CN111785244A - Acoustic focusing fraction vortex field transmitter - Google Patents
Acoustic focusing fraction vortex field transmitter Download PDFInfo
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Abstract
The invention discloses an acoustic focusing fractional vortex field transmitter, which comprises a structural plate, wherein a first group of spiral grooves and a second group of spiral grooves which are arranged in a concentric shaft mode are arranged on the structural plate, the second group of spiral grooves are positioned on the periphery of the first group of spiral grooves, and a preset distance is arranged between a spiral line of the second group of spiral grooves, which is closest to a central shaft, and a spiral line of the first group of spiral grooves, which is farthest from the central shaft. When incident ultrasonic waves pass through the acoustic focusing fractional vortex field transmitter, a transmission sound field transmits the focused ultrasonic waves to generate a fractional vortex field; while the vortex is focused in the space, fractional vortices with different topological charge numbers can be realized by adjusting the number of the first group of Archimedes spiral grooves and the second group of Archimedes spiral grooves; the structure can also be arbitrarily modulated according to different incident ultrasonic wavelengths. The passive artificial structure can modulate a transmission sound field only by the structure of the passive artificial structure, and is widely applied.
Description
Technical Field
The invention relates to an acoustic focusing fractional vortex field transmitter, belonging to the field of acoustic devices.
Background
Fractional vortex fields, which are characterized by radial phase distribution discontinuities, have attracted increasing attention over the past decade. On one hand, the fractional vortex field has a strong acoustic intensity region in an asymmetric hollow vortex optical beam, and can generate force in a certain direction, which is very beneficial to capture and manipulate particles. On the other hand it carries orbital angular momentum and can transfer it to the absorbed object, causing it to rotate. On the basis, the acoustic focusing fractional vortex field has very important value in practical application because the acoustic focusing fractional vortex field can provide stronger capture force, larger moment and deeper penetration depth. How to design an efficient, simple and low-cost acoustic focusing fractional vortex field transmitter is always a hot issue in the relevant research field.
At present, the mode of generating an acoustic focusing vortex field mainly depends on an active transducer array, the phase offset of each active transducer is controlled through an electrical means, and the arrangement shape of the active transducers is physically changed, so that the integral phase meets the requirement of fractional vortex field phase, and the curved arc surface of the active transducers enables sound waves to meet the requirement of sound wave focusing, thereby the whole transducer array can be regarded as a focusing fractional vortex field transmitter. The total sound field produced is the superposition of all active transducer sound fields.
However, relying on the acoustic focusing vortex field generated by the active transducer array has its own drawbacks and deficiencies. Firstly, tens of hundreds or even thousands of active transducers are usually required to generate the acoustic focusing vortex field, and the amplitude and phase of each active transducer are controlled by a complex circuit system, so that the application and development of the active transducer are greatly limited by huge design cost and complicated operation flow. Secondly, to achieve the effect of the fractional vortex field of acoustic focus, the transducer array is usually curved, which limits its application in some special scenarios (e.g. a planar structure is required to achieve the fractional vortex field of acoustic focus). It is therefore necessary and important to modulate the incident ultrasound emitted by the transducer with a simple artificial structure to produce focused acoustic fractional vortices of different topological charge numbers.
Disclosure of Invention
The invention provides a transmitter capable of generating an acoustic focusing fractional vortex field, wherein sound waves can generate focusing acoustic fractional vortex fields with different topological charge numbers in a propagation direction through mutual interference between special diffraction and transmission sound waves in a spiral groove.
In order to achieve the above object, the fractional vortex field transmitter for acoustic focusing of the present invention includes a structural plate, wherein the structural plate is provided with a first group of spiral grooves and a second group of spiral grooves which are arranged on the same central axis, the second group of spiral grooves is located at the periphery of the first group of spiral grooves, and a preset distance is provided between a spiral line of the second group of spiral grooves closest to the central axis and a spiral line of the first group of spiral grooves farthest from the central axis.
