Directional transmitting device for acoustic OAM (Operation Administration and Maintenance) signal

Abstract

The invention discloses a directional transmitting device for acoustic OAM signals, which comprises a phased array circuit, a planar fan-shaped transducer array, a sawtooth lens and two gradient lenses, and is characterized in that active phase control and passive phase modulation are combined, and the gradient lenses are adopted, so that sound waves can deflect along a fixed direction; the OAM signal with controllable order is generated at any position in a two-dimensional plane by utilizing the relative rotation of the two gradient lenses. According to the invention, efficient and flexible vortex sound beam generation can be realized, so that better transmission performance can be provided in underwater sound vortex communication, the processing process of the lens is simplified, the lens has remarkable advantages in the aspects of cost and flexibility, and a wide application prospect is shown.

Description

Technical Field

[0001] The invention relates to a directional transmitting device for acoustic OAM signals, belonging to the technical field of underwater data transmission and acoustic vortex communication applications. Background Art

[0002] Unlike plane waves, vortex beams are special beams with a spiral phase wavefront, and there is a phase singularity at the center of the vortex with zero field intensity. Mathematically, the phase distribution of a vortex beam can be described by exp(ilφ), where l is the topological charge and φ is the azimuth angle. The orbital angular momentum (OAM) carried by vortex beams, as a new degree of freedom, is expected to solve the current dilemma of limited communication resources. Since water molecules strongly absorb light waves and light waves are easily blocked and scattered by small particles in the ocean, sound waves have unique advantages over light waves in underwater communications. Based on the ability to accurately generate and control vortex acoustic beams, researchers have carried out research on OAM acoustic communication. In order to realize an OAM acoustic communication system with a simple structure and convenient control, the research team used a single-ring transceiver array to construct a theoretical model of OAM acoustic beam communication, and established a single-ring 16-source array experimental system to study the principle and performance of OAM multiplexing communication. This study provides a theoretical basis and technical support for the array design, data transmission, decoding and calibration of OAM acoustic beams in communication systems, and has broad application prospects.

[0003] At present, research in the field of acoustic vortex communication mainly focuses on coaxial transmission, but in actual communication, the receiving point and the transmitting point are often not on the same axis. Therefore, it is particularly necessary to effectively transmit energy-concentrated signals to a specific location, and the transmission direction can be freely adjusted, to build a safe, flexible, and highly controllable underwater acoustic vortex communication system. There are fewer studies on off-axis vortices. One study combined an iterative backpropagation algorithm with two 256-element transmitter arrays to construct a vortex sound beam at any two-dimensional position in space, but the large number of array elements increased costs and poor system flexibility. To solve this problem, some studies have constructed a directional off-axis acoustic vortex by introducing phase delay in the traditional planar sensor ring array, which greatly reduced the complexity of the system, but the change of the vortex center requires recalculation of the sound source array phase, and the adjustability and flexibility are still poor. Summary of the invention

[0004] The present invention aims to solve the deficiencies of the above-mentioned prior art and proposes a directional transmission device for acoustic OAM signals, so as to achieve efficient and flexible OAM acoustic beam generation, thereby providing better transmission performance in underwater acoustic vortex communication.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical scheme:

[0006] The directional transmitting device of an acoustic OAM signal of the present invention is characterized in that it comprises: a phased array circuit, a planar fan-shaped transducer array, a sawtooth lens and two gradient lenses;

[0007] The phased array circuit is connected to an external input power supply, and generates N square wave signals with programmable delays at a fixed frequency, which are then processed by a low-pass filter and a broadband power amplifier in sequence, thereby outputting N sinusoidal signals with controllable initial phases to the planar sector transducer array;

[0008] The planar sector transducer array is connected to a phased array circuit and generates an OAM target acoustic beam of arbitrary topological charge along a propagation axis according to the received sinusoidal signal;

[0009] The sawtooth lens is embedded in the surface of the planar sector transducer array, and the radii of the sawtooth lens and the planar sector transducer array are both set to be a;

[0010] After the OAM target acoustic beam is subjected to line-focusing phase modulation in the sawtooth lens, the modulated OAM target acoustic beam is output and deflected to the propagation axis at the same refraction angle γ for propagation, thereby controlling the propagation direction of the OAM target acoustic beam and generating a Bessel OAM acoustic beam with a non-diffraction characteristic;

