A closed vortex sound beam wrench based on multi-channel least square method

Abstract

The present application relates to a closed vortex sound beam wrench based on a multi-channel least square method, and belongs to the technical field of acoustic tweezers. The closed vortex sound beam wrench comprises a loudspeaker array, a guide tube, a microphone array and a closed cavity. The loudspeaker array is used to generate a vortex sound beam, which is transmitted to the closed cavity through the guide tube for controlling objects; the microphone array is connected with the closed cavity, and is used to collect sound field signals of the vortex sound beam and determine whether the vortex sound beam meets the precision requirement. The closed vortex sound beam wrench generates input signals of the loudspeaker array by using a multi-channel least square method, so that the loudspeaker array generates the vortex sound beam according to the input signals. The present application generates the vortex sound beam by using the multi-channel least square method, can use loudspeaker arrays of any size and array form, and greatly reduces the loss of sound energy; in addition, the least square method can also be used to construct the vortex sound beam to improve the upper limit of the topological series.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of acoustic tweezers, and relates to a closed vortex acoustic beam wrench based on a multi-channel least square method. BACKGROUND

[0002] Sound waves have both linear momentum and angular momentum, and thus have mechanical effects on objects. The linear momentum of sound waves produces a radiation force on objects, which can be used to control the position of objects or deform them. On the other hand, the transfer of angular momentum of sound waves produces a radiation torque, which can be used to rotate objects without contact. Since a vortex acoustic beam carries orbital angular momentum (OAM), many studies have used it as an acoustic wrench (rotator) or acoustic tweezers to manipulate micro- and macro-objects without contact. The acoustic field constructed by a vortex acoustic beam has a helical phase relationship proportional to the azimuthal angle, which is mathematically expressed as where represents the azimuthal angle, and l represents the topological order, that is, the number of wavelengths of the vortex acoustic beam within one circumference, and the positive and negative signs represent the rotation direction of the vortex.

[0003] A conventional vortex acoustic beam generating device usually adopts a circular loudspeaker array composed of N s (≥4|l|) equally spaced sound sources, which ensures that each loudspeaker has a phase delay of relative to the previous sound source, and the loudspeaker array emits sound according to this phase relationship to generate a single-OAM-mode vortex acoustic beam with a topological order of l. In order to ensure the above phase relationship, the transmitting end of the conventional vortex acoustic beam is usually in a free field or a near free field, which causes the acoustic energy of the vortex acoustic beam to be radiated to the entire free space and quickly dissipated, thereby causing the OAM and acoustic radiation torque carried by the vortex acoustic beam to quickly decrease. In addition, the loudspeaker array constructed in the conventional way needs to be fixed in a circular ring, and due to the complex installation method, the size and number of loudspeakers are limited, which further limits the amplitude of the OAM and acoustic radiation torque. The above factors greatly limit the application of the conventional vortex acoustic beam device in the field of contactless rotation of objects. SUMMARY

[0004] Therefore, the present application aims to provide a device that uses a multi-channel least square method to construct a vortex acoustic beam in a closed cavity for contactless rotation of objects and reduces the dissipation of acoustic energy.

[0005] To achieve the above-mentioned purpose, the present application provides the following technical solutions:

[0006] A closed-loop vortex beam wrench based on multi-channel least squares method includes a speaker array, a guide tube, a microphone array, and a sealed cavity. The speaker array generates a vortex beam, which propagates through the guide tube into the sealed cavity for manipulating objects. The microphone array is connected to the sealed cavity and is used to acquire the sound field signal of the vortex beam and determine whether the vortex beam meets accuracy requirements. This closed-loop vortex beam wrench uses a multi-channel least squares method to generate the input signal to the speaker array, which then generates the vortex beam based on this input signal.

[0007] Optionally, the enclosed cavity includes an outer circular tube, an inner circular tube, an upper cover plate, and a lower cover plate; the outer circular tube and the inner circular tube are disposed between the upper cover plate and the lower cover plate, and a sealed cavity is formed between the outer circular tube and the inner circular tube.

