Method for vortex acoustic beam demultiplexing based on rotational Doppler effect

Abstract

The present application relates to a kind of vortex sound beam demultiplexing method based on rotating Doppler effect, belong to acoustic communication technical field.The method is: first, construct a circular array sound source system and a microphone circular array;Multiplexed vortex sound beam is generated by circular array sound source system, then the time domain signal of equal interval microphone collection is extracted in turn, to measure the sound pressure spectrum varying with the rotation observer rotation speed;In spectrum, the peak value corresponding to each vortex sound beam topological series is identified, and according to the relationship between peak frequency and vortex sound beam topological series, the demultiplexing of multiplexed vortex sound beam is realized.The present application can avoid the problem of insufficient low-frequency response of single microphone, can quickly and simply carry out vortex sound beam demultiplexing, realizes real-time, large capacity, high-precision acoustic communication.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of acoustic communication, and relates to a vortex acoustic beam demultiplexing method based on a rotating Doppler effect. BACKGROUND

[0002] Due to the limitation of long-distance propagation of electromagnetic waves underwater, acoustic communication technology has irreplaceable significance in underwater positioning and communication applications. However, the lower frequency and propagation speed of acoustic waves compared to electromagnetic waves greatly limit the data volume and rate of acoustic communication. The orbital angular momentum (OAM) multiplexing technology based on vortex acoustic beams has gradually become an effective solution to improve the underwater acoustic communication capability in recent years due to its inherent orthogonality, latitude infinity, and compatibility with existing communication technologies. Vortex acoustic beams, also known as rotating acoustic waves, are the third type of acoustic wave similar to traveling waves and standing waves, with a spiral phase relationship proportional to the azimuth angle, mathematically expressed as where represents the azimuthal coordinate in the cylindrical coordinate system, l represents the OAM topological order, and represents the number of wavelengths of the vortex acoustic beam within a circumference, with positive and negative representing the vortex rotation direction. The communication technology based on vortex acoustic beams uses mutually orthogonal different topological order OAM as multiplexing channels, which can greatly improve the communication rate by combining with other advanced communication technologies (such as multi-channel input-output equalization technology). Vortex acoustic beam communication technology is divided into two parts: transmission end multiplexing and reception end demultiplexing.

[0003] The existing vortex beam demultiplexing technologies mainly adopt two methods: sound field inner product and metamaterial demodulation. The former uses the orthogonality of OAM to perform two-dimensional inner product on the multiplexed sound field and single-topological acoustic beam to extract the information of each channel. The latter makes the multiplexed sound field pass through the metamaterial structure, separates the OAM modes in space, and detects the information carried by each channel. In the article "High-speed acoustic communication by multiplexing orbital angular momentum", SHI et al. used a 26x26 microphone array to scan and measure a 48cmx48cm plane, and demodulated the multiplexed signal containing 8 OAM channels. In the articles "Principle and performance of orbital angular momentum communication of acoustic vortex beams on single-ring transceiver arrays" and "Spectrum decomposition-based orbital angular momentum communication of acoustic vortex beams using single-ring transceiver arrays", LI et al. and GUO et al. respectively used a circular microphone array to reduce the amount of inner product operation, but the sound field inner product method is still cumbersome and time-consuming. The metamaterial demodulation method does not require a microphone array, and the signal acquisition process is simple and efficient, but it has problems such as insertion loss, diffraction effect, and signal overlap.

[0004] In order to avoid the limitations of the above two methods, ZHANG et al. in the article "Spatiotemporal acoustic communication by a single sensor via rotational doppler effect" used a motor to drive a single microphone to rotate at a frequency Ω, and demodulated the OAM topological order information by measuring the rotational Doppler frequency shift effect (f D of the vortex beam, where f D represents the frequency after frequency shift, f0 represents the source frequency, and this method uses a single rotating microphone to realize real-time, large capacity and high precision communication with low-cost equipment. However, this method does not address the problem of insufficient low-frequency response of the microphone when l is negative and f D is close to 0Hz, nor does it explain the possible OAM channel crosstalk problem when the limit Doppler effect (f D <0Hz) occurs.

