CN115165078A - Structure and method for broadband high-resolution acoustic boundary detection based on trapped resonance - Google Patents

Abstract

The invention relates to a broad-band high-resolution acoustic boundary detection structure and method based on captured resonance. The detection structure is a hollow square cylinder as a whole, and the boundary detectors located at the lower part of the cylinder are alternately arranged from bottom to top. A narrow resonant cavity and a plurality of wide resonant cavities are formed, and the cross-sectional dimension of the narrow resonant cavity located at the lowermost layer is smaller than the cross-sectional dimension of the narrow resonant cavity located above it. Compared with the prior art, the present invention has the advantages of wide frequency band and high resolution.

Description

Structure and method of broadband high-resolution acoustic boundary detection based on trapped resonance

technical field

The invention relates to the field of physical acoustic imaging, in particular to an acoustic boundary detection structure and method based on trapped resonances (Trapped Resonances) for realizing broadband and high resolution.

Background technique

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. Due to the exponential decay of high spatial frequencies along the direction of wave propagation, fine features of the imaged object or details smaller than half a wavelength cannot be recovered in the final image. In order to To overcome this diffraction limit, various methods exist to achieve super-resolution imaging, including but not limited to metalens, time-reversal techniques, Fabry-Perot-type resonances, and acoustic negative refraction, and in some practical imaging situations, sometimes Only the edge information of the object needs to be extracted, because these edges carry the key information of the object, which will greatly reduce the amount of data that needs to be processed.

By exciting resonant trapping modes in cavities of different sizes, in this scenario, evanescent waves can be coupled with trapping modes and converted into propagating waves, and the bandgap of plane wave modes brought about by structural periodicity can remove lower spatial frequencies information. However, the previous edge detection technology based on this capture mode faces the problem of narrow bandwidth, and it does not explain which factors of this detection device have a greater impact on the imaging resolution, which limits the edge imaging to a certain extent. The application value of technology.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a broadband high-resolution acoustic boundary detection structure and method based on captured resonance in order to overcome the above-mentioned defects of the prior art.

The object of the present invention can be realized through the following technical solutions:

A broadband high-resolution acoustic boundary detection structure based on captured resonance, the detection structure is a hollow square cylinder as a whole, and a boundary detector located at the lower part of the cylinder consists of a plurality of narrow resonant cavities and A plurality of wide resonant cavities are formed, and the cross-sectional dimension of the narrow resonant cavity located at the lowermost layer is smaller than the cross-sectional dimension of the narrow resonant cavity located above it.

The minimum detectable width of the detection structure is slightly smaller than the cross-sectional dimension of the lowermost narrow resonant cavity.

The detection band bandwidth of the detection structure is widened by expanding the cross-sectional size of the narrow resonator located above the lowermost narrow resonator.

The detection structure also includes detection holes on the two opposite side walls of the upper part of the cylinder body, in which the acoustic probes are placed;

The to-be-detected device moves along the detection direction in a step-by-step manner.

The boundary detector is composed of a first narrow resonant cavity, a first wide resonant cavity, a second narrow resonant cavity, a second wide resonant cavity and a third narrow resonant cavity arranged from bottom to top. The structural dimensions of the resonator, the second narrow resonator and the third narrow resonator are respectively w ₁ ×w ₁ ×l, w ₂ ×w ₂ ×l, w ₃ ×w ₃ ×l, and w ₁ <w ₂ , w ₁ <w ₃ , the structural dimensions of the first wide resonant cavity and the second wide resonant cavity are both W×W×L, and l<L, w ₁ , w ₂ , and w ₃ are all smaller than W, and W is The side length of the square cavity inside the square cylinder.

The centers of all cavities lie on the same axis.

The sound probe specifically adopts a microphone, and the sound source specifically adopts a speaker.

An acoustic boundary detection method, comprising the following steps:

1) Build an anechoic environment: place the device to be detected, the detection structure and the sound source in a box, and cover the inner wall of the box with sound-absorbing cotton, fix the device to be detected on the stepper, and make the detection structure close to the to-be-detected device;

2) Move the device to be detected by the stepping machine in a precessive manner according to the set step size, and record the sound pressure of 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.

