A broadband asymmetric mode converter and asymmetric acoustic focusing lens device

Abstract

The application provides a broadband asymmetric mode converter and an asymmetric acoustic focusing lens device, the asymmetric mode converter comprising a phased unit, a cross solid and a convex waveguide, the phased unit having two rows of oppositely arranged Helmholtz resonators inside, a channel penetrating through the upper and lower ends of the phased unit between the two rows of Helmholtz resonators, the phased unit converting a plane wave into a first-order acoustic wave, the plane wave being able to pass through the convex waveguide while the first-order acoustic wave being unable to pass through the convex waveguide, and realizing one-way transmission of acoustic waves; the asymmetric acoustic focusing lens device comprising a plurality of asymmetric mode converters and a solid base, a plurality of circles of the asymmetric mode converters being arranged in an array on a plurality of circumferences with different diameters and with the center of the solid base as the center, the phase arrangement of the phased unit of each circle of the asymmetric mode converters being adjustable, the focal length of the asymmetric acoustic focusing lens device being adjustable, and the asymmetric acoustic focusing lens device having high transmittance characteristics and broadband characteristics.

Description

Technical Field

[0001] This invention belongs to the field of acoustic technology, and specifically relates to a broadband asymmetric mode converter and an asymmetric acoustic focusing lens device. Background Technology

[0002] Sound waves are common energy carriers in real life. Sound waves propagate bidirectionally in ordinary media, meaning their transmission performance is indistinguishable when incident from either side of the medium. If asymmetric sound wave transmission can be achieved, it can be applied to various important applications requiring specific control of sound energy. For example, in the field of ultrasound medicine, it can effectively reduce the damage of sound waves to normal tissues and ultrasound transducers, and improve the therapeutic efficacy of HIFU (High-Intensity Focused Ultrasound). Furthermore, the asymmetric sound wave transmission effect can also be used in the design and manufacture of unidirectional sound barriers, focused ultrasound therapy, and special industrial technology applications. Therefore, research on broadband asymmetric acoustic focusing lens devices is not only of fundamental academic significance but also holds great promise for broad applications in various important fields.

[0003] Currently, researchers both domestically and internationally mainly rely on two types of systems—nonlinear and linear—to realize unidirectional acoustic transmission devices.

[0004] (1) In nonlinear acoustics, acoustic diodes composed of nonlinear phononic crystals can realize the unidirectional sound transmission effect. When a sound wave of a specific frequency is incident on the acoustic diode in the forward direction, the second harmonic generated by the acoustic nonlinear mechanism is in the passband of the phononic crystal and thus passes through the system; while when the sound wave is incident in the reverse direction, due to the bandgap characteristics of the phononic crystal, the sound wave cannot pass through the system, thus realizing the asymmetric sound transmission effect.

[0005] (2) In linear acoustics, unidirectional acoustic devices based on a linear system composed of a diffraction structure and a two-dimensional phononic crystal can realize asymmetric sound wave transmission. When a sound wave is incident perpendicularly on the diffraction structure, diffracted sound waves are generated in different directions. The propagation direction of the diffracted sound waves is in the directional passband of the phononic crystal, and can pass through the phononic crystal and be distributed in different directions; however, when the sound wave is incident perpendicularly from one side of the phononic crystal, the sound wave is in the directional bandgap of the phononic crystal, and it is difficult to pass through the phononic crystal, thus realizing asymmetric transmission of sound waves.

[0006] The disadvantages of traditional technology are:

[0007] (1) Acoustic metasurfaces designed based on curled spatial structures can usually only achieve acoustic wave manipulation within a specific frequency band, with a narrow working frequency band and mostly a single frequency.

[0008] (2) The transmission energy of asymmetric acoustic transmission devices based on nonlinear effects is low, which makes it difficult to meet the needs of practical applications;

[0009] (3) Asymmetric acoustic transmission devices based on nonlinear effects are large in size and have low robustness.

[0010] The reasons for the defects of traditional technologies include:

[0011] (1) Acoustic metasurfaces designed based on folded space structures often have a labyrinthine configuration with a long and narrow propagation path, resulting in significant energy loss in the system.