[0005] Reference:

[0006] [1] Shi C, Duois M, Wang Y, Zhang X. High-speed acoustic communication by multiplexing orbital angular momentum [J]. Proceedings of the National Academy of Sciences of the United States of America, 2017, 114(28): 7250-7253.

[0007] [2] LI X, LI Y, MA Q, GUO G, et al. Principle and performance of orbital angular momentum communication of acoustic vortex beams on single-ring transceiver arrays [J]. Journal of Applied Physics, 2020, 127(12): 124902.

[0008] [3] GUO G, LI X, WANG Q, LI Y, et al. Spectrum decomposition-based obital angular momentum communication of acoustic vortex beams using single-ring transceiver arrays [J]. IEEE Transcations on Ultrasonics, Ferroelectrics, and Frequency Control, 2020, 68(4): 1399-1407.

[0009] [4] ZHANG C, JIANG X, HE J, et al. Spatiotemporal acoustic communication by a single sensor via rotational doppler effect [J]. Advanced Science. 2023, 2: 2206619. SUMMARY

[0010] Therefore, the present application aims to provide a vortex sound beam demultiplexing method based on the rotating Doppler effect, which measures the sound pressure spectrum changing with the rotating observer rotation speed by sequentially extracting the time domain signals of equally spaced microphones, and quickly demultiplexes the vortex sound beam based on the rotating Doppler effect, solving the problems of insufficient microphone response and channel crosstalk that may exist in single rotating microphone demultiplexing in the field of low-frequency acoustic communication.

[0011] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0012] A vortex sound beam demultiplexing method based on the rotating Doppler effect, which does not need to measure single-topology sound beams in advance, but directly measures the time domain sound pressure signals of multi-topology vortex sound beams using a stationary circular microphone array, and assumes that an observer rotates along the circular microphone array, sequentially extracts the sound pressure signals received by the observer, and finally demultiplexes based on the Doppler shift characteristics of the sound signals. Wherein, the rotating Doppler effect refers to that when the observer rotates in the vortex sound beam plane, the frequency f D of the received signal changes with the observer rotation speed Ω (f D =f0+lΩ).

[0013] The method specifically comprises: first, constructing a circular array sound source system and a circular array of microphones; generating multiplexed vortex sound beams through the circular array sound source system, and then sequentially extracting the time domain signals collected by equally spaced microphones to measure the sound pressure spectrum changing with the rotating observer rotation speed; identifying the peak value corresponding to each vortex sound beam topology order in the frequency spectrum, and realizing the demultiplexing of the multiplexed vortex sound beam according to the relationship between the peak frequency and the vortex sound beam topology order.

[0014] The circular array sound source system is composed of N s uniformly distributed sound sources along the circular ring, and each sound source has a phase delay of relative to the previous sound source to generate vortex sound beams, wherein l represents the topology order of the vortex sound beam.

[0015] Further, the sound pressure spectrum is generated as follows: the original signal is collected by the circular array of microphones, and then the original signals of each microphone in the circular array of microphones are sequentially collected at the same time interval to obtain the sound pressure signal p D , and p D is converted into the frequency spectrum P D by fast Fourier transform.

[0016] The time interval is ΔNΔt0, wherein ΔN and Δt0 are respectively:

[0017]

[0018] Δt0=1 / F s0

[0019] In the formula, round{·} represents an integer function, and Ω ar represents the rotation frequency of the rotating observer, F s0 represents the sampling frequency of the sound card, N r represents the total number of microphones.

[0020] Further, the demultiplexing of the multiplexed vortex sound beam is specifically:

[0021] In the spectrum, the peak values corresponding to different topological orders of the vortex sound beam are identified, if there is a peak value corresponding to a topological order in the spectrum, the topological order is decoded as 1, otherwise, it is decoded as 0.

[0022] The peak value corresponding to each topological order is represented as:

[0023] f D =|f0+lΩ|

[0024] In the formula, f0 represents the source frequency of the vortex sound beam, and Ω represents the actual discrete rotation frequency of the observer,

[0025] Further, the source frequency of the generated multiplexed vortex sound beam needs to satisfy:

[0026] f0>Ω·max(|l - |)

[0027] In the formula, l - represents a negative topological order.

