阅读说明：本技术 基于角向超构表面的声涡旋分离器 (Acoustic vortex separator based on angular super-structure surface ) 是由 伏洋洋 刘友文 徐亚东 于 2020-07-01 设计创作，主要内容包括：本发明揭示了一种基于角向超构表面的声涡旋分离器,所述声涡旋分离器包括中空设置的圆柱形波导及位于圆柱形波导内的相位渐变超构光栅,圆柱形波导的半径为R,相位渐变超构光栅的厚度为h,所述相位渐变超构光栅包括l<Sup>ξ</Sup>组扇形超结构,每个扇形超结构的角宽度为θ＝2π/l<Sup>ξ</Sup>,每个扇形超结构包括m组角宽度为θ<Sub>1</Sub>＝θ/m的扇形单结构,每个扇形超结构的相移分布φ<Sub>j</Sub>(θ)覆盖范围为2π,扇形超结构中相邻扇形单结构的相位差为φ<Sub>j</Sub>＝2π/m。本发明中揭示了基于相位渐变超构光栅的圆柱形波导中声涡旋的衍射机制,可以预测声涡旋的散射行为,提供了多个传播通道,突破了扭转相位单通道的限制；基于角向超构表面的声涡旋分离器可以实现声涡旋的非对称传输,为控制声学OAM开辟了新的可能性。(The invention discloses an acoustic vortex separator based on an angular metamaterial surface, which comprises a cylindrical waveguide arranged in a hollow mode and a phase gradient metamaterial grating positioned in the cylindrical waveguide, wherein the radius of the cylindrical waveguide is R, the thickness of the phase gradient metamaterial grating is h, and the phase gradient metamaterial grating comprises l ξ Grouping sector superstructures, each sector superstructures having an angular width θ of 2 π/l ξ Each sector superstructure comprising m groups of angular widths θ 1 Sector-shaped single structure of theta/m, phase shift distribution phi of each sector-shaped single structure j The coverage area of (theta) is 2 pi, and the phase difference of adjacent fan-shaped single structures in the fan-shaped superstructure is phi j 2 pi/m. The invention discloses a diffraction mechanism of acoustic vortex in a cylindrical waveguide based on a phase gradient super-structure grating, which can predict the scattering behavior of the acoustic vortex, provide a plurality of propagation channels and break through the limitation of twisting a phase single channel; the acoustic vortex separator based on the angular super-structure surface can realize the asymmetric transmission of acoustic vortex, and opens up a new possibility for controlling acoustic OAM。)

1. The acoustic vortex separator based on the angular metamaterial surface is characterized by comprising a cylindrical waveguide and a phase gradient metamaterial grating, wherein the cylindrical waveguide is arranged in a hollow mode, the phase gradient metamaterial grating is located in the cylindrical waveguide, the radius of the cylindrical waveguide is R, the thickness of the phase gradient metamaterial grating is h, and the phase gradient metamaterial grating comprises l^ξGrouping sector superstructures, each sector superstructures having an angular width θ of 2 π/l^ξEach sector superstructure comprising m groups of angular widths θ₁Sector-shaped single structure of theta/m, phase shift distribution phi of each sector-shaped single structure_jThe coverage area of (theta) is 2 pi, and the phase difference of adjacent fan-shaped single structures in the fan-shaped superstructure is phi_j＝2π/m。

2. The acoustic vortex separator based on angular metamorphic surface of claim 1 wherein the fan-shaped single structure includes a first fan-shaped unit and a second fan-shaped unit, the first fan-shaped unit is made of acoustically hard material which cannot penetrate sound waves, and the second fan-shaped unit is made of impedance matching material.

3. The angular microstructure surface based acoustic vortex separator of claim 2, wherein the refractive index of a different second sector unit of the sector superstructure is:

n_j＝1+(j-1)λ(mh)，j＝1,2…m；

where λ is the wavelength of the incident acoustic wave.

4. The acoustic vortex separator based on an azimuthal hyperstructure surface according to claim 3, wherein the radius R of the cylindrical waveguide is 0.64 λ.