[0012] (2) Due to the weak interaction between sound waves and nonlinear materials and the low transmittance, the efficiency of sound energy conversion from the fundamental wave to the second harmonic is low.

[0013] (3) Asymmetric acoustic transmission devices based on phononic crystals require a certain period of unit arrangement, which results in large device size and difficulty in integration. Summary of the Invention

[0014] In view of the fact that traditional asymmetric acoustic transmission devices have narrow operating bandwidths, or even single frequencies, and low transmittance, this invention provides a wideband asymmetric mode converter and an asymmetric acoustic focusing lens device, which can achieve asymmetric acoustic focusing effect at a specific position in free space and has high transmittance characteristics.

[0015] The present invention achieves the above-mentioned technical objectives through the following technical means.

[0016] A broadband asymmetric mode converter is characterized by comprising a phase control unit, a cross-shaped solid, and a convex waveguide.

[0017] Four phase control units are fixed at four recesses around the cross-shaped solid, and the cross-shaped solid and the four phase control units are connected to form a cuboid. The phase control unit has two rows of Helmholtz resonant cavities with openings facing each other. The two rows of Helmholtz resonant cavities are connected by a channel that runs through the upper and lower ends of the phase control unit. The Helmholtz resonant cavities are connected to the channel. The number of Helmholtz resonant cavities in each row is greater than or equal to two.

[0018] The convex waveguide is fixed above the cross-shaped solid and the phase control unit. The convex waveguide includes an upper square frame and a lower square frame connected by a "U"-shaped frame. The side length of the upper square frame is smaller than that of the lower square frame. The upper square frame, the "U"-shaped frame and the lower square frame form a convex cavity that runs through the upper and lower ends.

[0019] Furthermore, the phased array unit has a square cross-section with sides of 1.8cm ≤ w ≤ 2.2cm and a height of 2.25cm ≤ h ≤ 3cm. The channel width between the two rows of Helmholtz resonators is 0.1w ≤ w3 ≤ 0.25w. The wall thickness of the Helmholtz resonator is 0.05cm ≤ d ≤ 0.15cm, and the opening height of the Helmholtz resonator is...

[0020] The width of the four sides of the cross-shaped solid is 0.5cm≤w2≤1cm, and the height of the cross-shaped solid is 2.25cm≤h≤3cm.

[0021] The wall thickness of the convex waveguide is 0.05cm≤d≤0.15cm. The height of the lower square frame of the convex waveguide is 1.2cm≤h2≤1.8cm, and the side length of the lower square frame is 2w+w2. The height of the upper square frame of the convex waveguide is 0.9cm≤h1≤2cm, and the side length of the cavity inside the upper square frame is 2.2cm≤w1≤3cm.

[0022] Furthermore, each row of Helmholtz resonators contains four resonators.

[0023] Furthermore, the four phase control units are divided into two groups of phase control units with different phases. Each group of phase control units consists of two phase control units located in the same row and with the same phase.

[0024] A broadband asymmetric acoustic focusing lens device composed of the aforementioned asymmetric mode converters includes multiple asymmetric mode converters and a solid base. Several rings of asymmetric mode converters are arrayed on multiple circles of different diameters centered on the solid base. The number of asymmetric mode converters in each ring is an integer multiple of the specified number. The phase control units on each ring of asymmetric mode converters are divided into inner ring phase control unit groups and outer ring phase control unit groups with different distances from the center. The phase control units in the inner ring phase control unit groups of each ring of asymmetric mode converters have the same phase, and the phase control units in the outer ring phase control unit groups of each ring of asymmetric mode converters have the same phase. However, the phases of the phase control units in the inner ring phase control unit groups and the phase control units in the outer ring phase control unit groups of each ring of asymmetric mode converters are not the same.

[0025] Furthermore, the four asymmetric mode converters are arranged in an array on multiple circles of different diameters centered on the solid base. The asymmetric mode converters are configured from the center of the solid base outwards as follows:

[0026] The first, second, third, and fourth rings are uniform circular arrays of 4, 8, 8, and 24 asymmetric mode converters, respectively.

