Method and device for multiplexing and demultiplexing long-distance vortex acoustic beam in pipeline

Abstract

The invention relates to a multiplexing and demultiplexing method and device for a long-distance vortex acoustic beam in a pipeline, and belongs to the technical field of acoustic communication. A vortex acoustic beam communication system is constructed by adopting a ring emitter, a receiver array, a pipeline, a sound card and a computer, a sound source signal is generated at a signal sending end by adopting a multi-channel least square method, and the ring emitter array generates a multi-topological-charge vortex acoustic beam according to the sound source signal; the generated vortex sound beam is transmitted through a pipeline; at a signal receiving end, a multiplexing vortex sound beam transmitted in a pipeline is collected through a circular ring receiver array, the multiplexing vortex sound beam is compared with a complex sound pressure matrix of an element vortex sound beam, the normalized contribution degree of the element vortex sound beam in the multiplexing vortex sound beam is solved by means of a Tikhonov regularization algorithm, and then existence of a corresponding topological charge vortex sound beam is judged according to the contribution degree amplitude. And vortex acoustic beam demultiplexing is realized. According to the method, topological charge information of the multiplexing vortex acoustic beam can be accurately identified, and multiplexing and demultiplexing of the vortex acoustic beam are realized.

Description

Technical Field

[0001] This invention belongs to the field of acoustic communication technology and relates to a method for vortex beam multiplexing and demultiplexing for long-distance communication using ultrasonic vortex beams in a pipeline. Background Technology

[0002] Vortex acoustic beams carrying orbital angular momentum (OAM) exhibit highly attractive physical properties and show significant application potential in multiple fields, such as object manipulation, black hole simulation experiments, and especially in high-speed communications. OAM beams generate wave fields whose phase varies with azimuth angle, and their phase distribution can be expressed as... In the formula, These are the azimuth coordinates in cylindrical coordinate system. The imaginary unit, The topological charge (used to represent the number of wavelengths within the vortex circumference). Vortex beam communication technology consists of two parts: transmitter multiplexing and receiver demultiplexing.

[0003] In acoustic vortex beam generation technology, the low-frequency multi-channel least squares method exhibits significant advantages—compared to traditional low-frequency vortex beam generation methods, it offers significant advantages in sound energy utilization, transmitter placement flexibility, and sound field accuracy. Furthermore, in near-field scenarios, only a small number of transmitters and receivers are needed to multiplex high-topology vortex beams. However, due to the inherent defects of low-frequency sound waves, such as poor directivity and weak noise interference resistance, and the severe lateral diffusion of high-order topology vortex beams in free space, it is difficult to achieve long-distance, high-topology vortex beam multiplexing technology. In contrast, ultrasound possesses significant advantages in terms of good directionality and strong interference resistance. Combining the physical properties of ultrasound with channel waveguide technology holds promise for overcoming this bottleneck.

[0004] Current vortex beam demultiplexing techniques mainly include three categories: sound field inner product method, metamaterial demodulation method, and Doppler spectrum demodulation method. All of these methods have significant limitations. The inner product method has weak anti-interference capabilities and exhibits high sensitivity to measurement noise. While the metamaterial demodulation method offers simple and efficient signal acquisition, it is susceptible to insertion loss and diffraction effects in practical applications, and often suffers from OAM mode signal overlap. Doppler spectrum demodulation methods can be divided into two categories: one relies on mechanically driven Real Rotating Microphone (RRM) methods, and the other is based on static array timing processing of Virtual Rotating Receiver (VRR) methods. The former suffers from a decrease in signal-to-noise ratio due to mechanical vibration and noise, and the physical speed limit can easily cause channel crosstalk, especially in the ultrasonic band, where the speed required for demultiplexing is extremely high, which is almost impossible for mechanical systems to achieve; the latter avoids mechanical vibration and supports higher virtual speeds, but is limited by the Nyquist sampling law, and after frequency shift, it is easy to exceed the highest spectral frequency that the current system can measure, resulting in the loss of effective components of signals containing high topological charges.