Preferably, the acoustic impedance of the structural plate differs from the acoustic impedance of the background medium by a factor of at least 20.
Preferably, the first set of spiral grooves and the second set of spiral grooves each comprise one spiral groove, and the two spirals r of the first set of spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, two spirals r of the second set of spiral groovesIIIAnd rIVIs given by the equation
And rIV(θ)＝rIII(θ) + d, where d is set to the width of the first set of spiral grooves and the second set of spiral grooves, the width being smaller than the incident wavelength, g is set to the incident wavelength, r is set to the incident wavelength0Is the initial radius of the first set of helical grooves, r1The initial radius of the second set of spiral grooves is defined, and N is the number of turns of two spirals in the first set of spiral grooves and the second set of spiral grooves; m is a topological charge number and is arbitrarily selected from 0 to 1; the value of theta is from 0 to 2 pi/m.
Preferably, the first set of spiral grooves and the second set of spiral grooves each include 2 spiral groovesWherein two spirals r of the 1 st spiral groove of the first set of spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, where theta is from 0 to 2 pi/m; m is topological charge number and is arbitrarily selected from 1 to 2; r is0Two spirals r of the 2 nd spiral groove of the first set of spiral grooves are the initial radius of the first set of spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, where theta takes a value from 2 pi/m to 2 pi,
two spirals r 'of the 1 st of the second set of spiral grooves'IAnd r'IIAre respectively as
And r'II(θ)＝r′I(theta) + d, where theta is from 0 to 2 pi/m; r is1Two spirals r 'of the 2 nd spiral slot of the second set of spiral slots being the initial radius of the second set of spiral slots'IIIAnd r'IVAre respectively as
And r'IV(θ)＝r′III(theta) + d, where theta is from 0 to 2 pi/m; wherein d is set to the width of the first group of spiral grooves and the second group of spiral grooves, the width is smaller than the incident wavelength, N is the number of turns of the first group of spiral grooves and the second group of spiral grooves, and g is set to the incident wavelength.
Preferably, the set of spiral grooves and the second set of spiral grooves each include 3 spiral grooves, wherein two spirals r of the mth spiral groove of the first set of spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, where theta is from 2(M-1) pi/M to 2M pi/M, M is topological charge number and is arbitrarily chosen between 2 and 3, r is0The initial radius of the first group of spiral grooves is defined, M is less than or equal to 2 and is a positive integer; two spirals r of the 3 rd spiral groove of the first set of spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, where theta takes on a value from 4 pi/m to 2 pi;
two spirals r 'of the Mth of the second set of spiral grooves'IAnd r'IIAre respectively as
And r'II(θ)＝r′I(θ)+d，r1The initial radius of the second set of spiral grooves; two spirals r 'of 3 spiral slots of the second set of spiral slots'IIIAnd r'IVAre respectively as
And r'IV(θ)＝r′III(θ) + d, where d is set to the width of the first and second set of spiral grooves, which is less than the incident wavelength, N is the number of turns of the first and second set of spiral grooves, and g is set to the incident wavelength.
Preferably, the set of spiral grooves and the second set of spiral grooves each include 4 spiral grooves, wherein two spirals r of the mth spiral groove of the first set of spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, where theta is from 2(M-1) pi/M to 2M pi/M, M is the topological charge number and is arbitrarily chosen between 3 and 4, r is0The initial radius of the first group of spiral grooves is defined, M is less than or equal to 3 and is a positive integer; two spirals r of the 4 th spiral groove of the first set of spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, where theta takes on values from 6 pi/m to 2 pi;
two spirals r 'of the Mth of the second set of spiral grooves'IAnd r'IIAre respectively as
And r'II(θ)＝r′I(θ)+d，r1Two spirals r 'of the 4 spiral slots of the second set of spiral slots being an initial radius of the second set of spiral slots'IIIAnd r'IVAre respectively as
And r'IV(θ)＝r′III(θ) + d, where d is set to the width of the first and second set of spiral grooves, which is less than the incident wavelength, N is the number of turns of the first and second set of spiral grooves, and g is set to the incident wavelength.
