CN113406003A - Annular beam laser-based ultrasonic synthetic aperture focusing imaging device and method - Google Patents

Annular beam laser-based ultrasonic synthetic aperture focusing imaging device and method Download PDF

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CN113406003A
CN113406003A CN202110445131.0A CN202110445131A CN113406003A CN 113406003 A CN113406003 A CN 113406003A CN 202110445131 A CN202110445131 A CN 202110445131A CN 113406003 A CN113406003 A CN 113406003A
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CN113406003B (en
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陆健
顾豪栋
张宏超
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Nanjing University of Science and Technology
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/043—Analysing solids in the interior, e.g. by shear waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/04—Analysing solids
    • G01N29/06—Visualisation of the interior, e.g. acoustic microscopy
    • G01N29/0654—Imaging
    • G01N29/069—Defect imaging, localisation and sizing using, e.g. time of flight diffraction [TOFD], synthetic aperture focusing technique [SAFT], Amplituden-Laufzeit-Ortskurven [ALOK] technique
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/1702—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids
    • G01N2021/1706—Systems in which incident light is modified in accordance with the properties of the material investigated with opto-acoustic detection, e.g. for gases or analysing solids in solids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/023—Solids
    • G01N2291/0234—Metals, e.g. steel
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/0289—Internal structure, e.g. defects, grain size, texture

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Abstract

The invention discloses an ultrasonic synthetic aperture focusing imaging device and method based on annular beam laser, the device comprises an excitation light source system, a detection light source system, a signal output and control system and a system to be detected, a conical lens in the excitation light source system is used to change a single-point excitation beam into an annular excitation beam, a beam combining mirror in the detection light source system combines the detection beam and the annular excitation beam to be concentric, an interferometer is used to obtain vibration information of the surface of a sample to be detected, and finally a stepping motor in the system to be detected is used to complete two-dimensional scanning of the surface of the sample to be detected. The device reduces scanning time and greatly improves the working efficiency of the system while improving the identification capability and imaging resolution of micro defects in the detected defects.

Description

Annular beam laser-based ultrasonic synthetic aperture focusing imaging device and method
Technical Field
The invention belongs to the field of laser ultrasonic detection, and particularly relates to an ultrasonic synthetic aperture focusing imaging device and method based on annular beam laser.
Background
In the current industrial production, ultrasonic detection is generally adopted for detecting the defects of the metal aluminum products, but the defects are difficult to detect by adopting a conventional ultrasonic detection method due to the complex structure of the metal aluminum products. The traditional laser ultrasonic detection technology mainly depends on a coupling agent to couple an ultrasonic transducer with a detection sample, but the detection sample has a complex shape and cannot meet the requirement, so the traditional ultrasonic detection method has certain limitation.
In order to solve the limitations of the conventional ultrasonic contact detection, the research on the non-contact ultrasonic detection is forced to be in the eyebrow and eyelash. Air-coupled ultrasonic detection, electromagnetic-coupled ultrasonic detection and laser ultrasonic detection are non-contact ultrasonic detection technologies which exist at present. Air-coupled ultrasound uses the principle of matching acoustic impedances between air and an ultrasound source, but has a narrow frequency band and low matching efficiency, and can only perform nondestructive inspection on defects between thin plates, thereby causing deterioration in inspection efficiency and sensitivity. The electromagnetic coupling ultrasonic detection has great limitation on detecting samples, and can only detect ferromagnetic materials. Therefore, the laser ultrasonic detection has obvious advantages compared with the two methods, and the characteristics can effectively solve the above problems.
The laser ultrasonic detection technology is taken as a cross discipline technology, well combines the advantages of the ultrasound technology and the laser technology, applies the strong penetrating power of the traditional ultrasonic wave and the non-contact property of the optical detection, and realizes the nondestructive detection of the detected sample by exciting and receiving the ultrasonic wave by the laser.
The traditional laser ultrasonic detection technology can only detect the defect of the sub-millimeter size on the metal surface generally, but when the defect becomes the micrometer scale, the traditional laser ultrasonic detection technology is difficult to accurately position the defect. SAFT is an ultrasonic detection technique developed by synthetic aperture radar that can significantly improve the imaging quality. The SAFT is utilized to carry out laser ultrasonic nondestructive testing, and the resolution and contrast of laser ultrasonic imaging can be improved.
However, the conventional laser ultrasonic SAFT detection technology adopts single-point excitation and single-point scanning, and has the disadvantages of slow scanning speed and long consumption time.
