CN110487395A - Acoustics vortex field detector based on Fraunhofer diffraction principle - Google Patents
Acoustics vortex field detector based on Fraunhofer diffraction principle Download PDFInfo
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- G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
- G01H17/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves, not provided for in the preceding groups
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Abstract
The present invention relates to acoustics rotational field detector technologies fields, more particularly to the acoustics vortex field detector based on Fraunhofer diffraction principle, its technical solution is as follows: including substrate, acoustics vortex field detector is planar structure, the substrate is equipped with opening diffracting, it is controlled by the topological charge of size and location and incident sound rotational field to the opening diffracting, based on Fraunhofer diffraction principle, the sound vortex wave for carrying different topology lotus penetrates the opening diffracting, the far-field intensity distribution figure uniquely determined on the film viewing screen of far field, it is compared according to the calculated value of the different plot of light intensity and the far-field intensity distribution figure that are obtained on the far field film viewing screen, detection obtains the topological charge of incident sound rotational field.The present invention has rational design, and the method for the detectors measure acoustics rotational field topological charge is fairly simple, is easier to implement, in practical applications, can be in conjunction with existing acoustics vortex field emission device, realization sound vortex wave communication.
Description
Technical Field
The invention relates to the technical field of acoustic vortex field detectors, in particular to an acoustic vortex field detector based on the Fraunhofer diffraction principle.
Background
OAM has been gradually attracting research interest due to its orthogonality between different modes and the infinite number of modes. The orthogonal characteristic enables vortex electromagnetic waves to have low crosstalk when the vortex electromagnetic waves are transmitted coaxially, and therefore, the vortex electromagnetic waves can be regarded as another multiplexing mode, namely OAM mode multiplexing. Similarly, the research on the acoustic vortex field which carries orbital angular momentum and has the characteristic of spiral phase distribution has important value in practice. How to design a simple and effective acoustic vortex field detector has been a research hotspot in the related field.
The current research on the acoustic vortex field emitter is mature, and can be mainly divided into two main categories, namely an active method and a passive method. The former belongs to the acoustic phased array technology, and mainly utilizes a large number of acoustic transducers to arrange an acoustic array, and independently controls the phase delay of each transducer through an electrical means, the whole transducer array is regarded as a vortex field transmitter, and the generated sound field is the superposition of single transducers. Passive methods are mainly classified into three categories: the first is to use an acoustic wave propagation distance along the angleThe large size of the helically varying structure, typically in the order of tens of acoustic wavelengths, limits its practical application, particularly in the generation of low frequency acoustic vortex fields. The second type is that a subwavelength spiral acoustic grating is used for converting a plane acoustic wave into a vortex acoustic wave by utilizing the diffraction effect of the subwavelength spiral acoustic grating on the acoustic wave, and the structure has the advantage of a plane shape and can simply and conveniently generate a vortex with large topological load. The third category is to pass plane waves through a planar metasurface which has the advantages of high efficiency, small size and planarity.
In the optical field, scholars at home and abroad have proposed many different OAM detection schemes from the characteristics of vortex beams, mainly including methods of fundamental mode conversion, interferometer interference, mode classification, aperture diffraction, and the like. However, there is currently no study involving acoustic vortex field detectors. Since the acoustic vortex field detector also has a very important value in practical applications, it is necessary and important to design a simple and efficient acoustic vortex field detector.
Disclosure of Invention
Based on the technical problems in the prior art, the invention provides an acoustic vortex field detector based on the Fraunhofer diffraction principle.
The acoustic vortex field detector based on the Fraunhofer diffraction principle comprises a substrate, wherein the acoustic vortex field detector is of a plane structure, diffraction holes are formed in the substrate, the size and the position of each diffraction hole are controlled to be in contact with the topological charge of an incident acoustic vortex field, acoustic vortex waves carrying different topological charges penetrate through the diffraction holes based on the Fraunhofer diffraction principle, a uniquely determined far-field intensity distribution diagram is obtained on a far-field observation screen, and the topological charge of the incident acoustic vortex field is detected and obtained according to comparison of different light intensity diagrams obtained on the far-field observation screen and theoretical calculation values of the far-field intensity distribution diagram.
Further, the diffraction holes are one of circular holes, annular triangular holes or elliptical holes, and the number of the circular holes is at least 4.
Further, the device also comprises a background medium, wherein the background medium is water or air.
Further, the acoustic impedance of the background medium is at least 1/20 times the acoustic impedance of the substrate.
