A gradient impedance-matched directional sensing metamaterial structure and its design method

Abstract

This invention relates to the field of acoustic metamaterials technology, and in particular to a gradient impedance-matched directional sensing metamaterial structure and its design method. The metamaterial adopts a cylindrical symmetric core-shell configuration, internally divided into four orthogonal and physically independent sectors. Each sector contains an embedded, highly coiled fluid waveguide channel composed of five layers of mutually coupled arc-shaped waveguide units. The local cross-sectional area of ​​the channel continuously decreases in gradient from the incident sound wave direction to the sensor end, forming an acoustic horn model with gradually changing impedance. Four sensor interfaces are located at the innermost hard boundary at the center to extract and enhance the sound pressure signal. The accompanying directional sensing method performs spatial differential processing on the acquired signal based on a four-element array and constructs an analytical multipole error compensation model to eliminate high-order spatial harmonic interference. This invention eliminates impedance mismatch and "pulse contraction effect" from a physical mechanism perspective, significantly improves sound pressure gain and reduces energy dissipation, achieving high-precision sound source localization and tracking in deep subwavelengths and wide bandwidths.

Description

Technical Field

[0001] This invention relates to the field of acoustic metamaterials technology, and in particular to a gradient impedance matching directional sensing metamaterial structure and its design method. Background Technology

[0002] With the deep integration of the Internet of Things (IoT) and human-computer interaction technologies, intelligent micro-terminals are increasingly widely used in complex acoustic environments such as in-vehicle assistants, wearable devices, and smart cockpits. Achieving high-sensitivity, high-precision directional sensing within these compact physical spaces is a core bottleneck in the field of physical signal processing. However, at the subwavelength scale, the physical size of the sensing array is much smaller than the wavelength of sound waves, causing its spatial differential detection mechanism to be limited by the Rayleigh diffraction limit. The weak phase difference within extremely close spacing is easily masked by the inherent background noise of the sensor, resulting in extremely poor localization robustness of traditional beamforming techniques (such as GCC-PHAT and MUSIC) and linear solution models in low signal-to-noise ratio environments. Secondly, although existing research attempts to introduce spatially curled acoustic metamaterials with localized Mie resonance characteristics (such as core-shell structured superparticles CSM) to manipulate the sound field, their underlying waveguide design still has significant physical defects. Most designs do not consider the abrupt change in channel cross-sectional area; their geometric discontinuities and sharp corners induce strong acoustic boundary layer separation under hydrodynamic mechanisms. The resulting pulse-constriction effect leads to a sharp contraction of the effective flow cross-section, accompanied by severe thermoviscous dissipation. Experiments and simulations show that such non-ideal effects severely weaken the system's acoustic pressure gain and significantly limit its operating bandwidth, making it difficult to meet the demands of compact, high-sensitivity equipment in deep-sea or complex industrial scenarios. Furthermore, existing structures are prone to exciting complex high-order multipole modes when deviating from the resonant center point. These nonlinear modes induce severe spatial frequency aliasing and direction-finding distortion, resulting in systematic deviations in azimuth estimation results and severely impacting sensing accuracy and reliability across a wide bandwidth. Therefore, developing a directional sensing structure that can balance low-dissipation impedance matching and high-order error compensation has become a critical problem urgently needing to be solved in this field. Summary of the Invention

[0003] The purpose of this invention is to address the problems existing in the background technology by proposing a gradient impedance matching metamaterial (GIMM), which eliminates impedance mismatch through continuous gradient waveguide design and, together with an analytical multipole error compensation algorithm, achieves high-precision sound source localization over a wide frequency band.

[0004] The technical solution of the present invention, in its first aspect, provides a gradient impedance matching directional sensing metamaterial structure, wherein the structure as a whole has a cylindrical symmetrical core-shell configuration; The core-shell configuration is divided into four orthogonal and physically independent sectors, each containing a highly coiled fluid waveguide channel. The fluid waveguide channel adopts a spatial folding structure design, and the local cross-sectional area of ​​the channel decreases continuously along the incident direction of the sound wave to the sensor end, forming an acoustic horn model with gradually changing impedance. Four sensor interfaces are located at the innermost hard boundary at the center of the core-shell configuration, corresponding to the ends of the four sector waveguide channels.

