A system and method for testing the equivalent parameters of underwater acoustic metamaterials

Abstract

The application discloses a kind of underwater acoustic metamaterial equivalent parameter test methods: the incident signal and reflected signal of the front surface of material are measured, and the reflection coefficient R containing phase information under wide frequency is obtained;Transmission signal is measured on the back surface of material, and the transmission coefficient T containing phase information under wide frequency is obtained;According to R and T, the equivalent parameter is calculated using inversion method.The application also provides a kind of test system: signal testing device, including signal generator, transducer, hydrophone, power amplifier and oscilloscope;Three-dimensional moving device is used to control the position of transducer and hydrophone, and the incident signal, reflection signal and reflection signal are collected and recorded by oscilloscope;Signal post-processing module is obtained according to incident signal, reflection signal and reflection signal processing reflection coefficient and transmission coefficient, and equivalent parameter is calculated.The test method and system can obtain complex transmission and reflection coefficient with amplitude and phase information, so as to calculate the equivalent parameter of material by inversion method.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of acoustic parameter testing, and particularly relates to a system and method for testing equivalent parameters of underwater acoustic metamaterials. BACKGROUND

[0002] Acoustic metamaterials are a kind of artificial periodic materials with super-normal physical properties composed of sub-wavelength structural units. Because the structural scale is much smaller than the working wavelength, it cannot be distinguished by sound waves, so it can be regarded as a homogeneous material and described by equivalent parameters. By skillfully designing the structural units of the metamaterial, the transmission direction of the sound wave can be precisely controlled, thereby realizing unique functions that conventional materials do not have, such as negative refraction, negative reflection, acoustic invisibility, etc., which have broad application prospects in military invisibility, vibration and noise reduction, medical imaging, etc. For example, the Chinese patent with publication number CN113456839A discloses a double-negative acoustic metamaterial with dipole resonance enhancement; the invention also discloses the application of the above-mentioned double-negative acoustic metamaterial in craniocerebral ultrasonic imaging and high-intensity focused ultrasonic therapy. For example, the Chinese patent with publication number CN11126113A discloses a double-negative acoustic metamaterial based on Mie resonance for transcranial ultrasonic imaging, which can effectively eliminate the dissipation and distortion of sound waves by the skull.

[0003] As mentioned above, in the research of acoustic metamaterials, the testing of acoustic equivalent parameters is one of the important characteristics of acoustic metamaterials. In the existing testing methods (for reference, Zigoneanu L, Popa B L, Starr AF, et al. Design and measurements of a broadband two-dimensional acoustic metamaterial with anisotropic effective mass density [J]. Journal of Applied Physics, 2011, 109(5): 204301. and Cheng Y, Zhou C, Yuan B G, et al. Ultra-sparse metasurface for high reflection of low-frequency sound based on artificial Mie resonances [J]. Nature Materials, 2015, 14(10): 1013.), taking the transmission coefficient test as an example, researchers use the transmission signal with sample and the transmission signal without sample to obtain the transmission coefficient, which leads to the loss of part of the phase information, which is not completely consistent with the transmission coefficient containing phase information required by the parameter inversion method, resulting in deviation in the final calculation result.

[0004] Therefore, how to extract complete phase information and solve the problem of deviation of the result of equivalent parameters is a technical problem to be solved in the field. SUMMARY

[0005] The present application aims to provide a water acoustic metamaterial equivalent parameter testing system and method, obtain complex transmission and reflection coefficients with amplitude and phase information, and calculate the equivalent parameters of the material.

[0006] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0007] A water acoustic metamaterial equivalent parameter testing method, the testing method comprising:

[0008] (1) measuring the incident signal IN and the reflected signal RE of the front surface of the water acoustic metamaterial;

[0009] (2) obtaining the reflection coefficient with phase information under wide frequency by using the incident signal IN and the reflected signal RE;

[0010] (3) measuring the transmission signal TR of the back surface of the water acoustic metamaterial;

[0011] (4) obtaining the transmission coefficient with phase information under wide frequency by using the incident signal IN and the transmission signal TR;

[0012] (5) calculating the equivalent parameters according to the reflection coefficient and the transmission coefficient.

[0013] In the present application, the front surface represents the surface of the sample reached by the ultrasonic wave emitted by the transducer first, and the back surface represents the surface after the ultrasonic wave passes through the sample.

[0014] In step (2), the incident signal IN and the reflected signal RE are respectively subjected to Fourier transform and then divided to obtain the reflection coefficient with phase information under wide frequency.

[0015] In step (4), the incident signal IN and the transmission signal TR are respectively subjected to Fourier transform and then divided to obtain the transmission coefficient with phase information under wide frequency.

