A precision displacement measurement method based on acoustic artificial microstructure

Abstract

The application discloses a kind of precision displacement measurement methods based on acoustic artificial microstructure, first, constructs a displacement measuring device, including two coupled with artificial topological charge ±q track element atom, and load with the thread pitch d thread;By rotating one of track element atom, the interference of the transmission wave of two different transmission paths in mode space is realized;Second, incident sound wave is divided into two coupled two acoustic vortices carrying topological charge +q and-q by first track element atom;When rotating second track element atom, its relative angular position is θ, relative longitudinal displacement is Δd=θd / (2π);Two acoustic vortices finally cause the change of transmission wave interference intensity I after different transmission paths in mode space, thereby realizing the displacement measurement of micrometer scale.The application encodes displacement information in interference intensity, realizes acoustic precision displacement measurement, and has super-high resolution to displacement measurement.

Description

Technical Field

[0001] The present invention belongs to the field of acoustic displacement measurement, and in particular relates to a precision displacement measurement method based on acoustic artificial microstructures. Background Art

[0002] Precise displacement measurement plays a vital role in modern science and technology, covering a wide range of fields such as microscopy imaging, advanced manufacturing and gravitational wave detection. In the past few decades, light waves have become a powerful tool for precision displacement measurement in a wide range of applications from classical physics to quantum physics due to their ultra-high frequency (usually around 100THz) and complex interactions with matter. In recent years, progress in nanophotonics and micro / nano-fabrication technologies has promoted the emergence of a variety of new methods, including photonic gears, polarization-encoded metasurfaces and super-oscillating fields, which have been able to achieve high-precision displacement measurement. Notably, by breaking the half-wavelength diffraction limit, researchers have experimentally demonstrated methods with displacement resolution exceeding "λ / 800" (λ is the working wavelength).

[0003] However, in certain scenarios, such as underwater environments, biological tissue, and complex mechanical components, light waves are not the optimal choice for displacement measurement. In contrast, acoustic waves, due to their high energy transfer efficiency and excellent object penetration, hold great potential for achieving this goal. Despite these advantages, acoustic waves are rarely used for high-resolution displacement measurement today. This is primarily due to the low frequency of acoustic waves, typically below 100 MHz, six orders of magnitude lower than light. This limits their resolution, making them unable to match that of light waves. For example, conventional ultrasonic pulse-echo-based displacement sensor technology typically provides a resolution of 100 μm at 0.35 MHz, corresponding to a resolution of approximately λ / 10. While increasing the operating frequency can improve resolution, this straightforward approach is limited by the inherent cost of ultrasonic transducer technology and the associated equipment. Furthermore, measurement accuracy is limited by multiple factors, including echo sampling rate, electronic noise, and algorithmic processing. Consequently, achieving ultra-high-resolution displacement measurement in acoustics remains a challenging pursuit. Therefore, designing acoustic methods for achieving ultra-high-resolution displacement measurement is highly desirable. Summary of the Invention

[0004] Purpose of the invention: The present invention provides a precision displacement measurement method based on acoustic artificial microstructures. By measuring the interference intensity of the transmitted wave, the micrometer-scale displacement encoded in the interference intensity can be obtained to achieve the measurement function. This method has ultra-high resolution for displacement measurement.

[0005] Technical solution: The invention provides a method for precise displacement measurement based on acoustic artificial microstructures. The implementation process is as follows:

[0006] A displacement measurement device is constructed, comprising two coupled orbital meta-atoms with artificial topological charges ±q and loaded with threads of pitch d. Interference of transmitted waves from two different propagation paths in the mode space is achieved by rotating one of the orbital meta-atoms.

[0007] The incident acoustic wave is split into two coupled acoustic vortices carrying topological charges of +q and -q by the first orbital meta-atom. When the second orbital meta-atom is rotated to a relative angular position of θ, the relative longitudinal displacement is Δd = θd / (2π).

[0008] The two acoustic vortices pass through different transmission paths in the mode space and eventually cause the change of the interference intensity I of the transmitted wave I = 0.5I max [1+cos(4qπηΔd / d)]exp(-γΔd), where, I max is the normalized interference intensity; η is the phase distortion coefficient of the orbital element-atom after fabrication; γ is the attenuation coefficient of the system; Δd = a + bln (I + c), where a, b, and c are all fitting constants.

[0009] Furthermore, the two orbital meta-atoms each have q groups of fan-shaped cell groups, and each group of fan-shaped cell groups consists of two types of cells with phase shifts of "0" and "π".

[0010] Furthermore, the orbital meta-atom is processed using Future 8200Pro resin using 3D printing technology.

