Nonlinear compression and signal-to-noise ratio adaptive weighting all-in-focus imaging method and device

Abstract

The application relates to a nonlinear compression and signal-to-noise ratio adaptive weighting full-focus imaging method and device in the technical field of ultrasonic nondestructive testing. P Upper focus point poi ( x , z ) of the delay correction signal S ij ( x , z ); the nonlinear transformation of the p square root compression operator pair S ij ( x , z ) is carried out to obtain the compressed delay correction signal, and coherent superposition is carried out to obtain the full-focus intensity value of poi ( x , z ); the coherent factor poi ( x , z ) of the calculation CF ( x , z ) is obtained; a pixel local region is constructed with poi ( x , z ) as the center, and the signal-to-noise ratio SNR local ( x , z ) is calculated. The nonlinear compression operator with symbol reservation is introduced, and the double optimization strategy of the coherent factor and the local SNR adaptive weighting is combined, the effective reflection echo is enhanced on the basis of the improvement of the signal coherence, the defect signal integrity can be maintained while the structural noise is effectively suppressed, and the detection sensitivity and the imaging quality of the tiny defects in the coarse-grained material are significantly improved.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic nondestructive testing technology, and in particular to a nonlinear compression and signal-to-noise ratio adaptive weighted full-focus imaging method and apparatus. Background Technology

[0002] Coarse-grained materials (such as austenitic stainless steel) are prone to generating strong scattering noise during ultrasonic testing due to their large grain size and significant anisotropy. This results in low signal-to-noise ratio and blurred defect boundaries in traditional total focusing (TFM) imaging. While coherence factor weighted (CF-TFM) can partially suppress noise in existing technologies, it has the following limitations: 1. The coherence factor calculation is independent of the imaging process, leading to insufficient suppression of low-coherence regions (such as grain boundary scattering). 2. It does not utilize the nonlinear amplitude compression characteristics of delayed signals, resulting in limited noise suppression in low SNR scenarios. 3. It lacks adaptive optimization for local signal-to-noise ratio, making it difficult to adapt to the complex acoustic responses of coarse-grained materials with their microstructures. Summary of the Invention

[0003] To address the technical problems of high structural noise and low defect signal-to-noise ratio in existing ultrasonic testing of coarse-grained materials, this invention provides a nonlinear compression and signal-to-noise ratio adaptive weighted full-focus imaging method and apparatus.

[0004] This invention is achieved through the following technical solution:

[0005] In a first aspect, the present invention proposes a nonlinear compression and signal-to-noise ratio adaptive weighted full-focusing imaging method, which includes:

[0006] The imaging plane is calculated. P upper focal point poi ( x , z Delay correction signal S ij ( x , z ). Preserved by symbols p The root-order compression operator pairs S ij ( x , z A nonlinear transformation is performed to obtain the compressed delay correction signal. and to Coherent superposition is obtained poi ( x , z Full-focus intensity value I NTFM ( x , z ).based on calculate poi ( x, z coherence factor CF ( x , z ).by poi ( x , z Construct a local pixel region Ω centered on ) x , z ), and calculate Ω ( x , z signal-to-noise ratio SNR local ( x , z ).based on SNR local ( x , z Establish adaptive signal-to-noise ratio weights W SNR ( x , z ):

[0007] ;

[0008] α Indicates control parameters. Fusion I NTFM ( x , z ), CF ( x , z ), W SNR ( x , z )get poi ( x , z ) fusion value I mix ( x , z ).right I mix ( x , z After processing, it is converted to the decibel domain output, resulting in... poi ( x , z Output value I dB ( x , z Traversal P All focal points are used to obtain a full-focus ultrasound image.

[0009] Secondly, this invention also proposes a nonlinear compression and signal-to-noise ratio adaptive weighted full-focus imaging device, comprising: a two-dimensional array transducer and a data processing unit. The two-dimensional array transducer is used for data acquisition in a "single-transmit, full-receive" manner. The data processing unit is used to process the data acquired by the two-dimensional array transducer using the nonlinear compression and signal-to-noise ratio adaptive weighted full-focus imaging method described in the first aspect to obtain a full-focus ultrasound image.

[0010] Thirdly, the present invention also proposes a computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the nonlinear compression and signal-to-noise ratio adaptive weighted total focusing imaging method as described in the first aspect.