Disclosure of Invention
The invention aims to provide a focusing imaging device and a focusing imaging method based on annular beam laser ultrasonic synthetic aperture, which change single-point excitation into annular excitation by using a conical lens, improve the SAFT defect scanning speed, reduce the time consumed by scanning and further improve the working efficiency of a laser ultrasonic SAFT detection technology.
The technical solution for realizing the purpose of the invention is as follows: the utility model provides a focus image device is gathered based on annular beam laser supersound synthetic aperture, includes excitation light source system, detection light source system, system to be measured and signal output and control system, excitation light source system be used for using pulse laser to produce the excitation light source, detection light source system is used for producing detection light source and receiving ultrasonic signal, the system to be measured is used for placing the sample that awaits measuring and receives cyclic annular laser signal and reflection defect signal to use step motor to remove the sample that awaits measuring and accomplish the two-dimensional scanning, signal output and control system are used for output, control pulse laser and step motor of ultrasonic signal.
Furthermore, the excitation light source system comprises a pulse laser, a beam expander, a plane reflector, a conical lens and a focusing lens, wherein excitation light beams output by the pulse laser are expanded by the beam expander and reflected by the plane reflector, then the excitation light beams pass through the conical lens and are changed into annular light beams, and the annular light beams pass through the focusing lens and are focused on the surface of the sample to be detected to form laser ultrasound.
Furthermore, the detection light source system comprises an interferometer and a beam combining mirror, and the detection light beam emitted by the interferometer is combined with the annular excitation light beam through the beam combining mirror to be concentric.
Furthermore, the laser output by the pulse laser in the excitation light source system is pulse laser, and the laser output by the interferometer in the detection light source system is continuous laser.
Further, the signal output and control system is used for controlling various parameters of the pulse laser in the excitation light source system and the step length and step distance of the step motor in the system to be tested.
Further, the signal output and control system comprises an oscilloscope and a computer, the oscilloscope is connected with the interferometer in the detection light source system, receives the vibration signal detected by the interferometer and outputs the detected vibration signal to the computer, and the computer is connected with the pulse laser in the excitation light source system and the stepping motor in the area to be detected, and controls various parameters of the pulse laser and the stepping step length of the stepping motor.
Furthermore, the system to be tested comprises a sample to be tested and a stepping motor, the sample to be tested receives the annular light beam emitted by the excitation light source system, the reflected ultrasonic signal enters the detection light source system, and the stepping motor controls the position of the annular light beam irradiated on the sample to be tested to complete the two-dimensional scanning of the annular light beam on the surface of the sample to be tested.
The invention also provides a use method of the ring beam laser ultrasonic synthetic aperture focusing imaging device, which comprises the following steps:
step 1, a sample to be detected is placed in a scanning area in an excitation light source system, a conical lens is used for generating an annular excitation light beam, the annular excitation light beam is focused on the surface of the sample to be detected by a focusing lens, the annular excitation light beam generates an annular excitation area on the surface of the sample to be detected, a beam combining mirror is used for combining a detection light beam and the annular excitation light beam to be concentric, namely the detection is carried out at the center of the annular excitation area, each excitation point on the annular excitation area corresponds to a central detection point, an interferometer receives ultrasonic vibration information reflected by the central detection point, and the obtained result is input into a computer through an oscilloscope;
step 2, controlling the step length of the stepping motor by using a computer, moving to the next detection position according to the set step length, and repeating the step 2 until the two-dimensional scanning of the surface of the sample to be detected is completed;
step 3, according to the propagation characteristics of the ultrasonic waves in the sample to be detected, a computer is used for annularly subdividing the area to be detected to obtain data of pixel points in the sample to be detected, and the distance between each pixel point and an annular excitation point and a central detection point is calculated, namely the propagation path of the ultrasonic waves in the sample to be detected;
step 4, taking a point excitation point A on the annular excitation beam, setting B as a central detection point, C as a certain pixel point in the sample to be detected, and d1，d2Respectively representing the distance from the pixel point C to the excitation point A and the central detection point B, and v represents the propagation velocity of the ultrasonic wave in the sample to be detected; the ultrasonic signal excited by the excitation point A is rapidly transmitted in the sample, if the pixel point C is a defect, the ultrasonic wave is transmitted to the defect point C to be reflected, finally the reflected signal is received by the central detection point B, and the distance of the ultrasonic wave transmission is d-d in the process1+d2The central detection point receives a reflected echo signal of the ultrasonic wave at the moment t ═ d/v;
and 5, performing time-delay superposition on the reflection echo signals of the pixel points in the to-be-detected region of the sample to be detected by using a time-domain SAFT algorithm, and accumulating the calculation results of the central detection points corresponding to all the annular excitation points to obtain the imaging result of the internal defect position of the sample.