Preferably, the first set of spiral slots are archimedes spiral slots.
Preferably, the second set of spiral grooves are archimedes spiral grooves.
Preferably, the preset spacing is half the incident wavelength.
When incident ultrasonic waves pass through the focusing vortex field emitter, the transmission sound field generates focusing sound waves into a fractional vortex field; while the vortex is focused in the space, fractional vortices with different topological charge numbers can be realized by adjusting the number of the first group of spiral grooves and the second group of spiral grooves; the acoustic focusing fractional vortex field emitter can also be arbitrarily modulated according to different incident ultrasonic wavelengths. The passive artificial structure can modulate a transmission sound field only by the structure of the passive artificial structure, and is widely applied.
Drawings
FIG. 1 is a schematic diagram of an embodiment of an acoustic focusing vortex field emitter of the present invention in the x-z plane, wherein FIG. 1(a) is a schematic diagram in the x-y plane and FIG. 1(b) is a schematic diagram of a side view;
FIG. 2 is a schematic design diagram in the x-y plane of an acoustic focus fractional vortex field emitter producing a topological charge number of 0.5;
FIG. 3 is a schematic design diagram in the x-y plane of an acoustic focus fractional vortex field emitter producing a topological charge number of 1.25;
FIG. 4 is a schematic design diagram in the x-y plane of an acoustic focus fractional vortex field emitter producing a topological charge number of 1.5;
FIG. 5 is a schematic design diagram in the x-y plane of an acoustic focus fractional vortex field emitter producing a topological charge number of 1.75;
FIG. 6 is a schematic design diagram in the x-y plane of an acoustic focus fractional vortex field emitter producing a topological charge number of 2.5;
FIG. 7 is a schematic design diagram in the x-y plane of an acoustic focus fractional vortex field emitter producing a topological charge number of 3.5;
FIG. 8 is a simulated distribution plot at the focal plane of the acoustic fractional vortex field transmitter of the configuration shown in FIG. 2, wherein FIG. 8(a) is an intensity distribution plot and FIG. 8(b) is a phase distribution plot;
FIG. 9 is a simulated distribution plot at the focal plane of the acoustic fractional vortex field transmitter of the configuration shown in FIG. 3, wherein FIG. 9(a) is an intensity distribution plot and FIG. 9(b) is a phase distribution plot;
FIG. 10 is a simulated distribution plot at the focal plane of the acoustic fractional vortex field transmitter of the configuration shown in FIG. 4, wherein FIG. 10(a) is an intensity distribution plot and FIG. 10(b) is a phase distribution plot;
FIG. 11 is a simulated distribution plot at the focal plane of the acoustic fractional vortex field transmitter of the configuration shown in FIG. 5, wherein FIG. 11(a) is an intensity distribution plot and FIG. 11(b) is a phase distribution plot;
FIG. 12 is a simulated distribution plot at the focal plane of the acoustic fractional vortex field transmitter of the configuration shown in FIG. 6, wherein FIG. 12(a) is an intensity distribution plot and FIG. 12(b) is a phase distribution plot;
FIG. 13 is a simulated distribution plot at the focal plane of the acoustic fractional vortex field transmitter of the configuration shown in FIG. 7, wherein FIG. 13(a) is an intensity distribution plot and FIG. 13(b) is a phase distribution plot; and
FIG. 14(a), FIG. 14(b), FIG. 14(c), and FIG. 14(d) are intensity profiles in the x-z plane of the focused vortex field with topological charge numbers of 0.5, 1.5, 2.5, and 3.5, respectively.
Detailed Description
The invention will be further described with reference to the accompanying drawings.
