Wide-band high-resolution acoustic boundary detection structure and method based on capture resonance

Abstract

The present invention relates to a broadband high-resolution acoustic boundary detection structure and method based on capture resonance. The overall detection structure is a hollow square cylinder. The boundary detector located at the lower part of the cylinder is composed of a plurality of narrow resonance cavities and a plurality of wide resonance cavities alternately arranged from bottom to top. The cross-sectional size of the narrow resonance cavity at the lowermost layer is smaller than that of the narrow resonance cavity above it. Compared with the prior art, the present invention has the advantages of broadband and high resolution, etc.

Description

Technical Field

[0001] The present invention relates to the field of physical acoustic imaging, and in particular to an acoustic boundary detection structure and method with wide - band high - resolution based on Trapped Resonances. Background Art

[0002] Acoustic imaging has important potential in various applications, such as non - destructive detection, medical ultrasound diagnosis, and photoacoustic imaging. For any wave - based imaging system, the imaging resolution is limited by the diffraction limit. Since high - spatial - frequency components decay exponentially along the wave - propagation direction, fine features of the imaged object or details smaller than half - wavelength cannot be recovered in the final image. To overcome this diffraction limit, there are currently various methods for achieving super - resolution imaging, including but not limited to superlenses, time - reversal techniques, Fabry - Perot - type resonances, and acoustic negative refraction. In some actual imaging situations, sometimes only the edge information of the object needs to be extracted because these edges carry key information of the object, which also greatly reduces the amount of data to be processed.

[0003] By exciting resonance - trapping modes in cavities of different sizes, in this context, evanescent waves can couple with the trapping modes and be converted into propagating waves, and the bandgap of the plane - wave mode brought by the structural periodicity can remove lower - spatial - frequency information. However, the previous edge - detection techniques based on such trapping modes face the problem of narrow bandwidth, and it is not explained which factors of such detection devices have a greater impact on the imaging resolution, which to a certain extent limits the application value of this boundary - imaging technology. Summary of the Invention

[0004] The purpose of the present invention is to overcome the above - mentioned defects existing in the prior art and provide an acoustic boundary detection structure and method with wide - band high - resolution based on trapped resonances.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] An acoustic boundary detection structure with wide - band high - resolution based on trapped resonances, the overall detection structure is a hollow square cylinder, and the boundary detector at the lower part of the cylinder is composed of a plurality of narrow resonant cavities and a plurality of wide resonant cavities alternately arranged from bottom to top, and the cross - sectional size of the narrow resonant cavity at the lowermost layer is smaller than that of the narrow resonant cavity above it.

[0007] The minimum detectable width of this detection structure is slightly smaller than the cross - sectional size of the narrow resonant cavity at the lowermost layer.

[0008] By expanding the cross - sectional size of the narrow resonant cavity above the narrow resonant cavity at the lowermost layer to broaden the detection - frequency - band bandwidth of this detection structure.

[0009] The detection structure further includes detection holes for placing acoustic probes opened on two opposite side walls of the upper part of the cylinder, a device to be detected in close contact with the lowest narrow resonance cavity, and a sound source located below the device to be detected.

[0010] The device to be detected moves in a stepwise manner along the detection direction.

[0011] The boundary detector is composed of a first narrow resonance cavity, a first wide resonance cavity, a second narrow resonance cavity, a second wide resonance cavity, and a third narrow resonance cavity arranged from bottom to top. The structural dimensions of the first narrow resonance cavity, the second narrow resonance cavity, and the third narrow resonance cavity are w1×w1×l, w2×w2×l, and w3×w3×l respectively, and w1 < w2, w1 < w3. The structural dimensions of the first wide resonance cavity and the second wide resonance cavity are both W×W×L, and l < L, and w1, w2, and w3 are all smaller than W, where W is the side length of the square cavity inside the square cylinder.

[0012] The centers of all resonance cavities are located on the same axis.

[0013] The acoustic probe specifically uses a microphone, and the sound source specifically uses a speaker.

[0014] An acoustic boundary detection method includes the following steps:

[0015] 1) Build an anechoic environment: Place the device to be detected, the detection structure, and the sound source in a box, line the inner wall of the box with sound-absorbing cotton, fix the device to be detected on a stepping machine, and make the detection structure closely adhere to the device to be detected;

[0016] 2) Move the device to be detected in a precessional manner according to a set step size through the stepping machine, and record the sound pressure of the two detection holes;

[0017] 3) Obtain the distance between two peaks in the sound pressure curves of the two detection holes, and use this as the boundary length of the device to be detected.