[0005] Preferably, the fluid waveguide channel is composed of 5 layers of mutually coupled arc-shaped waveguide units.

[0006] Preferably, the fluid waveguide channel is located within the portion of each layer of circular arc waveguide unit, and its local cross-sectional radius is... Along the sound path Decrease linearly; Preferably, the portion of the fluid waveguide channel located at the coupling connection between layers has a constant cross-sectional radius to ensure a smooth transition of interlayer impedance.

[0007] Preferably, the four sensor interfaces are equidistantly distributed on the circumference of the metamaterial center with a diameter of 38.3 mm.

[0008] A second aspect of the present invention provides a directional sensing method using a gradient impedance matching directional sensing metamaterial structure, comprising the following steps: S1. Acoustic sensors installed at four sampling interfaces are used to synchronously collect the enhanced sound pressure signals at the end of each sector; S2. Perform spatial difference processing based on four array elements on the acquired enhanced sound pressure signal to extract the orthogonal differential sound pressure operator; S3. Based on the orthogonal differential sound pressure operator, calculate the initial direction of arrival estimation angle of the sound source; S4. Construct an analytical multipole error compensation model, calculate the error compensation value in the corresponding frequency band, and apply the error compensation value to the initial direction of arrival estimation angle to obtain the true direction of arrival after eliminating higher-order spatial harmonic interference. The initial direction of arrival (DOA) estimation angle is calculated using the four-quadrant arctangent function. .

[0009] Preferably, in step S2, the sound pressure signals of the two opposing sectors are respectively and The sound pressure signals of the other two opposing sectors are respectively and Orthogonal difference sound pressure operator and They are defined as follows: ; .

[0010] Preferably, in step S3, the initial direction-of-arrival estimation angle is obtained using the four-quadrant arctangent function. In step S4, the calculation formula for the analytical multipole error compensation model is as follows: The final calculated true direction of arrival: in, , , The coefficients of the frequency-dependent error tuning matrix are obtained by extracting historical sampling data through a least-squares global optimization fitting within a preset working frequency band.

[0011] Compared with the prior art, the present invention has the following beneficial technical effects: In this invention, impedance mismatch is eliminated through continuous gradient design, acoustic energy dissipation is reduced by 29%, peak sound pressure gain is increased by 43.0% compared with traditional cross-section abrupt structure, and average gain reaches 13.4dB.

[0012] This invention successfully removes third-order harmonic interference through algorithmic compensation, resulting in 92.2% of the estimation results having an error within 5.0°, and improving the accuracy by 17.2% compared to before compensation.

[0013] The system of this invention can maintain high-fidelity directional decoding capability within an ultra-wide frequency band of 300–1500Hz.

[0014] This invention eliminates impedance mismatch and "pulse contraction effect" from a physical mechanism perspective, significantly improves sound pressure gain and reduces energy dissipation, and achieves high-precision sound source localization and tracking in deep subwavelength and wide frequency band. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall core-shell configuration of GIMM; Figure 2 A schematic diagram of the waveguide path for a single sector cell in GIMM; Figure 3 Here are structural diagrams of GIMM and CSM, and the radius of a local cross-section is shown. Harmony and acoustic impedance With effective sound path The relationship between the changes and the sound pressure gain response in the 300–1500 Hz frequency band are compared.

[0016] Figure 4 The four sampling interfaces are equidistantly distributed in A schematic diagram on the reference circle; Figure 5 This represents the error distribution after compensation using the error mapping matrix.

[0017] Figure reference numerals: 01-04: Four independent sector units of GIMM; 0111-0115: Equal cross-section transition between two adjacent circular arc waveguide units; 0121-0125: Mutually coupled gradient cross-section radius circular arc waveguides. Detailed Implementation

[0018] Example 1 This embodiment provides a physical entity of a gradient impedance directional sensing metamaterial (GIMM). This metamaterial adopts a cylindrical symmetric core-shell configuration, and its overall physical envelope size is... .