[0027] Preferably, in the fourth ring, every three asymmetric mode converters are arranged in a straight line to form an asymmetric mode converter group, and the eight asymmetric mode converter groups are evenly distributed on a circle with the center of the solid base as the center.

[0028] Furthermore, the asymmetric acoustic focusing lens device is made of one of the following materials: plexiglass, plastic, or metal.

[0029] Furthermore, the phase control units of the inner and outer phase control unit groups on each asymmetric mode converter have a phase of 0 or π.

[0030] Furthermore, the focal length range of the asymmetric acoustic focusing lens device is 5-25cm.

[0031] Furthermore, the height of the solid base is 0.5cm≤h3≤3.5cm, and the side length of the solid base is 30cm≤a≤70cm.

[0032] The beneficial effects of this invention are:

[0033] The phased array unit in the asymmetric mode converter of this invention can convert a plane wave into a first-order acoustic wave. The plane wave can pass through the convex waveguide, while the first-order acoustic wave cannot. When the acoustic wave is incident from the top, the incident acoustic wave is a plane wave, which can pass through the convex waveguide. Then, the phased array unit converts the plane wave into a first-order acoustic wave and reaches the lower region of the asymmetric mode converter. When the acoustic wave is incident from the bottom, the incident acoustic wave is a plane wave, which is converted into a first-order acoustic wave by the phased array unit. The first-order acoustic wave will be reflected and refracted in the convex waveguide. The first-order acoustic wave cannot pass through the phased array unit, thus realizing unidirectional transmission of the acoustic wave.

[0034] In the asymmetric mode converter described in this invention, the phase control unit can also adjust the phase and transmittance of the phase control unit by adjusting the values ​​of w1 and h1 to meet the required phase distribution and transmittance.

[0035] The asymmetric acoustic focusing lens device of this invention, when a sound wave is incident from the top, forms a bright point in the central region, which is the focal point of the asymmetric acoustic focusing lens device. At the focal point, the transmitted sound energy reaches 28 times the incident sound wave energy, exhibiting high transmittance characteristics. Conversely, when a sound wave is incident from the bottom, the sound energy is very small, thus forming a good asymmetric acoustic focusing effect. Furthermore, the asymmetric acoustic focusing lens device can achieve an asymmetric acoustic focusing effect within the 5100-6300Hz range, with an operating bandwidth of up to 1200Hz, demonstrating wideband characteristics.

[0036] The asymmetric acoustic focusing lens device described in this invention can also adjust the focal length of the asymmetric acoustic focusing lens device by adjusting the phase arrangement of the phase control unit of each asymmetric mode converter, achieving focal length adjustment between 5-25cm, and is applicable to different working scenarios. Attached Figure Description

[0037] Figure 1 This is a perspective view of the asymmetric mode converter described in this invention.

[0038] Figure 2 This is an exploded view of the asymmetric mode converter described in this invention.

[0039] Figure 3 This is a three-dimensional schematic diagram of the interior of the present invention with a portion hidden.

[0040] Figure 4 In this invention Figure 3 The main view.

[0041] Figure 5 This is a spatial distribution diagram of the sound pressure amplitude generated when sound waves are incident from the top and bottom of the asymmetric mode converter.

[0042] Figure 6 This is a half-sectional perspective view of the phase control unit described in this invention.

[0043] Figure 7 The phase relationship diagram is generated by the phase control unit with different w3 and h4 values ​​in this invention.

[0044] Figure 8 This is a three-dimensional schematic diagram of the asymmetric acoustic focusing lens device described in this invention.

[0045] Figure 9 This is a top view of the asymmetric acoustic focusing lens device described in this invention.

[0046] Figure 10 This is a phase distribution diagram of the asymmetric acoustic focusing lens device according to Embodiment 3 of the present invention. The solid in the diagram includes a cross-shaped solid and a solid base.

[0047] Figure 11 The spatial distribution of acoustic energy generated by the sound waves incident from the top and bottom of the asymmetric acoustic focusing lens device in Embodiment 3 of the present invention is shown in (a) for top incident and (b) for bottom incident.

