CN111785244A - An Acoustic Focusing Fractional Vortex Field Emitter - Google Patents

Abstract

The invention discloses an acoustic focusing fractional vortex field transmitter, comprising a structural plate, wherein a first group of helical grooves and a second group of helical grooves arranged in a concentric axis manner are arranged on the structural plate, and a second group of helical grooves is arranged on the structural plate. The set of helical grooves is located on the periphery of the first set of helical grooves, and a preset distance is set between the helical line of the second set of helical grooves closest to the central axis and the helical line of the first set of helical grooves farthest from the central axis . In the present invention, when the incident ultrasonic wave passes through the acoustically focused fractional vortex field transmitter, the transmitted sound field will focus the ultrasonic wave to generate a fractional vortex field; while focusing the vortex in space, by adjusting the first group of Archimedes spirals The number of grooves and the second group of Archimedes spiral grooves can realize fractional vortices with different topological charges; the structure can also be arbitrarily modulated according to different incident ultrasonic wave lengths. The invention is a passive passive artificial structure, which can modulate the transmission sound field only by its own structure, and is widely used.

Description

An Acoustic Focusing Fractional Vortex Field Emitter

technical field

The invention relates to an acoustic focusing fractional vortex field transmitter, which belongs to the field of acoustic devices.

Background technique

Fractional vortex fields, characterized by radial phase distribution discontinuities, have attracted increasing attention over the past decade. On the one hand, the fractional vortex field has a strong sound intensity region in its asymmetric hollow vortex beam, which can generate force in a certain direction, which is very beneficial for trapping and manipulating particles. On the other hand, it carries orbital angular momentum and is able to transfer the orbital angular momentum to the absorbing object, thereby causing the object to rotate. On this basis, the acoustically focused fractional vortex field has very important value in practical applications because it can provide stronger trapping force, larger moment and deeper penetration depth. How to design an efficient, simple and low-cost acoustically focused fractional vortex field emitter has always been a hot issue in related research fields.

At present, the method of generating the acoustically focused vortex field mainly relies on the active transducer array. The phase shift of each active transducer is controlled by electrical means, and the arrangement shape of the active transducer is physically changed, so that its overall The phase satisfies the phase requirements of the fractional vortex field, and its curved arc surface makes the sound wave meet the requirements of sound wave focusing, so that the entire transducer array can be regarded as a focused fractional vortex field transmitter. The resulting total sound field is the superposition of all active transducer sound fields.

However, relying on the acoustically focused vortex field generated by the active transducer array also has its own shortcomings and deficiencies. First, in order to generate the acoustically focused vortex field, dozens, hundreds or even thousands of active transducers are usually required, and the amplitude and phase of each active transducer are controlled by a complex circuit system, resulting in huge design cost and cumbersomeness. Its operation process greatly limits its application and development. Secondly, in order to achieve the effect of the acoustically focused fractional vortex field, the transducer array is usually arranged into a curved surface, which also limits its application in some special scenarios (for example, a planar structure is required to realize the acoustically focused fractional vortex field). swirl field). Therefore, it is very necessary and important to modulate the incident ultrasonic waves emitted by the transducer through a simple artificial structure to generate focused acoustic fractional vortices with different topological charges.

SUMMARY OF THE INVENTION

The invention provides a transmitter capable of generating an acoustically focused fractional vortex field. The acoustic waves can generate focused acoustic fractions with different topological charges in the propagation direction through the mutual interference between the special diffraction in the helical groove and the transmitted acoustic waves. vortex field.

In order to achieve the above-mentioned purpose, the acoustically focused fractional vortex field transmitter of the present invention includes a structural plate, and the structural plate is provided with a first group of helical grooves and a second group of helical grooves arranged concentrically, The second group of helical grooves is located on the periphery of the first group of helical grooves, and a preset is set between the helical line of the second group of helical grooves closest to the central axis and the helical line of the first group of helical grooves farthest from the central axis spacing.

Preferably, the acoustic impedance of the structural plate is at least 20 times different from the acoustic impedance of the background medium.

和r_II(θ)＝r_I(θ)+d，第二组螺线槽的两根螺线r_III和r_IV的方程为

和r_IV(θ)＝r_III(θ)+d，其中d设置为第一组螺线槽以及第二组螺线槽的宽度，所述宽度小于入射波长，g设置为入射波长，r₀为第一组螺线槽的初始半径，r₁为第二组德螺线槽的初始半径，N为第一组螺线槽以及第二组螺线槽中两根螺线的圈数；m为拓扑荷数，在0到1之间任意取值；θ的取值从0到2π/m。Preferably, the first group of spiral grooves and the second group of spiral grooves each include one spiral groove, and the equations of the two spirals r _I and r _II of the first group of spiral grooves are respectively:

and r _II (θ)=r _I (θ)+d, the equations of the two spirals r _III and r _IV of the second set of spiral grooves are

and r _IV (θ) = r _III (θ) + d, where d is set to the width of the first set of helical grooves and the second set of helical grooves that is less than the incident wavelength, g is set to the incident wavelength, r ₀ is the initial radius of the first group of helical grooves, r ₁ is the initial radius of the second group of helical grooves, N is the number of turns of the first group of helical grooves and the two spirals in the second group of helical grooves; m is the topological charge, which can be any value between 0 and 1; the value of θ ranges from 0 to 2π/m.