[0011] The beneficial effects of this invention are as follows:

[0012] 1. This invention establishes a multi-feature fusion nonlinear full-focusing imaging model. Addressing the challenges of strong scattering noise and low defect signal-to-noise ratio in ultrasonic testing of coarse-grained materials, it introduces a sign-preserving nonlinear compression operator to achieve a balance between noise suppression and signal preservation. Simultaneously, it combines a dual optimization strategy of coherence factor and local SNR adaptive weighting to enhance effective reflected echoes while improving signal coherence. Furthermore, through nonlinear compression processing and dual-weighted fusion processing, it can effectively suppress structural noise while maintaining defect signal integrity, significantly improving the detection sensitivity and imaging quality of minute defects in coarse-grained materials, thereby overcoming the problem of poor imaging quality in coarse-grained media by traditional full-focusing methods.

[0013] 2. This invention innovatively incorporates a nonlinear compression operator, through sign preservation... p This invention employs root-law compression to achieve nonlinear suppression of noise energy while maintaining the integrity of phase information and improving dynamic range. Furthermore, it is the first to couple the coherence factor with the local signal-to-noise ratio (SNR) function, enabling pixel-level adaptive modulation and significantly improving signal recognition. In addition, the designed SNR weights can be dynamically adjusted based on local statistical characteristics, effectively suppressing shot noise, boundary blurring, and low-contrast artifacts, exhibiting regional adaptive characteristics. As a result, this invention achieves a 39.18 dB improvement in SNR compared to the traditional TFM algorithm in typical weld and composite material specimens.

[0014] 3. This invention employs a pre-calculated delay matrix and parallelization, which significantly reduces computation time and meets the requirements for real-time detection. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a flowchart of a nonlinear compression and signal-to-noise ratio adaptive weighted full-focusing imaging method;

[0017] Figure 2 This is a schematic diagram of the coarse-grained structure in the simulation;

[0018] Figure 3 This is a schematic diagram of the spectrum of the excitation signal in the simulation;

[0019] Figure 4 This is the imaging result of TFM in existing technology;

[0020] Figure 5 This is the imaging result of TFM-CF in the existing technology;

[0021] Figure 6 This is the imaging result of the imaging method of this invention in the simulation. Detailed Implementation

[0022] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] It should be noted that when a component is said to be "installed on" another component, it can be directly on the other component or it may be in a component that is centered on it. When a component is said to be "set on" another component, it can be directly set on the other component or it may also be in a component that is centered on it. When a component is said to be "fixed to" another component, it can be directly fixed to the other component or it may also be in a component that is centered on it.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "or / and" as used herein includes any and all combinations of one or more of the associated listed items.

[0025] This embodiment discloses a nonlinear full-focus ultrasound imaging method that combines coherence factor and adaptive signal-to-noise ratio (SNR) weighting, such as... Figure 1 As shown, it includes the following steps: full matrix data acquisition, delay correction and focus point selection, nonlinear compression processing, nonlinear full-focus stacking processing, coherence factor calculation, adaptive signal-to-noise ratio weighting, fusion-weighted imaging, image output and performance evaluation. Each step is described in detail below:

[0026] I. Full matrix data acquisition.

[0027] Using N A two-dimensional array transducer with individual elements acquires data in a "single-transmit, all-receive" manner, meaning that each time one element is excited to emit an ultrasonic pulse, all elements simultaneously receive the echo signal. In this way, after... N After the next pulse, the complete full matrix dataset can be obtained. G : G ={ U ( i,j,t )}. U ( i,j,t () represents the amplitude of the received signal. i , j ∈[1, N ]. i Indicates the number of the transmitting array element. j Indicates the receiver element number. t Indicates time. Furthermore, G The analytical dataset is obtained through Hilbert transform. : . This represents the amplitude of the received signal after analysis. Its analytical form is:

[0028] .

[0029] In the formula, This represents the Hilbert transform operator, used to recover the phase information of a signal.

[0030] II. Delay correction and focus point selection.

[0031] In the imaging plane P A uniform grid is established on top and a two-dimensional coordinate system is formed. P ( X , Z (Then, based on the transmitting and receiving array elements...) P At a certain focal point poi ( x , z Calculate propagation delay using geometric distance. t ij ( x, z ):

[0032] .

[0033] In the formula, d i ( x , z )express poi ( x , z The propagation distance from the launch array element. d j ( x , z )express poi ( x , z The propagation distance to the receiving array element. c It represents the speed of sound in the medium. x , z Represents coordinate values, and x ∈ X , z ∈ Z .