Further, let MiIs a central probe point corresponding to different excitation points on the annular excitation beam, i is 1,2,3, … N, S (M)iT) as central detecting point and different excitation points at t ═ (d)1+d2) The signal detected at time/v; if pixel C is defective, signal S (M)iT) a defect-induced reflection peak will appear; if pixel C is not defective, signal S (M)iAnd no reflection peak appears in t). The expression of performing inversion reconstruction on the pixel point C in the sample to be detected is sigma (C) to sigma S (M)iT); and finally, accumulating the calculation results of all the central detection points, and averaging the repeatedly superposed areas according to weights to realize the reconstruction of each point in the sample to be detected.
Compared with the prior art, the invention has the following beneficial effects:
(1) the device of this application can use in laser supersound nondestructive test technique, can obtain the ultrasonic signal who carries the sample internal defect that awaits measuring, uses conical lens to form annular excitation, compares with traditional laser supersound SAFT single-point detection, when improving the discernment ability and the imaging resolution ratio that detect the inside small defect of defect, has reduced the scanning time, has improved the work efficiency of system greatly.
(2) The device of the application has the advantages of simple structure, wide application range and high adjustability.
Drawings
FIG. 1 is a schematic diagram of the surface excitation of a sample to be measured in the present invention. Wherein, the light beam is irradiated on the surface of the sample to be detected through the conical lens to form annular excitation and single-point detection.
Fig. 2 is a focusing imaging device based on ring beam laser ultrasonic synthetic aperture in the invention. Wherein, 1 is a pulse laser in the laser light source system, 2 is a beam expander in the excitation light source system, 3 is a plane reflector in the excitation light source system, 4 is a conical lens in the excitation light source system, 5 is a focusing lens in the excitation light source system, 6 is an interferometer in the detection light source system, 7 is a beam combining lens in the detection light source system, 8 is an oscilloscope of the signal output and control system, 9 is a computer in the signal output and control system, 10 is a sample to be detected in the system to be detected, and 11 is a stepping motor in the system to be detected.
Fig. 3 is a three-dimensional schematic diagram of the ring laser ultrasonic testing of the sample 10 to be tested according to the present invention. Wherein A is an excitation point on the annular excitation beam, B is a central detection point, C is a pixel point in the sample 10 to be measured, and d1Distance of excitation point A to pixel point C, d2The distance from the central probe point B to the pixel point C.
Detailed Description
A focusing imaging device based on ring beam laser ultrasonic synthetic aperture is composed of an excitation light source system, a detection light source system, a signal output and control system and a system to be detected. As shown in fig. 1 and 2, the excitation light source system is configured to generate an excitation light source, the detection light source system is configured to generate a detection light source and receive a vibration ultrasonic signal, the signal output and control system is configured to receive an ultrasonic signal output by an oscilloscope, control a pulse laser and a stepper motor, the system to be detected is configured to place a sample to be detected and receive an annular excitation signal and a reflection detection signal, and the stepper motor is configured to move the sample to be detected to complete two-dimensional scanning.
Preferably, the excitation light source system is composed of a pulse laser 1, a beam expander 2, a plane reflector 3, a conical lens 4 and a focusing lens 5, the beam expander 2 is arranged along the direction of a laser source output by the pulse laser 1, the plane reflector 3, the conical lens 4 and the focusing lens 5 are sequentially arranged in the direction of a laser beam output by the pulse laser 1, the pulse laser beam expands after passing through the beam expander 2, the expanded beam forms an excitation annular beam after being reflected by the reflector 3 and passing through the conical lens 4, and the excitation annular beam is focused on a sample to be measured 10 in the system to be measured through the focusing lens 5.
Preferably, the detection light source system includes an interferometer 6 and a beam combiner 7, in the detection light beam direction output by the interferometer 6, the detection light beam output by the interferometer 6 passes through the beam combiner 7, the detection light beam and the excitation annular light beam are combined, the detection light beam is reflected by the beam combiner 7 and then irradiated in the system to be measured, and the detection light beam is reflected by the sample to be measured 10 and then returns to the interferometer 6 in the detection light source system again.