[0028] The beneficial effects of the present application are that: based on the rotating Doppler effect, the simple circular microphone array can be used to conveniently and quickly realize the demultiplexing of the multiplexed vortex sound beam, and at the same time, the problem of signal acquisition distortion caused by insufficient low-frequency response of the microphone when the topological order is negative can be effectively avoided; in addition, for vortex sound beam channel crosstalk, the present application limits the vortex sound beam source frequency to avoid the crosstalk problem. The device of the present application is simple to install, accurate in low-frequency measurement, and can measure multiple rotating speed conditions at one time.

[0029] Other advantages, objects, and features of the present application will be in part apparent and in part pointed out hereinafter in the specification, and will be observed by variations now being given or which may be apparent in the practice of the application. The objects and other advantages of the present application will be realized and attained by the embodiments particularly pointed out in the written description and claims hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0030] In order to make the purposes, technical solutions and advantages of the present application clearer, the preferred detailed description of the present application will be combined with the drawings as follows, wherein:

[0031] Figure 1 Structure diagram of vortex sound beam generation and collection device;

[0032] Figure 2 Structure diagram of microphone circular array;

[0033] Figure 3 Sound pressure spectrum obtained by sampling, Figure 3 (a) P spectrum of Ω = 28 Hz D spectrum, Figure 3 (b) P spectrum of Ω = 50 Hz D spectrum;

[0034] Figure 4 Structure diagram of spectrum of demultiplexing failure, Figure 4 (a) P spectrum of Ω = 30 Hz D spectrum, Figure 4 (b) P spectrum of Ω = 60 Hz D spectrum. DETAILED DESCRIPTION

[0035] The present application is described in the following by specific embodiments. Other advantages and effects of the present application can be easily understood by those skilled in the art from the disclosure of the present specification. The present application can also be implemented or applied by other different embodiments, and the details in the present specification can be modified or changed in various ways based on different views and applications without departing from the spirit of the present application. It should be noted that the diagrams provided in the following embodiments only illustrate the basic concept of the present application in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0036] Please refer to Figures 1-4 , a vortex sound beam demultiplexing method based on the rotating Doppler effect, the method first constructs a circular array sound source system and a microphone circular array; a multiplexed vortex sound beam is generated by the circular array sound source system, and then time domain signals collected by equally spaced microphones are extracted in sequence to measure sound pressure spectrum varying with rotating observer rotation speed; in the spectrum, peak values corresponding to each vortex sound beam topological order are identified, and demultiplexing of the multiplexed vortex sound beam is realized according to the corresponding relationship between peak frequency and vortex sound beam topological order.

[0037] The content of the present application is described in combination with embodiments:

[0038] In this embodiment, 16 loudspeakers (Visaton SC 8N) are used to form a uniformly distributed circular array (diameter of 480 mm) sound source system, as shown in Figure 1The introduction of the acoustic duct can reduce the diameter of the sound source (duct outlet) array to the same size as the microphone array and reduce the distance between them, thereby greatly reducing the sound wave diffraction effect and improving the signal-to-noise ratio of the microphone array when measuring the vortex sound beam. The loudspeaker is connected to the output end of the sound card (Antelope Orion32+) through the power amplifier (Shure TDA7498), and the data exchange between the sound card and the computer is performed through the AISO driver of MATLAB. In this embodiment, an 8-channel multiplex vortex sound beam (l is -4~4) is constructed, and the input signal of each loudspeaker is set as:

[0039]

[0040] where t is time, f0 represents the frequency of the vortex sound beam source, and is 120 Hz.

[0041] In this embodiment, the circular microphone array is composed of 32 1 / 4 inch microphones (BK 4958-A) which are uniformly distributed at equal intervals (11.25°) on a circular ring with a diameter of 160 mm, as shown in Figure 2 The microphone is connected to the input end of the sound card through the signal adapter (BK1704-C-102).