5. The acoustic vortex separator based on an azimuthal hyperstructure surface according to claim 3, characterised in that it satisfies:

wherein l^t、l^rTopological charges of reflected acoustic vortex and transmitted acoustic vortex respectively, n is diffraction order, lⁱⁿL is the topological charge of the incident acoustic vortex, and L is the number of times the acoustic wave propagates between the reflective surface and the transmissive interface.

6. Acoustic vortex based on angular metamorphic surfaces according to claim 1The spiral separator is characterized in that the fan-shaped single structure comprises a partition plate and fan-shaped resonators, each fan-shaped resonator comprises a plurality of rows of sub-resonators, each sub-resonator comprises a plurality of Helmholtz resonators and a cavity, the wall thickness of each Helmholtz resonator is t, and the height of an inner cavity of each Helmholtz resonator is w₀The height of the subresonator is w, and the w in different fan-shaped single structures in the fan-shaped superstructure₀Different from each other in terms of phase difference phi between adjacent fan-shaped single structures_j＝2π/m。

7. The angular metamaterial surface-based acoustic vortex separator of claim 6, wherein the phase-graded superstructure grating comprises 2 sets of sector superstructures, each sector superstructures comprising 5 sets of angular widths θ₁Each sector resonator comprises 4 rows of sub-resonators with a height w R/4, each sub-resonator comprises 4 helmholtz resonators and one cavity, and the partition has a size h × R × t.

8. The angular microstructure surface-based acoustic vortex separator of claim 7, wherein the sector superstructure comprises a first sector resonator, a second sector resonator, a third sector resonator, a fourth sector resonator and a fifth sector resonator, w of the first sector resonator, the second sector resonator, the third sector resonator, the fourth sector resonator and the fifth sector resonator, which are distributed in sequence₀The/w gradually decreases.

9. The acoustic vortex separator based on an angular metamorphic surface of claim 8 wherein the Helmholtz resonators in the fourth sector resonator have a cavity neck width that is less than the cavity neck widths of the Helmholtz resonators in the remaining sector resonators.

Technical Field

The invention belongs to the technical field of acoustic vortex propagation, and particularly relates to an acoustic vortex separator based on an angular super-structure surface.

Background

Swirl is a common phenomenon in fluid mechanics, such as eddies, smoke rings, and tornadoes. Inspired by hydrodynamic vortices, Coullet et al in 1989 proposed the concept of optical vortices by solving Maxwell-Bloch equations. Later, Allen et al found that optical vortices can carry Orbital Angular Momentum (OAM), expressed as a helical wave front exp (il θ), where the integer l is the topological charge and θ is the azimuthal angle. Unlike two states of the spin angular momentum of light, which is embodied by the chirality of circularly polarized light, the OAM state number of light is infinite. Due to the attractive nature of OAM, optical vortices have been extensively studied over the past decades, particularly on nanostructured surfaces. An artificial structure with sub-wavelength thickness provides an unprecedented way for OAM based applications, including OAM generation, OAM multiplexing and demultiplexing, spin to orbital angular momentum conversion, etc.

Unlike optical waves, acoustic waves carry only OAM, since acoustic waves are essentially scalar pressure fields, generally considered to be non-rotating. Acoustic vortices have recently gained widespread attention and several OAM-based applications such as particle manipulation, acoustic torque, etc. have been proposed. To generate acoustic vortices, both active and passive methods are employed. Active methods are typically implemented with a large number of active transducer arrays, which require conversion between acoustic and electrical signals and relatively complex feedback circuitry; passive methods can convert a uniform wavefront into a helical wavefront using a compact and low cost structure.

The acoustic super-surface is engineered with phase gradient, and usually a torsional phase method is used to obtain acoustic vortex, but the method has limited control capability on the acoustic field, so a deeper mechanism for manipulating the acoustic vortex is desired.

Therefore, in view of the above technical problems, there is a need to provide an acoustic vortex separator based on an angular metamorphic surface.

Disclosure of Invention

The invention aims to provide an acoustic vortex separator based on an angular metamaterial surface.