[0005] For the ultrasonic frequency band, the virtual rotation frequency may need to be as high as tens of thousands of hertz, causing the frequency-shifted signal to far exceed the highest measurable spectral frequency. Therefore, in the field of demultiplexing vortex beams (especially ultrasonic vortex beams), there is an urgent need for a demultiplexing method that is both highly robust and accurate, and does not require complex mechanical structures. Summary of the Invention

[0006] In view of this, the purpose of the present invention is to provide a method and apparatus for multiplexing and demultiplexing long-distance vortex sound beams in pipelines, so as to realize the multiplexing and demultiplexing of long-distance, high-topology vortex sound beams, and thereby realize long-distance communication using ultrasonic vortex sound beams in pipelines.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for multiplexing and demultiplexing a long-distance vortex sound beam within a pipe, comprising: At the signal transmitting end, a multi-channel least squares method is used to generate a sound source signal, and a multi-topology vortex sound beam is generated by a circular transmitter array according to the sound source signal; the generated vortex sound beam is then transmitted through a pipe. At the signal receiving end, the multiplexed vortex sound beam transmitted in the pipeline is collected by a circular receiver array and compared with the complex sound pressure matrix of the elementary vortex sound beam. The normalized contribution of the elementary vortex sound beam in the multiplexed vortex sound beam is solved by using the Tikhonov regularization algorithm. Then, the existence of the corresponding topological load vortex sound beam is determined based on the contribution amplitude, thus realizing the demultiplexing of the vortex sound beam.

[0008] Furthermore, at the signal receiving end, for the multiplexed vortex acoustic beam acquired by the circular receiver array, a Fast Fourier Transform is performed on the received signal of each receiver to extract the signal at the target frequency. The complex sound pressure levels at each point constitute the received signal vector:

[0009] In the formula, For the first Each channel at frequency Complex sound pressure levels at that location. This represents the total number of receivers in the circular receiver array.

[0010] Furthermore, after obtaining the received signal vector, single-topology vortex acoustic beams are used as the basic vortex acoustic beams for transmission and acquisition. A primary vortex acoustic beam used for reference at the target frequency The complex sound pressure values ​​at a given point constitute a complex sound pressure vector:

[0011] In the formula, Indicates the first The elementary vortex sound beam in the first Complex sound pressure levels at each receiver ; By combining the complex sound pressure value vectors of all elementary vortex sound beams column-wise, a complex sound pressure matrix of the elementary vortex sound beams is constructed. : ; Combining received signal vectors and matrices A regularized least squares optimization model is established to solve for the weights of each primitive vortex beam in the received multiplexed vortex beam signal. Then, the normalized contribution of each vortex beam is calculated, and the topological charge in the multiplexed vortex beam is identified by the normalized contribution of each primitive vortex beam.

[0012] Furthermore, a regularized least squares optimization model is established:

[0013] In the formula, For Tikhonov regularization parameters, It is a complex weight vector containing the weights of the vortex acoustic beams of each elementary element; The analytical solution to this model is: , Given the identity matrix, we obtain the complex weight vector. ,in For the first m The weight of each elementary vortex acoustic beam For the first The contribution of the first elementary vortex acoustic beam, then the first m The normalized contribution of each elementary vortex acoustic beam is:

[0014] The topological charge in the multiplexed vortex beam is identified by comparing the normalized contribution of each primitive vortex beam with a preset threshold.

[0015] Furthermore, the generation of the sound source signal using the multi-channel least squares method includes: defining the target sound pressure and phase of the multiplexed vortex sound beam generated by the circular transmitter array at the monitoring point; then measuring the frequency response function between each transmitter and receiver in the transmitter array and receiver array, and calculating the equalization filter through the frequency response function; finally, combining the target signal of the multiplexed vortex sound beam and the equalization filter, calculating the sound source signal through a computer, converting the sound source signal into a time-domain signal, and then driving the circular transmitter array to emit sound to generate the multiplexed vortex sound beam.