[0011] Furthermore, the thickness of the two meta-atoms is h=0.5λ, and the radius is R=0.25λ.

[0012] Furthermore, the two orbital meta-atoms are equipped with a shell integrally formed therewith on the sides to drive the meta-atoms to rotate, thereby achieving smooth coupling of acoustic waves between the two orbital meta-atoms.

[0013] Furthermore, the fan-shaped cells are designed by a gradient space folding metamaterial structure.

[0014] Furthermore, the central angle corresponding to each cell is α=π / q.

[0015] Furthermore, the fan-shaped cells with a phase shift of "0" directly use the fan-shaped cavity.

[0016] Furthermore, the fan-shaped cell with a phase shift of "π" includes a fan-shaped cavity and acoustic hard plates connected to the inner and outer walls and side walls; by changing the distance between two adjacent acoustic hard plates and the height of the acoustic hard plates, a fan-shaped cell with efficient transmission and phase shift matching is found.

[0017] Furthermore, the side wall thickness of the fan-shaped cavity is t=1 mm.

[0018] Beneficial effects: Compared with the prior art, the present invention has the following beneficial effects: the present invention realizes the interference of transmitted waves of two different transmission paths in the mode space through an orbital meta-atom in a torsional structure; further, by encoding the displacement information in the interference intensity, acoustic precision displacement measurement is realized, and the displacement measurement has ultra-high resolution. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a schematic diagram of the principle of the displacement measuring device proposed in the present invention;

[0020] Figure 2 Schematic diagram of the principle of the orbital meta-atom in the present invention;

[0021] Figure 3 This is a schematic diagram of the structure of the displacement measuring device proposed in the present invention;

[0022] Figure 4 Schematic diagram of the design principle of the fan-shaped cell in the present invention;

[0023] Figure 5 Photos of specific tests carried out in the present invention;

[0024] Figure 6 A schematic diagram of a specific test performed in the present invention;

[0025] Figure 7 It is a curve diagram of the sensitivity linear fitting area in the present invention;

[0026] Figure 8 This is a data graph showing that the displacement measurement device of the present invention achieves a 7.5 μm resolvable displacement function;

[0027] Figure 9 This is a data graph showing the displacement measurement device of the present invention achieving a 1.2 μm resolvable displacement function;

[0028] Figure 10 This is a data diagram of the displacement measurement device of the present invention regarding an unresolvable displacement of 0.3 μm; DETAILED DESCRIPTION

[0029] The present invention will be further described in detail below with reference to the accompanying drawings.

[0030] The present invention provides a method for precise displacement measurement based on acoustic artificial microstructures. Figure 1 As shown in Figure 1, the interaction between acoustic waves and displacement measuring devices can be used to achieve ultra-high resolution displacement measurement. Figure 2 、 Figure 3As shown in the figure, the displacement measurement device consists of two coupled identical orbital meta-atoms with artificial topological charges of ±q. The orbital meta-atoms are equipped with threads with a pitch of d. By rotating one of the orbital meta-atoms, interference of the transmitted waves of two different transmission paths in the mode space is achieved. Both orbital meta-atoms are composed of q groups of fan-shaped cells, each group of fan-shaped cell groups consists of two cells with phase shifts of "0" and "π", as shown in the figure. Figure 4 As shown, the central angle of each cell is α = π / q. In addition, the two orbital atoms need to process a certain shell for Figure 5 The test system is connected as shown. In order to allow the acoustic waves between the two orbital meta-atoms to couple smoothly, one of the orbital meta-atoms needs to have its shell less processed to make the meta-atom protrude. Figure 3 As shown on the left, the other orbital atom needs to process more shells to make the orbital atom concave. Figure 3 As shown on the right, by rotating the second orbital meta-atom, the distance and angular position of the two orbital meta-atoms can be adjusted, thereby affecting the interference intensity of the transmitted waves along two different transmission paths in the mode space.

[0031] The specific manifestation of displacement measurement in the displacement measurement device is that the incident plane wave will be divided into two vortices of equal size and opposite chirality after passing through the first orbital element atom. When these vortices pass through the second orbital element atom, they experience TP(+q,-q) and TP * (-q, +q) two different transmission paths. When the second orbital meta-atom has a relative angle θ with respect to the first one, a geometric phase difference of 2qθ is generated between the two vortices. In addition, due to the existence of the thread (whose pitch is d), after rotating at a certain angle, a certain gap Δd will be formed between the two orbital meta-atoms, causing the amplitude of the vortex to be attenuated in this gap. The final emitted wave is the superposition of the two vortices, and the intensity I of the emitted wave depends on the rotation angle θ and the pitch d of the thread, and the relationship between the rotation angle θ and the pitch d and the displacement information is Δd = θd / (2π). The two acoustic vortices pass through different transmission paths in the mode space and ultimately cause a change in the interference intensity I of the transmitted wave I = 0.5I max [1+cos(4qπηΔd / d)]exp(-γΔd), where, I max is the normalized interference intensity; η is the phase distortion coefficient of the orbital element after fabrication; and γ is the system's attenuation coefficient. After extensive fitting, the relationship between displacement and interference intensity is Δd = a + bln(I + c), where a, b, and c are fitting constants. Therefore, by measuring the interference intensity I of the outgoing wave, the corresponding displacement information Δd can be obtained.