In order to achieve the above object, an embodiment of the present invention provides the following technical solutions:

an acoustic vortex separator based on an angular metamorphic surface comprises a cylindrical waveguide arranged in a hollow mode and a phase positioned in the cylindrical waveguideThe radius of the cylindrical waveguide is R, the thickness of the phase gradient super-structure grating is h, and the phase gradient super-structure grating comprises l^ξGrouping sector superstructures, each sector superstructures having an angular width θ of 2 π/l^ξEach sector superstructure comprising m groups of angular widths θ₁Sector-shaped single structure of theta/m, phase shift distribution phi of each sector-shaped single structure_jThe coverage area of (theta) is 2 pi, and the phase difference of adjacent fan-shaped single structures in the fan-shaped superstructure is phi_j＝2π/m。

In one embodiment, the fan-shaped single structure comprises a first fan-shaped unit and a second fan-shaped unit, the first fan-shaped unit is made of an acoustically hard material which cannot penetrate through sound waves, and the second fan-shaped unit is made of an impedance matching material.

In one embodiment, the refractive index of a different second sector unit in the sector superstructure is:

n_j＝1+(j-1)λ(mh)，j＝1,2…m；

where λ is the wavelength of the incident acoustic wave.

In one embodiment, the radius R of the cylindrical waveguide is 0.64 λ.

In one embodiment, the acoustic vortex separator satisfies:

wherein l^t、l^rTopological charges of reflected acoustic vortex and transmitted acoustic vortex respectively, n is diffraction order, lⁱⁿL is the topological charge of the incident acoustic vortex, and L is the number of times the acoustic wave propagates between the reflective surface and the transmissive interface.

In one embodiment, the fan-shaped single structure comprises a partition plate and fan-shaped resonators, each fan-shaped resonator comprises a plurality of rows of sub-resonators, each sub-resonator comprises a plurality of helmholtz resonators and a cavity, the wall thickness of each helmholtz resonator is t, and the height of an inner cavity of each helmholtz resonator is w₀The height of the subresonator is w, and the w in different fan-shaped single structures in the fan-shaped superstructure₀Different from w to realize adjacent fan-shaped unijunctionsThe phase difference of the structure is phi_j＝2π/m。

In one embodiment, the phase-graded superstructure grating comprises 2 sets of sector superstructures, each sector superstructures comprising 5 sets of angular widths θ₁Each sector resonator comprises 4 rows of sub-resonators with a height w R/4, each sub-resonator comprises 4 helmholtz resonators and one cavity, and the partition has a size h × R × t.

In an embodiment, the sector superstructure includes a first sector resonator, a second sector resonator, a third sector resonator, a fourth sector resonator and a fifth sector resonator which are sequentially distributed, and w of the first sector resonator, the second sector resonator, the third sector resonator, the fourth sector resonator and the fifth sector resonator₀The/w gradually decreases.

In an embodiment, the helmholtz resonator of the fourth sector resonator has a cavity neck width smaller than the cavity neck widths of the helmholtz resonators of the remaining sector resonators.

Compared with the prior art, the invention has the following advantages:

the invention discloses a diffraction mechanism of acoustic vortex in a cylindrical waveguide based on a phase gradient super-structure grating, which can predict the scattering behavior of the acoustic vortex, provide a plurality of propagation channels and break through the limitation of twisting a phase single channel;

the acoustic vortex separator based on the angular super-structure surface can realize the asymmetric transmission of acoustic vortex, opens up new possibility for controlling acoustic OAM, and can be applied to various OAM devices, such as a multi-channel OAM converter, an OAM frequency divider, a one-way transmission OAM device, an OAM-based information communication device and the like.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

FIG. 1a is a schematic diagram of the construction of an acoustic vortex separator according to the present invention;

FIG. 1b is a schematic structural view of a single fan-shaped superstructure in an acoustic vortex separator of the present invention;

fig. 1c is a dispersion relation diagram of a propagation vortex mode in the cylindrical waveguide of the present invention, wherein a dotted line corresponds to R ═ 0.64 λ;