[0048] Figure 12 The spatial distribution of acoustic energy generated by sound waves incident from the top and bottom of the asymmetric acoustic focusing lens device at different input frequencies in Embodiment 3 of the present invention is shown in (a) for top incident and (b) for bottom incident.

[0049] Figure 13 The diagram shows the phase distribution of an asymmetric acoustic focusing lens device with a phase distribution of π-0-0-π-0-π-π-0 from the center outwards in Embodiment 4 of the present invention. The solid in the diagram includes a cross-shaped solid and a solid base.

[0050] Figure 14 The diagram shows the phase distribution of an asymmetric acoustic focusing lens device with a phase distribution of 0-π-π-0-π-0-π-0 from the center outwards in Embodiment 4 of the present invention. The solid in the diagram includes a cross-shaped solid and a solid base.

[0051] Figure 15The four embodiments of the present invention show the spatial distribution of acoustic energy generated by sound waves incident from the top and bottom of asymmetric acoustic focusing lens devices with different phase distributions. (a) is the spatial distribution of acoustic energy generated by an asymmetric acoustic focusing lens device with a phase distribution of π-0-0-π-0-π-π-0 from the center outwards, and (b) is the spatial distribution of acoustic energy generated by an asymmetric acoustic focusing lens device with a phase distribution of 0-π-π-0-π-0-π-0 from the center outwards.

[0052] In the figure, 1. Asymmetric mode converter; 11. Phased array unit; 111. Helmholtz resonant cavity; 12. Cross-shaped solid; 121. Recess; 122. Support; 13. Convex waveguide; 131. Upper square frame; 132. "U" shaped frame; 133. Lower square frame; 2. Solid base. Detailed Implementation

[0053] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0054] The present invention provides a wideband asymmetric mode converter, such as... Figure 1-4 As shown, it includes a phased array unit 11, a cross-shaped solid 12, and a convex waveguide 13.

[0055] Four phase control units 11 are respectively fixed at four recesses 121 around the cross-shaped solid 12. The cross-shaped solid 12 and the four phase control units 11 are connected to form a cuboid. The phase control unit 11 has two rows of Helmholtz resonant cavities 111 with openings facing each other. The two rows of Helmholtz resonant cavities 111 are connected by a channel that runs through the upper and lower ends of the phase control unit 11. The Helmholtz resonant cavities 111 are connected to the channel. The number of Helmholtz resonant cavities 111 in each row is greater than or equal to two. The phase control unit 11 has a square outer profile with a side length of 1.8cm ≤ w ≤ 2.2cm. This ensures that when the asymmetric mode converter forms an asymmetric acoustic focusing lens device, the width of each phase control unit 11 matches the phase width in the discrete phase distribution diagram. The height is 2.25cm ≤ h ≤ 3cm. The channel width between the two rows of Helmholtz resonators 111 is 0.1w ≤ w3 ≤ 0.25w. The wall thickness of the Helmholtz resonator 111 is 0.05cm ≤ d ≤ 0.15cm. The opening height of the Helmholtz resonator 111 is... This allows the plane wave to be converted into a first-order sound wave when it passes through the phase control unit 11. The width of the four sides 122 on the cross-shaped solid 12 is 0.5cm≤w2≤1cm, and the height of the cross-shaped solid 12 is 2.25cm≤h≤3cm. The cross-shaped solid 12 is used to connect the phase control unit 11 and fill the gap between adjacent phase control units 11.

[0056] The convex waveguide 13 is fixed above the cross-shaped solid 12 and the phased array unit 11. The convex waveguide 13 includes an upper square frame 131 and a lower square frame 133 connected by a U-shaped frame 132. The side length of the cross section of the upper square frame 131 is smaller than that of the lower square frame 133. The upper square frame 131, the U-shaped frame 132, and the lower square frame 133 form a convex cavity that runs through both ends. The wall thickness of the convex waveguide 13 is 0.05cm≤d≤0.15cm. The height of the lower square frame of the convex waveguide 13 is 1.2cm≤h2≤1.8cm, and the side length of the lower square frame is 2w+w2. The height of the upper square frame of the convex waveguide 13 is 0.9cm≤h1≤2cm, and the side length of the cavity inside the upper square frame is 2.2cm≤w1≤3cm. This causes the first-order sound wave to be reflected and refracted within the convex waveguide 13 when it propagates from below to above, preventing it from passing through the phase control unit 11.