When measuring the two-dimensional boundary of the device to be detected, after the detection of the one-dimensional boundary is completed, the device to be detected is rotated 90 degrees for detection to complete the detection of the other-dimensional boundary.

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

The invention is a broadband high-resolution acoustic boundary detection method based on captured resonance. The method realizes the acoustic boundary detection through asymmetric wide-narrow resonant cavity coupling. The cross-section of the detection device is a square with different width and width. Periodically arranging these wide and narrow resonant cavities can excite and capture resonance 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 latter two narrow resonances. The area of the cross-section of the cavity can further widen the measurement bandwidth of boundary detection. Through the parallel design of this narrow and wide resonant cavity, the structural periodicity can be broken, and the characteristics of high-resolution and wide-band measurement can be obtained at the same time.

Description of drawings

FIG. 1 is a schematic diagram of the detection structure, principle and imaging process of the present invention.

FIG. ₂ is a schematic diagram of broadband mode conversion in a broadband high _- resolution acoustic boundary detection method based on captured resonances of the present invention, wherein FIG. ₃ = 6.5mm broadband mode conversion schematic diagram, Figure (2b) is a schematic diagram of broadband mode conversion with structural parameters w ₁ =6.5mm, w ₂ =10mm, w ₃ =10mm.

Fig. 3 is a structural diagram of a device to be detected in a broadband high-resolution acoustic boundary detection method based on captured resonance of the present invention, wherein Fig. (3a) is a side view, and Fig. (3b) is a cross-sectional view.

FIG. 4 is a one-dimensional structure to be detected in a broadband high-resolution acoustic boundary detection method based on captured resonance of the present invention.

FIG. 5 is a schematic diagram of experimental placement in a broadband high-resolution acoustic boundary detection method based on captured resonances of the present invention.

FIG. 6 is a 5mm-wide detected structure fixed on the stepper machine and close to the detection device and moving to the left in a broadband high-resolution acoustic boundary detection method based on captured resonance of the present invention.

Fig. 7 is the experimental result of one-dimensional structure boundary detection in a broadband high-resolution acoustic boundary detection method based on captured resonance of the present invention, wherein Fig. (7a) is the experimental result of 5mm wide one-dimensional structure boundary detection, Fig. (7b) is the experimental result of the boundary detection of a one-dimensional structure with a width of 6.5 mm, and Figure (7c) is the experimental result of the boundary detection of a one-dimensional structure with a width of 10 mm.

8 is a comparison diagram of boundary detection experiment and simulation of normalized data of a 5mm wide one-dimensional structure at different frequencies in a broadband high-resolution acoustic boundary detection method based on captured resonance of the present invention, wherein, Figure (8a ) is a comparison diagram of the boundary detection experiment and simulation of the normalized data at 7790Hz for a 5mm wide one-dimensional structure, and Figure (8b) is the boundary detection experiment and simulation of a 5mm wide one-dimensional structure at 8046Hz. For comparison, Figure (8c) is a comparison diagram of the boundary detection experiment and simulation of the normalized data at 8837 Hz for a one-dimensional structure with a width of 5 mm.

Detailed ways

In order to make the technical means, creative features, achieved goals and effects of the invention easy to understand and understand, the present invention will be further described below with reference to the specific drawings.

Example

The present invention provides a broadband high-resolution acoustic boundary detection structure and method based on capture resonance, which takes into account imaging resolution, imaging quality and imaging bandwidth. The key influencing factor of wave trapping efficiency is that by increasing the side-length ratio of the narrow resonant cavity and 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 The rate is increased to 0.11λ. In theory, one-dimensional and two-dimensional object boundary detection can be achieved in the frequency band range of 7400Hz-9400Hz. As long as there is mode conversion, this frequency can be used for boundary detection. In actual situations, considering the loss and printing errors And the measurement error, the boundary imaging effect has certain requirements for the mode conversion intensity. In experiments, the present invention can achieve a measurable bandwidth of 900Hz and a minimum object boundary recognition of 5mm within the frequency bandwidth range of 7400Hz-9400Hz, which provides a more efficient method for subsequent boundary detection using the captured resonance mechanism.

