阅读说明：本技术 一种基于超声显微镜点聚焦换能器的自动对焦方法和系统 (Automatic focusing method and system based on point focusing transducer of ultrasonic microscope ) 是由 梁昊 吕科 薛健 于 2020-08-20 设计创作，主要内容包括：本申请实施例公开了一种基于超声显微镜点聚焦换能器的自动对焦方法和系统,其中所述方法包括：取得试件表面的A扫描信号图像；设置对焦参数；根据中介液温度对中介液中的声速进行修正,通过点聚焦换能器声学透镜的焦距、延时等参数计算上表面自动对焦的位置；通过离散小波分解和维纳反卷积对A扫描信号进行解析,得到试件的分层信息；根据试件的分层信息选择目标对焦中间层反射信号；移动换能器找到中间层反射信号最大的概略位置点坐标；移动点聚焦换能器回到最大的位置点坐标的上一坐标点；移动点聚焦换能器,找到反射信号最大值的精确位置点坐标,以完成自动对焦。有效提高超声显微镜点聚焦换能器在使用过程中的对焦速度和精度。(The embodiment of the application discloses an automatic focusing method and system based on an ultrasonic microscope point focusing transducer, wherein the method comprises the following steps: acquiring an A scanning signal image of the surface of the test piece; setting focusing parameters; correcting the sound velocity in the medium liquid according to the temperature of the medium liquid, and calculating the position of the upper surface automatic focusing through parameters such as the focal length and the time delay of the acoustic lens of the point focusing transducer; analyzing the A scanning signal through discrete wavelet decomposition and wiener deconvolution to obtain the layered information of the test piece; selecting a target focusing middle layer reflection signal according to the layering information of the test piece; moving the transducer to find the coordinates of the approximate position point with the maximum intermediate layer reflection signal; moving the point focusing transducer back to the last coordinate point of the maximum position point coordinate; and moving the point focusing transducer to find the precise position point coordinate of the maximum value of the reflected signal so as to complete automatic focusing. The focusing speed and precision of the ultrasonic microscope point focusing transducer in the using process are effectively improved.)

1. An auto-focusing method based on an ultrasonic microscope point focusing transducer, characterized in that the method comprises:

acquiring an A scanning signal image of the surface of the test piece;

setting focusing parameters, wherein the focusing parameters comprise a time delay parameter, a focal length parameter and a medium liquid temperature parameter of a point focusing transducer;

correcting the sound velocity in the medium liquid according to the temperature of the medium liquid, and calculating the position of the upper surface automatic focusing through the focal length and the time delay parameter of the acoustic lens of the point focusing transducer so as to move the point focusing transducer to the position to finish the upper surface automatic focusing;

analyzing the A scanning signal through discrete wavelet decomposition and wiener deconvolution to obtain the layered information of the test piece;

selecting a target focusing middle layer reflection signal according to the layering information of the test piece;

moving the transducer to find the coordinates of the approximate position point with the maximum intermediate layer reflection signal;

moving the point focusing transducer back to the last coordinate point of the maximum position point coordinate;

and moving the point focusing transducer to find the precise position point coordinate of the maximum value of the reflected signal so as to complete automatic focusing.

2. The method of claim 1, wherein the point focus transducer focal length parameter is calculated according to the formula:

F_L＝R/(1-c₀/c₁)

wherein R is the radius of curvature of the acoustic lens, c₀Representing the speed of sound in the mediating fluid, c₁Representing the speed of sound in the lens.

3. The method of claim 1, wherein the a-scan signal is composed of complex reflected waves of M-layer structure inside the detected object, and the a-scan signal is modeled as:

wherein n (t) is a noise function, which represents convolution, and x (t) is an incident signal function; if noise is not considered, y (t) is the convolution of x (t) and r (t).

4. The method of claim 1, wherein the moving transducer finding the location point coordinates where the intermediate layer reflected signal is maximum comprises:

controlling the transducer to vertically move to the upper surface of the test piece in a step of a set distance in the Z-axis direction, and analyzing the sampled A scanning signal to obtain a reflection signal of the middle layer; and judging whether the intermediate layer reflection signal is gradually enhanced or weakened, if so, the maximum value of the layered reflection signal appears between the last two set distance stepping coordinate points.

5. The method of claim 1, wherein the moving point focusing transducer, finding the precise location of the maximum of the reflected signal to accomplish auto-focusing, comprises:

and in the process of moving the point focusing transducer every time, acquiring an A scanning signal to analyze the signal, judging whether the reflected signal of the middle layer is gradually enhanced or weakened, if the reflected signal of the middle layer is weakened, determining the maximum value of the layered reflected signal and the corresponding Z-axis coordinate thereof, moving the ultrasonic transducer to the coordinate, and finishing the automatic focusing of the middle layer.