[0018] When measuring the two-dimensional boundary of the device to be detected, after completing the detection of the one-dimensional boundary, rotate the device to be detected by 90 degrees for detection to complete the detection of the other one-dimensional boundary.

[0019] Compared with the prior art, the present invention has the following advantages:

[0020] The present invention relates to a broadband high-resolution acoustic boundary detection method based on trapped resonance. This method realizes acoustic boundary detection through the coupling of asymmetric narrow and wide resonant cavities. The cross-section of the detection device is a square with different widths. By arranging these narrow and wide resonant cavities periodically, trapped resonance can be excited under set conditions. The present invention improves the boundary imaging resolution of the device to a certain extent by reducing the size of the first cross-section, and expands the cross-sectional areas of the latter two narrow resonant cavities, thereby broadening the measurement bandwidth of boundary detection. Through this parallel design of narrow and wide resonant cavities, the structural periodicity is broken, and the characteristics of high-resolution and broadband measurement can be obtained simultaneously. Description of the Drawings

[0021] Figure 1 It is a schematic diagram of the detection structure, principle and imaging process of the present invention.

[0022] Figure 2 It is a schematic diagram of broadband mode conversion in a broadband high-resolution acoustic boundary detection method based on trapped resonance of the present invention. Among them, Fig. (2a) is a schematic diagram of broadband mode conversion with structural parameters of w1 = 6.5 mm, w2 = 6.5 mm, and w3 = 6.5 mm, and Fig. (2b) is a schematic diagram of broadband mode conversion with structural parameters of w1 = 6.5 mm, w2 = 10 mm, and w3 = 10 mm.

[0023] Figure 3 It is a structural diagram of the device to be detected in a broadband high-resolution acoustic boundary detection method based on trapped resonance of the present invention. Among them, Fig. (3a) is a side view, and Fig. (3b) is a cross-sectional view.

[0024] Figure 4 It is a one-dimensional structure to be detected in a broadband high-resolution acoustic boundary detection method based on trapped resonance of the present invention.

[0025] Figure 5 It is a schematic diagram of experimental placement in a broadband high-resolution acoustic boundary detection method based on trapped resonance of the present invention.

[0026] Figure 6 It is a 5-mm-wide detected structure fixed on a stepping machine, close to the detection device and moving leftward in a broadband high-resolution acoustic boundary detection method based on trapped resonance of the present invention.

[0027] Figure 7 It is the experimental result of one-dimensional structure boundary detection in a broadband high-resolution acoustic boundary detection method based on trapped resonance of the present invention. Among them, Fig. (7a) is the experimental result of one-dimensional structure boundary detection with a width of 5 mm, Fig. (7b) is the experimental result of one-dimensional structure boundary detection with a width of 6.5 mm, and Fig. (7c) is the experimental result of one-dimensional structure boundary detection with a width of 10 mm.

[0028] Figure 8 This is a comparison diagram of boundary detection experiments and simulations of the data normalized separately at different frequencies for a 5-mm-wide one-dimensional structure in a broadband high-resolution acoustic boundary detection method based on trapped resonance according to the present invention. Among them, Fig. (8a) is a comparison diagram of boundary detection experiments and simulations of the data normalized separately at 7790 Hz for the 5-mm-wide one-dimensional structure, Fig. (8b) is a comparison diagram of boundary detection experiments and simulations of the data normalized separately at 8046 Hz for the 5-mm-wide one-dimensional structure, and Fig. (8c) is a comparison diagram of boundary detection experiments and simulations of the data normalized separately at 8837 Hz for the 5-mm-wide one-dimensional structure. Detailed implementation manners

[0029] In order to make the technical means, creative features, achieved purposes and effects of the invention easy to understand, the present invention will be further described below in conjunction with specific illustrations.

