Dynamic high-precision phased array based on acoustic metamaterial transducer unit

Abstract

The invention discloses a dynamic high-precision phased array based on acoustic super-structure transducer units, which comprises a plurality of same super-structure transducer units, each super-structure transducer unit comprises a metamaterial layer and a transduction element layer, the metamaterial layer is used for providing fixed phase shift, and the transduction element layer has a transverse size of wavelength level; the metamaterial layer comprises a longitudinal quadrupole and a monopole, and the phases of two poles in the longitudinal quadrupole are matched with the phase of the monopole. According to the dynamic high-precision phased array based on the meta-structure transducer unit, a passive acoustic meta-material and a dynamic phased array are combined, and on the premise that the array complexity is not increased and the physical structure is not changed, dynamic sound field regulation and control are achieved, and the spatial resolution approximates the acoustic diffraction limit; by greatly reducing the equivalent acoustic size of a phased array element and accurately matching the phase required by a sound field, the spatial aliasing effect is effectively eliminated, meanwhile, the high radiation efficiency is kept, and the spatial resolution is remarkably improved.

Description

Technical Field

[0001] The present invention relates to a dynamic high-precision phased array based on acoustic metamaterial transducer units, belonging to the field of acoustics. Background Art

[0002] Flexibly regulating sound waves in real time to achieve high-precision acoustic functions plays an important role in fields such as biomedical imaging and industrial non-destructive testing. The existing phased array (PA) technology can dynamically generate the required sound field by independently regulating the phase of each array element, and thus has been widely used. However, the spatial resolution of traditional phased arrays is limited by the manufacturing complexity and cost of array elements. The actual element size is much larger than the point source scale assumed by beamforming theory, resulting in difficulty in further improving the spatial resolution. In recent years, acoustic metamaterials (AMs) have achieved peculiar properties that do not exist in nature in a passive manner through ingeniously designed artificial structures, such as low-cost and high-precision wavefront manipulation at sub-wavelength scales. However, the acoustic functions of most acoustic metamaterials are fixed once manufactured and cannot be dynamically adjusted, which limits their flexibility in practical applications. Therefore, how to combine the dynamic regulation ability of existing phased arrays with the high-precision and low-cost advantages of acoustic metamaterials remains an urgent problem to be solved. Summary of the Invention

[0003] Object of the Invention: In order to overcome the deficiencies in the prior art, the present invention provides a dynamic high-precision phased array based on acoustic metamaterial transducer units, which can effectively eliminate the spatial aliasing effect without changing the physical structure of the unit, achieve precise phase matching with the target sound field, and realize more flexible and accurate sound field regulation.

[0004] Technical solution: To solve the above technical problems, the present invention discloses a dynamic high-precision phased array based on acoustic metamaterial transducer units. By introducing acoustic metamaterials into each unit, high-precision and low-cost dynamic wavefront modulation is achieved, thereby significantly improving the spatial resolution of phased array sound field manipulation. Specifically, the phased array is composed of multiple identical metamaterial transducer units, and each unit includes a metamaterial layer and a transducer element layer. The metamaterial transducer unit is modeled as an acoustic multipole model to approximate a point source with high radiation efficiency. In addition, the phased array can effectively eliminate the spatial aliasing effect without changing the physical structure of the unit, realizing more flexible and precise sound field control. Through two typical examples of high-precision multi-point acoustic focusing and sub-wavelength resolution acoustic imaging, the present invention demonstrates that it can achieve a resolution approaching the acoustic diffraction limit, which cannot be achieved by relying solely on acoustic phased array or metamaterial technology at present. Compared with the prior art, the present invention provides a simple and low-cost solution for dynamic high-precision acoustic wave manipulation, has important application value, and can be widely applied in fields such as biomedical imaging, ultrasonic therapy, and non-destructive testing.