6. An autofocus system based on an ultrasonic microscope point focus transducer, the system comprising:

the initial signal acquisition module is used for acquiring an A scanning signal image of the surface of the test piece;

the focusing parameter calculation module is used for setting focusing parameters, and the focusing parameters comprise a time delay parameter, a focal length parameter and an intermediate liquid temperature parameter of the point focusing transducer;

the upper surface automatic focusing module is used for correcting the sound velocity in the medium liquid according to the temperature of the medium liquid, and calculating the position of upper surface automatic focusing through the focal length and the time delay parameter of the acoustic lens of the point focusing transducer so as to move the point focusing transducer to the position to finish upper surface automatic focusing;

the layered information calculation module is used for analyzing the scanning signal A through discrete wavelet decomposition and wiener deconvolution to obtain layered information of the test piece;

the target focusing middle layer reflection signal determination module is used for selecting a target focusing middle layer reflection signal according to the layering information of the test piece;

the position point coordinate determination module with the maximum reflected signal is used for moving the transducer to find the position point coordinate with the maximum reflected signal of the middle layer;

the middle layer approximate focusing module is used for moving the point focusing transducer to return to the last coordinate point of the maximum position point coordinate;

and the automatic focusing module is used for moving the point focusing transducer and finding out the accurate position of the maximum value of the reflected signal so as to finish automatic focusing.

7. The system of claim 6, wherein in the focus parameter calculation module, the point focus transducer focal length parameter is calculated according to the formula:

F_L＝R/(1-c₀/c₁)

wherein R is the radius of curvature of the acoustic lens, c₀Representing the speed of sound in the mediating fluid, c₁Representing the speed of sound in the lens.

8. The system of claim 6, wherein the a-scan signal is composed of complex reflected waves of M-layer structure inside the detected object, and the a-scan signal is modeled as:

wherein n (t) is a noise function, which represents convolution, and x (t) is an incident signal function; if noise is not considered, y (t) is the convolution of x (t) and r (t).

9. The system of claim 6, wherein the location point coordinate determination module at which the reflected signal is a maximum is specifically configured to:

controlling the transducer to vertically move to the upper surface of the test piece in a step of a set distance in the Z-axis direction, and analyzing the sampled A scanning signal to obtain a reflection signal of the middle layer; and judging whether the intermediate layer reflection signal is gradually enhanced or weakened, and if the intermediate layer reflection signal is gradually weakened, the maximum value of the layered reflection signal appears between the last two set distance stepping coordinate points.

10. The system of claim 6, wherein the auto-focus module is specifically configured to:

in the process of moving the point focusing transducer each time, collecting an A scanning signal to analyze the signal, judging whether the reflected signal of the middle layer is gradually enhanced or weakened, if the reflected signal of the middle layer is gradually weakened, determining the maximum value of the layered reflected signal and the corresponding Z-axis coordinate thereof, moving the ultrasonic transducer to the coordinate, and finishing the automatic focusing of the middle layer.

Technical Field

The embodiment of the application relates to the technical field of acoustic technology and nondestructive testing, in particular to an automatic focusing method and system based on an ultrasonic microscope point focusing transducer.

Background

The ultrasonic microscope is nondestructive testing and microscopic imaging equipment widely adopted in high-tech manufacturing industries such as chip manufacturing, biomedicine, material science and the like. An ultrasonic microscope (such as an ultrasonic microscope schematic diagram of fig. 1) generally adopts a liquid immersion point focusing ultrasonic transducer (such as a point focusing ultrasonic transducer focusing schematic diagram of fig. 2), and the transducer can converge an acoustic beam at one point, so that the energy concentration of a convergence area is enhanced, the width of the acoustic beam is reduced, and the detection requirements of high sensitivity and high resolution can be met.

At present, an ultrasonic microscope generally adopts an artificial focusing method, the method is low in precision and efficiency, especially for high-integration IC chips, multilayer thin film materials and the like, the detection efficiency is greatly reduced by artificial focusing, and the detection effect is possibly influenced. In the process of scanning imaging and nondestructive testing of a test piece with a complex multilayer structure, particularly a tested piece such as a chip, by using a point focusing transducer, the focusing process of the intermediate layer requires an operator to have abundant working experience and long operation time. This also greatly limits the widespread use of ultrasound microscopes.

Currently, the layered structure and process of many inspected objects has reached the submicron level due to the continuous progress of the manufacturing process. Whereas point focus transducers above 50MHZ have a depth of field below 10 microns, scanning requires repeated adjustments to the vertical position of the transducer to match the focal plane to the target layer. Particularly, when a high-frequency ultrasonic transducer is used, the depth of field work is smaller, and higher focusing accuracy is required.

Disclosure of Invention

Therefore, the embodiment of the application provides an automatic focusing method and system based on an ultrasonic microscope point focusing transducer, which can realize rapid automatic focusing on the surface and the middle layer. The focusing speed and the focusing accuracy of the ultrasonic microscope point focusing transducer in the using process are effectively improved, the randomness and the uncertainty caused by manual operation in the focusing process are greatly reduced, the degree of dependence on the technical level and the working experience of an operator is reduced, the operation complexity is reduced, and the working efficiency is improved.