[0042] The original signal collected by the circular microphone array is represented as p(i,j), where i (1, 2, …, N t ) is the serial number of the sampling step (Δt0=1 / F s0 , F s0 is the sampling frequency of the sound card), and j (0~N r -1, N r represents the total number of microphones) is the serial number of the microphone encoded in the rotation direction of the observer. The imaginary observer rotates along the microphone array at an arbitrary rotation frequency Ω ar (Hz), and the movement time between adjacent two monitoring points is ΔNΔt0, where ΔN is:

[0043]

[0044] Δt0=1 / F s0

[0045] where round{·} represents the rounding function.

[0046] The actual discrete rotation frequency Ω of the observer and the received sound pressure signal p D are respectively:

[0047]

[0048] p D (m,Ω)=p(1+mΔN,m+js (4)

[0049] In the formula, m is an integer. In formula (4), if m+j s >N r ,m+j s N should be subtracted r Numbering starts again from 0 after each integer multiple of the given value. The time-domain signal p... D Converted to spectrum P via Fast Fourier Transform D :

[0050] P D (f,Ω)=FFT{p D (m,Ω)} (5)

[0051] The sampling step size and sampling frequency of the rotating observer are Δt and Δt, respectively. D =ΔNΔt0 and F sD =N r Ω, based on the Nyquist sampling theorem, P can be measured using a circular array of microphones. D highest frequency f max The relationship with the observer's rotation frequency Ω is:

[0052]

[0053] If the analysis frequency exceeds f max Then the spectrum P D Aliasing will occur. Furthermore, due to F... sD <F s0 It can be seen that the highest observer rotation speed Ω that can be measured using a circular array of microphones is... max for:

[0054]

[0055] A vortex sound beam was constructed using a circular array sound source system, and a 15-second sound pressure signal p(i,j) was measured. The sampling frequency F of the sound card was also measured. s0 Let the frequency be 96kHz. From equation (7), the measurable Ω is... max The frequency is 3kHz. Setting Ω to 10Hz~300Hz, from equation (6), we can see that f corresponds to Ω. max The lower and upper limits are 160Hz and 4.8kHz, respectively. Setting the FFT frequency resolution to 1Hz and the window function to a rectangular window will result in values ​​exceeding f... max P D Setting the value to 0 yields the normalized spectrum P. D like Figure 3 As shown in the figure, P D The peak frequency conforms to f D =|f0+lΩ|.

[0056] As Figure 3 (a), when Ω = 28 Hz, the 8-channel vortex sound beam does not occur the limit Doppler effect, the spectral peak frequency is consistent with f D = f0+ lΩ relationship, and each channel f D is arranged in order from small to large. When Ω = 50 Hz, as shown in Figure 3 (b), the channels of l = -4, -3 occur the limit Doppler effect, and the peak frequency is consistent with f D = |f0+ lΩ|, and each channel f D is no longer arranged in order from small to large. In addition, although the minimum effective frequency of BK 4958-A microphone is 10 Hz, the 8 Hz peak shown in the circle of Figure 3 (a) indicates that the microphone array effectively extracts the low-frequency signal close to 0 Hz, because the signal actually measured by the microphone array is a 120 Hz sine wave, avoiding the problem of insufficient low-frequency response often encountered by a single microphone. Figure 3 In addition to the peaks corresponding to the 8 channels, there are some other peaks with amplitudes much smaller than the peak of each channel, which may be caused by noise or signal processing errors.

[0057] According to Figure 3 the peak frequency of the spectrum shown in Figure 3 (a), the channel information of different l can be effectively identified, so the single spectrum extracted by the microphone circular array can be used for demultiplexing. By identifying the peak corresponding to different l, each l peak can be decoded by binary, if there is a peak corresponding to a certain l on the spectrum, it is decoded as 1, if there is no peak, it is decoded as 0, so the multiplexed OAM channel based on the single spectrum extracted by the microphone array can be demultiplexed, as shown in Figure 3 (a), the spectrum can be decoded as 11111111.