[0008] The upper cover plate is provided with several circular holes evenly distributed along the circumference for connecting and fixing the guide tube. The several circular holes are distributed in the ring of the upper cover plate separated by the outer and inner circular tubes.

[0009] Optionally, the outer circular tube wall is provided with several small holes evenly distributed along the circumference for fixing the microphone array.

[0010] Optionally, the closed-loop vortex beam wrench generates a vortex beam by using a microphone array as the monitoring point for the vortex beam. The target sound pressure and phase of the vortex beam generated by the speaker array at the monitoring point are shown in the following formula:

[0011]

[0012] In the formula, N l The maximum positive topological series that can be constructed is represented by l, where l represents the topological series, P0 represents any sound pressure level that a single loudspeaker can achieve, and n represents 0 to N. r -1 is the microphone serial number.

[0013] Based on signal P, the multi-channel least squares method is used. t Generate a frequency domain signal S, and calculate the time domain signal s of the vortex beam based on signal S:

[0014]

[0015] In the formula, f0 represents the frequency of the vortex beam, t represents the time series, and n represents 0 to N. r -1 is the microphone serial number; the speaker array is driven by this time domain signal s to produce sound, which generates a vortex sound beam.

[0016] Optionally, the way of judging whether the vortex sound beam generated by the loudspeaker array meets the accuracy requirement comprises: collecting the original signal of the vortex sound beam by the microphone array, then extracting the original signal of each microphone along the microphone array in turn based on the discrete frequency shift Omega to obtain a sound pressure signal, and converting the sound pressure signal into a frequency spectrum by using fast Fourier transform. If the peak frequency f of the frequency spectrum meets f D = |f0+lOmega| D , the vortex sound beam generated by the loudspeaker array meets the accuracy requirement.

[0017] wherein the discrete frequency shift Omega is represented as:

[0018]

[0019] In the formula, N r represents the number of microphones; Delta N Delta t0 represents the time interval of signal collection between adjacent sensors, which can also be understood as: when an imaginary observer rotates along the microphone array with the discrete frequency shift Omega, the movement time between adjacent two microphones.

[0020] The present application has the advantages that: the present application generates the vortex sound beam by using the multi-channel least square method, so that the loudspeaker array of any size and array form can be used, and the loss of sound energy can be greatly reduced; in addition, the present application can theoretically infinitely improve the radiated sound power of the sound wave (depending on the performance of the loudspeaker), and can greatly improve the amplitude of the OAM and the radiation torque of the vortex sound beam. In addition, the least square method is used to construct the vortex sound beam, which can break through the limitation of topological series , so that the upper limit of |l| is improved to

[0021] Other advantages, objects, and features of the present application will be in part apparent and in part pointed out hereinafter in the specification, and it is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory thereof, and are not restrictive of the present application, as claimed. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to make the objects, technical solutions and advantages of the present application clearer, the preferred embodiments of the present application will be described in detail below with reference to the drawings, in which:

[0023] Figure 1 The structural schematic diagram of the closed vortex sound beam wrench provided by an embodiment of the present application;

[0024] Figure 2 The structural schematic diagram of the closed cavity;

[0025] Figure 3 The hardware structure block diagram for calculating the vortex sound beam;

[0026] Figure 4 is a multi-channel least square method framework diagram;

[0027] Figure 5 is a vortex sound beam Doppler spectrum cloud chart. DETAILED DESCRIPTION

[0028] Other advantages and effects of the present application can be easily understood by those skilled in the art from the disclosure of the specification. The present application can also be implemented or applied by means of other different specific embodiments, and various modifications or changes can be made to the details in the specification based on different views and applications without departing from the spirit of the present application. It should be noted that the drawings 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.