In order to achieve the above object, the embodiments of the present application provide the following technical solutions:

according to a first aspect of embodiments of the present application, there is provided an autofocus method based on an ultrasound microscope point focus transducer, the method comprising:

acquiring an A scanning signal image of the surface of the test piece;

setting focusing parameters, wherein the focusing parameters comprise a time delay parameter, a focal length parameter and a medium liquid temperature parameter of a point focusing transducer;

correcting the sound velocity in the medium liquid according to the temperature of the medium liquid, and calculating the position of the upper surface automatic focusing through the focal length and the time delay parameter of the acoustic lens of the point focusing transducer so as to move the point focusing transducer to the position to finish the upper surface automatic focusing;

analyzing the A scanning signal through discrete wavelet decomposition and wiener deconvolution to obtain the layered information of the test piece;

selecting a target focusing middle layer reflection signal according to the layering information of the test piece;

moving the transducer to find the coordinates of the approximate position point with the maximum intermediate layer reflection signal;

moving the point focusing transducer back to the last coordinate point of the maximum position point coordinate;

and moving the point focusing transducer to find the precise position point coordinate of the maximum value of the reflected signal so as to complete automatic focusing.

Optionally, the focal length parameter of the point focus transducer is calculated according to the following formula:

F_L＝R/(1-c₀/c₁)

wherein R is the radius of curvature of the acoustic lens, c₀Representing the speed of sound in the mediating fluid, c₁Representing the speed of sound in the lens.

Optionally, the a-scan signal is composed of a complex reflected wave of an M-layer structure inside the detected object, and a model of the a-scan signal is as follows:

wherein n (t) is a noise function, which represents convolution, and x (t) is an incident signal function; if noise is not considered, y (t) is the convolution of x (t) and r (t).

Optionally, the moving transducer finding the position point coordinate where the intermediate layer reflection signal is maximum includes:

controlling the transducer to vertically move to the upper surface of the test piece in a step of a set distance in the Z-axis direction, and analyzing the sampled A scanning signal to obtain a reflection signal of the middle layer; and judging whether the intermediate layer reflection signal is gradually enhanced or weakened, and if the intermediate layer reflection signal is gradually weakened, the maximum value of the layered reflection signal appears between the last two set distance stepping coordinate points.

Optionally, the moving-point focusing transducer finding the precise location of the maximum of the reflected signal to accomplish auto-focusing comprises:

in the process of moving the point focusing transducer each time, collecting an A scanning signal to analyze the signal, judging whether the reflected signal of the middle layer is gradually enhanced or weakened, if the reflected signal of the middle layer is gradually weakened, determining the maximum value of the layered reflected signal and the corresponding Z-axis coordinate thereof, moving the ultrasonic transducer to the coordinate, and finishing the automatic focusing of the middle layer.

According to a second aspect of embodiments of the present application, there is provided an autofocus system based on an ultrasonic microscope point focus transducer, the system comprising:

the initial signal acquisition module is used for acquiring an A scanning signal image of the surface of the test piece;

the focusing parameter calculation module is used for setting focusing parameters, and the focusing parameters comprise a time delay parameter, a focal length parameter and an intermediate liquid temperature parameter of the point focusing transducer;

the upper surface automatic focusing module is used for correcting the sound velocity in the medium liquid according to the temperature of the medium liquid, and calculating the position of upper surface automatic focusing through the focal length and the time delay parameter of the acoustic lens of the point focusing transducer so as to move the point focusing transducer to the position to finish upper surface automatic focusing;

the layered information calculation module is used for analyzing the scanning signal A through discrete wavelet decomposition and wiener deconvolution to obtain layered information of the test piece;

the target focusing middle layer reflection signal determination module is used for selecting a target focusing middle layer reflection signal according to the layering information of the test piece;

the position point coordinate determination module with the maximum reflected signal is used for moving the transducer to find the approximate position point coordinate with the maximum reflected signal of the middle layer;

the middle layer approximate focusing module is used for moving the point focusing transducer to return to the last coordinate point of the maximum position point coordinate;

and the automatic focusing module is used for moving the point focusing transducer and finding out the accurate position point coordinate of the maximum value of the reflected signal so as to finish automatic focusing.

Optionally, in the focusing parameter calculating module, the focal length parameter of the point focusing transducer is calculated according to the following formula:

F_L＝R/(1-c₀/c₁)

wherein R is the radius of curvature of the acoustic lens, c₀Representing the speed of sound in the mediating fluid, c₁Representing the speed of sound in the lens.

Optionally, the a-scan signal is composed of a complex reflected wave of an M-layer structure inside the detected object, and a model of the a-scan signal is as follows:

wherein n (t) is a noise function, which represents convolution, and x (t) is an incident signal function; if noise is not considered, y (t) is the convolution of x (t) and r (t).