[0005] In the present invention, the metamaterial layer is realized by a combined model of longitudinal quadrupole and monopole, where the phases of the two poles of the quadrupole are consistent with that of the monopole, and the Purcell factor of the radiation efficiency of the combined model is 244.5 times that of the traditional point source. The metamaterial layer is a coiled space structure or a membrane resonant structure or a Helmholtz resonator structure. The metamaterial layer is a coiled space structure, which contains sound channels with different folding lengths to achieve phase delay, and matches the acoustic impedance of the sound channel and the transducer element through an impedance matching layer. Or the metamaterial layer is a layered medium thickness modulation structure, which contains a medium layer used to adjust phase accumulation, and forms a model by connecting different thickness medium layers in parallel. Or the metamaterial layer is a membrane resonant structure, which contains a thin film and an acoustic resonator cavity, and connects the thin film to the beginning of the resonator cavity to adjust the acoustic impedance. Or the metamaterial layer is a Helmholtz resonator structure, which contains a Helmholtz resonator and a straight tube, and connects the Helmholtz resonator in series with the straight tube, where the Helmholtz resonator serves as an acoustic reactance and the straight tube serves as an impedance matching element. The metamaterial layer is a Helmholtz resonator structure, which contains a Helmholtz resonator and a straight tube, and the Helmholtz resonator and the straight tube form a sub-wavelength hybrid resonance structure. The total width R of the metamaterial layer > λ / 2, and the total length L of the metamaterial layer < λ; the structural parameters of the Helmholtz resonator satisfy: the resonator width w3 < λ / 3, and the resonator opening length w2 < w3.

[0006] In the present invention, the coiled space structure realizes sub-wavelength phase modulation by folding the acoustic wave path; the layered medium thickness modulation structure realizes phase control by stacking different thickness layers; the membrane resonant structure realizes phase control by coupling the vibration of the thin film to regulate the acoustic impedance; the Helmholtz resonator structure generates phase delay through cavity resonance.

[0007] In the present invention, the ratio of the height h2 of the straight pipe to the height h3 of the Helmholtz resonator is 0.184h:0.456h, where h = λ / 6 and λ is the acoustic wavelength; the passive metamaterial layer realizes phase modulation from 0 to 2π by adjusting the height h2 of the straight pipe, and the acoustic transmittance is greater than 95%. The total width R of the metamaterial layer is λ, the structural thickness r is 0.02λ, the total height Z of the metamaterial layer is 0.17λ, and the total length L of the metamaterial layer is 2w, where w = 3λ / 8; the structural parameters of the Helmholtz resonator satisfy: the resonator spacing w1 = 0.23w, the resonator opening length w2 = 0.05w, the resonator width w3 = 0.2w, and the resonator cavity thickness h1 = 0.12h.

[0008] In the present invention, the active transducer layer and the passive metamaterial layer are connected by embedded integration, and the spatial resolution of the working area of the transducer unit approaches the acoustic diffraction limit.

[0009] As a specific implementation, the present invention adopts an acoustic metamaterial based on a hybrid resonance structure. By adjusting the coupling relationship between strong resonance modes, full-phase control from 0 to 2π and a transmittance of more than 95% are achieved, and a transducer sub-unit containing longitudinal quadrupole and monopole sound sources is constructed. Through two typical examples of high-precision acoustic focusing and sub-wavelength acoustic imaging, the present invention demonstrates that the ultrasonic phased array based on the metasurface transducer unit can achieve performance approaching the acoustic diffraction limit in both longitudinal and transverse resolutions, which cannot be achieved by relying solely on traditional phased array or acoustic metamaterial technologies. This solution can realize real-time sound field reconstruction, with spatial resolution close to the acoustic diffraction limit, and is fully compatible with the existing beamforming theory.