[0057] The following specific embodiments further explain the asymmetric mode converter and the asymmetric acoustic focusing lens device composed of the asymmetric mode converter described in this invention.

[0058] Example 1

[0059] The asymmetric mode converter 1 is constructed using a 3D-printed cross-shaped solid 12 with a side width of w2 = 1 cm and a height of h = 3 cm. The convex waveguide 13 has a wall thickness of d = 0.1 cm, a lower square frame with a height of h2 = 1.5 cm and a side length of 2w + w2 = 5 cm, and an upper square frame with a height of h1 = 1.5 cm and a cavity with a side length of w1 = 2.8 cm. Additionally, in this embodiment, each row of Helmholtz resonant cavities 111 consists of four units. The four phase control units 11 are divided into two groups based on phase, with the two phase control units 11 in each group arranged adjacent to each other. The outer contour of the cross-section of both groups of phase control units 11 has a side length of w = 2c. A square with height h = 3cm has a Helmholtz resonator 111 with wall thickness d = 0.1cm. Therefore, the internal cavity height h5 = (h - 8d) / 4 = 5.5mm. In one set of phase control units 11, the cavity width between the two rows of Helmholtz resonators 111 is w3 = 4.6mm, the opening height of the Helmholtz resonator 111 is h4 = 4.8mm, and the phase is 0. In another set of phase control units 11, the cavity width between the two rows of Helmholtz resonators 111 is w3 = 2.4mm, the opening height of the Helmholtz resonator 111 is h4 = 3.8mm, and the phase is π. The 3D printing material has a density of 1180kg / m³. 3 Epoxy resin with a longitudinal wave velocity of 2720 m / s and a transverse wave velocity of 1460 m / s, with environmental parameters including an air density of 1.21 kg / m³. 3The speed of sound is 343 m / s. A sound wave with a wavelength of λ = 6 cm is incident from the top and bottom respectively, yielding the following results: Figure 5 The diagrams shown depict the spatial distribution of sound pressure amplitudes generated when sound waves are incident from the top and bottom of the asymmetric mode converter. This demonstrates that when sound waves are incident from the top, they can pass through the asymmetric mode converter; however, when incident from the bottom, they cannot pass through the asymmetric mode converter 1, thus achieving a good unidirectional sound transmission effect. In the asymmetric mode converter described in this invention, the phase control unit 11 can convert a plane wave into a first-order sound wave. The plane wave can pass through the convex waveguide 13, while the first-order sound wave cannot. When sound waves are incident from the top, the incident sound wave is a plane wave, which can pass through the convex waveguide 13 and then be converted into a first-order sound wave by the phase control unit 11, reaching the area below the asymmetric mode converter. When sound waves are incident from the bottom, the incident sound wave is a plane wave, which is converted into a first-order sound wave by the phase control unit 11. The first-order sound wave is reflected and refracted within the convex waveguide 13 and cannot pass through the phase control unit 11, thus achieving unidirectional sound transmission.

[0060] Example 2

[0061] By adjusting the cavity width w3 formed between the two rows of Helmholtz resonant cavities 111 of the phase control unit 11, and the opening height h4 of the Helmholtz resonant cavity 111, the adjustment range of w3 is 2-5mm, the adjustment range of h4 is 2-5mm, the wall thickness of the Helmholtz resonant cavity 111 is kept at d = 0.1cm, the outer contour of the phase control unit 11 cross-section is kept as a square with a side length of w = 2cm, and the height is kept at h = 3cm, the following is obtained: Figure 7 The phase and transmittance of the phase control unit 11 with different w3 and h4 values ​​are shown. It can be seen that the phase and transmittance of the phase control unit 11 can be adjusted by adjusting the w3 and h4 values ​​to meet the required phase distribution and transmittance.