和r_II(θ)＝r_I(θ)+d，此时θ的取值从0到2π/m；m为拓扑荷数，在1到2之间任意取值；r₀为第一组螺线槽的初始半径，第一组螺线槽的第2个螺线槽的两根螺线r_III和r_IV的方程分别为

和r_IV(θ)＝r_III(θ)+d，此时θ的取值从2π/m到2π，Preferably, the first group of spiral grooves and the second group of spiral grooves each include two spiral grooves, wherein the two spiral grooves r _I and r of the first spiral groove of the first group of spiral grooves The equations of _II are

and r _II (θ)=r _I (θ)+d, at this time, the value of θ ranges from 0 to 2π/m; m is the topological charge, which can be any value between 1 and 2; r ₀ is the first group The initial radius of the helical groove, the equations of the two spirals r _III and r _IV of the second helical groove of the first group of helical grooves are respectively:

and r _IV (θ)=r _III (θ)+d, at this time, the value of θ ranges from 2π/m to 2π,

和r′_II(θ)＝r′_I(θ)+d，此时θ的取值从0到2π/m；r₁为第二组螺线槽的初始半径，第二组螺线槽的第2个螺线槽的两根螺线r′_III和r′_IV的方程分别为

和r′_IV(θ)＝r′_III(θ)+d，此时θ的取值从0到2π/m；其中d设置为第一组螺线槽以及第二组螺线槽的宽度，所述宽度小于入射波长，N为第一组螺线槽以及第二组螺线槽的圈数，g设置为入射波长。The equations of the two spirals r' _I and r' _II of the first spiral slot of the second group of spiral slots are respectively:

and r′ _II (θ)=r′ _I (θ)+d, at this time, the value of θ ranges from 0 to 2π/m; r ₁ is the initial radius of the second group of helical grooves. The equations of the two spirals r' _III and r' _IV of the second spiral slot are respectively

and r′ _IV (θ)=r′ _III (θ)+d, at this time, the value of θ ranges from 0 to 2π/m; where d is set to the width of the first group of helical grooves and the second group of helical grooves, The width is smaller than the incident wavelength, N is the number of turns of the first group of helical grooves and the second group of helical grooves, and g is set to the incident wavelength.

和r_II(θ)＝r_I(θ)+d，此时θ的取值从2(M-1)π/m到2Mπ/m，m为拓扑荷数，在2到3之间任意取值，r₀为第一组螺线槽的初始半径，M≤2，M为正整数；第一组螺线槽的第3个螺线槽的两根螺线r_III和r_IV的方程分别为

和r_IV(θ)＝r_III(θ)+d，此时θ的取值从4π/m到2π；Preferably, the set of helical grooves and the second set of helical grooves each include three helical grooves, wherein the two helical grooves r _I and r _II of the Mth helical groove of the first set of helical grooves The equations are

and r _II (θ)=r _I (θ)+d, at this time, the value of θ ranges from 2(M-1)π/m to 2Mπ/m, where m is the topological charge, which can be arbitrarily chosen between 2 and 3 value, r ₀ is the initial radius of the first group of helical grooves, M≤2, M is a positive integer; the equations of the two spirals r _III and r _IV of the third helical groove of the first group of helical grooves are respectively for

and r _IV (θ)=r _III (θ)+d, the value of θ is from 4π/m to 2π at this time;

和r′_II(θ)＝r′_I(θ)+d，r₁为第二组螺线槽的初始半径；第二组螺线槽的3个螺线槽的两根螺线r′_III和r′_IV的方程分别为

和r′_IV(θ)＝r′_III(θ)+d，其中d设置为第一组螺线槽以及第二组螺线槽的宽度，所述宽度小于入射波长，N为第一组螺线槽以及第二组螺线槽的圈数，g设置为入射波长。The equations of the two spirals r' _I and r' _II of the M-th spiral slot of the second group of spiral slots are respectively:

and r′ _II (θ)=r′ _I (θ)+d, r ₁ is the initial radius of the second group of helical grooves; the two spirals r′ _III of the three helical grooves of the second group of helical grooves and the equations of r′ _IV are respectively

and r′ _IV (θ)=r′ _III (θ)+d, where d is set to the width of the first set of helical grooves and the second set of helical grooves, the widths being smaller than the incident wavelength, and N is the first set of helical grooves. The number of turns of the wire groove and the second set of helical grooves, and g is set to the incident wavelength.