FIG. 1d is a schematic diagram of the diffraction of the acoustic vortex in the phase-graded superlattice grating of the present invention;

FIG. 2a and FIG. 2b are views of l in the present invention ^ξ2, m 5, topological charge lⁱⁿA sound field simulation diagram of incident acoustic vortex when the incident acoustic vortex is +/-1;

FIG. 3a is a schematic structural diagram of a fan-shaped single structure according to an embodiment of the present invention;

FIG. 3b is a cross-sectional view of a sector resonator in accordance with an embodiment of the present invention;

FIG. 3c is a graph of phase distribution and transmission coefficient of a sub-resonator according to an embodiment of the present invention;

FIG. 3d and FIG. 3e show a topological charge of l, respectively, in an embodiment of the present inventionⁱⁿSimulation diagram of sound field of incident sound vortex when the time is +/-1.

Detailed Description

The present invention will be described in detail below with reference to embodiments shown in the drawings. The embodiments are not intended to limit the present invention, and structural, methodological, or functional changes made by those skilled in the art according to the embodiments are included in the scope of the present invention.

Referring to fig. 1a and 1b, the invention discloses an acoustic vortex separator based on an angular metamaterial surface, which includes a hollow cylindrical waveguide 10 and a Phase-gradient gratings (PGM) 20 located in the cylindrical waveguide, the radius of the cylindrical waveguide is R, the thickness of the Phase-gradient gratings is h, and the Phase-gradient gratings 20 include l^ξ Grouping sector superstructures 21, each sector superstructures having an angular width θ of 2 π/l^ξEach sector superstructure comprising m groups of angular widths θ₁A fan-shaped superstructure 201 of theta/m, a phase shift distribution phi of each fan-shaped superstructure_jThe coverage area of (theta) is 2 pi, and the phase difference of adjacent fan-shaped single structures in the fan-shaped superstructure is phi_j＝2π/m。

Specifically, the fan-shaped single structure 201 includes a first fan-shaped unit 211 and a second fan-shaped unit 212, the first fan-shaped unit 211 is made of an acoustically hard material that cannot penetrate through sound waves, and the second fan-shaped unit 212 is made of an impedance matching material.

In order to realize the azimuthal phase gradient, the phase shift distribution on each fan-shaped single structure should cover the range of 2 pi, and the corresponding phase shift distribution can be realized by filling the second fan-shaped unit 212 with m impedance matching materials with different refractive indexes:

n_j＝ρ_j＝1+(j-1)λ(mh)，j＝1,2…m；

where λ is the wavelength of the incident acoustic wave.

Acoustically hard materials are not transparent to sound waves, so the coupling between these fan-shaped single structures is almost negligible. Since PGM devices have^ξThe unit with the group azimuth angle phase distribution covering 2 pi can provide an effective topological charge l with clockwise helicity^ξ。

As shown in FIG. 1c, for a cylindrical waveguide with a fixed radius, there is only a limited vortex mode [ -l ] in its topological charge^M,l^M]Wherein l is^MIndicating the maximum order of the vortex mode, "+" ("-") indicates the helicity (clockwise or counterclockwise) of the propagating vortex. Consider a topological charge of l ═ lⁱⁿThe incident acoustic Vortex (SV), the acoustic field of which is expressed as:

pⁱⁿ＝J_l(k_l,vr)/J_l(k_l,vR)exp(ilθ+ik_zz) (1)

wherein the content of the first and second substances,k_l,v、k_zrespectively the number of transverse waves and the number of longitudinal waves, k ₀2 pi/lambda is wave number in air, 1/J_l(k_l,vR) is a normalization factor. According to the OAM conservation principle and the surface grating diffraction law, the incident and reflection/transmission vortices of the reflection/transmission interface should follow the following formula by the topological charge conservation principle:

l^r(t)＝lⁱⁿ+nl^ξ(2)