Referring to fig. 1, which is a schematic diagram of an embodiment of an acoustic focusing fractional vortex field emitter according to the present invention, fig. 1(a) shows a schematic cross-sectional view of the acoustic focusing fractional vortex field emitter in an x-y plane, and this embodiment includes a structural plate, on which a first set of spiral grooves disposed concentrically with a central axis is disposed, including but not limited to archimedean spiral grooves (denoted by Part I in the figure) and a second set of archimedean spiral grooves (denoted by Part II in the figure), the second set of spiral grooves, including but not limited to archimedean spiral grooves, is disposed at the periphery of the first set of archimedean spiral grooves, and a spiral line of the second set of archimedean spiral grooves closest to the central axis is spaced from a spiral line of the first set of archimedean spiral grooves farthest from the central axis by half of an incident wavelength. Fig. 1(a) shows a schematic side view of an acoustic focusing fractional vortex field emitter, when a sound wave is vertically incident to the emitter along the z-axis, part of the sound wave passes through the archimedes spiral grooves and the other part of the sound wave is reflected by the hard surface of the structural plate, and the sound wave passing through each set of archimedes spiral grooves forms a fractional vortex. When the second set of archimedes spiral grooves is located at the periphery of the first set of archimedes spiral grooves, and the distance between the spiral line of the second set of archimedes spiral grooves closest to the central axis and the spiral line of the first set of archimedes spiral grooves farthest from the central axis is a preset distance, including but not limited to 0.5 wavelength (represented by 0.5g in the figure), the phase difference between the two sets of archimedes spiral grooves should be pi. Meanwhile, the path difference from the two sets of Archimedes spiral grooves to the focusing plane meets half wavelength, so that the total phase difference of the transmitted sound waves penetrating through the two sets of Archimedes spiral grooves is 2 pi. In this case, the acoustic fractional vortices that pass through the two sets of archimedes spiral grooves will interfere constructively strongly in the focal plane, thus achieving focused acoustic fractional vortices. When the preset distance is not the integral multiple of the half wavelength and the wavelength, the focusing sound fractional vortex can be generated, and the focusing position can move along with the change of the preset distance.
As shown in fig. 2, two sets of archimedes spiral grooves are formed in the structural plate, one spiral groove is formed in each set of archimedes spiral grooves, and two spirals r of the first set of archimedes spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, two spirals r of the second set of Archimedes spiral groovesIIIAnd rIVIs given by the equation
And rIV(θ)＝rIII(θ) + d. In specific implementations, d may be fixed to 0.5mm, N may be fixed to 4, g may be fixed to 1.5mm, and r may be fixed to 40＝12mm，r118.75mm, theta is from 0 to 2 pi/0.5. The inner and outer spiral lines are defined as being close to the central axis, and the inner spiral line is close to the central axis relative to the outer spiral line (the same applies to the following embodiments).
As shown in figure 3, two groups of Archimedes spiral grooves are formed in the structural plate, each group of Archimedes spiral grooves is provided with two spiral grooves, and two spirals r of the 1 st spiral groove of the first group of Archimedes spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, in which case theta is taken from 0 to 2 pi/1.25. Two spirals r of the 2 nd spiral groove of the first set of archimedes spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, in which case theta takes a value from 2 pi/1.25 to 2 pi. The second set of Archimedes spiral grooves except for the initial radius r1With a first set of Archimedes spiral grooves r0Otherwise, the other sets have the same form as the first set of archimedes' spiral grooves. In specific implementations, d may be fixed to 0.5mm, N may be fixed to 4, g may be fixed to 1.5mm, and r may be fixed to 40＝12mm，r118.75 mm. The inner and outer spiral lines are defined as being close to the central axis, and the inner spiral line is close to the central axis relative to the outer spiral line (the same applies to the following embodiments).
As shown in FIG. 4, two sets of Archimedes spiral grooves are formed on the structural plate, each set of Archimedes spiral grooves has two spiral grooves, and two spirals r of the 1 st spiral groove of the first set of Archimedes spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, in which case theta is taken from 0 to 2 pi/1.5. Two spirals r of the 2 nd spiral groove of the first set of archimedes spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, in which case theta takes a value from 2 pi/1.5 to 2 pi. The second set of Archimedes spiral grooves except for the initial radius r1With a first set of Archimedes spiral grooves r0Otherwise, the other sets have the same form as the first set of archimedes' spiral grooves. In specific implementations, d may be fixed to 0.5mm, N may be fixed to 4, g may be fixed to 1.5mm, and r may be fixed to 40＝12mm，r118.75 mm. The inner and outer spiral lines are defined as being close to the central axis, and the inner spiral line is close to the central axis relative to the outer spiral line (the same applies to the following embodiments).