和r_II(θ)＝r_I(θ)+d，此时θ的取值从2(M-1)π/m到2Mπ/m，m为拓扑荷数，在3到4之间任意取值，r₀为第一组螺线槽的初始半径，M≤3，M为正整数；第一组螺线槽的第4个螺线槽的两根螺线r_III和r_IV的方程分别为

和r_IV(θ)＝r_III(θ)+d，此时θ的取值从6π/m到2π；Preferably, the set of helical grooves and the second set of helical grooves each include 4 helical grooves, wherein the two helical grooves r _I and r _II of the Mth helical groove of the first set of helical grooves The equations are

And r _II (θ)=r _I (θ)+d, the value of θ is from 2(M-1)π/m to 2Mπ/m, m is the topological charge, which can be arbitrarily chosen between 3 and 4 value, r ₀ is the initial radius of the first group of helical grooves, M≤3, M is a positive integer; the equations of the two spirals r _III and r _IV of the fourth helical groove of the first group of helical grooves are respectively for

and r _IV (θ)=r _III (θ)+d, the value of θ is from 6π/m to 2π at this time;

和r′_II(θ)＝r′_I(θ)+d，r₁为第二组螺线槽的初始半径，第二组螺线槽的4个螺线槽的两根螺线r′_III和r′_IV的方程分别为

和r′_IV(θ)＝r′_III(θ)+d，其中d设置为第一组螺线槽以及第二组螺线槽的宽度，所述宽度小于入射波长，N为第一组螺线槽以及第二组螺线槽的圈数，g设置为入射波长。The equations of the two spirals r' _I and r' _II of the M-th spiral slot of the second group of spiral slots are respectively:

and r′ _II (θ)=r′ _I (θ)+d, r ₁ is the initial radius of the second group of helical grooves, and the two spirals r′ _III of the four helical grooves of the second group of helical grooves and the equations of r′ _IV are respectively

and r′ _IV (θ)=r′ _III (θ)+d, where d is set to the width of the first group of helical grooves and the second group of helical grooves, the widths being smaller than the incident wavelength, and N is the first group of helical grooves. The number of turns of the groove and the second set of helical grooves, g is set to the incident wavelength.

Preferably, the first group of spiral grooves are Archimedes spiral grooves.

Preferably, the second group of spiral grooves are Archimedes spiral grooves.

Preferably, the preset distance is half the incident wavelength.

In the present invention, when the incident ultrasonic wave passes through the focused vortex field transmitter, the transmitted sound field will focus the sound wave to generate a fractional vortex field; while focusing the vortex in space, by adjusting the first group of helical grooves and the second group of helical grooves The number of grooves can realize fractional vortex with different topological charges; the acoustically focused fractional vortex field transmitter can also be arbitrarily modulated according to different incident ultrasonic wave lengths. The invention is a passive passive artificial structure, which can modulate the transmission sound field only by its own structure, and is widely used.

Description of drawings

1 is a schematic diagram of the principle of an embodiment of an acoustic focusing vortex field transmitter of the present invention in the x-z plane, wherein FIG. 1(a) is a schematic diagram of the principle in the x-y plane, and FIG. 1(b) is a schematic diagram of the side operation;

Figure 2 is a schematic diagram of the design of an acoustically focused fractional vortex field emitter with a topological charge of 0.5 in the x-y plane;

Figure 3 is a schematic diagram of the design of an acoustically focused fractional vortex field emitter with a topological charge of 1.25 in the x-y plane;

Figure 4 is a schematic diagram of the design of an acoustically focused fractional vortex field emitter with a topological charge of 1.5 in the x-y plane;

Figure 5 is a schematic diagram of the design of an acoustically focused fractional vortex field emitter with a topological charge of 1.75 in the x-y plane;

Figure 6 is a schematic diagram of the design of an acoustically focused fractional vortex field emitter with a topological charge of 2.5 in the x-y plane;

Figure 7 is a schematic diagram of the design of an acoustically focused fractional vortex field emitter with a topological charge of 3.5 in the x-y plane;

Fig. 8 is a simulation distribution diagram of the acoustically focused fractional vortex field emitter of the structure shown in Fig. 2 on the focal plane, wherein Fig. 8(a) is an intensity distribution diagram, and Fig. 8(b) is a phase distribution diagram;

Fig. 9 is a simulation distribution diagram of the acoustically focused fractional vortex field emitter of the structure shown in Fig. 3 on the focal plane, wherein Fig. 9(a) is an intensity distribution diagram, and Fig. 9(b) is a phase distribution diagram;