Preferably, the signal output and control system comprises an oscilloscope 8 and a computer 9, the oscilloscope 8 is connected with the interferometer 6 in the detection light source system, receives the vibration signal detected by the interferometer 6, and outputs the detected vibration signal to the computer 9, the computer 9 is connected with the pulse laser 1 in the excitation light source system and the stepping motor 11 in the region to be detected, and various parameters of the pulse laser 1 and the stepping step length of the stepping motor 11 are controlled.
Preferably, the system to be measured includes a sample to be measured 10 and a stepping motor 11, the sample to be measured 10 receives an annular light beam emitted from an excitation light source system, an ultrasonic signal is reflected to enter the detection light source system, and the stepping motor 11 controls the position of the sample to be measured 10 irradiated by the annular light beam to complete two-dimensional scanning of the surface of the sample to be measured 10 by the annular light beam.
The invention is described in further detail below with reference to the accompanying drawings, in which:
examples
The utility model provides a based on annular beam laser supersound synthetic aperture focus image device, includes excitation light source system, surveys light source system, signal output and control system and system under test, combines fig. 2, explains the theory of operation of each subsystem in detail:
excitation light source system includes pulse laser 1, beam expander 2, plane mirror 3, conical lens 4 and focusing lens 5, cyclic annular laser signal arouse by pulse laser 1, through the 2 beam expansions of beam expander, secondly enter conical lens 4 behind plane mirror 3, become the beam expanding beam into annular light beam behind conical lens 4, annular light beam passes through focusing lens 5 and focuses on 10 surface excitation laser supersound of sample that awaits measuring.
The detection light source system comprises an interferometer 6 and a beam combining mirror 7, wherein the detection light source is excited by the interferometer 6, is concentrically combined with annular excitation light beams through the beam combining mirror 7 and is irradiated on the surface of a sample 10 to be detected after being reflected by the beam combining mirror 7, an ultrasonic signal is generated after the surface of the sample 10 to be detected is reflected by the detection light source, the annular excitation light beams are irradiated on the surface of the sample 10 to be detected to form ultrasonic waves, reflection echoes are formed after the internal defects of the sample 10 to be detected are reflected, and the reflection echoes cause the surface of the sample 10 to be detected to generate vibration ultrasonic signals.
The signal output and control system comprises an oscilloscope 8 and a computer 9, wherein the output of the ultrasonic signal is output to the oscilloscope 8 by an interferometer 6, then the oscilloscope 8 outputs the ultrasonic signal to the computer 9 to obtain a defect signal inside the sample 10 to be detected in real time, the computer 9 is connected with the pulse laser 1 in the excitation light source system, and the computer 9 is used for controlling various parameters of the pulse laser 1 to complete the generation of the annular excitation light beam to excite the ultrasonic signal on the sample 10 to be detected.
The system to be tested comprises a sample to be tested 10 and a stepping motor 11, wherein the sample to be tested 10 receives an annular light beam excited in an excitation light source system, a laser ultrasonic field is formed inside the sample to be tested 10, a reflection echo is generated after defect reflection and is transmitted to the surface of the sample to be tested 10 to form surface vibration, an interferometer 6 in a detection light source system receives a vibration ultrasonic signal, the stepping motor 11 controls the stepping step length and the stepping distance of the stepping motor 11 through a connection computer 9, and the two-dimensional scanning of the surface of the sample to be tested 10 is completed.
The use method of the ring beam laser ultrasonic synthetic aperture focusing imaging device comprises the following steps:
(1) the method comprises the steps of placing a sample 10 to be detected in a scanning area in an excitation light source system, generating an annular excitation light beam by using a conical lens 4, focusing the annular excitation light beam on the surface of the sample 10 to be detected by using a focusing lens 5, generating an annular excitation area on the surface of the sample 10 to be detected by using the annular excitation light beam, synthesizing and concentric a detection light beam and the annular excitation light beam by using a beam combining mirror 7, namely detecting in the center of the annular excitation area, wherein each excitation point on the annular excitation area corresponds to a central detection point, receiving ultrasonic vibration information reflected by the central detection point by using an interferometer 6, and inputting the obtained result into a computer 9 through an oscilloscope 8.
(2) And (3) controlling the step length of the stepping motor 11 by using the computer 9, moving to the next detection position according to the set step length, and repeating the step (2) until the two-dimensional scanning of the surface of the sample 10 to be detected is completed.