As shown in FIG. 5, two sets of Archimedes spiral grooves are formed on the structural plate, each set of Archimedes spiral grooves has two spiral grooves, and two spirals r of the 1 st spiral groove of the first set of Archimedes spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, in which case theta is taken from 0 to 2 pi/1.75. Two spirals r of the 2 nd spiral groove of the first set of archimedes spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, in which case theta takes a value from 2 pi/1.75 to 2 pi. The second set of Archimedes spiral grooves except for the initial radius r1With a first set of Archimedes spiral grooves r0Otherwise, the other sets have the same form as the first set of archimedes' spiral grooves. In specific implementations, d may be fixed to 0.5mm, N may be fixed to 4, g may be fixed to 1.5mm, and r may be fixed to 40＝12mm，r118.75 mm. The inner and outer spiral lines are defined as being close to the central axis, and the inner spiral line is close to the central axis relative to the outer spiral line (the same applies to the following embodiments).
As shown in FIG. 6, two sets of Archimedes spiral grooves are formed on the structural plate, each set of Archimedes spiral grooves has three spiral grooves, and two spirals r of the Mth spiral groove of the first set of Archimedes spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rIAnd (theta) + d, wherein the value of theta is from 2(M-1) pi/2.5 to 2M pi/2.5, M is less than or equal to 2, and M is a positive integer. Two spirals r of the 3 rd spiral groove of the first set of Archimedes spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, in which case theta takes a value from 4 pi/2.5 to 2 pi. The second set of Archimedes spiral grooves except for the initial radius r1With a first set of Archimedes spiral grooves r0Otherwise, the other sets have the same form as the first set of archimedes' spiral grooves. When specifically implemented, canBut are not limited to, fixed d 0.5mm, N4, g 1.5mm, r0＝12mm，r118.75 mm. The inner and outer spiral lines are defined as being close to the central axis, and the inner spiral line is close to the central axis relative to the outer spiral line (the same applies to the following embodiments).
As shown in fig. 7, two groups of archimedes spiral grooves are formed in the structural plate, each group of archimedes spiral grooves has four spiral grooves, and two spirals r of the mth spiral groove of the first group of archimedes spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rIAnd (theta) + d, wherein the value of theta is from 2(M-1) pi/3.5 to 2M pi/3.5, M is less than or equal to 3, and M is a positive integer. Two spirals r of the 4 th spiral groove of the first set of spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, in which case theta takes a value from 6 pi/3.5 to 2 pi. The second set of Archimedes spiral grooves except for the initial radius r1With a first set of Archimedes spiral grooves r0Otherwise, the other sets have the same form as the first set of archimedes' spiral grooves. In specific implementations, d may be fixed to 0.5mm, N may be fixed to 4, g may be fixed to 1.5mm, and r may be fixed to 40＝12mm，r118.75 mm. The inner and outer spiral lines are defined as being close to the central axis, and the inner spiral line is close to the central axis relative to the outer spiral line (the same applies to the following embodiments).