[0029] The drawings are only used for exemplary illustration, and the representation is only a schematic diagram, not a physical diagram, and should not be understood as a limitation on the present application; in order to better illustrate the embodiments of the present application, some components in the drawings may be omitted, enlarged or reduced, and do not represent the actual product size; it can be understood by those skilled in the art that some well-known structures and their descriptions in the drawings may be omitted.

[0030] The same or similar reference numerals in the drawings of the embodiments of the present application correspond to the same or similar components; in the description of the present application, it should be understood that if the terms "upper", "lower", "left", "right", "front", "back" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore the terms describing the positional relationship in the drawings are only used for exemplary illustration, and should not be understood as a limitation on the present application, for those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0031] To solve the problem that in the traditional vortex sound beam construction method, the loudspeakers need to be fixed in a circular ring and the size and number of the loudspeakers are limited, and the problem that the sound energy of the vortex sound beam at the emission end is radiated to the entire free space and dissipated, the present application proposes to construct a vortex sound beam by a multi-channel least square method, and simultaneously connect the loudspeaker array and a closed cavity through a sound guide pipe, so as to limit the vortex sound beam emitted by the loudspeakers in the closed cavity, so that the vortex sound beam can be constructed by any array, any size and number of loudspeakers, and energy dissipation caused by radiation of the vortex sound beam to the free space can be avoided.

[0032] Specifically, an embodiment of the present application provides a method for constructing a vortex sound beam, comprising:Figure 1 The illustrated vortex acoustic beam wrench can be used to rotate objects without contact. This acoustic wrench includes a speaker array, an adapter, a guide tube, and a sealed cavity. The speaker array can use speakers of any arrangement or shape; in this embodiment, a speaker matrix is ​​used. To reduce unnecessary sound dissipation and leakage, a guide tube with a certain wall thickness is used to guide the sound waves emitted by the speakers into the sealed cavity operating platform. This guide tube can be made of flexible tubing, allowing the sealed cavity to be placed in any orientation. For example, the sealed cavity can be placed on a horizontal plane to reduce the effect of gravity on the manipulated object, making it easier to rotate. An adapter is placed between the guide tube and the speakers to minimize sound energy loss.

[0033] The structure of a closed cavity is as follows Figure 2 As shown, it includes an outer circular tube, an inner circular tube, an upper cover plate, and a lower cover plate. The outer and inner circular tubes are positioned between the upper and lower cover plates, forming a sealed cavity that serves as the movement area for the manipulated object. The upper cover plate has N-shaped grooves evenly spaced along its circumference. s One round hole is used for connection with the guide tube, N s The number of loudspeakers; N-shaped holes are evenly spaced on the outer circular tube wall. R (N R =N s A series of small holes are used to house microphones with a diameter of 1 / 4 inch. This microphone array can be used to measure the frequency response function of the loudspeaker array to the enclosed cavity, thereby obtaining the input signal of the speaker according to the least squares method. It can also be used to detect the characteristics of the vortex beam within the enclosed cavity, thereby determining whether a sufficiently accurate vortex beam sound field has been constructed. The inner circular tube of the enclosed cavity is used to ensure that the manipulated object will not accidentally enter the inner circular tube. The acoustic radiation torque inside the inner circular tube is almost zero. The lower cover plate of the enclosed cavity can be a actually machined circular plate or any plane where the manipulated object is located. For example, when the enclosed cavity is placed on a horizontal table, the horizontal table can be used as the lower cover plate of the enclosed cavity.

[0034] In this embodiment of the vortex beam wrench, the first step is to ensure a seal between the inner and outer tubes and the lower cover. Then, the frequency response function matrix from the speaker array to the transmitting end circular microphone array is measured using a logarithmic sine sweep frequency method. Using the ideal sound pressure signal of the vortex beam in the microphone array as the target sound field, the speaker input signal is obtained using a multi-channel least squares method. Finally, a computer-controlled sound card and power amplifier transmit this input signal to the speaker to drive the speaker array to produce sound, thereby constructing single or multiple topologically ordered vortex beams within a closed cavity to drive the manipulated object to rotate. The computing hardware platform includes, for example,... Figure 3 As shown.