[0034] based on t ij ( x , z The corresponding delay correction signal is... S ij ( x , z )for:

[0035] .

[0036] III. Nonlinear compression processing.

[0037] This step is one of the key design features of this invention. Traditional TFM imaging is sensitive to strong noise, and weak defect signals are often masked. To improve the signal dynamic range, this invention innovatively introduces sign-preserving... p The root-order compression operator pairs S ij ( x , z A nonlinear transformation is performed to obtain the compressed delay correction signal. :

[0038] .

[0039] In the formula, sign (·)express sign A function used to preserve the phase polarity of a signal. p Indicates the compression order, and p∈[2,4], used to balance noise suppression and signal preservation. Through the nonlinear compression processing in this step, high-amplitude random noise can be weakened and low-amplitude effective reflection signals can be highlighted, making the defect edge features clearer.

[0040] IV. Nonlinear Total Focusing (NL-TFM) Superposition Processing.

[0041] After compressing all nonlinearities Coherent superposition is obtained poi ( x , z Full-focus intensity value I NTFM ( x , z ):

[0042] .

[0043] Compared to the stacking processing in traditional TFM imaging: This step is based on the signal obtained after nonlinear compression processing in the previous steps. I NTFM ( x , z It can adaptively reduce abnormally high amplitude interference echoes and improve the imaging contrast of low-energy scattering.

[0044] V. Coherence Factor Calculation.

[0045] To further enhance the phase consistency of the real reflected signal, the coherence factor is calculated. CF ( x , z ):

[0046] .

[0047] In the formula, β Indicates the coherence enhancement index, and β ∈[2,4]. In this calculation formula, the numerator represents the phase-consistent energy of all channels. The denominator is the total amplitude energy normalization term. CF ( x , z A larger value indicates a smaller phase difference between signals, representing the focal point. poi ( x , z The probability of a reflector being a real reflector is high. However, noise points or side lobes are more likely to be reflected. CF ( x , z It approaches 0.

[0048] VI. Adaptive weighted signal-to-noise ratio.

[0049] This step is another key design feature of this invention. It is for compensating the imaging plane. P Local signal-to-noise differences in different regions, poi ( x , z Construct a local pixel region Ω centered on ) x , z ), and calculate Ω ( x , z signal-to-noise ratio SNR local ( x , z ):

[0050] .

[0051] In the formula, μ Ω ( x , z ) represents Ω ( x , z The average pixel value within ) , σ Ω ( x , z ) represents Ω ( x , z The standard deviation of pixels within ) ε This represents a constant, typically a small value, to prevent division by zero errors. The Ω ( x , z The range is an area of ​​5×5 pixels or smaller.

[0052] Subsequently based on SNR local ( x , z Establish adaptive signal-to-noise ratio weights W SNR ( x , z ):

[0053] .

[0054] α Indicates control parameters, and α >0. α Used for control W SNR ( x , z Steepness: Greater α It can improve the local area Ω of the pixel ( x , z The enhancement amplitude is suitable for low-noise samples and is relatively small. α This is suitable for materials with high noise levels.

[0055] VII. Fusion weighted imaging.

[0056] Combination I NTFM ( x , z ), CF ( x , z ), W SNR ( x , z The three are then combined to obtain the final fusion value. I mix ( x , z ):

[0057] .

[0058] VIII. Image Output and Performance Evaluation.

[0059] To highlight the reflection area of ​​the defect, further [treatment / treatment] can be performed. I mix ( x , z The enhancement value is obtained by performing power-law enhancement processing. I enhanced ( x , z ):

[0060] .

[0061] in, γ Represents the enhancement coefficient, and γ ∈[0.4,0.6], used to control the strength of weak signal enhancement.

[0062] Then to I enhanced ( x , z The result value is obtained by normalization and median filtering. I out ( x , z ):

[0063] .

[0064] MedFilt2 stands for MedFilt2 function, used for median filtering.

[0065] Finally I out ( x , z Convert the output to the decibel (dB) domain to obtain poi (x , z Output value I dB ( x , z ):

[0066] .

[0067] In the formula, I out ( X , Z The ) represents the maximum value among all the focal point results. At this point, a specific focal point is calculated. poi ( x , z Output value I dB ( x , z Repeat or synchronize the above calculation process, traversing... P After focusing on all points, a complete full-focus ultrasound image is obtained, displaying the final imaging result. Furthermore, the overall signal-to-noise ratio can also be used to obtain the final image. SNR global Performance evaluation of full-focus ultrasound imaging. Overall signal-to-noise ratio. SNR global Defined as:

[0068] .