[0016] In step (5), the equivalent parameters include equivalent density, equivalent modulus, equivalent refractive index, and equivalent acoustic impedance.

[0017] Further, the inversion method is used to calculate the equivalent parameters, and the specific method is as follows:

[0018]

[0019]

[0020] p eff= Z / n

[0021] K eff = Z / n

[0022] wherein, p eff K eff is the equivalent modulus, Z is the equivalent impedance, n is the equivalent refractive index, R is the reflection coefficient, T is the transmission coefficient, k is the ultrasonic wave number, d is the thickness of the metamaterial, and m is the branch number.

[0023] wherein, m is 0 when the thickness of the metamaterial is much smaller than the wavelength of the sound wave.

[0024] The application also provides a test system for equivalent parameters of underwater acoustic metamaterials, which comprises:

[0025] a signal testing device, a signal generator, a transducer, a hydrophone, a power amplifier and an oscilloscope, the signal generator emits a specific modulated pulse signal, the transducer converts the electrical signal transmitted by the signal generator into a sound wave signal, the hydrophone detects the sound wave propagating in the water tank and converts it into an electrical signal again, the electrical signal is collected and recorded by the oscilloscope after passing through the power amplifier, and is output to a signal post-processing module;

[0026] a three-dimensional moving device for controlling the positions of the transducer and the hydrophone to obtain different collected signals;

[0027] a signal post-processing module for receiving and processing the collected signals to perform the test method described above.

[0028] The three-dimensional moving device is used to control the accurate positions of the transducer and the hydrophone, and can emit a pulse signal to control the triggering and collection of the oscilloscope after being connected to the oscilloscope, the test method for equivalent parameters of underwater acoustic metamaterials is used to set a moving program, and the automation and integration of three-dimensional movement and signal collection are realized. The signal post-processing module filters and delays the electrical signal output from the signal testing device and other post-processing to obtain a complex transmission and reflection coefficient with amplitude information and phase information, and then calculates the equivalent density, equivalent modulus, equivalent refractive index and equivalent acoustic impedance of the material by using a parameter inversion method.

[0029] The three-dimensional moving device moves the hydrophone to the position between the transducer and the sample to be measured, the signal generator emits a modulated pulse signal, the hydrophone receives a primary signal S1 directly from the transducer and a secondary signal S2 reflected from the sample to be measured, the first modulated signal is collected and recorded by the oscilloscope, and is output to the signal post-processing module, and the incident signal IN and the reflection signal RE of the front surface of the underwater acoustic metamaterial are obtained through delay processing.

[0030] The time difference t1 between the primary signal S1 and the secondary signal S2 in the first modulated signal is twice the time required for the sound wave to travel from the hydrophone to the sample to be measured, the primary signal S1 is delayed by 0.5t1 to be the incident signal IN of the front surface of the sample, and the secondary signal S2 is advanced by 0.5t1 to be the reflected signal RE of the front surface of the sample to be measured.

[0031] The transducer and the sample position are kept unchanged, the hydrophone is moved to the back of the sample by using a three-dimensional moving device, the hydrophone receives the transmission signal of the sample, collects and records as a second modulated signal, and outputs to a signal post-processing module; the sample and the hydrophone position are kept unchanged, the transducer is moved to the back of the hydrophone by using a three-dimensional moving device, the hydrophone receives the primary signal S3 directly from the transducer and the secondary signal S4 reflected from the sample, collects and records as a third modulated signal, and outputs to a signal post-processing module.

[0032] The time difference t2 between the primary signal S3 from the transducer and the secondary signal S4 reflected from the sample in the third modulated signal is twice the time required for the sound wave to travel from the hydrophone to the sample, and the second modulated signal is advanced by 0.5t2 to be the transmission signal TR of the back surface of the sample to be measured.

[0033] Based on the above test system, the acoustic signal of the sample surface is processed through the non-contact measurement of the test system and the material, so as to obtain the complex transmission reflection coefficient with amplitude and phase information, and the equivalent parameters of the material can be calculated by using the inversion method.

[0034] In the application, the acoustic metamaterials can be Helmholtz type metamaterials, film metamaterials, labyrinth type metamaterials, Mie resonance type metamaterials and the like, and the equivalent parameters of various acoustic metamaterials can be tested by using the method.