[0030] Embodiment

[0031] The present invention provides a broadband high-resolution acoustic boundary detection structure and method based on trapped resonance, which takes into account imaging resolution, imaging quality and imaging bandwidth. In the present invention, the characteristics of the trapping mode and the key influencing factors for the trapping efficiency of evanescent waves are given. By increasing the side length ratio of the narrow resonant cavity to the wide resonant cavity of the boundary detector, the detection bandwidth can be expanded. By breaking the periodicity of the structure and shrinking the first narrow resonant cavity, the imaging resolution can be increased to 0.11λ. Theoretically, one-dimensional and two-dimensional object boundary detection can be realized in the frequency band range of 7400 Hz - 9400 Hz. As long as there is mode conversion, this frequency can be used for boundary detection. In actual situations, considering losses, printing errors and measurement errors, there are certain requirements for the mode conversion intensity for the boundary imaging effect. Experimentally, the present invention can achieve a measurable bandwidth of 900 Hz and realize the recognition of the object boundary with a minimum size of 5 mm in the frequency band width range of 7400 Hz - 9400 Hz, providing a more efficient method for subsequent boundary detection using the trapped resonance mechanism.

[0032] The principle schematic or the schematic of the boundary imaging process of the present invention is as Figure 1 shown. This structure is composed of several square resonant cavities with different cross-sectional dimensions: the narrow cross-section includes three narrow resonant cavities t = w i ×w i (i = 1, 2, 3), the wide cross-section includes two wide resonant cavities T = W × W. The thicknesses of the narrow and wide resonant cavities are represented by L and l respectively. The corresponding structural parameters are W = 22.5 mm, L = 5 mm, w1 = 6.5 mm, w2 = 10 mm, w3 = 10 mm, l = 1.5 mm. In this example, the object to be imaged is several one-dimensional plates printed by three-dimensional resin. Its width is represented by the parameter s, as Figure 1As shown, the high- and low-spatial-frequency information generated by the incident sound wave on the object is represented by the attenuation line and the wavy line respectively. This boundary detector converts the evanescent wave carrying high-frequency spatial information into a propagable wave carrying low-frequency spatial information. On the other hand, the low-frequency spatial information will be converted into high-frequency spatial information and gradually attenuate within the boundary detector. In each detection, the object to be detected needs to be in an anechoic chamber, and the boundary detector is placed at a certain distance from the object to visually present the process of mode conversion and mode filtering. In practical applications, the boundary detector is in close contact with the object to be detected to improve the extraction efficiency of the evanescent wave. The object to be detected is moved in front of the boundary detector by a stepper motor, stepping in the y direction with a step size of 0.5 mm. Since the physical mechanism of edge detection used in the present invention is to capture resonance, according to the characteristics of captured resonance, the first antisymmetric mode in the wide resonant cavity, i.e., the (1,0) mode, can be used to represent the edge information of the object, such as Figure 1 the width s shown in the upper right corner.

[0033] The mode conversion spectral line of the detection structure can represent the broadband characteristics of the device. In Figure 2 it, the transmission coefficient T (m,n)(m',n') represents the transmission coefficient of the mode (m',n') in the incident mode (m,n). All these modes are waveguide modes with respect to the wide resonant cavity. It is worth noting that the waveguide modes (3,0), (5,0), and (7,0) are all evanescent waves on the wide resonant cavity with a frequency range of 7400 Hz to 9400 Hz. In the numerical calculation of the transmission characteristics, different wide cross-section waveguide modes are excited only 1 mm in front of the narrow resonant cavity with a size of w1×w1, and measurement points are set 65.5 mm after the last narrow resonant cavity (w3×w3) to detect the absorption of different modes by the wide waveguide cross-section. If the distance between the wide waveguide incident cross-section and the incident cross-section of the first narrow resonant cavity (w1×w1) is too long, it is difficult to achieve the mode conversion from high-spatial-frequency information to low-spatial-frequency information due to the exponential decay of the evanescent wave along the propagation direction. According to this characteristic, the distance between the first narrow resonant cavity and the object is crucial for the efficiency of mode conversion. Therefore, the input aperture of the boundary detector is designed as a narrow resonant cavity instead of a wide resonant cavity, such as Figure 1 the top of the structure is designed as a narrow waveguide cross-section (w1×w1), and such a design breaks the periodicity of the structure.