Fig. 10 is a simulation distribution diagram of the acoustically focused fractional vortex field emitter of the structure shown in Fig. 4 on the focal plane, wherein Fig. 10(a) is an intensity distribution diagram, and Fig. 10(b) is a phase distribution diagram;

Fig. 11 is a simulated distribution diagram of the acoustically focused fractional vortex field emitter of the structure shown in Fig. 5 in the focal plane, wherein Fig. 11(a) is an intensity distribution diagram, and Fig. 11(b) is a phase distribution diagram;

Fig. 12 is a simulation distribution diagram of the acoustically focused fractional vortex field emitter of the structure shown in Fig. 6 in the focal plane, wherein Fig. 12(a) is an intensity distribution diagram, and Fig. 12(b) is a phase distribution diagram;

Fig. 13 is a simulation distribution diagram of the acoustically focused fractional vortex field emitter of the structure shown in Fig. 7 in the focal plane, wherein Fig. 13(a) is an intensity distribution diagram, and Fig. 13(b) is a phase distribution diagram; and

Fig. 14(a), Fig. 14(b), Fig. 14(c), and Fig. 14(d) are the intensity distributions of the focused vortex field on the x-z plane with topological charges of 0.5, 1.5, 2.5, and 3.5, respectively .

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings.

As shown in FIG. 1, it is a schematic diagram of the principle of an embodiment of the acoustically focused fractional vortex field transmitter of the present invention. FIG. 1(a) shows a schematic cross-sectional view of the acoustically focused fractional vortex field transmitter in the x-y plane. This embodiment includes A structural plate, the structural plate is provided with a first group of spiral grooves arranged concentrically, including but not limited to Archimedes spiral grooves (represented by Part I in the figure) and a second group of Archimedes The spiral groove (represented by Part II in the figure), the second group of spiral grooves, including but not limited to the Archimedes spiral grooves are located on the periphery of the first group of Archimedes spiral grooves, and the second group of Archimedes spiral grooves The distance between the helix of the Meadian helical groove closest to the central axis and the helix of the first group of Archimedes helical grooves farthest from the central axis is half the incident wavelength. Figure 1(a) shows a schematic diagram of the side operation of the acoustically focused fractional vortex field transmitter. When the acoustic wave is perpendicularly incident on the transmitter along the z-axis direction, part of the acoustic wave passes through the Archimedes spiral groove and the other part is absorbed by the structural plate. A fractional vortex is formed by the sound waves that pass through each set of Archimedes' spiral grooves, reflected off of the hard surface. When the second group of Archimedes spiral grooves is located on the periphery of the first group of Archimedes spiral grooves, and the helix closest to the central axis of the second group of Archimedes spiral grooves is the same as the first group of Archimedes spiral grooves The distance between the spiral grooves farthest from the central axis is a preset distance, including but not limited to 0.5 wavelengths (represented by 0.5g in the figure), the distance between the two groups of Archimedes spiral grooves. The phase difference should be π. At the same time, the path difference from the two groups of Archimedes spiral grooves to the focusing plane satisfies half a wavelength, so the total phase difference of the transmitted acoustic waves through the two groups of Archimedes spiral grooves is 2π. In this case, the acoustic fractional vortices passing through the two sets of Archimedes spiral grooves will have strong constructive interference in the focusing plane, thus realizing the focused acoustic fractional vortices. Among them, when the preset spacing is an integer multiple of the half wavelength, the generated focused sound fractional vortex is the strongest. When the preset spacing is an integer multiple of the wavelength, the focused sound fractional vortex will not be generated. When the preset spacing is When it is not the half wavelength and the integer multiple of the wavelength, the focused acoustic fractional vortex can be generated and the focus position will move with the change of the preset distance.

和r_II(θ)＝r_I(θ)+d，第二组阿基米德螺线槽的两根螺线r_III和r_IV的方程为

和r_IV(θ)＝r_III(θ)+d。具体实现时，可以但不限于固定d＝0.5mm，N＝4,g＝1.5mm，r₀＝12mm，r₁＝18.75mm，θ的取值从0到2π/0.5。其中，内、外两根螺线和以与中心轴的距离远近来定义，内螺线相对于外螺线与中心轴的距离近(以下各实施例同)。As shown in Figure 2, two sets of Archimedes spiral grooves are opened on the structural board, each group of Archimedes spiral grooves has a spiral groove, and two sets of Archimedes spiral grooves in the first group The equations of the root spirals r _I and r _II are respectively

and r _II (θ)=r _I (θ)+d, the equations of the two spirals r _III and r _IV of the second set of Archimedes' spiral grooves are

and r _IV (θ)=r _III (θ)+d. In specific implementation, d=0.5 mm, N=4, g=1.5 mm, r ₀ =12 mm, r ₁ =18.75 mm may be fixed but not limited to, and the value of θ ranges from 0 to 2π/0.5. The sum of the inner and outer spirals is defined by the distance from the central axis, and the inner spiral is closer to the central axis than the outer spiral (the same in the following embodiments).