The schematic diagram of the principle of the present invention or the schematic diagram of the boundary imaging process is shown in Figure 1. The structure is composed of several square resonator cavities with different cross-sectional dimensions: the narrow cross-section includes three narrow resonator cavities t= _wi × _wi (i=1, 2,3), the wide section includes two wide resonators T=W×W, the thicknesses of the wide and narrow resonators are represented by L and l respectively, and the corresponding structural parameters are W=22.5mm, L=5mm, w ₁ =6.5mm , w ₂ =10mm, w ₃ =10mm, l=1.5mm, the object to be imaged in this example is several one-dimensional plates printed with three-dimensional resin, and its width is represented by the parameter s, as shown in Figure 1, the object is passed through the sound wave The high and low spatial frequency information generated by the incident is represented by the attenuation line and the wavy line, respectively. The boundary detector converts the evanescent wave carrying the high-frequency spatial information into a propagable wave carrying the low-frequency spatial information. On the other hand, the low-frequency spatial information It will be converted into high-frequency spatial information and gradually attenuated in the boundary detector. In each detection, the detected object needs to be carried out in an anechoic chamber, and the boundary detector is placed at a certain distance from the object to avoid The process of mode conversion and mode filtering is intuitively presented. In practical applications, the boundary detector is closely contacted with the detected object to improve the extraction efficiency of evanescent waves, and the detected object is moved in front of the boundary detector through a stepping motor. The step is moved along the y direction, and the step length is 0.5mm. Since the physical mechanism of edge detection used in the present invention is to capture resonance, according to the characteristics of the captured resonance, the first antisymmetric mode in the wide resonant cavity can be utilized, That is, the (1,0) pattern to represent the edge information of the object, such as the width s shown in the upper right corner of Figure 1.

The mode conversion spectral lines of the detection structure can represent the broadband characteristics of the device. In Figure 2, the transmission coefficient T _(m,n)(m',n') represents the mode (m',n') under the incident mode (m,n). n') transmission coefficients, all of these modes are relative to the waveguide modes of the wide resonator, it is worth noting that the waveguide modes (3,0)(5,0)(7,0) in the frequency range 7400Hz～9400Hz The wide resonators are all evanescent waves. In the numerical calculation of the transmission characteristics, the different wide-section waveguide modes are excited only 1 mm in front of the narrow resonator of size w _{1 ×} w ₁ . ×w ₃ ) 65.5mm after setting the measuring point to detect the absorption of different modes of the wide waveguide section, if the distance between the wide wave guide entrance section and the first narrow resonator entrance section (w ₁ ×w ₁ ) is too long, due to evanescent The wave decays exponentially along the propagation direction, and it is difficult to achieve mode conversion from high spatial frequency information to low spatial frequency information. According to this feature, the distance between the first narrow resonator and the object is critical to the efficiency of mode conversion. Therefore, the input aperture of the boundary detector is designed as a narrow resonator instead of a wide resonator. The top of the structure in Figure 1 is designed as a narrow waveguide section (w ₁ ×w ₁ ), which breaks the periodicity of the structure.