[0069] In the formula, I max Indicates the peak intensity of the reflection region of the defect. I bg This represents the average value of the background area.

[0070] To verify the effectiveness and beneficial effects of this invention, finite element simulations were performed on coarse-grained materials, and the results were validated. The experimental data were obtained from a numerical simulation using 316L austenitic stainless steel as the model, which exhibits typical coarse-grained microstructure characteristics. The modeling and signal generation process is as follows:

[0071] (1) Establishment of the coarse-grained structure model. For example... Figure 2 As shown.

[0072] 1. Grain generation: The Voronoi algorithm is used on the MATLAB platform to generate two-dimensional grain topologies with statistical distribution characteristics.

[0073] 2. Material property assignment: Different elastic constant matrices are assigned to each grain in the COMSOL multiphysics platform. Furthermore, random grain orientations are introduced based on the Bond transformation to reflect the coarse-grained anisotropy characteristics.

[0074] 3. Boundary conditions: A Rayleigh damping absorption layer is applied to the model boundary to reduce reflection interference. The layer is 1 mm thick and has a damping coefficient of [missing value]. a according to distributed.

[0075] (2) Ultrasonic excitation and generation of full-focus ultrasound imaging.

[0076] 1. Ultrasonic excitation.

[0077] like Figure 3 As shown, the excitation signal is a three-cycle Hanning window modulated sine wave:

[0078] .

[0079] Speed ​​of sound set c =5850m / s, 32 transducer elements, 0.6 mm spacing. Each element is sequentially excited using COMSOL's array excitation module, and the full matrix echo signal is acquired in a "single transmit, full receive" manner. The signal is then transformed into an analytic signal using the Hilbert transform.

[0080] 2. Generation of full-focus ultrasound images.

[0081] Delay compensation and focus point were performed on FMC data using the MATLAB platform. poi ( x , z The corresponding propagation time is t ij ( x , z This allows us to obtain the delay correction signal after delay compensation. S ij ( x , z ).right S ij ( x , z Symbol preservation p The root-order compression yields the compressed delay correction signal. ,right Coherent superposition is obtained poi ( x , z Full-focus intensity value I NTFM ( x , z ).

[0082] Calculate coherence factor CF ( x , z ),β Take 3.5. Calculate Ω ( x , z signal-to-noise ratio SNR local ( x , z ): Selects a 2×2 pixel region centered on the current pixel. Based on SNR local ( x , z The signal-to-noise ratio adaptive weights are calculated. W SNR ( x , z ).

[0083] Fusion I NTFM ( x , z ), CF ( x , z ), W SNR ( x , z )get poi ( x , z ) fusion value I mix ( x , z The output is after normalization, filtering, and logarithmic compression. poi ( x , z Output value I dB ( x , z Traversal P All focal points are used to obtain a full-focus ultrasound image.

[0084] (3) Verification and comparison.

[0085] Based on the signal set of coarse-grained materials obtained from the above simulation, the imaging results of the imaging method of this invention are compared with those of existing TFM and TFM-CF algorithms. Figure 4 , Figure 5 , Figure 6 As shown: Figure 4 The imaging results of TFM, Figure 5 The imaging results for TFM-CF Figure 6The images shown are the imaging results of the imaging method of this invention. It can be seen that the nonlinear compression and signal-to-noise ratio adaptive weighted full-focus imaging method proposed in this invention has significantly enhanced noise suppression capability against anisotropic coarse-grained backgrounds. The defect signal-to-noise ratio is improved by 39.18 dB and 15.54 dB compared with traditional TFM and TFM-CF, respectively, with clear detail boundaries and significantly reduced background noise.

[0086] In another embodiment, a nonlinear compression and signal-to-noise ratio adaptive weighted full-focus imaging device is proposed, comprising: a two-dimensional array transducer, a data processing unit, and a display unit. The two-dimensional array transducer is used for data acquisition in a "single-transmit, full-receive" manner. The data processing unit processes the data acquired by the two-dimensional array transducer using the nonlinear compression and signal-to-noise ratio adaptive weighted full-focus imaging method described in the above embodiment to obtain a full-focus ultrasound image. The display unit displays the full-focus ultrasound image as a color image.