[0016] Furthermore, the target sound pressure and phase of the multiplexed vortex beam at the monitoring point are expressed as follows:

[0017] In the formula, This represents the ideal value for multiplexed vortex acoustic beams. This represents any sound pressure level that can be achieved after a single transmitter emits sound. This indicates the total number of receivers in the circular receiver array. n Represents 0~ Receiver serial number 1 This represents the maximum topological charge of the multiplexed vortex acoustic beam.

[0018] The equalization filter is represented as:

[0019] In the formula, It is the frequency response function. Here, I is the regularization parameter, and I is the identity matrix. The sound source signal is then represented as .

[0020] In a second aspect, the present invention provides an apparatus for implementing the method described in the first aspect, the apparatus comprising a circular transmitter array, a circular receiver array, a conduit, a sound card, and a computer.

[0021] The computer is used to generate the sound source signal of the multiplexed vortex beam, and at the same time demultiplexes the multiplexed vortex beam sampling signal transmitted by the sound card. The sound card is used to receive sound source signals and drive the circular transmitter array to generate multiplexed vortex sound beams, and at the same time to sample the multiplexed vortex sound beams received by the circular receiver array. The circular transmitter array and the circular receiver array are coupled to both ends of the pipe to enable the transmission and reception of the multiplexed vortex acoustic beam within the pipe.

[0022] The beneficial effects of this invention are as follows: (1) This invention overcomes the defect of easy energy diffusion in free space of traditional vortex sound beams by combining ultrasonic waves with a pipe waveguide structure. The pipe acts as a sound waveguide, using its rigid boundary to constrain the propagation of sound waves, suppressing radial energy dissipation, and realizing long-distance concentrated transmission of sound energy. At the same time, the high-frequency characteristics of ultrasonic waves themselves can further ensure the stability of high-order topological vortex sound beams during transmission, enabling the communication system to maintain signal integrity in complex environments, avoiding signal attenuation caused by diffusion, and providing a reliable foundation for long-distance acoustic communication.

[0023] (2) The present invention adopts the VABMD demultiplexing method, which does not rely on any mechanical rotating parts or metamaterial structures, avoiding problems such as noise and speed limitation introduced by mechanical vibration. At the same time, it overcomes the defects of insertion loss and mode crosstalk, effectively suppresses the interference caused by measurement noise and intermodal coupling, and significantly improves the robustness and accuracy of demultiplexing.

[0024] Other advantages, objectives, and features of the invention will be set forth in part in the description which follows, and in part will be apparent to those skilled in the art from the following examination, or may be learned from practice of the invention. The objectives and other advantages of the invention can be realized and obtained through the following description. Attached Figure Description

[0025] To make the objectives, technical solutions, and advantages of the present invention clearer, the preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings, wherein: Figure 1 This is a schematic diagram of a pipeline ultrasonic vortex beam multiplexing and demultiplexing system provided in an embodiment of the present invention; Figure 2 This is a nodal diagram showing the sound pressure distribution across the cross-section of a circular pipe. Figure 3 This is a schematic diagram of a multi-channel least squares equalization system. Figure 4 This is a schematic diagram of a circular array of ultrasonic transmitters and receivers. Figure 5 This is a diagram illustrating the normalized contribution. Detailed Implementation

[0026] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0027] The accompanying drawings are for illustrative purposes only and are schematic diagrams, not actual pictures. They should not be construed as limiting the invention. To better illustrate the embodiments of the invention, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product dimensions. It is understandable to those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings.