[0062] Example 3

[0063] Several asymmetric mode converters 1 are arrayed on multiple circles of different diameters centered on the solid base 2. The number of asymmetric mode converters 1 in each circle is an integer multiple of 4. The phase control units 11 on each circle of asymmetric mode converters 1 are divided into inner circle phase control unit groups and outer circle phase control unit groups with different distances from the center. The phase control units 11 in the inner circle phase control unit groups on each circle of asymmetric mode converters 1 have the same phase, and the phase control units 11 in the outer circle phase control unit groups on each circle of asymmetric mode converters 1 have the same phase. However, the phases of the phase control units 11 in the inner circle phase control unit groups and the phase control units 11 in the outer circle phase control unit groups on each circle of asymmetric mode converters 1 are different, thus forming the broadband asymmetric acoustic focusing lens device of the present invention.

[0064] By 3D printing asymmetric acoustic focusing lens devices, such as Figure 8-9 As shown, the solid in the figure includes a solid base 2 and a cross-shaped solid 12. The printed asymmetric acoustic focusing lens device structure consists of four rings of the asymmetric mode converter 1 arranged in an array on multiple circles of different diameters centered on the solid base 2. The asymmetric mode converter 1 is configured from the center of the solid base 2 outwards as follows:

[0065] The first, second, and third rings are uniform circular arrays of 4, 8, and 8 asymmetric mode converters 1, respectively; the fourth ring consists of 3 asymmetric mode converters 1 arranged in a straight line to form an asymmetric mode converter group, and the 8 asymmetric mode converter groups are uniformly circular arrayed on the solid base 2 with the center of the solid base 2 as the center.

[0066] The 3D-printed asymmetric acoustic focusing lens device has the same parameters for its asymmetric mode converter 1 as in Example 1. The solid base 2 has a height of h3 = 1 cm and a side length of a = 50 cm. The cavity width w3 and the opening height h4 of the Helmholtz resonators 111 formed between the inner and outer ring phase control units 11 of each asymmetric mode converter 1 are controlled. Figure 10 As shown, the phase arrangement of the phase control unit 11 in each revolution of the asymmetric mode converter 1 satisfies the following: from the center of the solid base 2 outwards, the phases are π-0-π-0-0-π-π-0. When the phase of the phase control unit 11 is 0, the cavity width formed between the two rows of Helmholtz resonant cavities 111 of the phase control unit 11 is w3 = 4.6 mm, and the opening height of the Helmholtz resonant cavity 111 is h4 = 4.8 mm. When the phase of the phase control unit 11 is π, the cavity width formed between the two rows of Helmholtz resonant cavities 111 of the phase control unit 11 is w3 = 2.4 mm, and the opening height of the Helmholtz resonant cavity 111 is h4 = 3.8 mm. The 3D printing material has a density of 1180 kg / m³. 3 Epoxy resin with a longitudinal wave velocity of 2720 m / s and a transverse wave velocity of 1460 m / s, with environmental parameters including an air density of 1.21 kg / m³. 3 The speed of sound is 343 m / s. Sound waves with a wavelength of λ = 6 cm are incident from the top and bottom respectively, yielding the following results: Figure 11The illustration shows the spatial distribution of acoustic energy generated when sound waves are incident from the top and bottom of the asymmetric acoustic focusing lens device in this embodiment. It can be seen that when the sound wave is incident from the top, it can pass through the asymmetric acoustic focusing lens device, and the acoustic energy is focused in the region z = -7cm, meaning the focal length of the asymmetric acoustic focusing lens device is 7cm. When the sound wave is incident from the bottom, it cannot pass through the lens. Further, we show the acoustic energy distribution on the zx section (R1 and R3) selected at y = 0 and the xy section (R2 and R4) selected at z = -7cm. It can be seen that for the case of sound waves incident from the top, the acoustic energy forms a bright point in the central region, which is the focal point of the asymmetric acoustic focusing lens device described in this invention. At the focal point, the transmitted acoustic energy reaches 28 times the incident sound wave energy, indicating that the asymmetric acoustic focusing lens device has high transmittance characteristics. For the case of sound waves incident from the bottom, the acoustic energy is very small, thus forming a good asymmetric point focusing effect.