[0058] It should be noted that the single spectrum demultiplexing method described in the present application has the problems of weak signal or channel crosstalk when Ω ≥ f0 / |l|. For example, Figure 4 (a) shows the spectrum P D when Ω = f0 / |-4| = 30 Hz, this spectrum lacks the channel information of l = -4, because at Ω = 30 Hz, f D = 0 Hz, the observer rotates synchronously with the vortex sound beam, and the received acoustic signal is very weak. Figure 4 (b) shows the spectrum P D when Ω = 60 Hz, this spectrum not only lacks the channel information of l = -2 (f D = 0 Hz), but also the two channels of l = -3, -1 crosstalk with each other, because at Ω = 60 Hz, the f D of the two channels are both 60 Hz. Therefore, when demultiplexing the single spectrum, fD = 0 Hz and f D (l a ) = f D (l b ) These two cases, i.e., should be met:

[0059] Ω ≠ f0 / |l - | (8)

[0060] |f0+l a Ω|≠|f0+l b Ω| (9)

[0061] In the formula, l - is the negative order of OAM, l a and l b are two different OAM orders. Only when the limit Doppler effect occurs, f D (l a ) = f D (l b ) can occur, so further solving formula (9) obtains:

[0062]

[0063] In the formula, l′ a and l′ b respectively represent the channel OAM orders before and after the limit Doppler effect occurs, wherein l′ b is the negative order, and |l′ b | > |l′ a |. The two failure forms of the above single spectrum demultiplexing occur in the rotation speed region where the limit Doppler effect occurs, in order to completely avoid the failure, Ω < f0 / max(|l - |) should be selected, i.e., f0> Ω·max(|l - |).

[0064] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application and not to limit, although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the technical solutions, and they should be covered in the scope of the claims of the present application.

Claims

1. A vortex acoustic beam demultiplexing method based on the rotating Doppler effect, characterized in that: The method first constructs a circular array sound source system and a circular array of microphones; it then generates a multiplexed vortex sound beam through the circular array sound source system, and sequentially extracts the time-domain signals collected by equally spaced microphones to measure the sound pressure spectrum as the observer's rotational speed changes; it identifies the peak value corresponding to each topological order of the vortex sound beam in the spectrum, and demultiplexes the multiplexed vortex sound beam based on the relationship between the peak frequency and the topological order of the vortex sound beam; specifically, the demultiplexing of the multiplexed vortex sound beam involves identifying the peak value corresponding to different topological orders of the vortex sound beam in the spectrum, and if a peak value corresponding to a certain topological order exists in the spectrum, then that topological order is decoded as 1, otherwise it is decoded as 0. The peak values ​​corresponding to each topological series are represented as follows: In the formula, This indicates the frequency of the vortex beam source. This represents the topological order of the vortex beam. This represents the observer's actual discrete rotational frequency. ,in Indicates the total number of microphones. The time interval between two adjacent microphones is the movement of an observer as they rotate along the microphone array.

2. The vortex acoustic beam demultiplexing method according to claim 1, characterized in that: The circular array sound source system consists of It consists of sound sources that are evenly distributed along a circular ring.

3. The vortex acoustic beam demultiplexing method according to claim 2, characterized in that: In the circular array sound source system, each sound source has relative to the previous sound source. The phase delay is used to generate a vortex acoustic beam, in which This represents the topological order of the vortex acoustic beam.

4. The vortex acoustic beam demultiplexing method according to claim 1, characterized in that: The sound pressure spectrum is generated as follows: the original signal is acquired through a circular array of microphones, and then the original signals of each microphone in the circular array are acquired sequentially at the same time intervals to obtain the sound pressure signal. By using Fast Fourier Transform Convert to spectrum .

5. The vortex acoustic beam demultiplexing method according to claim 4, characterized in that: The time interval is ,in and They are respectively: In the formula, This represents the floor function. This indicates the rotation frequency of the rotating observer. This indicates the sampling frequency of the sound card. This represents the total number of microphones in the circular microphone array.

6. The vortex acoustic beam demultiplexing method according to claim 1, characterized in that: The source frequency of the generated multiplexed vortex beam needs to satisfy: In the formula, Represents a negative topological series. This represents the observer's actual discrete rotation frequency.

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