[0034] It is found in the simulation that the bandwidth of mode conversion depends on the side length (w) of the narrow resonant cavity i)sensitive, rather than other structural parameters. Figures (2a) and (2b) show the transmission spectra of the incident (0,0)(1,0)(3,0)(5,0)(7,0) modes. The parameters of the two structures are w1 = 6.5mm, w2 = 6.5mm, w3 = 6.5mm (prior art) and w1 = 6.5mm, w2 = 10mm, w3 = 10mm (the present invention), respectively. It can be seen that the structural parameters of w1 = 6.5mm, w2 = 10mm, and w3 = 10mm have a wider mode conversion frequency band and a wider imaging frequency range. Due to the trapped resonance coupling between the three narrow resonators and the wide resonator, three transmission peaks are excited under the excitation of the antisymmetric waveguide mode. The filtering of the plane wave is mainly caused by the bandgap of the entire structure. Comparing Figures (2a) and (2b), the bandwidth of the mode conversion is determined by the ratio of the narrow resonator length w i and the wide resonator length W. However, as the narrow resonators (w2, w3) in Figure (2b) are broadened, the plane mode (0,0) is more likely to propagate due to its strong scattering, despite the bandgap effect. This can be explained by the reduced contrast between w i and W, which leads to a decrease in the scattering ability of the plane wave. In addition, the thermo-viscous loss will further reduce this scattering. It is found in the simulation that the parameters w2 = 10mm and w3 = 10mm provide a good trade-off between a wide frequency band and plane wave suppression. However, for an object smaller than the input aperture of the boundary detector, the narrow aperture cannot be semi-occluded during the entire detection process. In this case, the quality of the trapped resonance decreases, resulting in poor coupling between the evanescent wave near the object edge and the antisymmetric waveguide eigenmode. This indicates that if the size of the narrow resonator (w1) at the input aperture is reduced to be comparable to the object, the edge information of some smaller objects can be obtained. Through numerical optimization, the parameters w1 = 6.5mm, w2 = 10mm, and w3 = 10mm are selected to balance the relationship between good imaging resolution and a wide frequency band.

[0035] In this example, the boundary detector contains three resonant narrow resonators and two resonant wide resonators, and their sizes are as Figure 1 shown. The centers of the resonant narrow resonators and the centers of the resonant wide resonators are located on the same axis.

[0036] By broadening the widths of the latter two narrow resonators, the bandwidth of the mode conversion can be broadened, and the conversion of the mode represents the measurable frequency band range of the detection device.

[0037] The method for boundary detection using this detection structure in this embodiment includes the following steps:

[0038] Step 1: First, an anechoic environment for the test platform needs to be built, and the device to be detected (such as Figure 4As shown, the four holes at the bottom are convenient for installation on the stepper motor. The width of the narrow strip at the uppermost end is 5 mm), the detection structure (the structure is as Figure 3 shown. There is a rectangular plane at the front end of the device to be detected, which can reduce the influence of other acoustic modes near the narrow opening and improve the imaging quality), and the speaker (sound source) is placed in a box. The speaker and the detection device are at the same height, and the distance is 330 mm, as Figure 5 shown. The inner wall of the box is covered with sound-absorbing cotton, which absorbs the reflected wave and the direct wave to provide anechoic environment. Due to the high detection accuracy, the device to be detected can be fixed on the stepper motor, and the step distance is 0.5 mm, as Figure 6 shown. Note that the detection structure must be closely attached to the detection device to be imaged. If this condition is not met, the imaging quality will be reduced, and the detection of the one-dimensional structure boundary with a minimum width of 5 mm cannot be achieved. Place the acoustic probe in the two detection small holes of the detection structure (the distance between the two detection points from the uppermost narrow resonant cavity is 65.5 mm), and ensure the good sealing of the detection small holes, otherwise there may be a large error in the measurement results.

[0039] Step 2: On the basis of building a good test platform, move the device to be detected that needs to be imaged in a precessional manner through the stepper motor, with a step size of 0.5 mm, and record the sound pressure of the two detection small holes. When the device to be detected moves from one end of the device to be detected to the other end of the structure, the detection can be completed;

[0040] Step 3: Use formula (1):

[0041]

[0042] The intensity a of the (1,0) mode of the relative position of the device to be detected with respect to the detection device can be obtained (1,0) , where p1 and p2 are the sound pressures at Mic.1 and Mic.2 (microphones) in Figure 1 . The detection point is at a position 65.5 mm from the upper cross-section of the third narrow resonant cavity w3×w3. The peak-to-peak spacing of the intensity spectrum of this mode can represent the boundary information of the object. Similarly, the object can be rotated 90 degrees for measurement to obtain the boundary information in the other direction of the imaged object, and the boundary detection of the two-dimensional object can be completed.