Optionally, the module for determining the coordinates of the position point with the maximum reflection signal is specifically configured to:

controlling the transducer to vertically move to the upper surface of the test piece in a step of a set distance in the Z-axis direction, and analyzing the sampled A scanning signal to obtain a reflection signal of the middle layer; and judging whether the intermediate layer reflection signal is gradually enhanced or weakened, and if the intermediate layer reflection signal is gradually weakened, the maximum value of the layered reflection signal appears between the last two set distance stepping coordinate points.

Optionally, the auto-focusing module is specifically configured to:

in the process of moving the point focusing transducer each time, collecting an A scanning signal to analyze the signal, judging whether the reflected signal of the middle layer is gradually enhanced or weakened, if the reflected signal of the middle layer is gradually weakened, determining the maximum value of the layered reflected signal and the corresponding Z-axis coordinate thereof, moving the ultrasonic transducer to the coordinate, and finishing the automatic focusing of the middle layer.

In summary, the embodiment of the present application provides an automatic focusing method and system based on an ultrasonic microscope point focusing transducer, by obtaining an a scanning signal image of a surface of a test piece; setting focusing parameters, wherein the focusing parameters comprise a time delay parameter, a focal length parameter and a medium liquid temperature parameter of a point focusing transducer; correcting the sound velocity in the medium liquid according to the temperature of the medium liquid, and calculating the position of the upper surface automatic focusing through the focal length and the time delay parameter of the acoustic lens of the point focusing transducer so as to move the point focusing transducer to the position to finish the upper surface automatic focusing; analyzing the A scanning signal through discrete wavelet decomposition and wiener deconvolution to obtain the layered information of the test piece; selecting a target focusing middle layer reflection signal according to the layering information of the test piece; moving the transducer to find the coordinates of the approximate position point with the maximum intermediate layer reflection signal; moving the point focusing transducer back to the last coordinate point of the maximum position point coordinate; and moving the point focusing transducer to find the precise position point coordinate of the maximum value of the reflected signal so as to complete automatic focusing. The focusing speed and the focusing accuracy of the ultrasonic microscope point focusing transducer in the using process are effectively improved, the randomness and the uncertainty caused by manual operation in the focusing process are greatly reduced, the degree of dependence on the technical level and the working experience of an operator is reduced, the operation complexity is reduced, and the working efficiency is improved.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It should be apparent that the drawings in the following description are merely exemplary, and that other embodiments can be derived from the drawings provided by those of ordinary skill in the art without inventive effort.

The structures, ratios, sizes, and the like shown in the present specification are only used for matching with the contents disclosed in the specification, so that those skilled in the art can understand and read the present invention, and do not limit the conditions for implementing the present invention, so that the present invention has no technical significance, and any structural modifications, changes in the ratio relationship, or adjustments of the sizes, without affecting the functions and purposes of the present invention, should still fall within the scope of the present invention.

FIG. 1 is a schematic diagram of an ultrasonic microscope provided by an embodiment of the present application;

fig. 2 is a focusing schematic diagram of a point focusing ultrasonic transducer provided in an embodiment of the present application;

fig. 3 is a schematic flow chart of an automatic focusing method based on an ultrasonic microscope point focusing transducer according to an embodiment of the present application;

FIG. 4 is a logic flow diagram of a method for automatically focusing an intermediate layer according to an embodiment of the present application;

fig. 5 is an a-scan echo signal of the flip chip provided in the embodiment of the present application;

fig. 6 is a schematic diagram illustrating analysis of layered information of a plastic packaged chip according to an embodiment of the present application;

fig. 7 is a schematic diagram illustrating a layered information analysis of a flip chip according to an embodiment of the present application;

FIG. 8 is a schematic diagram of a focusing curve of a reflected signal according to an embodiment of the present disclosure;

fig. 9 is a block diagram of an autofocus system based on an ultrasonic microscope point focusing transducer according to an embodiment of the present application.

Detailed Description

The present invention is described in terms of particular embodiments, other advantages and features of the invention will become apparent to those skilled in the art from the following disclosure, and it is to be understood that the described embodiments are merely exemplary of the invention and that it is not intended to limit the invention to the particular embodiments disclosed. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

In view of the above problems, the embodiments of the present application provide an automatic focusing technique based on an ultrasonic microscope point focusing transducer, which can effectively solve the problems of slow focusing speed and low precision of the ultrasonic microscope point focusing transducer, and improve the imaging quality and nondestructive testing efficiency of an ultrasonic microscope. As shown in fig. 3, the method comprises the steps of:

step 301: an a-scan signal image of the specimen surface is acquired.

Step 302: and setting focusing parameters, wherein the focusing parameters comprise a time delay parameter, a focal length parameter and a medium temperature parameter of the point focusing transducer.

Step 303: and correcting the sound velocity in the medium liquid according to the temperature of the medium liquid, and calculating the position of the upper surface automatic focusing through the focal length and the time delay parameters of the acoustic lens of the point focusing transducer so as to move the point focusing transducer to the position to finish the upper surface automatic focusing.