[0028] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "front," and "rear" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present invention. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0029] To achieve long-distance, high-topology vortex beam multiplexing and demultiplexing, this invention proposes a method for multiplexing vortex beams using a multi-channel least squares approach, and demultiplexing using a vortex beam mode decomposition method combined with a Tikhonov regularization algorithm. Specifically, the multiplexing process employs a multi-channel least squares approach, using a compact ultrasonic array arranged in a circular ring within a conduit to excite ultrasonic waves, thus constructing a multiplexed vortex beam with multiple topological loads. The conduit acts as an acoustic waveguide, effectively suppressing energy dissipation, while the ultrasonic wave carrier, with its high frequency, high directivity, and strong anti-interference capabilities, ensures efficient excitation and stable transmission of higher-order modes. Demultiplexing employs Vortex Acoustic Beam Modal Decomposition (VABMD): The signal acquired by the receiving array is compared with the complex sound pressure matrix of a single topological charge vortex beam (primary vortex beam). The normalized contribution of the primary vortex beam in the multiplexed signal is calculated using the Tikhonov regularization algorithm. The presence of the corresponding topological charge vortex beam is then determined based on the contribution amplitude, ultimately achieving ultrasonic vortex beam demultiplexing. Through the coordinated operation of this multiplexing and demultiplexing method, high-precision, highly robust long-distance ultrasonic vortex beam communication within pipelines is finally realized.

[0030] In an "ideal" fluid with zero viscosity and no thermal conductivity, sound waves propagate without energy loss within a rigid-walled circular pipe, satisfying the following: (1) in, Represents the radial distribution function. Represents the circumferential phase factor. Represents the axial distribution function. The circumferential phase factor of the pipe sound pressure field, representing the time-harmonic vibration factor, is equivalent to the circumferential phase factor of the vortex sound beam. ( Both define the same spiral wavefront through the same circumferential phase distribution, and the higher-order circumferential modes ( The research on this topic is transformed into the study of the characteristics of the corresponding topologically charged vortex sound beam. The radial rigid boundary constraint is the core, which fundamentally eliminates the physical basis for the geometric diffusion of sound waves into free space, transforming it from a diffused spherical wave into a pipe-mode wave guided axially.

[0031] In a circular pipe, sound wave propagation often exhibits cylindrical wave characteristics, especially when the sound wave frequency is higher than a certain frequency, the radial distribution of the wave field is no longer a simple plane wave attenuation.

[0032] The general solution for the radial distribution of sound waves in cylindrical coordinates is: (2) in, Represents the first kind of Bessel function, To represent the second kind of Bessel function, Indicates the radial wave number.

[0033] exist At point 0 (the axis), the pressure approaches infinity. However, the sound pressure at all points must be finite; therefore, the constant... It must be zero. At the junction with the pipe wall ( The radial velocity of ) must be zero. Therefore: (3) (4) The solution to the equation is the zero of the derivative of the Bessel function. That is, there exists a series of eigenvalues. ( Let be the circumferential modal order. (where is the radial modal order), such that: (5) in, Indicates radial wavenumber, Indicates the pipe radius.

[0034] The axial acoustic wavenumber in the pipeline (ideal environment) is: (6) in, Represents the total wavenumber in free space. Indicates the axial wave number.

[0035] like (That is, the total wavenumber is large enough to exceed the radial wavenumber), then If it is a real number, sound waves can propagate.

[0036] like (That is, the total wave number equals the radial wave number), which is the critical point for sound wave propagation.

[0037] like (If the total wavenumber is less than the radial wavenumber), then It is an imaginary number, corresponding to a "cutoff wave" (amplitude decays exponentially and cannot propagate).

[0038] This is the key to enabling pipelines to achieve long-distance transmission, meeting the requirements under ideal conditions. .

[0039] Under ideal conditions (non-viscous, thermally conductive, static medium), the frequency can also be used to determine whether a sound wave can propagate inside a pipe.

[0040] when This is the boundary condition for whether sound waves can propagate inside a pipe.

[0041] The joint organization includes: (7) The excitation frequency can be expressed as: (8) in, Indicates the excitation frequency. It indicates the speed of sound.

[0042] when Therefore Substituting into equation (6), we get , ,Right now If it is a real number, sound waves can propagate.