[0011] In a direction perpendicular to the surface of the planar sector transducer array, two gradient lenses are placed at equal intervals in sequence at a position where the distance between the two gradient lenses is d, and the interval between the two gradient lenses is also d; the rotation angle range of the two gradient lenses is [-π,π];

[0012] After the Bessel OAM acoustic beam is phase modulated in the first gradient lens, it is deflected at a fixed angle to propagate away from the propagation axis, enters the second gradient lens for phase modulation again, and continues to deflect at the fixed angle to propagate away from the propagation axis, and finally outputs an acoustic OAM signal;

[0013] By adjusting the rotation angles of the first and second gradient lenses to change the phase modulation effect between the first and second gradient lenses, the transmission direction of the Bessel OAM acoustic beam can be flexibly adjusted to achieve directional transmission of the acoustic OAM signal.

[0014] The directional transmission device of an acoustic OAM signal described in the present invention is also characterized in that, based on the linear relationship between the bottom angle α of the sawtooth lens and the focal length, the range of the bottom angle α of the sawtooth lens is determined to be π / 8-π / 4.

[0015] Furthermore, according to the base angle α of the sawtooth lens, the phase modulation function of the sawtooth lens is designed using equation (1): , which is used to perform line-focusing phase modulation on the OAM target acoustic beam;

[0016] (1)

[0017] In formula (1), b is a constant, and b=1.53 / tan(α). The value of b can be determined according to the base angle α. is the distance between any point on the sawtooth lens and the center of the sawtooth lens, is the azimuth angle of any point on the sawtooth lens, is the polar coordinate of any point on the surface of the sawtooth lens.

[0018] Furthermore, according to the generalized Fresnel law, the phase modulation function of the first gradient lens is designed using equation (2): , and used to phase modulate the Bessel OAM acoustic beam;

[0019] (2)

[0020] In formula (2), b 1 is the gradient phase change rate of the first gradient lens, and b 1 ∈[2π / 100, -2π / 10].

[0021] Furthermore, the phase modulation function of the second gradient lens is Phase modulation function with the first gradient lens same.

[0022] Furthermore, the joint phase modulation function of the two gradient lenses is designed according to the following steps: , to change the phase modulation effect between the first and second gradient lenses:

[0023] Step a: Adjust the rotation angle of the first gradient lens to θ 1 Then, the phase modulation function of the first gradient lens is designed using equation (3): :

[0024] (3)

[0025] Step b: Adjust the lens rotation angle of the second gradient to θ 2 Then, the phase modulation function of the second gradient lens is designed using equation (4): :

[0026] (4)

[0027] Step c: Assume θ 1 = -θ 2, using formula (5) to determine the joint phase modulation effect of the first gradient lens and the second gradient lens after rotation :

[0028] (5).

[0029] Furthermore, the coverage range of the acoustic OAM signal is any position within a circle with a radius R centered outward from the propagation axis.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] 1. The present invention designs a gradient lens based on a simplified annular planar fan-shaped transducer array by integrating active phase control and passive phase modulation. This technical feature can effectively deflect sound waves in a fixed direction, overcoming the problems of unstable sound wave deflection and poor directionality in traditional methods. Combined with the sawtooth phase modulation structure, the present invention can form an off-axis quasi-Bessel vortex sound beam, ensuring that the angular position of the vortex sound beam is linearly related to the rotation angle of the gradient lens, thereby greatly improving the controllability and accuracy of the sound beam, and providing higher performance for a variety of application scenarios.

[0032] 2. The present invention proposes to use two gradient lenses to form a lens group, avoiding the complexity of processing multiple different gradient lenses. This design scheme can generate a vortex center at any position on a two-dimensional plane simply by rotating the two lenses at any angle, which significantly simplifies the manufacturing process. The radial displacement of the vortex center is determined by the relative rotation angle between the two gradient lenses. This flexibility solves the limitation of the fixed position of the vortex center in the prior art, making the positioning of the vortex sound beam more accurate and convenient.