Step 304: and analyzing the A scanning signal through discrete wavelet decomposition and wiener deconvolution to obtain the layered information of the test piece.

Step 305: and selecting a target focusing middle layer reflection signal according to the layering information of the test piece.

Step 306: the transducer is moved to find the approximate location point coordinates where the reflected signal from the intermediate layer is the largest.

Step 307: the moving point focus transducer returns to the last coordinate point of the maximum location point coordinates.

Step 308: and moving the point focusing transducer to find the precise position point coordinate of the maximum value of the reflected signal so as to complete automatic focusing.

In one possible implementation, in step 302, the point focus transducer focal length parameter is calculated according to the following equation (1):

F_L＝R/(1-c₀/c₁) … … formula (1)

Wherein R is the radius of curvature of the acoustic lens, c₀Representing the speed of sound in the intervening fluid,c₁representing the speed of sound in the lens.

In one possible embodiment, the a-scan signal is composed of a complex reflected wave of an M-layer structure inside the detected object, and the model of the a-scan signal is shown in formula (2):

wherein n (t) is a noise function, which represents convolution, and x (t) is an incident signal function; if noise is not considered, y (t) is the convolution of x (t) and r (t).

In one possible embodiment, in step 306, the moving transducer finds the coordinates of the position point where the intermediate layer reflection signal is maximum, including: controlling the transducer to vertically move to the upper surface of the test piece in a step of a set distance in the Z-axis direction, and analyzing the sampled A scanning signal to obtain a reflection signal of the middle layer; and judging whether the intermediate layer reflection signal is gradually enhanced or weakened, and if the intermediate layer reflection signal is gradually weakened, the maximum value of the layered reflection signal appears between the last two set distance stepping coordinate points.

In one possible embodiment, in step 308, the moving point focusing transducer finds the precise location of the maximum of the reflected signal to accomplish the auto-focusing, including: in the process of moving the point focusing transducer each time, collecting an A scanning signal to analyze the signal, judging whether the reflected signal of the middle layer is gradually enhanced or weakened, if the reflected signal of the middle layer is gradually weakened, determining the maximum value of the layered reflected signal and the corresponding Z-axis coordinate thereof, moving the ultrasonic transducer to the coordinate, and finishing the automatic focusing of the middle layer.

In order to make the method for automatically focusing the middle layer of the test piece by the focusing transducer facing the ultrasonic microscope point provided by the embodiment of the present application clearer, the embodiment of the present application is further described in detail with reference to fig. 4:

in the step (1), an initial a-scan echo signal image of the sample surface is obtained.

In the step (2), setting relevant parameters, including: delay, focus of the ultrasonic transducer, temperature of the intervening liquid (typically water).

In the step (3), the program accurately corrects the sound velocity in the water according to the water temperature, the accurate position of the upper surface automatic focusing is accurately calculated through the focal length and the time delay of the acoustic lens of the transducer, and the point focusing transducer is moved to the position to finish the upper surface automatic focusing.

Fig. 2 shows a focusing principle diagram of a point focusing ultrasonic transducer, wherein the focal distance calculation formula of the point focusing transducer can be calculated according to formula (3):

F_L＝R/(1-c₀/c₁) … … formula (3)

Wherein R is the radius of curvature of the acoustic lens, c₀Representing the speed of sound in water, c₁Representing the speed of sound in the lens, let T be the time for the sound wave to reach the transducer plane T, then equation (4):

t＝2L/c₀+2H/c₁… … formula (4)

Wherein, 2H/c₁I.e. the delay time t of the ultrasonic transducer_d。

In order to calculate the focusing position more accurately, the embodiment of the present application considers the influence of the temperature on the sound velocity in water, and corrects the sound velocities at different temperatures, as shown in formula (5):

c₀＝1452(1+2.9376×10^-5temp+1.90574×10^-6temp²) … … formula (5)

The ultrasonic scanning microscope represents the coordinate position of the Z axis in the sound path time t. When t is 2F, as shown in the formula (8-9)_L/c₀+t_dThe time t of the sound path is the coordinate position of the Z axis, and the parameter F_L，c₀，t_dAll known, so the automatic upper surface focusing is done.

In the step (4), the scanning signal A is analyzed to obtain the layering information of the test piece.

The A scanning signal is composed of complex reflected waves of a multi-layer structure in the detected piece, the reflectivity r (t) of the ultrasonic signal is an impulse response function of the ultrasonic scanning microscope, x (t) is an incident signal function, and y (t) is an observed A scanning signal. The reflectivity r (t) of the ultrasound signal is calculated according to equation (6):

Z₁and Z₂The acoustic impedances of the water and the test piece are respectively, and are described here with the reflected signal of the flip chip, and as shown in fig. 5(a), the Z-axis coordinate position after the focusing of the upper surface is made to be the origin of coordinates.