It is found in the simulation that the bandwidth of the mode conversion is sensitive to the side length ( _wi ) of the narrow resonator rather than other structural parameters. Figures (2a) and (2b) show that (0,0)(1,0)(3, 0)(5,0)(7,0) mode incident transmission spectra, the parameters of the two structures are w ₁ =6.5mm, w ₂ =6.5mm, w ₃ =6.5mm (prior art) and w ₁ =6.5mm, w ₂ =10mm, w ₃ =10mm (the present invention), it can be seen that the structural parameters of w ₁ =6.5mm, w ₂ =10mm, w ₃ =10mm have wider mode conversion frequency band and wider imaging In the frequency range, due to the trapped resonance coupling between the three narrow resonators and the wide resonators, there are three transmission peaks under the excitation of the antisymmetric waveguide mode, and the filtering of the plane wave is mainly caused by the band gap of the whole structure, compare Fig. (2a) and (2b), the bandwidth of mode conversion is determined by the ratio of the narrow cavity length _wi to the wide cavity length W, however, with the widening of the narrow cavity (w ₂ , w ₃ ) in Fig. (2b), the planar mode (0,0) propagates more easily despite its bandgap effect due to its strong scattering, which can be explained by the reduced contrast between _wi and W, which leads to a reduction in the plane-wave scattering ability. In addition, thermal viscous losses will further reduce this scattering, the parameters w ₂ = 10mm and w ₃ = 10mm were found in simulations to provide a good trade-off between broadband and plane wave rejection, but for sizes smaller than boundary detectors For objects with input apertures, the narrow opening cannot be semi-occluded during the entire detection process. In this case, the quality of the captured resonance decreases, resulting in poor coupling between the evanescent wave near the edge of the object and the antisymmetric waveguide eigenmodes. , which shows that if the size of the narrow resonant cavity (w ₁ ) at the input aperture is reduced to be comparable to the object, some edge information of the smaller object can be obtained. Through numerical optimization, w ₁ =6.5mm, w ₂ = 10mm, w ₃ =10mm parameters to balance the relationship between better imaging resolution and wide frequency band.

In this example, the boundary detector contains three resonant narrow resonators and two resonant wide resonators, and their dimensions are shown in Figure 1. The center of the resonant narrow resonator and the center of the resonant wide resonator are located on the same axis.

By widening the width of the latter two narrow resonators, the bandwidth of the mode conversion can be widened, and the mode conversion represents the measurable frequency band range of the detection device.

In this embodiment, the method for boundary detection using the detection structure includes the following steps:

Step 1: First of all, it is necessary to build an anechoic environment for the test platform, and install the device to be detected (as shown in Figure 4, the four holes at the bottom are easy to install on the stepper, and the width of the narrow strip at the top is 5mm), the detection structure (structure As shown in Figure 3, there is an extra rectangular plane at the front end of the device to be detected, which can reduce the influence of other sound wave modes near the narrow opening and improve the imaging quality) and the speaker (sound source) are placed in a box, and the speaker and the detection device are placed in a box. At the same height, the distance is 330mm. As shown in Figure 5, the inner wall of the box is covered with sound-absorbing cotton. The sound-absorbing cotton absorbs reflected waves and direct waves to provide an echo-free environment. Due to the high detection accuracy, the device to be detected can be On the machine, the stepping distance is 0.5mm, as shown in Figure 6. Note that the detection structure must be close to the detection device to be imaged. If this condition is not met, the imaging quality will be reduced, and the minimum 5mm wide cannot be achieved. For one-dimensional structure boundary detection, place the acoustic probe in the two detection holes of the detection structure (the distance between the two detection points and the upper narrow resonant cavity is 65.5mm.), and ensure the detection hole is well sealed, otherwise There may be large errors in the measurement results.

Step 2: On the basis of building the test platform, move the device to be detected to be imaged in a precession manner through a stepper, the step length is 0.5mm, and record the sound pressure of the two detection holes, when the device to be detected is detected The detection can be completed by moving from one end of the device to be detected to the other end of the structure;

Step 3: Using Equation (1):

The (1,0) mode intensity a _(1,0) of the device to be detected relative to the position of the detection device can be obtained, p ₁ and p ₂ are the sound pressures at Mic.1 and Mic.2 (microphones) in Figure 1, the The detection point is 65.5mm away from the upper cross-section of the third narrow resonant cavity w ₃ ×w ₃ . 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 to carry out The boundary information in the other direction of the imaging object can be obtained by measuring, and the boundary detection of the two-dimensional object can be completed.