和r_II(θ)＝r_I(θ)+d,此时θ的取值从0到2π/1.25。第一组阿基米德螺线槽的第2个螺线槽的两根螺线r_III和r_IV的方程分别为

和r_IV(θ)＝r_III(θ)+d，此时θ的取值从2π/1.25到2π。第二组阿基米德螺线槽除了初始半径r₁与第一组阿基米德螺线槽r₀不同，其它与第一组阿基米德螺线槽有相同的形式。具体实现时，可以但不限于固定d＝0.5mm，N＝4,g＝1.5mm，r₀＝12mm，r₁＝18.75mm。其中，内、外两根螺线和以与中心轴的距离远近来定义，内螺线相对于外螺线与中心轴的距离近(以下各实施例同)。As shown in Figure 3, two sets of Archimedes spiral grooves are opened on the structural board, each group of Archimedes spiral grooves has two spiral grooves, and the first group of Archimedes spiral grooves has two spiral grooves. The equations of the two spirals r _I and r _II of each spiral slot are

And r _II (θ)=r _I (θ)+d, the value of θ is from 0 to 2π/1.25 at this time. The equations of the two spirals r _III and r _IV of the second spiral groove of the first group of Archimedes spiral grooves are respectively

and r _IV (θ)=r _III (θ)+d, where the value of θ ranges from 2π/1.25 to 2π. The second group of Archimedes spiral grooves has the same form as the first group of Archimedes spiral grooves except that the initial radius r ₁ is different from that of the first group of Archimedes spiral grooves r ₀ . In specific implementation, d=0.5 mm, N=4, g=1.5 mm, r ₀ =12 mm, and r ₁ =18.75 mm may be fixed, but not limited to. The sum of the inner and outer spirals is defined by the distance from the central axis, and the inner spiral is closer to the central axis than the outer spiral (the same in the following embodiments).

和r_II(θ)＝r_I(θ)+d,此时θ的取值从0到2π/1.5。第一组阿基米德螺线槽的第2个螺线槽的两根螺线r_III和r_IV的方程分别为

和r_IV(θ)＝r_III(θ)+d，此时θ的取值从2π/1.5到2π。第二组阿基米德螺线槽除了初始半径r₁与第一组阿基米德螺线槽r₀不同，其它与第一组阿基米德螺线槽有相同的形式。具体实现时，可以但不限于固定d＝0.5mm，N＝4,g＝1.5mm，r₀＝12mm，r₁＝18.75mm。其中，内、外两根螺线和以与中心轴的距离远近来定义，内螺线相对于外螺线与中心轴的距离近(以下各实施例同)。As shown in Figure 4, two sets of Archimedes spiral grooves are opened on the structural plate, each group of Archimedes spiral grooves has two spiral grooves, and the first group of Archimedes spiral grooves has two spiral grooves. The equations of the two spirals r _I and r _II of each spiral slot are

And r _II (θ)=r _I (θ)+d, the value of θ is from 0 to 2π/1.5 at this time. The equations of the two spirals r _III and r _IV of the second spiral groove of the first group of Archimedes spiral grooves are respectively

and r _IV (θ)=r _III (θ)+d, where the value of θ ranges from 2π/1.5 to 2π. The second group of Archimedes spiral grooves has the same form as the first group of Archimedes spiral grooves except that the initial radius r ₁ is different from that of the first group of Archimedes spiral grooves r ₀ . In specific implementation, d=0.5 mm, N=4, g=1.5 mm, r ₀ =12 mm, and r ₁ =18.75 mm may be fixed, but not limited to. The sum of the inner and outer spirals is defined by the distance from the central axis, and the inner spiral is closer to the central axis than the outer spiral (the same in the following embodiments).