Assuming that the detected object has M layers in common, the model of the a-scan signal can be expressed as formula (7):

wherein n (t) is noise; denotes convolution, x (t) is the incident signal. If noise is not considered, y (t) can be considered as a convolution of x (t) and r (t).

In the case of scanning imaging and nondestructive testing of complex multilayer structures, in particular of complex multilayer structures such as chips, due to the manufacturing process of the test piece, the thickness of the layered structure is often lower than the wavelength of the acoustic signal of the point-focus transducer, so that signal superposition may occur in many cases, for example, in the bonding layer of a flip chip as shown in fig. 5, s (t) of fig. 5₁)、s(t₂)、s(t₃) Echo signals of the upper surface layer, the welding layer and the substrate layer respectively, and when the thickness of the welding layer is larger than the wavelength of the point focusing transducer, the echo signal s (t)₂) And s (t)₃) With better separation, the echo signal s (t) is obtained when the thickness of the welding layer is less than the wavelength of the point focusing transducer₂) And s (t)₃) And the mutual superposition occurs, and at the moment, the echo signals of the welding layer and the substrate layer cannot be found, so that the automatic focusing of the middle layer cannot be finished.

In the embodiment of the application, the discrete wavelet decomposition is adopted to carry out multi-scale analysis on the ultrasonic signals, and the discrete wavelet transformation can decompose the signals into different frequency bands by utilizing sub-band filtering; wavelet analysis and deconvolution are combined to realize sub-band decomposition of the ultrasonic echo signals. According to the Mallat algorithm, the signal can be decomposed into the following two parts in the expression as in equation (8):

in the formula (I), the compound is shown in the specification,in order to be a discrete approximation of the same,for discrete details, h₀And h₁Respectively, decomposing low-pass and high-pass filter coefficients. In order to reduce the non-zero coefficient, the present embodiment selects wavelet basis functions such as daubechies, Coiflet, and the like having shapes similar to the waveforms of the functional ultrasound signals as mother wavelets. It can decompose the signal N times, 2^NIs the length of the signal to be decomposed. The decomposed scale is determined according to the actual conditions such as the number of sampling points, the noise size and the like, the time domain resolution is reduced due to overhigh decomposition scale, and the noise cannot be effectively inhibited due to overlow decomposition scale. In the embodiment of the present application, the decomposition coefficient is set to 2-3. The low-frequency inband signal preserves much of the information of the useful signal, so the same mother wavelet function is selected, forPerforming single reconstruction to obtain reconstructed signalAs an input signal for subsequent processing.

After wavelet decomposition, Wiener deconvolution filtering (Wiener) is adopted to continue processing signals in the ground frequency band, and Wiener deconvolution is a deconvolution method widely applied to signal and image processing. The wiener deconvolution filter can be expressed as equation (9):

where R (ω) and Y (ω) are the Fourier transforms of R (t) and Y (t), respectively, X (ω) is the energy density spectrum of the incident signal X (t), Q is the noise retardation factor, and the value of Q in the present embodiment is set to | X (ω) & gt²1% of the maximum value. Conventional wiener deconvolution assumes that the frequency of the incident signal remains constant in propagation. However, the a-scan signal has a large waveform distortion during propagation. The frequency and amplitude will decrease continuously, and the traditional wiener deconvolution is not suitable for processing the echo signal of the ultrasonic scanning microscope. Therefore, firstly, the discrete wavelet preprocesses the ultrasonic signal, eliminates signal distortion in the transmission process, and can improve poor filtering effect of wiener deconvolution, and as shown in fig. 6 and 7, originally superposed echo information can be well separated.

In the step (5), the intermediate layer reflection signal which needs to be focused is selected.

After the layered signals are analyzed through discrete wavelet and wiener deconvolution, overlapped signals are separated, separated intermediate layer reflection signals can be accurately found, and an intermediate layer needing focusing is selected.

In the step (6), the transducer is moved to find the coordinate of the maximum value of the reflected signal. The point focus transducer was programmed to move vertically in steps of 10 microns along the Z-axis toward the specimen. And when the intermediate layer moves for one step, acquiring the scanning signal A to analyze the signal, and recording and searching the position point coordinate with the maximum intermediate layer reflection signal.

After the approximate focusing process begins, the transducer is controlled to vertically move to the upper surface of the test piece in a step of 10 micrometers in the Z-axis direction, the sampled A scanning signal is analyzed, the reflection signal of the middle layer is obtained, the reflection signal of the middle layer is gradually enhanced at the moment, and if the reflection signal is weakened, the maximum value of the layered reflection signal is shown to be between the last two 10-micrometer step coordinate points. If the intensity of the reflected signal in this process is taken as the ordinate and the Z-axis displacement is taken as the abscissa, the reflected signal focusing curve in fig. 8 can be obtained.

Step (7), moving the transducer back to the last node of the maximum. And moving the ultrasonic transducer to the last stepping coordinate point of the position to complete the approximate focusing of the middle layer.