[0010] For a dynamic high-precision phased array based on the metasurface transducer unit of the present invention, an acoustic metasurface transducer unit model is constructed: The acoustic metasurface transducer unit of the present invention includes a metamaterial layer and a transducer element layer: The metamaterial layer constructs a multipole phase mask by designing a fixed phase shift. The transverse size of the transducer element layer is at the wavelength level and is integrated with the metamaterial layer to achieve high-precision dynamic acoustic wave control. This unit combines longitudinal quadrupoles and monopole sound sources to construct a multipole model to equivalent a point sound source, where the phases of the two poles of the quadrupole are consistent with those of the monopole, while significantly reducing the equivalent acoustic size of the element and maintaining high radiation efficiency. Compared with the traditional point sound source, the Purcell factor used to describe the radiation intensity is increased by 244.5 times. The acoustic metasurface transducer realizes precise sound field control by precisely matching the phase of the target sound field.

[0011] Establishing a high-resolution working area: The lateral dimension of the transducer units in existing phased arrays is usually at the wavelength level, violating the Nyquist criterion, resulting in spatial aliasing effects and unable to achieve high-spatial-resolution acoustic field control. The present invention constructs an equivalent point source model. By comparing the acoustic radiation characteristics of a line source and a point source in the target area, it reveals the key influence of the equivalent acoustic size on spatial resolution. By reducing the equivalent acoustic size through the metamaterial transducer units, the aliasing effect in the working area is eliminated, and the spatial resolution and acoustic wave manipulation performance are improved.

[0012] Acoustic focusing approaching the acoustic diffraction limit: Acoustic focusing is a classical application of phased arrays and plays an important role in fields such as biomedical imaging, therapy, and non-destructive testing. The present invention utilizes the phased array based on the metamaterial transducer units described above. By applying a typical phase delay distribution, high-precision acoustic focusing in the longitudinal and transverse directions is achieved.

[0013] Sub-wavelength acoustic imaging approaching the acoustic diffraction limit: Acoustic imaging has important application values in medical diagnosis and industrial inspection due to its non-invasive characteristics. In the present invention, an object to be imaged with sub-wavelength characteristics is placed in the focal plane (y = f) and scanned. Since the metamaterial transducer units have higher focusing resolution, the sub-wavelength details of the imaging target can be clearly resolved. Specifically, for a 3-mm thick plastic plate with a double-slit width of 0.3λ, the phased array based on the metamaterial transducer units can clearly resolve the overall pattern shape and the sub-wavelength details of the line edges on the imaging plane.

[0014] In the present invention, the passive metamaterial layer provides a customized phase shift (θ2 = θ1 + π).

[0015] In the present invention, the diffraction angle θ of the aliasing effect is:

[0016]

[0017] where d i is the distance between the centers of each transducer unit when mapped to the focal semi-circle, and f is the longitudinal focal length.

[0018] In the present invention, the compared acoustic radiation characteristics are that the velocity potential of the traditional transducer is equal to the convolution of the velocity potential of the metamaterial transducer unit and a rectangular function, which is equivalent to multiplying by the sampling function Sa(·) in the wave vector space. The velocity potential of the line source is:

[0019]

[0020] Φ linear (r) is the velocity potential of the line source located at the position r, k x and k y are the wave vector components of the x-axis and y-axis respectively, Q0 represents the source strength, is the initial phase of the nth sub-unit. The velocity potential of the metasurface transducer unit is:

[0021]

[0022] where Φ point (r) is the velocity potential of the acoustic metamaterial transducer located at position r. The velocity potential of the line source is equal to the convolution of the velocity potential of the metasurface transducer and the rectangular function, which is:

[0023]

[0024] where rect(·) is the rectangular function, when |x| ≤ R / 2 At When * is the convolution operator. The far-field velocity potential of the acoustic longitudinal quadrupole is:

[0025]

[0026] where ρ = 1.29 Kg / m 3 is the air density, c = 343 m / s is the air velocity, k represents the wave number, r is the distance from the source to the observation point, Q 1,2 is a constant, d is the distance between two opposite monopoles, D is the distance between two opposite dipoles, and θ is the angle of the directivity pattern. The acoustic performance of the phased array is verified by the pressure acoustics module, the thermoviscous acoustics module, and the acoustic-thermoviscous interaction module.