(3) According to the propagation characteristic of the ultrasonic wave in the sample 10 to be measured, the computer 9 is used for annularly subdividing the area to be measured to obtain data of pixel points in the sample 10 to be measured, and the distance between each pixel point and an annular excitation point and a central detection point is calculated, namely the propagation path of the ultrasonic wave in the sample 10 to be measured.
(4) Taking a point on the annular excitation beam, wherein the excitation point A, the point B are central detection points, the point C is a certain pixel point in the sample 10 to be detected, and the point d is1，d2The distances from the pixel point C to the excitation point a and the central detection point B are respectively, and v represents the propagation velocity of the ultrasonic wave in the sample 10 to be measured. The ultrasonic signal excited by the excitation point A is rapidly transmitted in the sample, if the pixel point C is a defect, the ultrasonic wave is transmitted to the defect point C to be reflected, finally, the reflected signal is received by the central detection point B, and the distance of the ultrasonic wave transmission is d-d in the process1+d2And the central detection point receives a reflection echo signal of the ultrasonic wave at the time t-d/v.
(5) And (3) performing time-delay superposition on the reflection echo signals of the pixel points in the region to be detected of the sample 10 to be detected by utilizing a time domain SAFT algorithm, and accumulating the calculation results of the central detection points corresponding to all the annular excitation points to obtain the imaging result of the internal defect position of the sample.
As shown in fig. 3, the size of the three-dimensional aluminum block sample is 20.00mm × 20.00mm × 20.00mm, the upper surface of the aluminum block sample is a free plane, and the step length of the stepping motor 11 is set to 1 mm. And modulating the annular excitation light beam by using an excitation light source system, focusing the annular excitation light beam to an excitation position arranged on the upper surface of the aluminum block, moving the position of the aluminum block sample by using a stepping motor, sequentially exciting laser ultrasound at each excitation position by using the annular excitation light beam, simultaneously sequentially receiving ultrasonic echo signals at a central detection point by using an interferometer 6, inputting the obtained result into a computer 9 through an oscilloscope 8, and repeating the steps until the two-dimensional scanning of the upper surface of the aluminum block sample is completed. The upper surface A of the aluminum block is an excitation point in an annular excitation beam, B is a central detection point, C is a pixel point in the aluminum block, d1Distance of excitation point A to pixel point C, d2The distance from the central detection point B to the pixel point C, v is the wave velocity of the ultrasonic wave, MiIs a central probe point corresponding to different excitation points on the annular excitation beam, i is 1,2,3, … N, S (M)iT) as central detecting point and different excitation points at t ═ (d)1+d2) The signal detected at time/v. If pixel C is defective, signal S (M)iT) a defect-induced reflection peak will appear; if pixel C is not defective, signal S (M)iAnd no reflection peak appears in t). The expression of performing inversion reconstruction on the pixel point C in the aluminum block sample is sigma (C) to sigma S (M)iT). And finally, accumulating the calculation results of all the central detection points, and averaging the repeatedly superposed areas according to weights to reconstruct each point in the aluminum block sample.

Claims (10)

1. The utility model provides a focus image device based on annular beam laser supersound synthetic aperture which characterized in that, includes excitation light source system, detection light source system, system under test and signal output and control system, excitation light source system be used for using pulse laser to produce the excitation light source, detection light source system is used for producing detection light source and receiving ultrasonic signal, the system under test is used for placing the sample that awaits measuring and receives cyclic annular laser signal and reflection defect signal to use step motor to remove the sample that awaits measuring and accomplish the two-dimensional scanning, signal output and control system are used for output, the control pulse laser ware and the step motor of ultrasonic signal.
2. The focusing and imaging device based on the ring-beam laser ultrasonic synthetic aperture according to claim 1, wherein the excitation light source system comprises a pulse laser (1), a beam expander (2), a plane reflector (3), a conical lens (4) and a focusing lens (5), the excitation light beam output by the pulse laser (1) is expanded by the beam expander (2) and reflected by the plane reflector (3) and then is changed into a ring-beam after passing through the conical lens (4), and the ring-beam is focused on the surface of the sample (10) to be measured after passing through the focusing lens (5) to form laser ultrasound.
3. The ring-beam laser-based ultrasonic synthetic aperture focusing imaging device according to claim 2, wherein the detection light source system comprises an interferometer (6) and a beam combining mirror (7), and the detection light beam emitted by the interferometer (6) is combined concentrically with the ring-shaped excitation light beam through the beam combining mirror (7).