[0035] Another embodiment of the present application provides a method for generating the vortex sound beam of the acoustic wrench, which is as follows:

[0036] When generating the multiplexed vortex sound beam through an arbitrary distributed loudspeaker array, a circular ring microphone array is used as the monitoring point of the vortex sound beam, which is composed of N r equally spaced microphones. The target sound pressure and phase of the vortex sound beam generated by the loudspeaker array at the monitoring point have the following characteristics:

[0037]

[0038] In the formula, P t represents the ideal value of the multiplexed vortex sound beam, N l represents the maximum positive topological order that can be constructed, l represents the topological order, P0 represents the arbitrary sound pressure amplitude that can be reached by a single loudspeaker, and n represents the microphone serial number from 0 to N r -1.

[0039] This embodiment uses a multi-channel least square equalization system as shown in Figure 4 to generate the target vortex sound beam, and G represents the entire physical transmission path composed of the output end of the sound card, the power amplifier, the loudspeaker, and the environment. The ideal vortex sound beam sound field P t is input to the equalization filter (represented by an N s ×N r complex matrix) added before the sound card, and the signal S of the sound source is calculated by the computer through the following formula:

[0040]

[0041] In order to make the constructed sound field close to the target sound field P t , and G together form an equalization system that should satisfy:

[0042]

[0043] In the formula, I represents the unit matrix, and Δ represents the delay of the hardware system. The least square method is used, and the Tikhonov regularization parameter λ is introduced, and the calculation of S is as follows:

[0044]

[0045] The solution of the above formula is:

[0046]

[0047]

[0048] where the superscript H denotes the transpose of a matrix. is N r S is a complex matrix, whose elements are the frequency response functions between each microphone and speaker in the microphone matrix and speaker matrix, which can be measured by the log-sine sweep method. The time-domain signal s of a single frequency vortex beam can be calculated from the signal S:

[0049]

[0050] where t is the time sequence.

[0051] After the vortex beam is generated by the speaker array using the multi-channel least square method, the sound field signal of the vortex beam is further measured by the circular microphone array. The original signal is collected by the microphone circular array, and the Doppler spectrum received by the observer when rotating at multiple rotation speeds is extracted through signal processing to determine whether a vortex beam with sufficient precision is constructed.

[0052] Specifically, the signal processing method is as follows:

[0053] The original time-domain signal collected by the microphone array is denoted as p(i,j), where i(1,2,…,N t ) is the sequence number of the sampling step (denoted as Δt0=1 / F s0 , F s0 is the sampling frequency of the sound card), and j is the sequence number of the microphone (0~N r -1) encoded in the rotation direction of the observer. It is assumed that an observer rotates at an arbitrary rotation frequency Ω ar (Hz) along the microphone array, and the movement time between adjacent microphones is ΔNΔt0, where ΔN is:

[0054]

[0055] where round is the MATLAB rounding function. The actual discrete rotation frequency Ω of the observer and the received sound pressure signal p D are respectively:

[0056]

[0057] p D (m,Ω)=p(1+(m-1)ΔN,m′-1)

[0058] where m represents an integer that increases from 1. When m r , m′=m; when m r , m′ is the remainder integer obtained by dividing m by N r . The time-domain signal p D is converted into a frequency spectrum P​D As follows:

[0059] P D (f,Ω)=FFT{p D (m,Ω)}

[0060] In the formula, f represents the spectral frequency, and FFT is the MATLAB fast Fourier transform function.