[0027] In the present invention, the typical phase delay distribution is:

[0028]

[0029] where x0 is the distance from any position on the phased array to the center, and f is the focal length.

[0030] Beneficial effects: The dynamic high-precision phased array based on the metasurface transducer unit of the present invention combines passive acoustic metamaterials with a dynamic phased array, and realizes dynamic high-precision acoustic functions without increasing the array complexity and changing the physical structure; by greatly reducing the equivalent acoustic size of the phased array elements, accurately matching the phases required by the sound field, effectively eliminating the spatial aliasing effect, while maintaining high radiation efficiency, significantly improving the spatial resolution; as a specific implementation, the present invention constructs a multipole model composed of acoustic longitudinal quadrupoles and monopoles on the transducer unit, changing the sound radiation directivity and reducing the equivalent acoustic size; through two representative applications of acoustic focusing and subwavelength imaging, it is verified that the proposed scheme can achieve real-time sound field reconstruction, and the spatial resolution approaches the acoustic diffraction limit, overcoming the limitations of traditional phased arrays and additive manufacturing technologies; the present invention provides a phased array technology platform with low cost, high precision and dynamic control, and is expected to achieve breakthrough progress in the field of acoustic manipulation. Description of the Drawings

[0031] Figure 1 is a schematic diagram of the structure of the transducer unit of the present invention;

[0032] Figure 2 is a schematic diagram showing the variation of the transmittance and phase of the transducer unit of the present invention with the height of the straight tube;

[0033] Figure 3 is a comparison diagram of the far-field radiation of the transducer unit between the present invention and the existing phased array;

[0034] Figure 4 is a sound field distribution diagram of the transducer unit of the present invention;

[0035] Figure 5 is a comparison diagram of the acoustic performance of the working areas between the present invention and the existing phased array;

[0036] Figure 6 is the transverse and longitudinal focusing scan sound pressure diagram of the present invention.

[0037] Figure 7 is an experimental device diagram for testing the acoustic manipulation performance of the present invention;

[0038] Figure 8 is a comparison diagram of the acoustic focusing sound pressure fields between the present invention and the existing phased array;

[0039] Figure 9 is a subwavelength imaging device diagram of the present invention;

[0040] Figure 10 is a comparison schematic diagram of the subwavelength double-slit imaging performance between the present invention and the existing phased array. Detailed Embodiments

[0041] The present invention will be further described in detail below with reference to the drawings.

[0042] The present invention proposes a dynamic high-precision phased array based on metamaterial transducer units, which includes a number of identical acoustic metamaterial transducer units. The connection method of adjacent acoustic metamaterial transducer units is the same as that of a conventional phased array. The acoustic metamaterial transducer unit includes a metamaterial layer and a transducer element layer: the metamaterial layer constructs a multipole phase mask by designing a fixed phase shift, and the model of the transducer element layer is a 3411 flat transducer with a lateral dimension of the wavelength level, which is integrated with the passive metamaterial layer to achieve high-precision dynamic acoustic wave regulation. As Figure 1 shown, the ratio of the straight tube height h2 to the Helmholtz resonator height h3 is 0.184h:0.456h, where h = λ / 6 and λ is the acoustic wave wavelength; the total width R of the metamaterial layer = λ, the structural thickness r = 0.02λ, the total height Z of the metamaterial layer = 0.17λ, and the total length L of the metamaterial layer = 2w, where w = 3λ / 8; the structural parameters of the Helmholtz resonator satisfy: the resonator spacing w1 = 0.23w, the resonator opening length w2 = 0.05w, the resonator width w3 = 0.2w, and the resonator cavity thickness h1 = 0.12h. As Figure 2 shown, the passive metamaterial layer realizes phase modulation from 0 to 2π by adjusting the straight tube height h2, and the acoustic wave transmittance is greater than 95%. As Figure 3 shown, this unit combines a longitudinal quadrupole and a monopole sound source to construct a multipole model to equivalent a point sound source, while significantly reducing the equivalent acoustic size of the element and maintaining high radiation efficiency. As Figure 4 shown by the spatial distribution of the sound pressure of the metamaterial transducer in , compared with the traditional point sound source method, the Purcell factor used to describe the radiation intensity is increased by 244.5 times, verifying the superior performance of this structure in sound field regulation. The acoustic metamaterial transducer realizes precise sound field regulation by accurately matching the phase of the target sound field. Among them, the acoustic performance of the metamaterial transducer is verified by the pressure acoustics module, the thermoviscous acoustics module, and the acoustic-thermoviscous interaction module.