[0032] Example 1: Under the operating wavelength of λ = 100 mm, three orbital meta-atoms were designed, each with q = 4 and d = 3 mm, 10 mm, and 16 mm. In each case, the orbital meta-atom had a thickness of h = 0.5λ and a radius of R = 0.25λ. Two meta-atoms were placed in a waveguide with a radius of R = 0.25λ to form a displacement measurement device. Initially, the distance between the two meta-atoms was zero. As the rotation angle θ of the second meta-atom increased, the distance between them also increased.

[0033] The fan-shaped cells of the orbital meta-atom are designed using a gradient spatial folding metamaterial structure. Fan-shaped cells with a phase shift of "0" use a direct fan-shaped cavity. Fan-shaped cells with a phase shift of "π" consist of a fan-shaped cavity, three acoustic hard plates connected to the outer wall, and two acoustic hard plates connected to the inner wall. These five acoustic hard plates are evenly distributed alternately at the center of the cell. The thickness of the upper and lower walls of the fan-shaped cell is t1 = 2 mm, the thickness of each acoustic hard plate is t2 = 1 mm, the distance between each two adjacent acoustic hard plates is t3, and the height of each acoustic hard plate is t4. To prevent interference between adjacent cells, the sidewall thickness of the fan-shaped cavity is t = 1 mm. By varying the spacing t3 between adjacent acoustic hard plates and the acoustic hard plate t4, fan-shaped cells with high transmission efficiency and a phase shift of "π" are found, thus forming the orbital meta-atom.

[0034] Example 2: Use 3D printing technology to process the designed orbital atom using the future 8200Pro resin and place it in the center of the impedance tube. Figure 5 As shown. Using the computer-controlled data acquisition card, a signal with a frequency of 3430Hz is output from the AO end. This signal is transmitted to the speaker on the left side of the impedance system through the power amplifier, as shown Figure 6 As shown in the figure, in the impedance tube, the left speaker generates sound waves. These waves pass through the sample under test and are absorbed by the sound-absorbing cotton. The sound pressure signals in front of and behind the sample under test are transmitted to the AI ​​terminal of the data acquisition card through four microphones. The computer analyzes and processes these signals to obtain the interference intensity I.

[0035] The designed d = 16mm orbital meta-atom was placed in the above impedance system. The second orbital meta-atom was rotated every 1.5° and the interference intensity I of the transmitted wave was measured. The interference intensity was measured 100 times at each angle and the average was taken to improve the measurement accuracy. A specific rotation angle θ corresponds to a specific displacement Δd. Therefore, using the measured data, the fitting formula Δd = a + bln(I + c) can be obtained, where a = 3.13974, b = -227.25081, and c = 0.02147.

[0036] Afterwards, the second orbital meta-atom was twisted to four different positions P1, P2, P3, and P4. In each case, the interference intensity was repeatedly measured to obtain displacement information. The average values ​​of the measured interference intensity I were 0.63126, 0.25022, 0.06465, and 0.00393, respectively, and the corresponding displacements Δd were 130μm, 329μm, 590μm, and 868μm, respectively. In these four cases, the displacements measured by the physical micrometer were 130μm, 328μm, 583μm, and 865μm, respectively. Comparing the above-mentioned displacement results with those measured by the physical micrometer, it can be found that the maximum error between the two is 0.2%.