wherein l^r(t)To reflect (transmit) the topological charge of the acoustic vortex, n is the diffraction order, and similar to the critical angle in generalized Snell's law, PGM has a critical topological charge in the cylindrical waveguide, defined as l^c＝l^M-l^ξ. For incident SV, its topological charge is within the critical charge (i.e. /)ⁱⁿ∈[-l^M,l^c]) It will be directly distorted by PGM, its topological charge being converted to:

l^t＝lⁱⁿ+l^ξ(3)

this is equivalent to n being 1 in formula (2), however, when the topological charge l of the incident SV isⁱⁿ>l^cWhen the incident SV cannot pass through the PGM, SV causes multiple reflections within the PGM, and the number of times a wave propagates within the PGM is defined as L. If the wave makes L round trips between the reflecting surface and the transmission interface, the phase difference between adjacent cells per period is delta phi ═ (2 pi/m) L, and when the diffraction order of the scattering SV is n, the equivalent topological charge provided by the PGM is nl^ξEquivalent phase difference per cycle of adjacent structural units

If the two phase differences (Δ φ and)

) Being able to match each other means that the incident SV will leave the super-structured grating in the nth order of diffraction order as the wave oscillates back and forth within the structure element with the propagation order L. Due to the fact thatⁱⁿ>l^cAnd L>It seems impossible to realize that the effective diffraction order at 0 satisfies n.ltoreq.0, but if 2 π phase is repeatedly applied to Δ φ, the phase matching relationship is established as

(q is a positive integer), that is:

L＝qm+n (4)

in a subwavelength superstructure grating, a 2 pi (q ═ 1) phase repetition is sufficient to achieve the phase matching condition, i.e., L ═ m + n. When L is an odd number, is the transmission SV of the nth diffraction order; and when L is an even number, it is the reflection SV of the nth diffraction order. By linking equation (2) and equation (4), the diffraction law for SVs is further given as:

since the reflection and transmission SVs of high diffraction order have mirror symmetry, i.e., the helicity of the reflection SV is opposite in sign to that of the transmission SV, at "l^r"to add" - "symbol.

From the diffraction law of equation (5), we can use PGM to predict the diffraction phenomena of SVs in a cylindrical waveguide. For an incident SV with topological charge within the critical value, one transmission will occur in the grating, and then the incident SV is converted to a transmission SV with n equal to 1, independent of m. For topological charges that exceed the critical charge, multiple reflections will occur within the PGM. When the odd (even) propagation path of the internally propagated wave reaches the diffraction condition, a strong transmission (reflection) SV can be generated by following equation (5). In some cases, although there are several diffraction orders at the same time for one incident SV, the largest diffraction order is preferred due to the smallest number of propagation (i.e., the smallest resonance length). Furthermore, if PGM is designed as odd and even number of structural units, the scattering inversion effect (i.e. transmission and reflection inversion) of the incident SV can occur in higher order diffraction due to the odd-even transition of the propagation number.

To verify the correctness of the above theory, a numerical simulation of the scattering behavior of SVs in a cylindrical waveguide with PGM was performed. Satisfy in all cases

R is 0.64 λ, h is 0.5 λ, and λ is 10 cm. For the sake of simulation, a circle with 0.05R is inserted in the center of PGMA column.

Selecting the radius of the waveguide as 0.64 lambda, and the maximum propagation order of SVs in the waveguide is l^MTwo fan-shaped superstructures, i.e. l, are designed for the phase-gradient superstructure grating PGM^ξ2 (see fig. 1c), the critical topological charge is l ^c0. If each sector superstructure is composed of 5 sector single structures (m ═ 5), with different OAM (l)ⁱⁿ∈[-2,2]) The scattering phenomenon of the incident SV (1) can be predicted from equations (3) to (5).

lⁱⁿ∈[-2,l^c]The time-incident SV will propagate following equation (3), as can be seen in FIG. 2a, lⁱⁿIncident SVs at-1 will convert to l ^t0 and l ^t1 transmitted beam.

lⁱⁿ∈(l^c,2]The diffraction behavior of the incident SVs becomes complex. lⁱⁿWhen the maximum diffraction order is 1, n is-1, the propagation number is even, and L is m + n is 4, so that L is represented by the following formula of formula (5)^rThere should be a reflected SV at 1, as shown in the numerical simulation of fig. 2 b.