[0035] The application provides a method and a system for completely measuring the acoustic signal of a material surface, so as to obtain the complex transmission reflection coefficient with complete amplitude and phase information, and acoustic parameters such as equivalent density and equivalent modulus can be measured by using the inversion method on the basis, which provides an important characterization method for acoustic metamaterials. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 In order to simulate the relative equivalent parameters of water by using the original method and the method of the application, (a) the transmission coefficient measured by the original method, (b) the transmission coefficient measured by the application, (c) the equivalent parameters measured by the original method, and (d) the equivalent parameters measured by the application;

[0037] Figure 2 In order to test the sample of the bubble silica gel metamaterial in the embodiment, the topography of the sample is shown in the figure;

[0038] Figure 3 Fig. 1 is a schematic diagram of the equivalent parameter testing method of the present application, (a) acquisition of the first modulation signal, (b) acquisition of the second modulation signal, and (c) acquisition of the third modulation signal;

[0039] Figure 4 Fig. 2 is the acoustic performance of the acoustic metamaterial tested in the example, (a) signal diagram of the first modulation signal, (b) transmission coefficient, (c) reflection coefficient, and (d) equivalent parameter. DETAILED DESCRIPTION

[0040] The present application will be further described in conjunction with the examples and the accompanying drawings. Herein, the examples of the present application and the descriptions thereof are used to explain the present application, but not as a limitation of the present application.

[0041] The testing system provided by the present application obtains the complex transmission and reflection coefficients with amplitude and phase information by contactless measurement and processing of the acoustic signals of the sample surface, so as to calculate the equivalent parameters of the material by inversion method. The transmission coefficient with complete information should be the ratio of the transmission signal of the back surface of the sample to the incident signal of the front surface of the sample after Fourier transform, and the reflection coefficient with complete information should be the ratio of the reflection signal of the front surface of the sample to the incident signal of the front surface of the sample after Fourier transform.

[0042] The relative equivalent parameters of water are simulated and tested by using the original method and the present method, as shown in Fig. 1. Figure 1 As shown in Fig. 1, the transmission coefficient measured by the original method lacks phase information and cannot calculate the relative equivalent parameters of water; while the transmission coefficient measured by the present method has complete phase information and can calculate the relative equivalent parameters of water as 1, which is consistent with the actual value. The original method is the existing testing technical means mentioned in the background art.

[0043] On this basis, the equivalent parameters of the metamaterial are tested, and the testing sample of the present example is a bubble silica gel metamaterial, as shown in Fig. 2, which can occur monopole resonance and dipole resonance at 400-800 kHz, thereby generating negative equivalent modulus and negative equivalent density in this frequency band. Figure 2

[0044] Step 1, connection and centering of the testing system. The DC circuit of the three-dimensional moving device is connected to the oscilloscope, and the transducer and the hydrophone are fixed on the clamping positions of the three-dimensional moving device, respectively; the signal generator is connected to the transducer, the hydrophone is connected to the power amplifier, and the power amplifier is connected to the oscilloscope. The transducer and the hydrophone are centered.

[0045] Step 2, acquisition of the first modulation signal. The sample is fixed at an appropriate position in the water tank, as shown in Fig. 3. Figure 3 ​(a) The hydrophone is moved to the position between the transducer and the sample using the 3D moving device. The signal generator sends a modulated pulse. The hydrophone receives the primary signal directly from the transducer and the secondary signal reflected from the sample. The first modulated signal (signal 1) is collected by the oscilloscope.

[0046] Step 3, obtaining the second modulated signal. As shown in (b) of Figure 3 (b) The transducer and the sample are kept in the same position. The hydrophone is moved to the position behind the sample using the 3D moving device. The hydrophone receives the transmission signal of the sample. The second modulated signal (signal 2) is collected by the oscilloscope.

[0047] Step 4, obtaining the third modulated signal. As shown in (c) of Figure 3 (c) The sample and the hydrophone are kept in the same position. The transducer is moved to the position behind the hydrophone using the 3D moving device. The hydrophone receives the primary signal directly from the transducer and the secondary signal reflected from the sample. The third modulated signal (signal 3) is collected by the oscilloscope.

[0048] Step 5, post-processing to obtain the incident / reflected / transmitted signals of the front and back surfaces of the sample. The time difference t1 between the primary signal S1 and the secondary signal S2 of the first modulated signal is twice the time required for the sound wave to travel from the hydrophone to the sample, as shown in (a) of Figure 4 Therefore, delaying the S1 signal by 0.5t1 is the incident signal IN of the front surface of the sample, and advancing the S2 signal by 0.5t1 is the reflected signal RE of the front surface of the sample; similarly, the time difference t2 between the primary signal and the secondary signal of the third modulated signal is twice the time required for the sound wave to travel from the hydrophone to the sample, advancing the second modulated signal by 0.5t2 is the transmitted signal TR of the back surface of the sample.

[0049] Step 6, post-processing to invert the acoustic parameters of the sample. The incident / reflected / transmitted signals under the frequency spectrum are obtained by Fourier transform, and the transmission coefficient and the reflection coefficient containing phase and amplitude information are calculated, the calculation formula is as follows:

[0050]

[0051]

[0052] The calculation results are shown in (b) of Figure 4 and (c) of 4.