Further, the detection performance of the device is analyzed through extraction and processing of the planar intensity distribution of the light intensity graph.
Further, the substrate is a stainless steel substrate, and the density and the sound velocity of the substrate are 7600-8000kg/m3And 4800-5200 m/s.
Further, the operating frequency of the acoustic vortex field detector is 285-310 kHz.
Compared with the prior art, the invention has the beneficial effects that:
1. based on the Fraunhofer diffraction principle, under different frequencies, the topological charge of an unknown incident acoustic vortex wave is quantitatively detected according to an obtained far-field intensity distribution graph and a far-field intensity distribution graph calculated by a theoretical formula;
2. the structure designed by the invention is a passive device, and does not need to be controlled by an additional circuit means, so that the method is suitable for most environments including air and underwater;
3. the structure designed by the invention is easy to process and low in cost, and the size of the device can be adjusted according to the requirement.
The invention has reasonable design, the method for measuring the topological load of the acoustic vortex field by the detector is simpler and easier to implement, and in practical application, the detector can be combined with the existing acoustic vortex field transmitter to realize acoustic vortex wave communication.
Drawings
FIG. 1 is a schematic design diagram of circular hole arrays, circular triangular holes and circular elliptical holes corresponding to three diffraction screens (a), (b) and (c);
FIG. 2 is a simulated intensity profile of the diffraction screen of FIG. 1 in a first state (a);
FIG. 3 is a simulated intensity distribution plot for the second condition of the diffraction screen (a) of FIG. 1;
FIG. 4 is a simulated intensity profile of the diffraction screen (b) of FIG. 1;
FIG. 5 is a simulated intensity and phase profile of the diffraction screen (c) of FIG. 1;
fig. 6 is a schematic diagram of an incident acoustic vortex wave translated from the central axis of the interference screen (a) and the interference screen (b) not perpendicular to the central axis of the incident acoustic field.
FIG. 7 is a simulated intensity profile of the interference screen (a) of FIG. 6;
FIG. 8 is a simulated intensity profile of the interference screen (b) of FIG. 6;
fig. 9 is a simulated intensity profile for the simultaneous presence of translation and deflection angles.
Detailed Description
The present invention will be further illustrated with reference to the following specific examples.
Example one
As shown in fig. 1 (a), the substrate includes a substrate with a circular diffraction hole structure, where the number of circular holes N =6, an incident acoustic vortex wave reaches the circular hole array diffraction screen of fig. 1 (a) after propagating for a certain distance, and the intensity distribution of an acoustic field is extracted after propagating for a certain distance through the diffraction screen. The theoretical calculation procedure is as follows:
the sound field of any point of the acoustic vortex field can be usedIs shown in whichIs the amplitude and l is the topological charge. The intensity distribution obtained after passing through the multi-circular-hole interference screen is
（1）
Wherein,and c is the density and speed of sound of the background medium. For an incident acoustic vortex field topological charge of l, an intensity distribution diagram passing through an interference screen with a circular hole number of N is
（2）
Wherein，And z is the distance of the porous interference screen from the viewing plane.
Further, formula (3) can be derived from formula (2)
（3）
Equation (3) is reduced to be equal to equation (2). It can be derived from equation (3) that, for a multi-circular aperture interference screen with a circular aperture number N, the intensity distribution center characteristics of l = m and l = m + N are the same, and the intensity distribution diagram is periodic with a period of N. I.e. the range over which the topological charge is detected is equal to the number of circular holes.
In addition, it can be easily deduced from equation (2): when the topological charges of incident acoustic vortex waves are l = m and l = -m for the same diffraction screen, the far-field interference intensity pattern is symmetrical about the x axis. Due to this characteristic, the acoustic vortex field detector designed by the present invention cannot distinguish between positive and negative topological charges.
Simulated intensity profiles obtained by simulation of this configuration of fig. 1 (a) are shown in fig. 2 and 3. At the frequency of 300kHz, the radius of the stainless steel substrate is 20mm, the radius r =0.4mm of the circular hole, and the distance from the center of the circular hole to the center of the stainless steel substrate is a =5 mm. Setting the phase difference between adjacent point sound sources as，Is the initial phase of the nth point sound source. As can be seen from FIG. 2, for acoustic vortex waves carrying different topological charges, incident on interference screens with different hole numbers, the obtained far-field intensity distribution map is unique. Furthermore, as can be seen from fig. 2 (a), the central features of the far-field intensity profiles of l =0 and l =4 are the same for N = 4. And as can be seen from fig. 3, the simulated intensity profile is symmetric about the x-axis when the topological loading of the incident acoustic vortex is l =5 and l = -5, and l =6 and l = -6. The characteristics are consistent with the result obtained by theoretical calculation, the simulation result is compared with the theoretical calculation result, the topological load carried by the unknown incident acoustic vortex field can be obtained quantitatively, and the designed structure can perfectly detect the topological load carried by the acoustic vortex field.