[0043] In the present invention, the lateral dimension of the transducer unit of the existing phased array is usually of the wavelength level, which violates the Nyquist criterion, resulting in a spatial aliasing effect and unable to achieve high-spatial-resolution sound field regulation. Among them, the diffraction angle relative to the normal of the inner surface of the transducer will show spatial aliasing, as Figure 5 shown:

[0044]

[0045] where d i is the distance between the centers of each transducer unit when mapped to the focal semi-circle. To solve this problem, the present invention reveals the key influence of the equivalent acoustic size on the spatial resolution by comparing the acoustic radiation characteristics of a line sound source and a point sound source in the target area. The velocity potential of the traditional transducer is:

[0046]

[0047] where, Φ linear (r) is the velocity potential of the line source at position r, k x and k y are the wave vector components along the x-axis and y-axis respectively, Q0 represents the source strength, is the initial phase of the nth sub-unit. The velocity potential of the metasurface transducer unit is:

[0048]

[0049] where Φ point (r) is the velocity potential of the metasurface transducer at position r. The velocity potential of the traditional ultrasonic phased array is equal to the convolution of the velocity potential of the metasurface transducer unit and the rectangular function, which is:

[0050]

[0051] where rect(·) is the rectangular function, when |x| ≤ R / 2 at when * is the convolution operator. The far-field velocity potential of the acoustic longitudinal quadrupole is:

[0052]

[0053] where ρ = 1.29 Kg / m 3 is the air density, c = 343 m / s is the air velocity, k represents the wave number, r is the distance from the source to the observation point, Q 1,2 is a constant, d is the distance between two opposite monopoles, D is the distance between two opposite dipoles, and θ is the angle of the directivity pattern. The velocity potential of the traditional phased array is equal to the convolution of the velocity potential of the dynamic high-precision ultrasonic phased array based on the metasurface transducer and the rectangular function, which is equivalent to multiplying by the sampling function of Sa(·) in the wave vector space. By reducing the equivalent acoustic size through the metasurface transducer unit, the aliasing effect in the working area is eliminated, and the spatial resolution and acoustic wave manipulation performance are improved.

[0054] In the present invention, acoustic focusing is a classical application of the phased array and plays an important role in fields such as biomedical imaging, treatment, and non-destructive testing. The present invention utilizes the above phased array based on the metasurface transducer unit, by applying a typical phase delay distribution on the phased array

[0055]

[0056] where, x0 is the distance from any position on the phased array to the center, and f is the focal length. The phase is controlled using a field-programmable gate array FPGA. AsFigure 6 As shown, through longitudinal and transverse focusing experiments, the high-precision performance of this phased array in dynamic sound field regulation was further verified. Numerical simulations verified the longitudinal focusing ability of the proposed meta-transducer structure along the central axis from (0, 1λ) to (0, 6λ). The full width at half maximum (FWHM) of the beams generated by the present invention is smaller than that of traditional phased arrays, and high-precision foci can be achieved without generating aliasing artifacts, which verifies its acoustic performance under ideal conditions to a great extent. By showing transverse focusing from (-5λ, 4λ) to (5λ, 4λ) in Figure 6 , the versatility of manipulating acoustic energy in space was further demonstrated. As Figure 7 shown, the two-dimensional field scan in the focusing experiment was along the x-axis from -3λ to 3λ and along the y-axis from 2λ to 6λ, covering the measured foci. By comparing the foci at (0, 3λ) and (0, 5λ) and the combination between (0, 3λ) and (R, 3λ), the longitudinal and transverse acoustic focusing capabilities between the phased array based on meta-transducer elements and the traditional phased array were compared, as Figure 8 shown. The results show that the phased array based on meta-transducer elements has more than 65% improvement in focusing performance compared with the traditional ultrasonic phased array.