In an embodiment of the present invention, to further illustrate the diffraction pattern of SVs in cylindrical waveguides with PGMs, a Helmholtz resonator is used to design l^ξA phase-graded super grating (PGM) of 2, 5, and 10 cm.

In particular, the phase-graded superstructure grating (PGM) comprises 2 groups (l)^ξ2) the sector superstructures shown in fig. 3a, each sector superstructures having an angular width θ 2 pi/2, each sector superstructures comprising 5 groups (m 5) of angular widths θ₁A phase shift distribution phi of each sector superstructure 31 of 36 DEG_jThe coverage area of (theta) is 2 pi, and the phase difference of adjacent fan-shaped single structures in the fan-shaped superstructure is phi_j＝2π/5。

Referring to fig. 3a and 3b, the fan-shaped single structure 31 includes a partition 311 and fan-shaped resonators 312, the partition has a size h × R × t, each fan-shaped resonator 312 includes 4 rows of sub-resonators 3121, the height w of the sub-resonators is R/4 1.6cm, each sub-resonator 3121 includes 4 helmholtz resonators 3122 and one cavity 3123, and the wall thickness t of the helmholtz resonator is 1.5mm, the height of the inner cavity of the Helmholtz resonator is w₀The height of the subresonator is w and the width of the cavity neck (i.e., the width of the opening in FIG. 3 b) is w_neck1.5mm, w in different fan-shaped single structures in the fan-shaped superstructure₀Different from each other in terms of phase difference phi between adjacent fan-shaped single structures_j＝2π/5。

Phase distribution and transmission coefficient of the subresonators referring to fig. 3c, it can be seen that by varying the height (w) of the cavity₀/w), the sub-resonators can cover the entire 2 pi phase range with a transmission factor greater than 90%.

The sector superstructure includes a first sector resonator, a second sector resonator, a third sector resonator, a fourth sector resonator and a fifth sector resonator which are sequentially distributed, and different helmholtz resonators are selected from the 5 sector resonators (w corresponding to circle in fig. 3 c)₀Value of/w) w₀W in the first, second, third, fourth and fifth sector resonators₀The/w gradually decreases.

Further, since the transmittance of the fourth sector resonator (91%) is slightly lower than that of the other sector resonators (95% or more). By varying the cavity size, w, of the fourth sector resonator_neck＝1.1mm、w₀The transmission increased to 95.3% without changing the phase shift at 6.33 mm. Therefore, the transmission coefficients of the five phase-gradient resonators exceed 95%.

Refer to FIG. 3d and FIG. 3e for lⁱⁿThe simulated plot of the sound field of the incident SVs at ± 1 is substantially identical to the ideal results of fig. 2a and 2 b. It can be seen that lⁱⁿIncident SVs have different scattering processes,/, at + -1^tCan be transmitted from PGM at 1 (see fig. 3d), l^rIs almost reflected back (see fig. 3e) at 1, and therefore, for side-incident vortex sound waves (l)ⁱⁿCan realize OAM separation when SV (l)ⁱⁿ1 or lⁱⁿ-1) at incidence from both left and right sides, an asymmetric transmission of SV in the waveguide can be achieved.

According to the technical scheme, the invention has the following beneficial effects:

the invention discloses a diffraction mechanism of acoustic vortex in a cylindrical waveguide based on a phase gradient super-structure grating, which can predict the scattering behavior of the acoustic vortex, provide a plurality of propagation channels and break through the limitation of twisting a phase single channel;

the acoustic vortex separator based on the angular super-structure surface can realize the asymmetric transmission of acoustic vortex, opens up new possibility for controlling acoustic OAM, and can be applied to various OAM devices, such as a multi-channel OAM converter, an OAM frequency divider, a one-way transmission OAM device, an OAM-based information communication device and the like.

It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein. Any reference sign in a claim should not be construed as limiting the claim concerned.

Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.