Example two
As shown in fig. 1 (b), when the incident acoustic wave is a vortex wave, the wave field expression at the annular triangular hole plane (z = 0) is as follows:
（4）
wherein, l is the number of topological charges,coordinates in the plane of the triangular hole;is the beam waist size of the swirling sound beam impinging on the triangular aperture.
When the vortex sound beam irradiates on the annular triangular hole diffraction screen, the sound field expression in the Fraunhofer diffraction area is as follows:
(5)
whereinIs a function of transmittance.
The simulated intensity profile obtained by simulating the structure of FIG. 1 (b) is shown in FIG. 4. For FIG. 4, at a frequency of 300kHz, the outer edge length of the diffraction screen is 8.5mm and the inner edge length is 4mm for the annular triangular holes of FIGS. (a), (c), (d) and (h), i.e., the ratio of the inner edge length to the outer edge length of the triangular holes is. (a) The (c) is the simulation result of the topological charge of 1, and the (e) to (f) are the simulation results of the topological charge of 2, wherein the difference lies in that the ratio of the outer side length to the inner length is changed. (a) And (e) the ratio of the inner and outer side lengths isThe ratio of the inner side length to the outer side length of (b) to (f) isThe ratio of the inner side length to the outer side length of (c) to (g) is. (d) And (h) is an intensity profile with topological charges of-1 and-2. As can be seen from FIG. 4, whenThe intensity pattern tapers as it becomes larger. And, when the topological charge changes from a positive topological charge to a negative topological charge, the intensity profile is correspondingly rotated by 180 °. From the simulation results, it can be seen that the absolute value of the topological charge is equal to the bright point outside the triangular lattice in the diffraction pattern minus 1, and the sign of the topological charge can be determined by the orientation of the triangular lattice in the diffraction pattern. These characteristics are consistent with the results derived from the above theory, and the size of the topological charge can be visually judged from the simulation intensity distribution diagram.
EXAMPLE III
As shown in fig. 1 (c), the substrate including the diffraction holes has an annular elliptical structure, and the theoretical derivation is the same as that of the annular triangular hole diffraction screen. The simulation is performed directly on this structure. At a frequency of 300kHz, the annular elliptical hole diffraction screen of FIG. 1 (c) is designed such that the major and minor axes of the outer ring are 2.3mm and 1.8mm, respectively, and the major and minor axes of the inner ring are 1.84mm and 1.44mm, respectively. The simulation results are shown in fig. 5.
From the simulation results, fig. 5 shows that: when the topological charge of the incident acoustic vortex is 1, the intensity distribution center has a dark spot, and the phase distribution center has a singularity; when the topological charge of the incident acoustic vortex is 2, the intensity distribution center has two dark spots, and the phase distribution center has two singularities. According to the method, the topological charge carried by the incident acoustic vortex can be detected from the characteristics of intensity distribution and phase distribution. These characteristics show that the designed structure can perfectly detect the topological load carried by the acoustic vortex field.
The above-described cases are all based on the case where the transmission axis of the acoustic wave and the center of the interference screen are on the same straight line and the interference screen is perpendicular to the transmission axis. In practice, however, this ideal situation is difficult to achieve. For such undesirable conditionsAn example of a circular aperture array diffraction screen is given in the present invention. Fig. 6 (a) is a schematic diagram of the center of the circular hole array diffraction screen shifted parallel to the transmission axis, and (b) is an example of a schematic diagram when the angle between the interference screen and the transmission axis is not 90 °, that is, a deflection angle is provided. Fig. 7 is a simulated intensity profile of fig. 6 (a). The acoustic vortex wave with topological charge l =2 is incident on the interference screen with N =5, and d is the different translation. As can be seen from the results, when the parallel shift occurs, the intensity profile also shifts, and as the amount of shift increases, the intensity profile is distorted, and the intensity distribution is not uniform. But inIn this case, the topological charge of the incident sound field can be resolved. Fig. 8 corresponds to the simulated intensity profile of fig. 6 (b). From the simulation results, when a deflection angle occurs, the simulation results are also distorted and the intensity distribution is not uniform, and the distortion and the non-uniform distribution become more and more obvious along with the increase of the angle.In time, the topological load of the incident sound field can be analyzed from the simulation result. However, if the offset amount and the deflection angle occur simultaneously, the distortion becomes more significant, and the accuracy of detection is greatly reduced. Fig. 9 shows a simulation result diagram for this case.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.