In this example, only the imaging results of one-dimensional objects are shown. As shown in Figure 7, three one-dimensional objects are measured in this example, and the widths are 5mm, 6.5mm and 10mm respectively. The present invention has better resolution for these one-dimensional objects. Compared with the structure that does not break the symmetry in the prior art, the imaging resolution and bandwidth have been improved to a certain extent. In Figure 8, the boundary measurement of the minimum structure of 5mm is more clearly displayed As a result, in the vicinity of the three mode conversion transmission peaks in Fig. 2, three boundary imaging frequencies of 7790 Hz, 8046 Hz and 8837 Hz were selected, and the data obtained from the experiment and simulation were normalized respectively, which proved that the detection structure has a broadband boundary. The ability to detect, and the experiment and simulation are in good agreement.

Claims (10)

1. A broadband high-resolution acoustic boundary detection structure based on captured resonance, the detection structure as a whole is a hollow square cylinder, and the boundary detector located at the lower part of the cylinder consists of a plurality of narrow resonances alternately arranged from bottom to top The cavity is composed of a plurality of wide resonant cavities, and is characterized in that the cross-sectional dimension of the narrow resonant cavity located at the lowermost layer is smaller than the cross-sectional dimension of the narrow resonant cavity located above it. 2 . The broadband high-resolution acoustic boundary detection structure based on trapped resonance according to claim 1 , wherein the minimum detectable width of the detection structure is slightly smaller than the cross-sectional dimension of the lowermost narrow resonant cavity. 3 . 3. A broadband high-resolution acoustic boundary detection structure based on trapped resonance according to claim 1, characterized in that the detection is broadened by expanding the cross-sectional size of the narrow resonant cavity located above the lowermost narrow resonant cavity The probe band bandwidth of the structure. 4. a kind of wide-band high-resolution acoustic boundary detection structure based on capturing resonance according to claim 1, is characterized in that, this detection structure also comprises the detection small that is provided with acoustic probe on two opposite side walls of the upper part of the cylinder. A hole, a device to be probed in close contact with the lowermost narrow resonant cavity, and a sound source located below the device to be probed. 5 . The broadband high-resolution acoustic boundary detection structure based on captured resonance according to claim 4 , wherein the to-be-detected device moves along the detection direction in a stepwise manner. 6 . 6 . The broadband high-resolution acoustic boundary detection structure based on captured resonance according to claim 1 , wherein the boundary detector consists of a first narrow resonant cavity, a first A wide resonant cavity, a second narrow resonant cavity, a second wide resonant cavity and a third narrow resonant cavity are formed, and the structural dimensions of the first narrow resonant cavity, the second narrow resonant cavity and the third narrow resonant cavity are respectively w ₁ ×w ₁ ×l, w ₂ ×w ₂ ×l, w ₃ ×w ₃ ×l, and w ₁ <w ₂ , w ₁ <w ₃ , the first wide resonant cavity and the second wide resonant cavity are The structural dimensions are all W×W×L, and l<L, w ₁ , w ₂ , and w ₃ are all smaller than W, and W is the side length of the square cavity inside the square cylinder. 7 . The broadband high-resolution acoustic boundary detection structure based on trapped resonance according to claim 1 , wherein the centers of all resonant cavities are located on the same axis. 8 . 8 . The broadband high-resolution acoustic boundary detection structure based on captured resonance according to claim 4 , wherein the acoustic probe is specifically a microphone, and the sound source is a speaker. 9 . 9. An acoustic boundary detection method applying the broadband high-resolution acoustic boundary detection structure according to any one of claims 1-8, is characterized in that, comprising the following steps: 1) Build an anechoic environment: place the device to be detected, the detection structure and the sound source in a box, and cover the inner wall of the box with sound-absorbing cotton, fix the device to be detected on the stepper, and make the detection structure close to the to-be-detected device; 2) Move the device to be detected by the stepping machine in a precessive manner according to the set step size, and record the sound pressure of 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. 10. An acoustic boundary detection method according to claim 9, wherein when measuring the two-dimensional boundary of the device to be detected, after completing the detection of the one-dimensional boundary, the measurement device to be detected is rotated 90 degrees for detection, Complete the detection of another dimension boundary.

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