The four transmitters of fig. 2 to 7 were simulated, the background medium was set to water, the frequency of the incident ultrasonic wave was fixed at 1MHz, and the material coefficient of the structural plate was set to stainless steel. As shown in fig. 8-13, the intensity and phase profiles of the focused acoustic fractional vortices generated by the corresponding structured plate at 1MHz with topological charge numbers of 0.5, 1.25, 1.5, 1.75, 2.5, 3.5 in the focal plane (such as, but not limited to, the plane 5.4 incident wavelengths (λ) from the exit face), respectively. The high intensity sound energy is concentrated and distributed on an asymmetrical circular ring, and the circumference of the asymmetrical circular ring is gradually increased along with the increase of the topological charge number. Meanwhile, the corresponding phase distribution has phase singularity shift and varied phase change in a circle, and the acoustic characteristics are matched with the properties of the acoustic fractional vortex field with corresponding topological charge number, which shows that the acoustic focusing fractional vortex field transmitter with the six structures shown in fig. 2-7 can well modulate incident ultrasonic waves in a focusing plane to generate the focusing fractional vortex field.
As shown in fig. 10, intensity profiles of focused acoustic fractional vortices with topological charge numbers of 0.5, 1.5, 2.5, 3.5 are generated in the x-z plane for the corresponding structural plates, respectively, at 1 MHz. The background medium was water, the frequency of the incident acoustic wave was fixed to 1MHz, and the material coefficient of the structural plate was stainless steel. Most of the acoustic energy is concentrated in a region of finite length in the z-direction and as the topological charge number increases the two regions of finite length will split into two and the distance between the two regions will gradually increase. These acoustic characteristics are matched with the properties of the acoustic focus fractional vortex field of the corresponding topological charge number. This illustrates that the transmitter we designed is able to modulate the incident ultrasound wave in the propagation direction to produce the required focused ultrasound fractional vortex field.
The acoustic focusing vortex field emitter of each embodiment of the invention is a plane structure, the thickness of the emitter in the transmission direction has almost no influence on the result, the thickness of the emitter can be changed according to the actual requirement, and when the incident ultrasonic wave emitted by the transducer passes through the acoustic fractional vortex field emitter, the transmission sound field generates ultrasonic focusing fractional vortex; while the fractional vortexes are focused in space, the focused acoustic fractional vortexes with different topological charge numbers can be realized by adjusting the number of the Archimedes spiral grooves of each group. The present acoustic vortex field emitter embodiments can also be arbitrarily modulated according to different incident ultrasound wavelengths. The passive artificial structure can modulate a transmission sound field only by the structure of the passive artificial structure, and further can generate acoustic fraction vortex fields with different topological charge numbers in a transmission direction through the mutual interference between special diffraction in a spiral groove and transmission sound waves, so that the passive artificial structure has a wide application range.
The above description is only of the preferred embodiments of the present invention, and it should be noted that: it will be apparent to those skilled in the art that various modifications and adaptations can be made without departing from the principles of the invention, and such modifications and adaptations are intended to be within the scope of the invention.
Claims (9)
1. An acoustic focus fractional vortex field transmitter, comprising: including a structural slab, be provided with the first group's spiral groove and the second group's spiral groove that set up according to the same center pin mode on the structural slab, the second group's spiral groove is located the periphery of first group's spiral groove, and sets up the preset interval between the helix that the second group's spiral groove is nearest apart from the center pin and the helix that first group's spiral groove is farthest apart from the center pin.
2. The acoustic focus fractional vortex field emitter of claim 1, wherein: the acoustic impedance of the structural plates differs from the acoustic impedance of the background medium by a factor of at least 20.
3. The acoustic focus fractional vortex field emitter of claim 2, wherein: the first group of spiral grooves and the second group of spiral grooves respectively comprise a spiral groove, and two spirals r of the first group of spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, two spirals r of the second set of spiral groovesIIIAnd rIVIs given by the equation
And rIV(θ)＝rIII(θ) + d, where d is the width of the first and second set of spiral grooves, said width being smaller than the incident wavelength, g is the incident wavelength, r0Is the initial radius of the first set of helical grooves, r1Is the initial radius of the second set of spiral grooves, and N is the first set of spiralsThe number of turns of two spirals in the wire grooves and the second group of spiral wire grooves, m is the topological charge number, and the value is randomly selected from 0 to 1; the value of theta ranges from 0 to 2 pi/m.