[0043] when Therefore Substituting into equation (6), we get , ,Right now Since it is an imaginary number, sound waves cannot propagate.

[0044] The acoustic modes in a circular pipe are determined by the mode ordinal number ( , Characterization. For hard-walled boundary conditions, the excitation frequency of this mode depends on the eigenvalues. ,Right now derivative of the first Bessel function The Each root. Its specific spatial distribution is manifested as a nodal pattern on the cross-section, such as... Figure 2 As shown.

[0045] To investigate the maximum value of the topological charge of the vortex acoustic beam excited in a pipe under ideal conditions, the radial modal index is usually limited to a low value. =0), which can excite higher-order circumferential modes (i.e., larger topological charges) at the same frequency. ).

[0046] The range of modal excitation frequencies inside the pipe is ( =0): (9) For example, the intention is to stimulate the maximum topological load. vortex sound beam, pipe radius Selected as 22.5 mm, speed of sound It is 340 m / s. The value depends on the pipe mode ( , Based on the above formula, the analysis is as follows: (10) (11) As can be seen from equation (11), in order to stimulate The vortex acoustic beam can be generated using a general-purpose ultrasonic transmitter and receiver with a frequency of 40 kHz. However, due to limitations imposed by viscosity and thermal conduction losses, and more importantly by the number of transmitter arrays, theoretically at least four transmitters are required. With 4×14 transmitters, it is difficult to excite a vortex beam with a topological charge of 14 in a small pipe.

[0047] To address the aforementioned problems, one embodiment of the present invention provides a vortex beam multiplexing method based on multi-channel least squares. Specifically, using a circular array as the emission point, the target sound pressure and phase of the multiplexed vortex beam generated by the transmitter array at the monitoring point have the following characteristics:

[0048] in, This represents the ideal value for multiplexed vortex acoustic beams. This represents any sound pressure level that can be achieved after a single transmitter emits sound. This indicates the total number of receivers in the receiver array. n Represents 0~ Receiver serial number, This represents the maximum topological charge of the multiplexed vortex acoustic beam.

[0049] use Figure 3 The multi-channel least-squares equalization system shown generates the target vortex acoustic beam, in which G This represents the entire physical transmission path consisting of the sound card output, transmitter, receiver, and environment. It represents the ideal vortex sound beam sound field. Input to the equalizer filter added before the sound card (Depend on × The complex matrix representation of , where (This represents the total number of transmitters in the transmitting ring array), and the signal of the sound source is calculated by the computer using the following formula. S : (13) in, 0~ The transmitter serial number.

[0050] In order to make the constructed sound field approximate the target sound field , and The equilibrium system composed of each other It should meet the following requirements: (14) In the formula, I is the identity matrix. The delay is due to hardware system latency. The least squares method is employed, and Tikhonov regularization parameters are introduced. Calculate S as: (15) The solution to equation (15) is expressed as: (16) (17) Where H represents the transpose of the matrix; for × A complex matrix, representing The measured value, whose elements are the frequency response functions between each transmitter and receiver in the receiver array and transmitter array, can be obtained by the logarithmic sinusoidal sweep frequency method. From the signal... S It can calculate the time-domain signal of a single-frequency vortex beam. s : (18) in, t Representing a time series, Indicates the target frequency.

[0051] For the demultiplexing of ultrasonic vortex beams in pipelines, this embodiment proposes to first use a circular receiver array to measure the sound field signal of the vortex beam, acquire the original signal through the circular receiver array, and then obtain the normalized contribution of each elementary vortex beam through signal processing.

[0052] The specific signal processing method is as follows: The raw time-domain signal acquired by the microphone array is ,in (1,2, …, ) is the sampling step size ( , The serial number (for the sound card's sampling frequency) It is a microphone serial number (0 to 1) encoded sequentially according to the observer's rotation direction. , (Total number of microphones). Perform a Fast Fourier Transform (FFT) on the signal of each channel to obtain its spectrum. , and at the target frequency The complex sound pressure value is extracted and used to construct the received signal vector, as shown in the following formula: (19) in, For the first Each channel at frequency The complex sound pressure level at the target frequency. The frequency of the signal that needs to be emitted to excite the target vortex acoustic beam.