和r_II(θ)＝r_I(θ)+d,此时θ的取值从0到2π/1.75。第一组阿基米德螺线槽的第2个螺线槽的两根螺线r_III和r_IV的方程分别为

和r_IV(θ)＝r_III(θ)+d，此时θ的取值从2π/1.75到2π。第二组阿基米德螺线槽除了初始半径r₁与第一组阿基米德螺线槽r₀不同，其它与第一组阿基米德螺线槽有相同的形式。具体实现时，可以但不限于固定d＝0.5mm，N＝4,g＝1.5mm，r₀＝12mm，r₁＝18.75mm。其中，内、外两根螺线和以与中心轴的距离远近来定义，内螺线相对于外螺线与中心轴的距离近(以下各实施例同)。As shown in Figure 5, two sets of Archimedes spiral grooves are set on the structural board, each group of Archimedes spiral grooves has two spiral grooves, and the first group of Archimedes spiral grooves is the first The equations of the two spirals r _I and r _II of each spiral slot are

And r _II (θ)=r _I (θ)+d, the value of θ is from 0 to 2π/1.75 at this time. The equations of the two spirals r _III and r _IV of the second spiral groove of the first group of Archimedes spiral grooves are respectively

and r _IV (θ)=r _III (θ)+d, where the value of θ ranges from 2π/1.75 to 2π. The second group of Archimedes spiral grooves has the same form as the first group of Archimedes spiral grooves except that the initial radius r ₁ is different from that of the first group of Archimedes spiral grooves r ₀ . In specific implementation, d=0.5 mm, N=4, g=1.5 mm, r ₀ =12 mm, and r ₁ =18.75 mm may be fixed, but not limited to. The sum of the inner and outer spirals is defined by the distance from the central axis, and the inner spiral is closer to the central axis than the outer spiral (the same in the following embodiments).

和r_II(θ)＝r_I(θ)+d，此时θ的取值从2(M-1)π/2.5到2Mπ/2.5，M≤2，M为正整数。第一组阿基米德螺线槽的第3个螺线槽的两根螺线r_III和r_IV的方程分别为

和r_IV(θ)＝r_III(θ)+d，此时θ的取值从4π/2.5到2π。第二组阿基米德螺线槽除了初始半径r₁与第一组阿基米德螺线槽r₀不同，其它与第一组阿基米德螺线槽有相同的形式。具体实现时，可以但不限于固定d＝0.5mm，N＝4,g＝1.5mm，r₀＝12mm，r₁＝18.75mm。其中，内、外两根螺线和以与中心轴的距离远近来定义，内螺线相对于外螺线与中心轴的距离近(以下各实施例同)。As shown in Figure 6, two sets of Archimedes spiral grooves are opened on the structural board, each group of Archimedes spiral grooves has three spiral grooves, and the Mth of the first group of Archimedes spiral grooves The equations of the two spirals r _I and r _II of the spiral groove are respectively

and r _II (θ)=r _I (θ)+d, at this time, the value of θ ranges from 2(M-1)π/2.5 to 2Mπ/2.5, M≤2, and M is a positive integer. The equations of the two spirals r _III and r _IV of the third spiral slot of the first group of Archimedes spiral slots are respectively

and r _IV (θ)=r _III (θ)+d, where the value of θ ranges from 4π/2.5 to 2π. The second group of Archimedes spiral grooves has the same form as the first group of Archimedes spiral grooves except that the initial radius r ₁ is different from that of the first group of Archimedes spiral grooves r ₀ . In specific implementation, d=0.5 mm, N=4, g=1.5 mm, r ₀ =12 mm, and r ₁ =18.75 mm may be fixed, but not limited to. The sum of the inner and outer spirals is defined by the distance from the central axis, and the inner spiral is closer to the central axis than the outer spiral (the same in the following embodiments).

和r_II(θ)＝r_I(θ)+d，此时θ的取值从2(M-1)π/3.5到2Mπ/3.5，M≤3，M为正整数。第一组螺线槽的第4个螺线槽的两根螺线r_III和r_IV的方程分别为

和r_IV(θ)＝r_III(θ)+d，此时θ的取值从6π/3.5到2π。第二组阿基米德螺线槽除了初始半径r₁与第一组阿基米德螺线槽r₀不同，其它与第一组阿基米德螺线槽有相同的形式。具体实现时，可以但不限于固定d＝0.5mm，N＝4,g＝1.5mm，r₀＝12mm，r₁＝18.75mm。其中，内、外两根螺线和以与中心轴的距离远近来定义，内螺线相对于外螺线与中心轴的距离近(以下各实施例同)。As shown in Figure 7, two sets of Archimedes spiral grooves are set on the structural board, each group of Archimedes spiral grooves has four spiral grooves, and the Mth of the first group of Archimedes spiral grooves is The equations of the two spirals r _I and r _II of each spiral slot are

and r _II (θ)=r _I (θ)+d, at this time, the value of θ ranges from 2(M-1)π/3.5 to 2Mπ/3.5, M≤3, and M is a positive integer. The equations of the two spirals r _III and r _IV of the fourth spiral slot of the first group of spiral slots are respectively

and r _IV (θ)=r _III (θ)+d, where the value of θ ranges from 6π/3.5 to 2π. The second group of Archimedes spiral grooves has the same form as the first group of Archimedes spiral grooves except that the initial radius r ₁ is different from that of the first group of Archimedes spiral grooves r ₀ . In specific implementation, d=0.5mm, N=4, g=1.5mm, r ₀ =12mm, and r ₁ =18.75mm may be fixed, but not limited to. The sum of the inner and outer spirals is defined by the distance from the central axis, and the inner spiral is closer to the central axis than the outer spiral (the same in the following embodiments).