[0033] 3. The present invention can generate a quasi-Bessel vortex acoustic beam with controllable order at any position in a two-dimensional plane by phase modulation of a planar fan-shaped transducer array. This technology not only provides a solid theoretical basis and technical support for the directional transmission of vortex acoustic beams, but also significantly reduces the overall cost of the system. Compared with the traditional off-axis vortex acoustic beam construction method, the present invention shows greater flexibility and economy in both manufacturing and operation, especially in the field of underwater acoustic vortex communication, and has broad application prospects and can meet diverse communication needs.

[0034] 4. The present invention can achieve higher signal transmission efficiency and longer transmission distance, solve the problem of serious signal attenuation in the prior art, and thus improve the reliability and stability of underwater acoustic communication. This provides important technical support for the development of future underwater detection, monitoring and communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1The present invention is a schematic diagram of a complete transmission system of a directional acoustic OAM signal transmitting device, wherein: 1 is a phased array circuit, 2 is a planar fan-shaped transducer array, 3 is a sawtooth lens, 4 is a first gradient lens, and 5 is a second gradient lens.

[0036] Figure 2 Schematic diagram of radial position control of acoustic OAM signal of the present invention. Figure 2 (a) in the figure shows the acoustic pressure distribution of the OAM signal at radial displacement distance 1, distance 2, and distance 3 from left to right. Figure 2 (b) shows the phase distribution of OAM signals at radial displacement distances 1, 2, and 3 from left to right.

[0037] Figure 3 Schematic diagram of the angular position control of the acoustic OAM signal of the present invention. Figure 3 (a) in the figure shows the acoustic pressure distribution of the OAM signal at angular position 1, position 2 and position 3 from left to right. Figure 3 (b) shows the phase distribution of OAM signals at angular positions 1, 2 and 3 from left to right.

[0038] Figure 4 is the acoustic field distribution diagram of the OAM signal with topological charge l = 1–4 generated by the first and second gradient lenses at a fixed rotation angle in the present invention; wherein, Figure 4 (a) shows the acoustic pressure distribution of OAM signals with topological charges equal to 1, 2, 3 and 4 from left to right. Figure 4 (b) shows the phase distribution of OAM signals with topological charge equal to 1, 2, 3 and 4 from left to right. DETAILED DESCRIPTION

[0039] In this embodiment, a directional transmitting device for acoustic OAM signals, such as Figure 1 As shown, the whole transmitting system includes: a phased array circuit, a planar fan-shaped transducer array, a sawtooth lens and two gradient lenses;

[0040] The phased array circuit is connected to an external input power supply and generates N = 16 programmable delayed square wave signals at a fixed frequency. After being processed by a low-pass filter and a broadband power amplifier, N initial phase-controllable sinusoidal signals are output to the planar fan-shaped transducer array. The number of fan-shaped transducers is M, and the fan angle of each fan-shaped transducer is According to the phase encoding principle, the initial phase of the sinusoidal signal that excites the mth sector transducer is .

[0041] The planar sector transducer array is connected to the phased array circuit and generates an OAM target acoustic beam with an arbitrary topological charge size of l along the propagation axis according to the received sinusoidal signal;

[0042] The sawtooth lens is nested on the surface of the planar sector transducer array. There must be no gap between the sawtooth lens and the planar sector transducer array. The radii of the sawtooth lens and the planar sector transducer array are both set to be a. According to the linear relationship between the bottom angle α of the sawtooth lens and the focal length, the range of the bottom angle α of the sawtooth lens is determined to be π / 8-π / 4.

[0043] After the OAM target acoustic beam is subjected to line-focusing phase modulation in the sawtooth lens, the modulated OAM target acoustic beam is output and deflected to the propagation axis at the same refraction angle γ for propagation, thereby controlling the propagation direction of the OAM target acoustic beam and generating a Bessel OAM acoustic beam with non-diffraction characteristics;

[0044] In this embodiment, according to the base angle α of the sawtooth lens, the phase modulation function of the sawtooth lens is designed using equation (1): , which is used to perform line-focusing phase modulation on the OAM target acoustic beam;

[0045] (1)

[0046] In formula (1), b is a constant, and b=1.53 / tan(α). The value of b can be determined according to the base angle α. is the distance between any point on the sawtooth lens and the center of the sawtooth lens, is the azimuth angle of any point on the sawtooth lens, is the polar coordinate of any point on the surface of the sawtooth lens. For locations where the sawtooth lens is thick, the phase compression method is used to compress the sawtooth lens and the sawtooth lens is designed as a thin lens. This can reduce the attenuation of the OAM target sound beam when it propagates in the sawtooth lens. At the same time, a basic thickness d is added to the sawtooth lens. min =1mm, to avoid the formation of standing waves.

