shifting from signal analysis techniques corresponding to human ears to image diagnosis techniques corresponding to eyes. Conventional image diagnostic techniques are intended for still images typified by B-mode tomographic images and C-mode tomographic images, but the present invention is applied to new ultrasonic diagnostic imaging techniques for moving images. Is also possible.

It is a figure explaining the Example of this invention. It is a figure explaining Experimental example 1 of this invention. It is a figure explaining Experimental example 1 of this invention. It is a figure explaining Experimental example 2 of this invention. It is a figure explaining Experimental example 3 of this invention.

Claims (6)

An oscillation laser that scans the surface of the subject and irradiates a plurality of measurement points on the scanning path of the pulsed laser light to generate thermally excited ultrasonic waves, and is attached to the subject and fixed, and the plurality of measurement points in the heat pumping ultrasonic waves generated and a receiving piezoelectric sensor that detect in synchronism with the pulse of the laser light, ultrasound imaging apparatus propagating on the subject. An oscillation laser that scans the surface of the subject and irradiates a plurality of measurement points on the scanning path of the pulsed laser light to generate thermally excited ultrasonic waves, and is attached to the subject and fixed, and the plurality of measurement points in the said heat excitation ultrasonic waves generated received piezoelectric sensor that detect in synchronism with the pulse of the laser beam, and the a / D converter, and a computer, an ultrasound image propagating on the subject Device.
The A / D converter performs A / D conversion on a signal related to the ultrasonic wave detected by the reception piezoelectric sensor to obtain waveform string data,
An imaging apparatus for ultrasonic waves propagating on a subject , wherein the personal computer records the waveform string data and images the waveform string data by luminance-modulating the amplitude value at each time. 3. The ultrasonic imaging apparatus for propagating ultrasonic waves on a subject according to claim 2 , wherein the images obtained by imaging are continuously displayed in time series. An oscillation laser scans the surface of the subject and irradiates a plurality of measurement points with pulsed laser light along a scanning path, generates thermally excited ultrasonic waves at the plurality of measurement points, and applies the ultrasonic waves to the subject. Detection is performed in synchronization with the pulse of the laser beam by a receiving piezoelectric sensor attached to a specimen, and the detected signal is used as waveform string data, and the amplitude value at each time of the waveform string data is intensity-modulated to generate an image. An imaging method for ultrasonic waves propagating on a subject , characterized in that The oscillation laser scans the surface of the subject, irradiates a plurality of measurement points with pulsed laser light along the scanning path, generates thermally excited ultrasonic waves at the plurality of measurement points, and applies the ultrasonic waves to the subject. Detected in synchronization with the pulse of the laser beam by a receiving piezoelectric sensor mounted on and fixed to the signal, and the detected signal is recorded on a personal computer as waveform string data by an A / D converter, and the recorded waveform is recorded by the personal computer. An imaging method of ultrasonic waves propagating on a subject , wherein the column data is imaged by intensity-modulating the amplitude value at each time. 6. The method for imaging an ultrasonic wave propagating on a subject according to claim 4, wherein the images obtained by imaging are continuously displayed in time series.