[0037] Example 3: The sensitivity of the designed displacement precision measurement device based on acoustic artificial microstructure is affected by two independent degrees of freedom (q and d). Among the three orbital atoms designed in Example 1, the device with d = 3 mm has the greatest sensitivity. Figure 7 Within the linear region shown in Figure 1, the small displacement is repeatedly measured by recording the interference intensity 100 times. The histogram of the normalized intensity distribution at two different positions is shown in Figure 2. Figure 8 As shown. Each histogram is fitted with a Gaussian function, and it can be found that the displacement between the two distinguishable peaks is 7.5μm. The Gaussian fitting curve is used to estimate the accuracy of the designed displacement precision measurement device based on acoustic artificial microstructures through the error transfer function, and the estimated measurement error is σ = 0.5μm. Further reducing the displacement, as shown Figure 9 As shown in Figure 1, the difference between the two positions is close to the level of just being distinguishable (defined as the peak of one histogram being on the boundary of the half-width at half-maximum of the other). In this case, the displacement between the two distinguishable peaks is 1.2 μm, and the estimated error is σ = 0.2 μm, which almost reaches the diffraction-limited resolution. When the displacement is further reduced to 0.3 μm, as shown in Figure 1, the difference between the two positions is close to the level of just being distinguishable (defined as the peak of one histogram being on the boundary of the half-width at half-maximum of the other). In this case, the displacement between the two distinguishable peaks is 1.2 μm, and the estimated error is σ = 0.2 μm, which almost reaches the diffraction-limited resolution. Figure 10 As shown in the figure, the distinction between the two positions becomes less obvious, and the error percentage is about 33.3%. Therefore, when d = 3 mm, the designed precision displacement measurement device based on acoustic artificial microstructure can distinguish a small displacement of 1.2 μm at a frequency of 3.43 kHz, and its displacement measurement resolution is about λ / 10 5 .

[0038] This invention exploits the mode evolution characteristics of acoustic waves and orbital meta-atoms to achieve acoustic interference, encoding displacement information in the interference intensity of the transmitted waves. This allows the design of a device with ultra-high displacement resolution. This research result provides new ideas and methods for acoustic displacement measurement and has important theoretical and applied value.

[0039] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A precision displacement measurement method based on acoustic artificial microstructure, characterized in that: The implementation process is as follows: A displacement measurement device is constructed, comprising two coupled orbital meta-atoms with artificial topological charges ±q and loaded with threads of pitch d. Interference of transmitted waves from two different propagation paths in the mode space is achieved by rotating one of the orbital meta-atoms. The incident acoustic wave is split into two coupled acoustic vortices carrying topological charges of +q and -q by the first orbital meta-atom. When the second orbital meta-atom is rotated to a relative angular position of θ, the relative longitudinal displacement is Δd = θd / (2π). The two acoustic vortices pass through different transmission paths in the mode space and eventually cause the change of the interference intensity I of the transmitted wave I = 0.5I max [1+cos(4qπηΔd / d)]exp(-γΔd), where, I max is the normalized interference intensity; η is the phase distortion coefficient of the orbital element-atom after fabrication; γ is the attenuation coefficient of the system; Δd = a + bln (I + c), where a, b, and c are all fitting constants.

2. The method for precise displacement measurement based on acoustic artificial microstructure according to claim 1, characterized in that: The two orbital meta-atoms each have q groups of fan-shaped cell groups, and each group of fan-shaped cell groups consists of two types of cells with phase shifts of "0" and "π".

3. The method for precise displacement measurement based on acoustic artificial microstructure according to claim 1, characterized in that: The orbital atom is made using 3D printing technology and Future 8200Pro resin.

4. The method for precise displacement measurement based on acoustic artificial microstructure according to claim 1, characterized in that: The thickness of the two orbital meta-atoms is h = 0.5λ, and the radius is R = 0.25λ.

5. The method for precise displacement measurement based on acoustic artificial microstructure according to claim 1, characterized in that: A shell integrally formed with the two orbital meta-atoms is added to the sides of the two orbital meta-atoms to drive the orbital meta-atoms to rotate, thereby achieving smooth coupling of acoustic waves between the two orbital meta-atoms.

6. The method for precise displacement measurement based on acoustic artificial microstructure according to claim 2, characterized in that: The fan-shaped cells are designed by a gradient space folding metamaterial structure.

7. The method for precise displacement measurement based on acoustic artificial microstructure according to claim 2, characterized in that: The central angle corresponding to each cell is α=π / q.

8. The method for precise displacement measurement based on acoustic artificial microstructure according to claim 2, characterized in that: The fan-shaped cells with a phase shift of "0" directly use the fan-shaped cavity.

9. The method for precise displacement measurement based on acoustic artificial microstructure according to claim 2, characterized in that: The fan-shaped cell with a phase shift of "π" includes a fan-shaped cavity and acoustic hard plates connected to the inner and outer walls and side walls; by changing the distance between two adjacent acoustic hard plates and the height of the acoustic hard plates, a fan-shaped cell with efficient transmission and phase shift matching is found.

10. The method for precise displacement measurement based on acoustic artificial microstructure according to claim 9, characterized in that: The side wall thickness of the fan-shaped cavity is t=1 mm.

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