[0057] In the present invention, acoustic imaging has important application values in medical diagnosis and industrial inspection due to its non-invasive characteristics. The object to be imaged with sub-wavelength characteristics in the present invention is placed on the focusing plane (y = f), and scanned along the x-axis through a two-dimensional precision moving platform, as Figure 9 shown. Since the meta-transducer elements have higher focusing resolution, the sub-wavelength details of the imaging target can be clearly resolved. As Figure 10 shown, the phased array based on meta-transducer elements can resolve a slit of 0.3λ, and the overall pattern shape on the imaging plane and the sub-wavelength details of the line edges are all reconstructed with high quality, verifying the significant improvement in resolution of this design.

[0058] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A dynamic high-precision phased array based on an acoustic metatransducer unit, characterized in that: It includes a number of identical metasurface transducer units for reducing the equivalent acoustic size of array units. The metasurface transducer unit includes a metamaterial layer and a transducer element layer; the lateral dimension of the transducer element layer is at the wavelength level.

2. The dynamic high-precision phased array based on the acoustic metatransducer unit according to claim 1, characterized in that: The metamaterial layer is a coiled space structure or a layered dielectric thickness modulation structure or a membrane resonance structure or a Helmholtz resonator structure.

3. The dynamic high-precision phased array based on the acoustic metatransducer unit according to claim 2, characterized in that: The metamaterial layer is a coiled space structure, including acoustic channels with different folding lengths and an impedance matching layer.

4. The dynamic high-precision phased array based on the acoustic metatransducer unit according to claim 2, characterized in that: The metamaterial layer is a layered dielectric thickness modulation structure, including dielectric layers with different thicknesses.

5. The dynamic high-precision phased array based on the acoustic metatransducer unit according to claim 2, characterized in that: The metamaterial layer is a membrane resonance structure, including a thin film and an acoustic resonance cavity.

6. The dynamic high-precision phased array based on the acoustic metatransducer unit according to claim 2, characterized in that: The metamaterial layer is a Helmholtz resonator structure, including a Helmholtz resonator and a straight tube. The Helmholtz resonator is connected in series with the straight tube, where the Helmholtz resonator serves as an acoustic reactance and the straight tube serves as an impedance matching element.

7. The dynamic high-precision phased array based on the acoustic metatransducer unit according to claim 6, characterized in that: The ratio of the height h2 of the straight tube to the height h3 of the Helmholtz resonator ranges from 0.2 to 1; the total width R of the metamaterial layer > λ / 2, and the total length L of the metamaterial layer < λ; the structural parameters of the Helmholtz resonator satisfy: resonator width w3 < λ / 3, resonator opening length w2 < w3, where λ is the acoustic wave wavelength.

8. The dynamic high-precision phased array based on the acoustic metatransducer unit according to claim 7, characterized in that: The ratio of the height h2 of the straight tube to the height h3 of the Helmholtz resonator is 0.184h:0.456h, where h = λ / 6 and λ is the acoustic wave wavelength; the total width R of the metamaterial layer = λ, the structural thickness r = 0.02λ, the total height Z = 0.17λ, and the total length L = 2w, where w = 3λ / 8; the structural parameters of the Helmholtz resonator satisfy: resonator spacing w1 = 0.23w, resonator opening length w2 = 0.05w, resonator width w3 = 0.2w, and resonator cavity thickness h1 = 0.12h.

9. The dynamic high-precision phased array based on the acoustic metatransducer unit according to claim 1, characterized in that: The metamaterial layer and the transducer element layer are connected through embedded integration.

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