[0061] The sampling step and sampling frequency of the rotating observer depend on the motion time between adjacent microphones, which are Δt D = ΔNΔt0and F sD = N r Ω, based on the Nyquist sampling theorem, the highest frequency f D of P max measured by the circular microphone array is:

[0062]

[0063] If the analysis frequency exceeds f max , the spectrum P D will be aliased. On the other hand, it can be known from F sD <F s0 that the highest observer rotation frequency Ω max measured by the circular microphone array is:

[0064]

[0065] As Figure 5 shown in the figure, the Doppler spectrum cloud of the vortex sound beam with f0(the vortex sound beam source frequency) of 120 Hz, l of -4 and -7 is constructed by using 16 loudspeakers. It can be seen that, Figure 4 the spectral peak frequency f D coincides with the frequency f0+lΩ|after the rotation Doppler shift, i.e., f D = |f0+lΩ|, which shows that the vortex sound beam with the topological order up to can be accurately constructed by using the multi-channel least square method.

[0066] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can be modified or replaced equivalently without departing from the purpose and scope of the present technical solutions, which should be covered in the scope of the claims of the present application.

Claims

1. A closed vortex beam wrench based on a multi-channel least square method, characterized in that: The closed vortex sound beam wrench comprises a loudspeaker array, a guide pipe, a microphone array and a closed cavity; the loudspeaker array is used to generate a vortex sound beam, the vortex sound beam is transmitted into the closed cavity through the guide pipe and is used to manipulate an object; the microphone array is connected with the closed cavity and is used to collect sound field signals of the vortex sound beam and determine whether the vortex sound beam meets precision requirements; The closed vortex sound beam wrench generates input signals of the loudspeaker array by using a multi-channel least square method, so that the loudspeaker array generates the vortex sound beam according to the input signals. The closed cavity comprises an outer circular pipe, an inner circular pipe, an upper cover plate and a lower cover plate; the outer circular pipe and the inner circular pipe are arranged between the upper cover plate and the lower cover plate, and a sealed cavity is formed between the outer circular pipe and the inner circular pipe and is used as a movement area of the manipulated object.

2. The closed scroll whorl sonic beam wrench of claim 1, wherein: The upper cover plate is provided with a plurality of circular holes which are equally spaced along a circumference and are used to connect and fix the guide pipe; the circular holes are distributed in a circular ring which is separated by the outer circular pipe and the inner circular pipe.

3. The closed scroll whorl sonic beam wrench of claim 1 or 2, wherein: A plurality of small holes which are equally spaced along a circumference are arranged on a wall surface of the outer circular pipe and are used to fix the microphone array.

4. The closed scroll whorl sonic beam wrench of claim 1, wherein: The closed vortex sound beam wrench generates the vortex sound beam in the following manner: the microphone array is used as a monitoring point of the vortex sound beam, and target sound pressure and phase of the vortex sound beam generated by the loudspeaker array at the monitoring point are as follows: wherein denotes the maximum positive topological order that can be constructed, denotes the topological order, denotes the arbitrary sound pressure amplitude that can be achieved by a single loudspeaker, n denotes denotes the microphone sequence number; by a multichannel least squares method based on signals generating a frequency domain signal based on signals computing a time domain signal of a vortex beam is: wherein denotes the frequency of the acoustic vortex beam, denotes a time series, denotes a microphone sequence number; from this time domain signal drives a loudspeaker array to emit sound, i.e. to generate an acoustic vortex beam.

5. The closed scroll whirlwind sound beam wrench of claim 4, wherein: The method for judging whether the vortex sound beam generated by the loudspeaker array meets the accuracy requirement comprises: collecting the original signal of the vortex sound beam by the microphone array, and then converting the original signal into a frequency spectrum based on the discrete frequency conversion The original signal of each microphone is extracted along the microphone array to obtain a sound pressure signal, and the sound pressure signal is converted into a frequency spectrum by using a fast Fourier transform; if the peak frequency of the frequency spectrum is consistent with the peak frequency of the frequency spectrum of the original signal of the vortex sound beam, then the vortex sound beam generated by the loudspeaker array meets the accuracy requirement; the discrete frequency conversion is represented as: ​ In the formula, represents the number of microphones, represents the time interval of signal collection between adjacent sensors.

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