4. The device for forming an image based on ring-beam laser ultrasonic synthetic aperture focus according to claim 3, wherein the laser output by the pulse laser (1) in the excitation light source system is pulse laser, and the laser output by the interferometer (6) in the detection light source system is continuous laser.
5. The ring-beam laser-based ultrasonic synthetic aperture focusing imaging device according to claim 1, wherein the signal output and control system is used for controlling various parameters of the pulse laser (1) in the excitation light source system and the step length and step distance of the stepping motor (11) in the system to be measured.
6. The ring beam laser based ultrasonic synthetic aperture focusing imaging device according to claim 5, wherein the signal output and control system comprises an oscilloscope (8) and a computer (9), the oscilloscope (8) is connected with the interferometer (6) in the detection light source system, receives the vibration signal detected by the interferometer (6), and outputs the detected vibration signal to the computer (9), the computer (9) is connected with the pulse laser (1) in the excitation light source system and the stepping motor (11) in the area to be detected, and various parameters of the pulse laser (1) and the stepping step length of the stepping motor (11) are controlled.
7. The device according to claim 6, wherein the system to be measured includes a sample (10) to be measured and a stepping motor (11), the sample (10) to be measured receives the annular beam emitted from the excitation light source system, the ultrasonic signal is reflected to the detection light source system, and the stepping motor (11) controls the position of the annular beam irradiated on the sample (10) to be measured, so as to complete the two-dimensional scanning of the surface of the sample (10) to be measured by the annular beam.
8. A method of using the ring beam laser based ultrasonic synthetic aperture focusing imaging apparatus according to any one of claims 1-7, comprising the steps of:
step 1, a sample (10) to be detected is placed in a scanning area in an excitation light source system, a conical lens (4) is used for generating an annular excitation light beam, a focusing lens (5) is used for focusing the annular excitation light beam on the surface of the sample (10) to be detected, the annular excitation light beam generates an annular excitation area on the surface of the sample (10) to be detected, a beam combining mirror (7) is used for combining and concentric detection light beams and the annular excitation light beam, namely detection is carried out at the center of the annular excitation area, each excitation point on the annular excitation area corresponds to a central detection point, an interferometer (6) receives ultrasonic vibration information reflected by the central detection point, and the obtained result is input into a computer (9) through an oscilloscope (8);
step 2, controlling the step length of the stepping motor (11) by using the computer (9), moving to the next detection position according to the set step length, and repeating the step 2 until the two-dimensional scanning of the surface of the sample (10) to be detected is completed;
step 3, according to the propagation characteristic of the ultrasonic wave in the sample (10) to be detected, a computer (9) is used for annularly subdividing the area to be detected to obtain data of pixel points in the sample (10) to be detected, and the distance between each pixel point and an annular excitation point and a central detection point is calculated, namely the propagation path of the ultrasonic wave in the sample (10) to be detected;
step 4, taking a point excitation point A on the annular excitation beam, setting B as a central detection point, C as a certain pixel point in the sample (10) to be detected, and d1，d2Respectively representing the distance from the pixel point C to the excitation point A and the central detection point B, and v represents the propagation velocity of the ultrasonic wave in the sample (10) to be detected; the ultrasonic signal excited by the excitation point A is rapidly transmitted in the sample, if the pixel point C is a defect, the ultrasonic wave is transmitted to the defect point C to be reflected, finally, the reflected signal is received by the central detection point B, and the distance of the ultrasonic wave transmission is d-d in the process1+d2The central detection point receives a reflected echo signal of the ultrasonic wave at the moment t ═ d/v;
and 5, performing time-delay superposition on the reflected echo signals of the pixel points in the region to be detected of the sample (10) to be detected by using a time-domain SAFT algorithm, and accumulating the calculation results of the central detection points corresponding to all the annular excitation points to obtain the imaging result of the internal defect position of the sample.
9. The method of claim 8, wherein let M beiIs a central probe point corresponding to different excitation points on the annular excitation beam, i is 1,2,3, … N, S (M)iT) as central detecting point and different excitation points at t ═ (d)1+d2) The signal detected at time/v; if pixel C is defective, signal S (M)iT) a defect-induced reflection peak will appear; if pixel C is not defective, signal S (M)iAnd no reflection peak appears in t).
10. The method as claimed in claim 9, wherein the expression for performing the inversion reconstruction on the internal pixel point C of the sample to be tested is Σ (C) ═ Σ S (M)iT); finally, the calculation results of all the central detection points are accumulated, and the repeatedly superposed areas are averaged according to weight, namelyThe reconstruction of each point in the sample to be detected can be realized.
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