[0043] In this example, only the imaging results of one-dimensional objects are shown. As Figure 7 shown, three one-dimensional objects with widths of 5 mm, 6.5 mm, and 10 mm are measured in this example. The present invention has good resolution for these one-dimensional objects, and the imaging bandwidth is about 900 Hz. Compared with the structures that do not break symmetry in the prior art, both the imaging resolution and the bandwidth have certain improvements. In Figure 8 , the boundary measurement results of the minimum structure of 5 mm are more clearly shown. InFigure 2 Near the three mode conversion transmission peaks, boundary imaging at three frequencies of 7790 Hz, 8046 Hz, and 8837 Hz was selected, and the data obtained from experiments and simulations were normalized respectively, demonstrating that the detection structure has the ability of broadband boundary detection, and the experiments and simulations are in good agreement.

Claims

1. A broadband high-resolution acoustic boundary detection structure based on capture resonance. The overall detection structure is a hollow square cylinder. The boundary detector at the lower part of the cylinder is composed of a plurality of narrow resonance cavities and a plurality of wide resonance cavities alternately arranged from bottom to top. It is characterized in that, The cross-sectional size of the narrow resonance cavity at the bottommost layer is smaller than that of the narrow resonance cavity above it; The detection structure further includes detection holes for placing acoustic probes opened on two opposite sidewalls at the upper part of the cylinder, a device to be detected in close contact with the bottommost narrow resonance cavity, and a sound source located below the device to be detected; The centers of all the resonance cavities are located on the same axis.

2. The broadband high-resolution acoustic boundary detection structure based on capture resonance according to claim 1, wherein The minimum detectable width of the detection structure is slightly smaller than the cross-sectional size of the narrow resonance cavity at the bottommost layer.

3. The broadband high-resolution acoustic boundary detection structure based on capture resonance according to claim 1, characterized in that The detection frequency band bandwidth of the detection structure is broadened by expanding the cross-sectional size of the narrow resonance cavity above the bottommost narrow resonance cavity.

4. An acoustic boundary detection structure with wide bandwidth and high resolution based on capture resonance according to claim 1, characterized in that The device to be detected moves along the detection direction in a step-by-step manner.

5. An acoustic boundary detection structure with wide bandwidth and high resolution based on capture resonance according to claim 1, characterized in that The boundary detector is composed of a first narrow resonance cavity, a first wide resonance cavity, a second narrow resonance cavity, a second wide resonance cavity, and a third narrow resonance cavity arranged from bottom to top. The structural dimensions of the first narrow resonance cavity, the second narrow resonance cavity, and the third narrow resonance cavity are w1×w1×l, w2×w2×l, and w3×w3×l respectively, and w1 < w2, w1 < w3. The structural dimensions of the first wide resonance cavity and the second wide resonance cavity are both W×W×L, and l < L, and w1, w2, and w3 are all smaller than W, where W is the side length of the square cavity inside the square cylinder.

6. The broadband high-resolution acoustic boundary detection structure based on capture resonance according to claim 4, characterized in that The acoustic probe specifically uses a microphone, and the sound source specifically uses a speaker.

7. An acoustic boundary detection method applying the broadband high-resolution acoustic boundary detection structure according to any one of claims 1-6, characterized in that, It includes the following steps: 1) Build an anechoic environment: Place the device to be detected, the detection structure, and the sound source in a box, line the inner wall of the box with sound-absorbing cotton, fix the device to be detected on a stepping machine, and make the detection structure closely adhere to the device to be detected; 2) Move the device to be detected in a precessional manner according to a set step size through the stepping machine, and record the sound pressure at the two detection holes; 3) Obtain the distance between two peaks in the sound pressure curves of the two detection holes, and use this as the boundary length of the device to be detected.

8. An acoustic boundary detection method according to claim 7, characterized in that When measuring the two-dimensional boundary of the device to be detected, after completing the detection of the one-dimensional boundary, rotate the device to be detected by 90 degrees for detection to complete the detection of the other-dimensional boundary.

Images