[0067] Adjusting the frequency of the incident wave, sound waves with frequencies f = 5100Hz, 5500Hz, 5900Hz, and 6300Hz were selected, and the sound waves were incident from the top and bottom of the asymmetric acoustic focusing lens device, respectively, to obtain the following results: Figure 12 The image shows the spatial distribution of acoustic energy generated when sound waves are incident from the top and bottom of the asymmetric acoustic focusing lens device at different input frequencies. It can be seen that the asymmetric acoustic focusing effect can be achieved in the range of 5100-6300Hz, and the working bandwidth can reach 1200Hz. The asymmetric acoustic focusing lens device has wide bandwidth characteristics.

[0068] Example 4

[0069] Two sets of asymmetric acoustic focusing lens devices were 3D printed, such as... Figure 13 , 14 As shown, the phase arrangement of the phase control units 11 of each turn of the two sets of asymmetric mode converters 1 satisfies the following conditions: from the center of the solid base 2 outwards, they are π-0-0-π-0-π-π-0 and 0-π-π-0-π-0-π-0 respectively. When the phase of the phase control unit 11 is 0, the cavity width formed between the two rows of Helmholtz resonant cavities 111 of the phase control unit 11 is w3 = 4.6 mm, and the opening height of the Helmholtz resonant cavity 111 is h4 = 4.8 mm; when the phase of the phase control unit 11 is π, the cavity width formed between the two rows of Helmholtz resonant cavities 111 of the phase control unit 11 is w3 = 2.4 mm, and the opening height of the Helmholtz resonant cavity 111 is h4 = 3.8 mm. The remaining parameters are the same as in Embodiment 3. A sound wave with a wavelength of λ = 6 cm is incident from the top and from the bottom, respectively, to obtain the following results: Figure 15 The diagram shows the spatial distribution of acoustic energy generated when sound waves are incident from the top and bottom of an asymmetric acoustic focusing lens device with different phase distributions in this embodiment.

[0070] Therefore, when a sound wave is incident from the top, it can pass through the asymmetric acoustic focusing lens device, and the acoustic energy of the two sets of asymmetric acoustic focusing lens devices is focused on the regions z = -10cm (cross-sections R5 and R6) and z = -20cm (cross-sections R9 and R10), respectively. That is, the focal lengths of the asymmetric acoustic focusing lens devices are 10cm and 20cm, respectively. When a sound wave is incident from the bottom, the emitted acoustic energy is very small (cross-sections R7 and R8 combined or R11 and R12 combined). Therefore, the asymmetric acoustic focusing lens device of the present invention can adjust the focal length of the asymmetric acoustic focusing lens device by adjusting the phase arrangement of the phase control unit 11 of each asymmetric mode converter 1, and can be applied to different working scenarios.

[0071] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A wideband asymmetric mode converter, characterized in that, It includes a phase control unit (11), a cross-shaped solid (12), and a convex waveguide (13); Four phase control units (11) are fixed at four recesses (121) around a cross-shaped solid (12). The cross-shaped solid (12) and the four phase control units (11) are connected to form a cuboid. The phase control unit (11) has two rows of Helmholtz resonant cavities (111) with openings facing each other. There is a channel between the two rows of Helmholtz resonant cavities (111) that runs through the upper and lower ends of the phase control unit (11). The Helmholtz resonant cavities (111) are connected to the channel. The number of Helmholtz resonant cavities (111) in each row is greater than or equal to two. The four phase control units (11) are divided into two groups of phase control units with different phases. Each group of phase control units consists of two phase control units (11) located in the same row and with the same phase. The convex waveguide (13) is fixed above the cross-shaped solid (12) and the phase control unit (11). The convex waveguide (13) includes an upper square frame (131) and a lower square frame (133) connected by a "U"-shaped frame (132). The side length of the cross section of the upper square frame (131) is smaller than the side length of the cross section of the lower square frame (133). The upper square frame (131), the "U"-shaped frame (132) and the lower square frame (133) form a convex cavity that runs through both the upper and lower ends.