[0047] In the direction perpendicular to the surface of the plane sector transducer array, two gradient lenses are placed at equal intervals in sequence at a position with a distance d from the sawtooth lens, and the interval between the two gradient lenses is also d. Since the spherical wave will have a divergence effect, if the interval is set too large, it will affect the sound beam quality of the Bessel OAM sound beam. If the interval is set too small, the reflection and refraction effect between the first gradient lens and the second gradient lens will be increased. Therefore, d is set to 1mm, and the rotation angle range of the two gradient lenses is [-π,π];

[0048] After the Bessel OAM acoustic beam is phase modulated in the first gradient lens, it is deflected at a fixed angle to propagate away from the propagation axis, enters the second gradient lens for phase modulation again, and continues to deflect at a fixed angle to propagate away from the propagation axis, and finally outputs an acoustic OAM signal;

[0049] In this embodiment, according to the generalized Fresnel refraction law, the phase modulation function of the first gradient lens is designed using equation (2): , and used to phase modulate the Bessel OAM acoustic beam;

[0050] (2)

[0051] In formula (2), b 1 is the gradient phase change rate of the first gradient lens, and b 1 ∈[2π / 100, -2π / 10]. In the design and processing of the first gradient lens, the principle of phase compression also needs to be used to compress the thickness of the first gradient lens to make it a thin lens, so as to reduce the attenuation of the sound wave when it propagates in the first gradient lens.

[0052] Phase modulation function of the second gradient lens Phase modulation function with the first gradient lens same.

[0053] By adjusting the rotation angles of the first and second gradient lenses to change the phase modulation effect between the first and second gradient lenses, the transmission direction of the Bessel OAM acoustic beam can be flexibly adjusted to achieve directional transmission of the acoustic OAM signal.

[0054] In this embodiment, the joint phase modulation function of two gradient lenses can be designed according to the following steps: , to change the phase modulation effect between the first and second gradient lenses:

[0055] Step a: With the help of the first gradient lens, the OAM signal can only be displaced by a fixed distance ∆d, changing the rotation angle θ 1 The angular position of the acoustic OAM signal can be adjusted. The rotation angle of the first gradient lens is adjusted to θ 1 Then, the phase modulation function of the first gradient lens is designed using equation (3): :

[0056] (3)

[0057] Step b: Adjust the lens rotation angle of the second gradient to θ 2 Then, the phase modulation function of the second gradient lens is designed using equation (4): :

[0058] (4)

[0059] Step c: Assume θ 1 = -θ 2 , using formula (5) to determine the joint phase modulation effect of the first gradient lens and the second gradient lens after rotation :

[0060] (5).

[0061] In formula (5), the combined effect modulation effect obtained by rotating the first gradient lens and the second gradient lens is equivalent to a gradient phase equal to The gradient lens, the gradient size and the rotation angle θ 1 There is a cosine function change relationship between them.

[0062] The range is [0,2b 1 ], change θ 1 The distance between the acoustic OAM signal and the center of the observation surface can be controlled, such as Figure 2 shown.

[0063] By rotating the two gradient lenses at an angle β at the same time, the angular position of the acoustic OAM signal can be controlled, such as Figure 3 shown.

[0064] The range is [0,2b 2 ], so the coverage range of the acoustic OAM signal is: any position within a circle with a radius R centered on the propagation axis.

[0065] After the distance between the acoustic OAM signal and the center of the observation surface and the azimuth position are adjusted, the topological charge of the acoustic OAM signal can be adjusted by changing the excitation sinusoidal signals of different sectors of the planar sector transducer array, such as Figure 4 As shown, the absolute value of the topological charge that can be controlled is limited by the number of sound sources and needs to be less than (M-1) / 2.

[0066] In summary, the directional transmitting device of the present invention combines active phase control with passive phase modulation and adopts a gradient lens design, so that the sound wave can be deflected in a fixed direction. By utilizing the relative rotation of two gradient lenses, it is possible to generate an acoustic OAM signal with controllable topological charge at any position in a two-dimensional plane. This method not only simplifies the lens processing process, but also has significant advantages in cost and flexibility, showing broad application prospects.