[0087] In another embodiment, a computer-readable storage medium is also proposed, which stores a computer program that, when executed by a processor, implements the steps of the nonlinear compression and signal-to-noise ratio adaptive weighted full-focus imaging method as described in the above embodiments. This computer-readable storage medium may include, but is not limited to: an electrical connection having one or more wires, a portable computer disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof.

[0088] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0089] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A nonlinear compression and signal-to-noise ratio adaptive weighted total focusing imaging method, characterized in that, It includes: The imaging plane is calculated. P upper focal point poi ( x , z Delay correction signal S ij ( x , z ); Preserved by symbols p The root-order compression operator pairs S ij ( x , z A nonlinear transformation is performed to obtain the compressed delay correction signal. and to Coherent superposition is obtained poi ( x , z Full-focus intensity value I NTFM ( x , z ); based on calculate poi ( x , z coherence factor CF ( x , z ); by poi ( x , z Construct a local pixel region Ω centered on ) x , z ), and calculate Ω ( x , z signal-to-noise ratio SNR local ( x , z ); based on SNR local ( x , z Establish adaptive signal-to-noise ratio weights W SNR ( x , z ): ； α Indicates control parameters; Fusion I NTFM ( x , z ), CF ( x , z ), W SNR ( x , z )get poi ( x , z ) fusion value I mix ( x , z ); right I mix ( x , z After processing, it is converted to the decibel domain output, resulting in... poi ( x , z Output value I dB ( x , z ); Traversal P All focal points are used to obtain a full-focus ultrasound image.

2. The nonlinear compression and signal-to-noise ratio adaptive weighted full-focusing imaging method according to claim 1, characterized in that, The total focusing imaging method employs a N The two-dimensional array transducer with individual elements collects data in a "single-transmit, full-receive" manner. Each time an array element is excited, it emits an ultrasonic pulse. N The full matrix dataset is obtained after the next pulse. G : G ={ U ( i,j,t )}; U ( i, j,t () represents the amplitude of the received signal. i Indicates the number of the transmitting array element. j Indicates the receiver element number. t Indicates time; based on U ( i,j,t ) is processed to obtain S ij ( x , z ).

3. The nonlinear compression and signal-to-noise ratio adaptive weighted full-focusing imaging method according to claim 2, characterized in that, get S ij ( x , z The methods include: Will G The analytical dataset is obtained through Hilbert transform. : ; This represents the amplitude of the received signal after analysis. exist P Based on the transmitting array element and the receiving array element poi ( x , z Calculate the propagation delay using geometric distance. t ij ( x , z ); Will t ij ( x , z ) Integration get S ij ( x , z ): .

4. The nonlinear compression and signal-to-noise ratio adaptive weighted full-focusing imaging method according to claim 2, characterized in that, Full Focus Intensity Value I NTFM ( x , z ) by all nonlinear compression The result is obtained after coherent superposition.

5. The nonlinear compression and signal-to-noise ratio adaptive weighted full-focusing imaging method according to claim 1, characterized in that, right S ij ( x , z The formula for performing nonlinear transformation is: ； In the formula, sign (·)express sign function, p Indicates the compression order.

6. The nonlinear compression and signal-to-noise ratio adaptive weighted full-focusing imaging method according to claim 1, characterized in that, Signal-to-noise ratio SNR local ( x , z ) by Ω( x , z The average pixel value within ) and Ω ( x , z The ratio of the standard deviation of pixels within the range is calculated.

7. The nonlinear compression and signal-to-noise ratio adaptive weighted full-focusing imaging method according to claim 1, characterized in that, Will CF ( x , z ), W SNR ( x , z )and I NTFM ( x , z Multiply the absolute values ​​of ) to obtain the fusion value. I mix ( x , z ).

8. The nonlinear compression and signal-to-noise ratio adaptive weighted full-focusing imaging method according to claim 1, characterized in that, right I mix ( x , z The processing methods include: first, ... I mix ( x , z The process involves power-law enhancement, followed by normalization and median filtering.

9. A nonlinear compression and signal-to-noise ratio adaptive weighted total focusing imaging device, characterized in that, It includes: Two-dimensional array transducers are used for data acquisition in a "single-transmit, full-receive" manner; A data processing unit is used to process the data acquired by the two-dimensional array transducer using the nonlinear compression and signal-to-noise ratio adaptive weighted full-focus imaging method as described in any one of claims 1 to 8, so as to obtain a full-focus ultrasound image.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed by a processor, implements the steps of the nonlinear compression and signal-to-noise ratio adaptive weighted total focusing imaging method as described in any one of claims 1 to 8.

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