The four transmitters shown in Figures 2 to 7 are simulated, the background medium is set to water, the frequency of incident ultrasonic waves is fixed to 1MHz, and the material coefficient of the structural plate is set to stainless steel. As shown in Fig. 8 to Fig. 13 , the corresponding structural plates have a topological charge of 0.5 at 1 MHz and in a focal plane (such as but not limited to a plane 5.4 incident wavelengths (λ) away from the exit plane). Intensity profile and phase profile of the focused acoustic fractional vortex at 1.25, 1.5, 1.75, 2.5, 3.5. The high-intensity acoustic energy is concentrated on an asymmetrical ring and the circumference of the asymmetrical ring gradually increases with the increase of the topological charge. At the same time, the phase singularity shift and more and more phase changes appear in the corresponding phase distribution within a circle, and these acoustic characteristics are consistent with the properties of the acoustic fractional vortex field of the corresponding topological charge, illustrating Fig. 2-Fig. The acoustically focused fractional vortex field transmitters of the six structures shown in 7 can well modulate the incident ultrasonic waves in the focal plane to generate a focused fractional vortex field.

As shown in Figure 10, the intensity distributions of the focused acoustic fractional vortices with topological charges of 0.5, 1.5, 2.5, and 3.5 generated by the corresponding structural plates at 1 MHz and in the x-z plane, respectively. The background medium was set as water, the frequency of the incident acoustic wave was fixed at 1 MHz, and the material coefficient of the structural plate was set as stainless steel. Most of the acoustic energy is concentrated in a region of finite length in the z direction and with the increase of the topological charge, the two regions of finite length will split into two and the distance between the two regions will gradually increase. These acoustic features are consistent with the properties of the acoustically focused fractional vortex fields of the corresponding topological charges. This shows that our designed transmitter can modulate the incident ultrasonic wave in the propagation direction to generate the required focused ultrasonic fractional vortex field.

The acoustically focused vortex field transmitter of each embodiment of the present invention is a planar structure, and its thickness in the propagation direction has little effect on the results. The thickness of the transmitter can be changed according to actual needs. When the incident ultrasonic wave passes through the acoustic fractional vortex field transmitter, the transmitted sound field will generate an ultrasonic focused fractional vortex; while focusing the fractional vortex in space, by adjusting the number of Archimedes spiral grooves in each group, Focused acoustic fractional vortices with different topological charges can be realized. Each embodiment of the acoustic vortex field transmitter can also be arbitrarily modulated according to different incident ultrasonic wave lengths. The invention is a passive passive artificial structure, which can modulate the transmission sound field only by its own structure, and then can produce different propagation directions through the special diffraction in the spiral groove and the mutual interference between the transmission sound waves. Acoustic fractional vortex field of topological charge, which has a wide range of applications.

The above is only the preferred embodiment of the present invention, it should be pointed out: for those of ordinary skill in the technical field, on the premise of not departing from the principle of the present invention, several improvements and modifications can also be made, and these improvements and modifications should also be It is regarded as the protection scope of the present invention.

Claims (9)

1. an acoustic focusing fractional vortex field transmitter, characterized in that: comprising a structural plate, the structural plate is provided with a first group of helical grooves and a second group of helical grooves that are arranged in a concentric axis mode, The second group of helical grooves is located on the periphery of the first group of helical grooves, and a pre-set is set between the helical line of the second group of helical grooves closest to the central axis and the helical line of the first group of helical grooves farthest from the central axis Set the spacing. 2 . The acoustically focused fractional vortex field transmitter according to claim 1 , wherein the acoustic impedance of the structural plate is at least 20 times different from the acoustic impedance of the background medium. 3 . 3. The acoustically focused fractional vortex field transmitter according to claim 2, wherein the first group of helical grooves and the second group of helical grooves each comprise one helical groove, and the first group of helical grooves The equations of the two spirals r _I and r _II are respectively

and r _II (θ)=r _I (θ)+d, the equations of the two spirals r _III and r _IV of the second set of spiral grooves are