[0053] Launch and collect separately common A single topological charge vortex beam (primary vortex beam, with known topological charge values) is used for reference at the target frequency. The complex sound pressure values ​​are extracted from each location to form a complex sound pressure vector, as shown in the following formula: (20) in, Indicates the first The elementary vortex sound beam in the first Complex sound pressure levels at each receiver.

[0054] By combining the complex sound pressure value vectors of all elementary vortex sound beams column-wise, a complex sound pressure matrix of the elementary vortex sound beams is constructed. : (twenty one) To solve for the weights of each elementary vortex beam in the received multiplexed vortex beam signal, a regularized least squares optimization model is established: (twenty two) in, Here, is the Tikhonov regularization parameter, used to suppress noise coupling between different topological loads. The analytical solution to this optimization problem is: (twenty three) From equation (23), the complex weight vector can be obtained. , its first The modulus of each component is , indicating the first The contribution of each primitive vortex acoustic beam.

[0055] Define the normalized contribution of each primitive vortex beam. As shown in the following formula: (twenty four) By normalizing the contribution of each elementary vortex acoustic beam The topological charge in the multiplexed vortex beam is identified by comparing it with a preset threshold.

[0056] The effectiveness of this invention is verified through the following experiments: Using a common radius of 22.5 mm, the length ( The length of the 2 m PVC pipe is the ratio of its length to the length of the ultrasonic wave. The ultrasonic transmitter is model MA40S4S, with a single diameter of 10 mm and a length of 7 mm. The ultrasonic receiver is model MA40S4R, with the same dimensions as the transmitter (10 mm diameter and 7 mm length). Due to the limitations of the selected pipe size, 16 ultrasonic transmitters and 12 ultrasonic receivers are used respectively, arranged as follows: Figure 4 As shown. An Antelope Orion 32+ GEN4 sound card is used. This device has 32 transmit and receive channels, and a sampling rate of 192 kHz is selected, which can meet the high-precision acquisition requirements of ultrasonic signals. The ultrasonic transmitter, ultrasonic receiver, sound card, and pipes are connected according to... Figure 1 The connection method is used to build a pipeline ultrasonic vortex beam multiplexing and demultiplexing system.

[0057] according to This system is capable of constructing the highest topological charge of a vortex acoustic beam. The value is 4, and it has 8 channels for multiplexing and demultiplexing. The capability is 4 to -4. This system is used to handle topological loads. =1, 2, 3 multiplexed ultrasonic (40 kHz) vortex beams were demultiplexed, and the normalized contribution values ​​of each elementary vortex beam after demultiplexing using the VABMD method are as follows: Figure 5 As shown, the method provided by this invention can successfully identify the topological charge information of each multiplexed vortex beam. Therefore, this invention can achieve long-distance (235 times wavelength), high topological charge ultrasonic vortex beam multiplexing and demultiplexing. To expand application scenarios, the number of transmitters and receivers can be increased by adding a transition device, thereby increasing the number of topological charges of the multiplexed and demultiplexed vortex beams.

[0058] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for multiplexing and demultiplexing long-distance vortex sound beams within a pipeline, characterized in that, At the signal transmitting end, a multi-channel least squares method is used to generate a sound source signal, and a multi-topology vortex sound beam is generated by a circular transmitter array according to the sound source signal; the generated vortex sound beam is then transmitted through a pipe. At the signal receiving end, the multiplexed vortex sound beam transmitted in the pipeline is collected by a circular receiver array and compared with the complex sound pressure matrix of the elementary vortex sound beam. The normalized contribution of the elementary vortex sound beam in the multiplexed vortex sound beam is solved by using the Tikhonov regularization algorithm. Then, the existence of the corresponding topological load vortex sound beam is determined based on the contribution amplitude, thus realizing the demultiplexing of the vortex sound beam.