2. The broadband asymmetric mode converter according to claim 1, characterized in that, The outer contour of the phase control unit (11) has a side length of 1.8cm ≤ w A square with a diameter ≤2.2cm and a height ≤2.25cm. h ≤3cm, the channel width between the two rows of Helmholtz resonant cavities (111) is 0.

1. w ≤ w 3≤0.25 w The wall thickness of the Helmholtz resonator (111) is 0.05 cm ≤ d ≤0.15cm, the opening height of the Helmholtz resonator (111) is h / 15 ≤ h 4 ≤ h / 6 ; The width of the four supporting sides (122) on the cross-shaped solid (12) is 0.5cm≤ w 2≤1cm, the height of the cross-shaped solid (12) is 2.25cm≤ h ≤3cm; The wall thickness of the convex waveguide (13) is 0.05cm≤ d ≤0.15cm, the height of the square frame under the convex waveguide (13) is 1.2cm≤ h 2≤1.8cm, the side length of the lower square frame is 2 w + w 2. The height of the square frame on the convex waveguide (13) is 0.9cm≤ h 1≤2cm, the side length of the cavity inside the upper square frame is 2.2cm≤ w 1≤3cm.

3. The broadband asymmetric mode converter according to claim 2, characterized in that, The number of Helmholtz resonators (111) in each row is four.

4. A broadband asymmetric acoustic focusing lens device comprising the broadband asymmetric mode converter as described in claim 1, characterized in that, The system includes multiple broadband asymmetric mode converters (1) and a solid base (2). Several circles of broadband asymmetric mode converters (1) are arranged in an array on multiple circles of different diameters with the center of the solid base (2) as the center. The number of broadband asymmetric mode converters (1) in each circle is an integer multiple of 4. The phase control units (11) on each circle of broadband asymmetric mode converters (1) are divided into inner circle phase control unit groups and outer circle phase control unit groups with different distances from the center. The phase control units (11) in the inner circle phase control unit group on each circle of broadband asymmetric mode converters (1) have the same phase. The phase control units (11) in the outer circle phase control unit group on each circle of broadband asymmetric mode converters (1) have the same phase. The phase control units (11) in the inner circle phase control unit group and the phase control units (11) in the outer circle phase control unit group on each circle of broadband asymmetric mode converters (1) have different phases.

5. The broadband asymmetric acoustic focusing lens device according to claim 4, characterized in that, The broadband asymmetric mode converter (1) described in circle 4 is arranged in an array on multiple circles of different diameters centered on the solid base (2). The broadband asymmetric mode converter (1) is configured from the center of the solid base (2) outwards as follows: The first, second, third, and fourth rings are 4, 8, 8, and 24 wideband asymmetric mode converters (1) in a uniform circular array.

6. The broadband asymmetric acoustic focusing lens device according to claim 5, characterized in that, In the fourth circle, every three broadband asymmetric mode converters (1) are arranged in a straight line to form a broadband asymmetric mode converter group. The eight broadband asymmetric mode converter groups are evenly distributed on the circumference with the center of the solid base (2) as the center.

7. The broadband asymmetric acoustic focusing lens device according to claim 4, characterized in that, The asymmetric acoustic focusing lens device is made of one of the following materials: plexiglass, plastic, or metal.

8. The broadband asymmetric acoustic focusing lens device according to claim 4, characterized in that, The phase control units (11) of the inner and outer phase control units of the wideband asymmetric mode converter (1) are 0 or π.

9. The broadband asymmetric acoustic focusing lens device according to claim 4, characterized in that, The focal length range of the asymmetric acoustic focusing lens device is 5-25cm.

10. The broadband asymmetric acoustic focusing lens device according to claim 4, characterized in that, The solid base (2) has a height of 0.5cm or less. h 3≤3.5cm, the side length of the solid base (2) is 30 cm≤ a ≤70 cm.

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