and r _IV (θ)=r _III (θ)+d, where d is the width of the first set of helical grooves and the second set of helical grooves, and the width is smaller than the incident wavelength, g is the incident wavelength, and r ₀ is the first The initial radius of a group of spiral grooves, r ₁ is the initial radius of the second group of spiral grooves, N is the number of turns of the first group of spiral grooves and the two spiral grooves in the second group of spiral grooves, m is the topology The number of charges, which can be any value between 0 and 1; the value of θ ranges from 0 to 2π/m. 4. The acoustically focused fractional vortex field transmitter according to claim 2, wherein the first group of helical grooves and the second group of helical grooves each comprise two helical grooves, wherein, The equations of the two spirals r _I and r _II of the first spiral slot of the first group of spiral slots are respectively

and r _II (θ)=r _I (θ)+d, at this time, the value of θ ranges from 0 to 2π/m; m is the topological charge, which can be any value between 1 and 2; r ₀ is the first group The initial radius of the helical groove; the equations of the two spirals r _III and r _IV of the second helical groove of the first group of helical grooves are respectively

and r _IV (θ)=r _III (θ)+d, the value of θ is from 2π/m to 2π at this time; The equations of the two spirals r' _I and r' _II of the first spiral slot of the second group of spiral slots are respectively:

and r′ _II (θ)=r′ _I (θ)+d, at this time, the value of θ ranges from 0 to 2π/m; r ₁ is the initial radius of the second group of helical grooves. The equations of the two spirals r' _III and r' _IV of the second spiral slot are respectively

and r′ _IV (θ)=r′ _III (θ)+d, at this time, the value of θ ranges from 0 to 2π/m; where d is the width of the first group of spiral grooves and the second group of spiral grooves, so The width is smaller than the incident wavelength, N is the number of turns of the first group of helical grooves and the second group of helical grooves, and g is set to the incident wavelength. 5 . The acoustically focused fractional vortex field transmitter according to claim 2 , wherein the set of helical grooves and the second set of helical grooves each comprise 3 helical grooves, wherein, 6 . The equations of the two spirals r _I and r _II of the M-th spiral groove of the first group of spiral grooves are respectively:

and r _II (θ)=r _I (θ)+d, at this time, the value of θ ranges from 2(M-1)π/m to 2Mπ/m; m is the topological charge, which can be arbitrarily chosen between 2 and 3 value; r ₀ is the initial radius of the first group of helical grooves, M≤2, M is a positive integer; the equations of the two spirals r _III and r _IV of the three helical grooves of the first group of helical grooves are respectively

and r _IV (θ)=r _III (θ)+d, the value of θ is from 4π/m to 2π at this time; The equations of the two spirals r' _I and r' _II of the M-th spiral slot of the second group of spiral slots are respectively:

and r′ _II (θ)=r′ _I (θ)+d, r ₁ is the initial radius of the second group of helical grooves; the two spirals r′ _III of the three helical grooves of the second group of helical grooves and the equations of r′ _IV are respectively

and r′ _IV (θ)=r′ _III (θ)+d; where d is set to the width of the first group of helical grooves and the second group of helical grooves, the width is less than the incident wavelength, and N is the first group of helical grooves. The number of turns of the wire groove and the second set of helical grooves, and g is set to the incident wavelength. 6. The acoustically focused fractional vortex field transmitter according to claim 2, wherein the set of helical grooves and the second set of helical grooves each comprise 4 helical grooves, wherein, The equations of the two spirals r _I and r _II of the M-th spiral groove of the first group of spiral grooves are respectively:

and r _II (θ)=r _I (θ)+d, at this time, the value of θ ranges from 2(M-1)π/m to 2Mπ/m; m is the topological charge, which can be arbitrarily selected between 3 and 4 value; r ₀ is the initial radius of the first group of helical grooves, M≤3, M is a positive integer; the equations of the two spirals r _III and r _IV of the four helical grooves of the first group of helical grooves are respectively

and r _IV (θ)=r _III (θ)+d, the value of θ is from 6π/m to 2π at this time; The equations of the two spirals r' _I and r' _II of the M-th spiral slot of the second group of spiral slots are respectively:

and r′ _II (θ)=r′ _I (θ)+d, r ₁ is the initial radius of the second group of helical grooves, and the two spirals r′ _III of the four helical grooves of the second group of helical grooves and the equations of r′ _IV are respectively

and r′ _IV (θ)=r′ _III (θ)+d, where d is set to the width of the first set of helical grooves and the second set of helical grooves, the widths being smaller than the incident wavelength, and N is the first set of helical grooves. The number of turns of the wire groove and the second set of helical grooves, and g is set to the incident wavelength. 7 . The acoustically focused fractional vortex field transmitter according to claim 1 , wherein the first group of helical grooves is an Archimedes helical groove. 8 . 8 . The acoustically focused fractional vortex field transmitter of claim 1 , wherein the second group of helical grooves is an Archimedes helical groove. 9 . 9 . The acoustically focused fractional vortex field transmitter according to claim 1 , wherein the preset distance is half an incident wavelength. 10 .

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