2. The method according to claim 1, characterized in that, At the signal receiving end, for the multiplexed vortex acoustic beam acquired by the circular receiver array, a Fast Fourier Transform is performed on the received signal of each receiver to extract the signal at the target frequency. The complex sound pressure levels at each point constitute the received signal vector: In the formula, For the first Each channel at frequency Complex sound pressure levels at that location. This represents the total number of receivers in the circular receiver array.

3. The method according to claim 2, characterized in that, After obtaining the received signal vector, single-topology vortex acoustic beams are used as the basic vortex acoustic beams for transmission and acquisition. A primary vortex beam used for reference at the target frequency The complex sound pressure values ​​at a given point constitute a complex sound pressure vector: In the formula, Indicates the first The elementary vortex sound beam in the first Complex sound pressure levels at each receiver ; By combining the complex sound pressure value vectors of all elementary vortex sound beams column-wise, a complex sound pressure matrix of the elementary vortex sound beams is constructed. : ; Combining received signal vectors and matrices A regularized least squares optimization model is established to solve for the weights of each primitive vortex beam in the received multiplexed vortex beam signal. Then, the normalized contribution of each vortex beam is calculated, and the topological charge in the multiplexed vortex beam is identified by the normalized contribution of each primitive vortex beam.

4. The method according to claim 3, characterized in that, Establish a regularized least squares optimization model: In the formula, For Tikhonov regularization parameters, It is a complex weight vector containing the weights of the vortex acoustic beams of each elementary element; The analytical solution to this model is: , Given the identity matrix, we obtain the complex weight vector. ,in For the first m The weight of each elementary vortex acoustic beam For the first The contribution of the first elementary vortex acoustic beam, then the first m The normalized contribution of each elementary vortex acoustic beam is: The topological charge in the multiplexed vortex beam is identified by comparing the normalized contribution of each primitive vortex beam with a preset threshold.

5. The method according to claim 1, characterized in that, The method of generating sound source signals using the multi-channel least squares approach includes: defining the target sound pressure and phase of the multiplexed vortex sound beam generated by the circular transmitter array at the monitoring point; then measuring the frequency response function between each transmitter and receiver in the transmitter and receiver arrays, and calculating the equalization filter using the frequency response function; finally, combining the target signal of the multiplexed vortex sound beam with the equalization filter, calculating the sound source signal using a computer, converting the sound source signal into a time-domain signal, and then driving the circular transmitter array to emit sound to generate the multiplexed vortex sound beam.

6. The method according to claim 5, characterized in that, The target sound pressure and phase of the multiplexed vortex beam at the monitoring point are expressed as follows: In the formula, This represents the ideal value for multiplexed vortex acoustic beams. This represents any sound pressure level that can be achieved after a single transmitter emits sound. This indicates the total number of receivers in the circular receiver array. n Represents 0~ Receiver serial number 1 This represents the maximum topological charge of the multiplexed vortex acoustic beam. The equalization filter is represented as: In the formula, It is the frequency response function. Here, I is the regularization parameter, and I is the identity matrix. The sound source signal is then represented as .

7. An apparatus for implementing the method according to any one of claims 1 to 6, characterized in that, This includes a circular transmitter array, a circular receiver array, pipes, a sound card, and a computer; The computer is used to generate the sound source signal of the multiplexed vortex beam, and at the same time demultiplexes the multiplexed vortex beam sampling signal transmitted by the sound card; The sound card is used to receive sound source signals and drive the circular transmitter array to generate multiplexed vortex sound beams, and at the same time to sample the multiplexed vortex sound beams received by the circular receiver array. The circular transmitter array and the circular receiver array are coupled to both ends of the pipe to enable the transmission and reception of the multiplexed vortex acoustic beam within the pipe.

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