[0019] like Figure 1 and Figure 2 As shown, the structure is uniformly divided into four orthogonal and physically independent sectors (01-04) in the plane. Each sector unit contains a highly coiled fluid waveguide channel, which consists of five layers of mutually coupled arc-shaped waveguide units (0121-0125). The portion of the fluid waveguide channel located within each layer of arc-shaped waveguide units has a local cross-sectional radius. Along the sound path Linear reduction; the fluid waveguide channel is located at the coupling connection between layers (equal cross-section transition 0111-0115), and its cross-sectional radius remains constant to ensure a smooth transition of interlayer impedance.

[0020] This spatial folding design greatly extends the effective path of sound waves within a limited radial space, thereby exciting a highly directional local Mie resonance effect in the low-frequency domain (300–1500Hz).

[0021] The core feature of this embodiment lies in the gradient cross-section design of the waveguide channel. For example... Figure 3 As shown by the red curve in (b), the vertical axis is the cross-sectional radius r, and the horizontal axis is the sound path L. Along the direction of sound wave propagation from the external inlet to the internal sensor interface, the local cross-sectional radius of the single-layer circular arc waveguide is... With effective sound path Linear reduction. This continuous gradient evolution constructs an acoustic horn model with gradually changing impedance, eliminating the acoustic impedance mismatch and "pulse contraction effect" caused by abrupt changes in cross-section in traditional structures from a physical mechanism perspective. At the transition point (0111-0115) between adjacent two layers of circular arc waveguide units, a constant cross-section transition section is used for coupling to ensure smooth transmission of acoustic energy within the waveguide.

[0022] The four sampling interfaces are located at the innermost hard boundary of the housing, such as Figure 4 The equidistant distribution shown is in The sensor is positioned on the reference circle. This arrangement utilizes standing wave theory, enabling the sensor to be located at the antinodes of the sound pressure distribution, thereby accurately extracting the sound pressure signal amplified by the impedance matching mechanism.

[0023] Example 2 This embodiment, based on the hardware structure of Embodiment 1 above, provides a high-precision Direction of Arrival (DOA) resolution method. The specific steps are as follows: The first step is to synchronously acquire complex sound pressure signals using acoustic sensors placed at four sampling interfaces. , , , .

[0024] The second step is to define the orthogonal differential sound pressure operator. and The calculation formula is as follows: This differential mechanism can spontaneously filter out spatially isotropic monopole modes. ), and selectively amplify the dipole mode carrying the orientation information ( ).

[0025] The third step is to use the four-quadrant arctangent function to extract the initial azimuth estimation angle of the sound source. : The fourth step is that a deviation from the resonance point will excite a third-order cylindrical harmonic (…). Higher-order modal interferences, such as those from [unspecified mode], cause direction-finding distortion. This embodiment introduces an analytical error compensation model: in, , , The coefficients of the error tuning matrix at the corresponding frequency are obtained by applying the least squares method to optimize the fitting of the full spectrum within the 300–1500 Hz frequency band.

[0026] Final high-precision direction of arrival Derived using the following formula: .

[0027] Example 3 To verify the superiority of the structure described in this invention, the GIMM described in Example 1 was compared with the traditional cross-sectional step change structure (CSM) under the same physical volume and effective acoustic path. To ensure control of the comparison variables, the new and old models were strictly aligned with the macroscopic geometric boundaries: completely identical outer physical envelopes, an equal number of 5-layer arc waveguide units, and consistent initial incident cross-sectional area and effective unfolded acoustic path.

[0028] Unlike the continuous gradient evolution in this study, traditional CSMs fail to achieve a smooth transition of the internal waveguide cross-section; such as Figure 3 (b) and Figure 3 As shown in (c), the abrupt change in cross-section at the transition point leads to a strong acoustic impedance mismatch. Figure 3 The full-frequency sound field simulation of (d) further reveals that although both excite highly overlapping resonant modes in the frequency domain, the peak sound pressure gain of GIMM reaches 28.9 dB, significantly exceeding that of CSM (20.9 dB). In terms of average sound pressure gain across the entire frequency band, GIMM (14.7 dB) achieves an absolute improvement of approximately 4.4 dB over CSM (10.3 dB). This comparative result strongly demonstrates that, under the same physical volume constraints, the gradient impedance architecture of GIMM has significant advantages in suppressing acoustic energy dissipation and improving physical gain.