Claims (7)
1. The acoustic vortex field detector based on the Fraunhofer diffraction principle comprises a substrate, is of a planar structure, and is characterized in that diffraction holes are formed in the substrate, the size and the position of each diffraction hole are controlled to be in contact with the topological charge of an incident acoustic vortex field, based on the Fraunhofer diffraction principle, acoustic vortex waves carrying different topological charges penetrate through the diffraction holes, a uniquely determined far-field intensity distribution diagram is obtained on a far-field observation screen, and the topological charge of the incident acoustic vortex field is detected and obtained by comparing different light intensity diagrams obtained on the far-field observation screen with theoretical calculation values of the far-field intensity distribution diagram.
2. The Fraunhofer diffraction principle-based acoustic vortex field detector of claim 1, wherein the diffraction holes are one of circular holes, circular triangular holes or elliptical holes, wherein the number of circular holes is at least 4.
3. The Fraunhofer diffraction principle-based acoustic vortex field detector of claim 1, further comprising a background medium, wherein the background medium is water or air.
4. The Fraunhofer diffraction principle-based acoustic vortex field detector of claim 3, wherein the acoustic impedance of the background medium is at least 1/20 times the acoustic impedance of the substrate.
5. The acoustic vortex field detector based on the Fraunhofer diffraction principle of claim 1, characterized in that the detection performance of the device is analyzed by extraction and processing of the planar intensity distribution of the light intensity map.
6. The acoustic vortex field detector based on Fraunhofer diffraction principle as claimed in claim 1, wherein said substrate is a stainless steel substrate, and the density and sound velocity of said substrate are 7600-8000kg/m respectively3And 4800-5200 m/s.
7. The acoustic vortex field detector based on the Fraunhofer diffraction principle of claim 1, wherein the operating frequency of the acoustic vortex field detector is 285-310 kHz.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112254811A (en) * | 2020-10-16 | 2021-01-22 | 南开大学 | Optical system for rapidly detecting vortex light beam topological charge number by utilizing triangular annular mask |
| CN112880978A (en) * | 2021-01-15 | 2021-06-01 | 中国科学院上海光学精密机械研究所 | Device and method for measuring angular momentum number of vortex optical orbit |
| CN114822482A (en) * | 2022-03-11 | 2022-07-29 | 南京师范大学 | Coupled acoustic vortex transmitter and application thereof |
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| CN105444896A (en) * | 2015-11-30 | 2016-03-30 | 河南科技大学 | Vortex light beam topology charge measuring method based on hexagram hole diffraction |
| CN105466577A (en) * | 2016-01-18 | 2016-04-06 | 河南科技大学 | Perfect vortex light beam topological load measurer and method based on light intensity analysis |
| CN106932107A (en) * | 2017-04-07 | 2017-07-07 | 哈尔滨工业大学 | A kind of topological charge measurement apparatus based on far field construction principle |
| CN109029745A (en) * | 2018-08-24 | 2018-12-18 | 深圳大学 | Ears circle diffraction diaphragm and vortex light topological charge number detection system and detection method |
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Patent Citations (5)
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| US20040009063A1 (en) * | 2002-07-12 | 2004-01-15 | Polacsek Ronald R. | Oscillating system entraining axial flow devices |
| CN105444896A (en) * | 2015-11-30 | 2016-03-30 | 河南科技大学 | Vortex light beam topology charge measuring method based on hexagram hole diffraction |
| CN105466577A (en) * | 2016-01-18 | 2016-04-06 | 河南科技大学 | Perfect vortex light beam topological load measurer and method based on light intensity analysis |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN112254811A (en) * | 2020-10-16 | 2021-01-22 | 南开大学 | Optical system for rapidly detecting vortex light beam topological charge number by utilizing triangular annular mask |
| CN112880978A (en) * | 2021-01-15 | 2021-06-01 | 中国科学院上海光学精密机械研究所 | Device and method for measuring angular momentum number of vortex optical orbit |
| CN114822482A (en) * | 2022-03-11 | 2022-07-29 | 南京师范大学 | Coupled acoustic vortex transmitter and application thereof |
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