[0053] The equivalent density ρ eff , the equivalent modulus K eff and other acoustic parameters are calculated by the parameter inversion method, and the calculation formula is as follows:

[0054]

[0055]

[0056] p eff = Z * n

[0057] K eff = Z / n

[0058] The calculation results are shown in (d) of FIG. 6. Figure 4

[0059] The above detailed description of the specific embodiments has described the technical solutions and beneficial effects of the present application. It should be understood that the above description is only the most preferred embodiment of the present application and is not intended to limit the present application. Any modifications, supplements, and equivalent replacements made within the principle range of the present application should be included in the protection scope of the present application.​

Claims

1. A method for testing equivalent parameters of underwater acoustic metamaterials, characterized in that, The test method comprises: (1) measuring an incident signal at a front surface of an underwater acoustic metamaterial IN and a reflected signal RE ; (2) using the incident signal IN and the reflected signal RE to obtain a reflection coefficient with phase information at a wide frequency; (3) measuring a transmission signal of a back surface of an underwater acoustic metamaterial TR ; (4) using the incident signal IN and the transmitted signal TR to obtain a wideband phase- containing transmission coefficient; (5) calculating equivalent parameters according to the reflection coefficient and the transmission coefficient.

2. The method of claim 1, wherein, In step (2), the incident signal IN and the reflected signal RE are respectively Fourier transformed and divided to obtain the reflection coefficient with phase information under wide frequency.

3. The method of claim 1, wherein, In step (4), the incident signal IN and the transmitted signal TR are respectively Fourier transformed and divided to obtain the phase information-containing transmission coefficient under wideband.

4. The method of claim 1, wherein, In step (5), the equivalent parameters include equivalent density, equivalent modulus, equivalent refractive index and equivalent acoustic impedance.

5. The method of claim 1, wherein, The equivalent parameters are calculated by using an inversion method, and the method is as follows: ; ; ; ; wherein, is the equivalent density, is the equivalent modulus, Z is the equivalent impedance, n is the equivalent refractive index, R is the reflection coefficient, T is the transmission coefficient, k is the ultrasonic wave number, d is the metamaterial thickness, and m is the number of branches.

6. A system for testing the equivalent parameters of underwater acoustic metamaterials, characterized in that it comprises: The test system comprises: a signal test device, a signal generator, a transducer, a hydrophone, a power amplifier and an oscilloscope, the signal generator transmits a specific modulated pulse signal, the transducer converts the electric signal transmitted by the signal generator into an acoustic wave signal, the hydrophone detects the acoustic wave propagating in the water tank and converts it into an electric signal again, the signal is collected and recorded by the power amplifier and the oscilloscope, and is output to a signal post-processing module; a three-dimensional moving device for controlling the positions of the transducer and the hydrophone to obtain different collected signals: the hydrophone is moved to the position between the transducer and the sample to be measured, the signal generator transmits a modulated pulse signal, the hydrophone receives a primary signal S1 directly from the transducer and a secondary signal S2 reflected from the sample to be measured, the first modulated signal is collected and recorded by the oscilloscope, and is output to the signal post-processing module; the position of the transducer and the sample is kept unchanged, the hydrophone is moved to the rear of the sample by using the three-dimensional moving device, the hydrophone receives the transmission signal of the sample, the second modulated signal is collected and recorded, and is output to the signal post-processing module; the position of the sample and the hydrophone is kept unchanged, the transducer is moved to the rear of the hydrophone by using the three-dimensional moving device, the hydrophone receives a primary signal S3 directly from the transducer and a secondary signal S4 reflected from the sample, the third modulated signal is collected and recorded, and is output to the signal post-processing module; a signal post-processing module for receiving and processing the collected signals to execute the method according to any one of claims 1-5.

7. The system for testing the equivalent parameters of underwater acoustic metamaterials of claim 6, wherein, The time difference t1 between the primary signal S1 and the secondary signal S2 in the first modulated signal is twice the time required for the sound wave to travel from the hydrophone to the sample under test, and delaying the primary signal S1 by 0.5t1 is the incident signal on the front surface of the sample IN Advancing the secondary signal S2 by 0.5t1 is the reflected signal on the front surface of the sample under test RE.

8. The system for testing the equivalent parameters of underwater acoustic metamaterials of claim 6, wherein, The time difference t2 between the primary signal S3 from the transducer in the third modulated signal and the secondary signal S4 reflected from the sample is twice the time required for the acoustic wave to travel from the hydrophone to the sample. The second modulated signal is advanced by 0.5t2 as the transmission signal of the back surface of the sample to be measured TR .

Images