[0029] like Figure 5 As shown, after applying the analytical error compensation algorithm described in Example 2, the DOA estimation accuracy is significantly improved. The global average error is controlled at around 2.5°, and within a confidence interval of ±5°, the prediction accuracy increases from approximately 72% before compensation to over 89.3%. This invention eliminates impedance mismatch and "pulse contraction effect" from a physical mechanism perspective, significantly improves sound pressure gain and reduces energy dissipation, achieving high-precision sound source localization and tracking in deep subwavelengths and wide bandwidths.

[0030] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A gradient impedance-matched directional sensing metamaterial structure, characterized in that, The structure as a whole has a cylindrical, symmetrical core-shell configuration; The core-shell configuration is divided into four orthogonal and physically independent sectors, each containing a highly coiled fluid waveguide channel. The fluid waveguide channel adopts a spatial folding structure design, and the local cross-sectional area of ​​the channel decreases continuously along the incident direction of the sound wave to the sensor end, forming an acoustic horn model with gradually changing impedance. Four sensor interfaces are located at the innermost hard boundary at the center of the core-shell configuration, corresponding to the ends of the four sector waveguide channels.

2. The gradient impedance matching directional sensing metamaterial structure according to claim 1, characterized in that, The fluid waveguide channel consists of five layers of mutually coupled arc-shaped waveguide units.

3. The gradient impedance matching directional sensing metamaterial structure according to claim 1, characterized in that, The fluid waveguide channel is located within the circular arc waveguide unit of each layer, and its local cross-sectional radius is... Along the sound path It decreases linearly.

4. The gradient impedance matching directional sensing metamaterial structure according to claim 1, characterized in that, The fluid waveguide channel is located at the coupling connection between layers, and its cross-sectional radius remains constant to ensure a smooth transition of interlayer impedance.

5. The gradient impedance matching directional sensing metamaterial structure according to claim 1, characterized in that, The four sensor interfaces are equidistantly distributed on the circumference of the metamaterial center, which has a diameter of 38.3 mm.

6. A directional sensing method using a gradient impedance matching directional sensing metamaterial structure, employing the directional sensing metamaterial structure according to any one of claims 1-5, characterized in that, Includes the following steps: S1. Acoustic sensors installed at four sampling interfaces are used to synchronously collect the enhanced sound pressure signals at the end of each sector; S2. Perform spatial difference processing based on four array elements on the acquired enhanced sound pressure signal to extract the orthogonal differential sound pressure operator; S3. Based on the orthogonal differential sound pressure operator, calculate the initial direction of arrival estimation angle of the sound source; S4. Construct an analytical multipole error compensation model, calculate the error compensation value in the corresponding frequency band, and apply the error compensation value to the initial direction of arrival estimation angle to obtain the true direction of arrival after eliminating higher-order spatial harmonic interference. The initial direction of arrival (DOA) estimation angle is calculated using the four-quadrant arctangent function. .

7. The directional sensing method for gradient impedance matching directional sensing metamaterial structures according to claim 6, characterized in that, In step S2, let the sound pressure signals of the two opposing sectors be respectively and The sound pressure signals of the other two opposing sectors are respectively and Orthogonal difference sound pressure operator and They are defined as follows: ； 。 8. The directional sensing method for gradient impedance matching directional sensing metamaterial structures according to claim 6, characterized in that, In step S3, the initial direction-of-arrival estimation angle is obtained using the four-quadrant arctangent function. In step S4, the calculation formula for the analytical multipole error compensation model is as follows: The final calculated true direction of arrival: in, , , The coefficients of the frequency-dependent error tuning matrix are obtained by extracting historical sampling data through a least-squares global optimization fitting within a preset working frequency band.

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