4. The acoustic focus fractional vortex field emitter of claim 2, wherein: the first group of spiral grooves and the second group of spiral grooves respectively comprise 2 spiral grooves, wherein,
two spirals r of the 1 st spiral groove of the first set of spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, where theta is from 0 to 2 pi/m; m is topological charge number and is arbitrarily selected from 1 to 2; r is0Is the initial radius of the first set of helical flutes; two spirals r of the 2 nd spiral groove of the first set of spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, where theta takes on values from 2 pi/m to 2 pi;
two spirals r 'of the 1 st of the second set of spiral grooves'IAnd r'IIAre respectively as
And r'II(θ)＝r′I(theta) + d, where theta is from 0 to 2 pi/m; r is1Two spirals r 'of the 2 nd spiral slot of the second set of spiral slots being the initial radius of the second set of spiral slots'IIIAnd r'IVAre respectively as
And r'IV(θ)＝r′III(theta) + d, where theta is from 0 to 2 pi/m; wherein d is the width of the first set of spiral grooves and the second set of spiral grooves, said width being less than the incident wavelength, N is the first set of spiralsThe number of turns, g, of the grooves and the second set of spiral grooves is set to the incident wavelength.
5. The acoustic focus fractional vortex field emitter of claim 2, wherein: the group of spiral grooves and the second group of spiral grooves respectively comprise 3 spiral grooves, wherein,
two spirals r of the Mth spiral groove of the first group of spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, where theta takes on a value from 2(M-1) pi/M to 2M pi/M; m is topological charge number and is randomly selected from 2 to 3; r is0The initial radius of the first group of spiral grooves is defined, M is less than or equal to 2 and is a positive integer; two spirals r of 3 spiral grooves of the first group of spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, where theta takes on a value from 4 pi/m to 2 pi;
two spirals r 'of the Mth of the second set of spiral grooves'IAnd r'IIAre respectively as
And r'II(θ)＝r′I(θ)+d，r1The initial radius of the second set of spiral grooves; two spirals r 'of 3 spiral slots of the second set of spiral slots'IIIAnd r'IVAre respectively as
And r'IV(θ)＝r′III(θ) + d; wherein d is set to the width of the first group of spiral grooves and the second group of spiral grooves, the width is smaller than the incident wavelength, N is the number of turns of the first group of spiral grooves and the second group of spiral grooves, and g is set to the incident wavelength.
6. The acoustic focus fractional vortex field emitter of claim 2, wherein: the group of spiral grooves and the second group of spiral grooves respectively comprise 4 spiral grooves, wherein,
two spirals r of the Mth spiral groove of the first group of spiral groovesIAnd rIIAre respectively as
And rII(θ)＝rI(theta) + d, where theta takes on a value from 2(M-1) pi/M to 2M pi/M; m is topological charge number and is arbitrarily selected from 3 to 4; r is0The initial radius of the first group of spiral grooves is defined, M is less than or equal to 3 and is a positive integer; two spirals r of 4 spiral grooves of the first group of spiral groovesIIIAnd rIVAre respectively as
And rIV(θ)＝rIII(theta) + d, where theta takes on values from 6 pi/m to 2 pi;
two spirals r 'of the Mth of the second set of spiral grooves'IAnd r'IIAre respectively as
And r'II(θ)＝r′I(θ)+d，r1Two spirals r 'of the 4 spiral slots of the second set of spiral slots being an initial radius of the second set of spiral slots'IIIAnd r'IVAre respectively as
And r'IV(θ)＝r′III(θ) + d, where d is set to the width of the first and second set of spiral grooves, which is less than the incident wavelength, N is the number of turns of the first and second set of spiral grooves, and g is set to the incident wavelength.
7. The acoustic focus fractional vortex field emitter of claim 1, wherein: the first set of spiral grooves are Archimedes spiral grooves.
8. The acoustic focus fractional vortex field emitter of claim 1, wherein: the second group of spiral grooves are Archimedes spiral grooves.
9. The acoustic focus fractional vortex field emitter of claim 1, wherein: the preset spacing is half the incident wavelength.
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