In fig. 8, after finding the maximum reflection position outlined by the curve, the ultrasonic transducer is moved to the previous step coordinate of the position in preparation for starting the fine focusing process.

And (8) accurately finding the largest reflecting surface. And continuously moving the point focusing transducer along the Z-axis test piece by 1 micron step to find the accurate position of the maximum value of the reflected signal, thereby completing automatic focusing.

In the process of moving each time, scanning signals A are collected to analyze the signals, the reflection signals of the middle layer are gradually enhanced at the moment, if the reflection signals are weakened, the maximum value of the layered reflection signals and the corresponding Z-axis coordinate can be obtained, the ultrasonic transducer is moved to the coordinate, and then the accurate focusing of the middle layer is completed. Fig. 6 and 7 are diagrams illustrating the effects of focusing and scanning imaging, respectively focusing on the intermediate layer of the reflected signal S2 and focusing on the intermediate layer of the reflected signal S3.

Compared with the manual focusing technology which is commonly adopted at present, the automatic focusing technology of the ultrasonic microscope point focusing transducer provided by the embodiment of the application effectively improves the focusing speed and accuracy of the ultrasonic microscope point focusing transducer in the using process, greatly reduces the randomness and uncertainty caused by manual operation in the focusing process, reduces the degree of dependence on the technical level and the working experience of operators, reduces the operation complexity and improves the working efficiency.

The embodiment of the application discloses an automatic focusing technology for an ultrasonic microscope point focusing transducer, which comprises the steps of collecting and designing A scanning signals, setting the parameters of the point focusing transducer and the temperature parameters, automatically completing the focusing of the upper surface, analyzing the signals to find a middle reflecting layer, moving the point focusing transducer to find the maximum position of the signal amplitude value in the range of the middle layer, and completing the automatic focusing of the middle layer. The upper automatic focusing process accurately corrects the sound velocity in water according to the water temperature. In the process of analyzing the reflected signals, the overlapped signals are separated by using discrete wavelets and wiener deconvolution filtering, and the reflected signals in the middle layer can be clearly positioned. The problems of low focusing speed and low precision of the point focusing transducer of the ultrasonic microscope can be effectively solved, and the imaging quality and the nondestructive testing efficiency of the ultrasonic microscope are improved.

In summary, the embodiment of the present application provides an automatic focusing method and system based on an ultrasonic microscope point focusing transducer, by obtaining an a scanning signal image of a surface of a test piece; setting focusing parameters, wherein the focusing parameters comprise a time delay parameter, a focal length parameter and a medium liquid temperature parameter of a point focusing transducer; correcting the sound velocity in the medium liquid according to the temperature of the medium liquid, and calculating the position of the upper surface automatic focusing through the focal length and the time delay parameter of the acoustic lens of the point focusing transducer so as to move the point focusing transducer to the position to finish the upper surface automatic focusing; analyzing the A scanning signal through discrete wavelet decomposition and wiener deconvolution to obtain the layered information of the test piece; selecting a target focusing middle layer reflection signal according to the layering information of the test piece; moving the transducer to find the coordinates of the approximate position point with the maximum intermediate layer reflection signal; moving the point focusing transducer back to the last coordinate point of the maximum position point coordinate; and moving the point focusing transducer to find the precise position point coordinate of the maximum value of the reflected signal so as to complete automatic focusing. The focusing speed and the focusing accuracy of the ultrasonic microscope point focusing transducer in the using process are effectively improved, the randomness and the uncertainty caused by manual operation in the focusing process are greatly reduced, the degree of dependence on the technical level and the working experience of an operator is reduced, the operation complexity is reduced, and the working efficiency is improved.

Based on the same technical concept, the embodiment of the present application further provides an autofocus system based on an ultrasonic microscope point focusing transducer, as shown in fig. 9, the system includes:

an initial signal acquiring module 901, configured to acquire an a-scan signal image of a surface of a test piece.

And a focusing parameter calculating module 902, configured to set a focusing parameter, where the focusing parameter includes a delay parameter, a focal length parameter, and a temperature parameter of the medium of the point focusing transducer.

And an upper surface autofocus module 903, configured to correct the sound velocity in the intermediate liquid according to the temperature of the intermediate liquid, and calculate an upper surface autofocus position by using the focal length and the delay parameter of the acoustic lens of the point focusing transducer, so as to move the point focusing transducer to the position to complete upper surface autofocus.

And the hierarchical information calculation module 904 is configured to analyze the a scanning signal through discrete wavelet decomposition and wiener deconvolution to obtain hierarchical information of the test piece.

And a target focusing intermediate layer reflection signal determination module 905, configured to select a target focusing intermediate layer reflection signal according to the layering information of the test piece.

And a location point coordinate determination module 906 for moving the transducer to find the location point coordinate where the reflected signal of the middle layer is the maximum.