Claims

1. A directional transmitting device for acoustic OAM signals, characterized in that: include: a phased array circuit, a planar sector transducer array, a sawtooth lens, and two gradient lenses; The phased array circuit is connected to an external input power supply, and generates N square wave signals with programmable delays at a fixed frequency, which are then processed by a low-pass filter and a broadband power amplifier in sequence, thereby outputting N sinusoidal signals with controllable initial phases to the planar sector transducer array; The planar sector transducer array is connected to a phased array circuit and generates an OAM target acoustic beam of arbitrary topological charge along a propagation axis according to the received sinusoidal signal; The sawtooth lens is embedded in the surface of the planar sector transducer array, and the radii of the sawtooth lens and the planar sector transducer array are both set to be a; After the OAM target acoustic beam is subjected to line-focusing phase modulation in the sawtooth lens, the modulated OAM target acoustic beam is output and deflected to the propagation axis at the same refraction angle γ for propagation, thereby controlling the propagation direction of the OAM target acoustic beam and generating a Bessel OAM acoustic beam with a non-diffraction characteristic; In a direction perpendicular to the surface of the planar sector transducer array, two gradient lenses are placed at equal intervals in sequence at a position where the distance between the two gradient lenses is d, and the interval between the two gradient lenses is also d; the rotation angle range of the two gradient lenses is [-π,π]; After the Bessel OAM acoustic beam is phase modulated in the first gradient lens, it is deflected at a fixed angle to propagate away from the propagation axis, enters the second gradient lens for phase modulation again, and continues to deflect at the fixed angle to propagate away from the propagation axis, and finally outputs an acoustic OAM signal; By adjusting the rotation angles of the first and second gradient lenses to change the phase modulation effect between the first and second gradient lenses, the transmission direction of the Bessel OAM acoustic beam can be flexibly adjusted to achieve directional transmission of the acoustic OAM signal.

2. The directional transmission device of an acoustic OAM signal according to claim 1, characterized in that: According to the linear relationship between the base angle α of the sawtooth lens and the focal length, the range of the base angle α of the sawtooth lens is determined to be π / 8-π / 4.

3. The directional transmission device of an acoustic OAM signal according to claim 1, characterized in that: According to the base angle α of the sawtooth lens, the phase modulation function of the sawtooth lens is designed using equation (1): , which is used to perform line-focusing phase modulation on the OAM target acoustic beam; (1) In formula (1), b is a constant, and b=1.53 / tan(α). The value of b can be determined according to the base angle α. is the distance between any point on the sawtooth lens and the center of the sawtooth lens, is the azimuth angle of any point on the sawtooth lens, is the polar coordinate of any point on the surface of the sawtooth lens.

4. The directional transmission device of an acoustic OAM signal according to claim 1, characterized in that: According to the generalized Fresnel law, the phase modulation function of the first gradient lens is designed using equation (2): , and used to phase modulate the Bessel OAM acoustic beam; (2) In formula (2), b1 is the gradient phase change rate of the first gradient lens, and b1∈[2π / 100, -2π / 10].

5. The directional transmission device of an acoustic OAM signal according to claim 4, characterized in that: The phase modulation function of the second gradient lens Phase modulation function with the first gradient lens same.

6. The directional transmission device of an acoustic OAM signal according to claim 1, characterized in that: The joint phase modulation function of two gradient lenses is designed as follows: , to change the phase modulation effect between the first and second gradient lenses: Step a: After adjusting the rotation angle of the first gradient lens to θ1, use equation (3) to design the phase modulation function of the first gradient lens: : (3) Step b: After adjusting the rotation angle of the second gradient lens to θ2, the phase modulation function of the second gradient lens is designed using equation (4): : (4) Step c: Assuming θ1=-θ2, use equation (5) to determine the combined phase modulation effect of the first gradient lens and the second gradient lens after rotation: : (5)。 7. The design method for directional acoustic OAM signal transmission according to claim 1, characterized in that: The coverage range of the acoustic OAM signal is any position within a circle with a radius R outward from the propagation axis.

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