An intermediate layer overview focus module 907 for moving the point focus transducer back to a point that is the last coordinate of the maximum overview position point coordinates.

An autofocus module 908 is used to move the point focus transducer to find the precise location point coordinates of the maximum of the reflected signal to accomplish autofocus.

Optionally, in the focusing parameter calculating module 902, the focal length parameter of the point focusing transducer is calculated according to the following formula (1).

In one possible implementation, the a-scan signal is composed of a complex reflected wave of an M-layer structure inside the detected object, and the model of the a-scan signal is shown in formula (2).

In a possible implementation manner, the module 906 for determining coordinates of a position point where the reflected signal is maximum is specifically configured to: controlling the transducer to vertically move to the upper surface of the test piece in a step of a set distance in the Z-axis direction, and analyzing the sampled A scanning signal to obtain a reflection signal of the middle layer; and judging whether the intermediate layer reflection signal is gradually enhanced or weakened, and if the intermediate layer reflection signal is gradually weakened, the maximum value of the layered reflection signal appears between the last two set distance stepping coordinate points.

Optionally, the auto-focusing module 908 is specifically configured to: in the process of moving the point focusing transducer each time, collecting an A scanning signal to analyze the signal, judging whether the reflected signal of the middle layer is gradually enhanced or weakened, if the reflected signal of the middle layer is gradually weakened, determining the maximum value of the layered reflected signal and the corresponding Z-axis coordinate thereof, moving the ultrasonic transducer to the coordinate, and finishing the automatic focusing of the middle layer.

Based on the same technical concept, an embodiment of the present application further provides an apparatus, including: the device comprises a data acquisition device, a processor and a memory; the data acquisition device is used for acquiring data; the memory is to store one or more program instructions; the processor is configured to execute one or more program instructions to perform the method.

Based on the same technical concept, the embodiment of the present application also provides a computer-readable storage medium, wherein the computer-readable storage medium contains one or more program instructions, and the one or more program instructions are used for executing the method.

In the present specification, each embodiment of the method is described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. Reference is made to the description of the method embodiments.

It is noted that while the operations of the methods of the present invention are depicted in the drawings in a particular order, this is not a requirement or suggestion that the operations must be performed in this particular order or that all of the illustrated operations must be performed to achieve desirable results. Additionally or alternatively, certain steps may be omitted, multiple steps combined into one step execution, and/or one step broken down into multiple step executions.

Although the present application provides method steps as in embodiments or flowcharts, additional or fewer steps may be included based on conventional or non-inventive approaches. The order of steps recited in the embodiments is merely one manner of performing the steps in a multitude of orders and does not represent the only order of execution. When an apparatus or client product in practice executes, it may execute sequentially or in parallel (e.g., in a parallel processor or multithreaded processing environment, or even in a distributed data processing environment) according to the embodiments or methods shown in the figures. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, the presence of additional identical or equivalent elements in a process, method, article, or apparatus that comprises the recited elements is not excluded.

The units, devices, modules, etc. set forth in the above embodiments may be implemented by a computer chip or an entity, or by a product with certain functions. For convenience of description, the above devices are described as being divided into various modules by functions, and are described separately. Of course, in implementing the present application, the functions of each module may be implemented in one or more software and/or hardware, or a module implementing the same function may be implemented by a combination of a plurality of sub-modules or sub-units, and the like. The above-described embodiments of the apparatus are merely illustrative, and for example, the division of the units is only one logical division, and other divisions may be realized in practice, for example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form.

Those skilled in the art will also appreciate that, in addition to implementing the controller as pure computer readable program code, the same functionality can be implemented by logically programming method steps such that the controller is in the form of logic gates, switches, application specific integrated circuits, programmable logic controllers, embedded microcontrollers and the like. Such a controller may therefore be considered as a hardware component, and the means included therein for performing the various functions may also be considered as a structure within the hardware component. Or even means for performing the functions may be regarded as being both a software module for performing the method and a structure within a hardware component.

The application may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, classes, etc. that perform particular tasks or implement particular abstract data types. The application may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices.

From the above description of the embodiments, it is clear to those skilled in the art that the present application can be implemented by software plus necessary general hardware platform. Based on such understanding, the technical solutions of the present application may be embodied in the form of a software product, which may be stored in a storage medium, such as a ROM/RAM, a magnetic disk, an optical disk, or the like, and includes several instructions for enabling a computer device (which may be a personal computer, a mobile terminal, a server, or a network device) to execute the method according to the embodiments or some parts of the embodiments of the present application.

The embodiments in the present specification are described in a progressive manner, and the same or similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. The application is operational with numerous general purpose or special purpose computing system environments or configurations. For example: personal computers, server computers, hand-held or portable devices, tablet-type devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable electronic devices, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like.

The above-mentioned embodiments are further described in detail for the purpose of illustrating the invention, and it should be understood that the above-mentioned embodiments are only illustrative of the present invention and are not intended to limit the scope of the present invention, and any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the scope of the present invention.