A directional transmission device for acoustic OAM signals

Abstract

The present invention discloses a directional transmission device for acoustic OAM signals, comprising a phased array circuit, a planar sector transducer array, a sawtooth lens, and two gradient lenses. By combining active phase control with passive phase modulation and employing a gradient lens design, acoustic waves can be deflected along a fixed direction. The relative rotation of the two gradient lenses enables the generation of controllable-order OAM signals at any position within a two-dimensional plane. The present invention enables efficient and flexible vortex beam generation, thereby providing superior transmission performance in underwater acoustic vortex communications. This not only simplifies the lens manufacturing process but also offers significant advantages in cost and flexibility, demonstrating broad application prospects.

Description

Technical Field

[0001] The present 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 front. A phase singularity at the center of the vortex and zero field intensity exist. Mathematically, the phase distribution of a vortex beam can be described by exp(ilφ), where l is the topological charge and φ is the azimuthal angle. The orbital angular momentum (OAM) carried by vortex beams, as a new degree of freedom, holds promise for addressing the current challenges of limited communication resources. Because water molecules strongly absorb light waves and light waves are easily blocked and scattered by small particles in the ocean, acoustic waves offer unique advantages over light waves in underwater communications. Based on the ability to accurately generate and control vortex acoustic beams, researchers have begun studying OAM acoustic communication. To achieve a simple and easily controllable OAM acoustic communication system, the research team constructed a theoretical model for OAM acoustic beam communication using a single-ring transceiver array. They also established an experimental system with a single-ring 16-source array and studied the principles and performance of OAM multiplexing communication. This research provides a theoretical foundation and technical support for array design, data transmission, decoding, and calibration of OAM acoustic beams in communication systems, and holds 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, how to effectively transmit the energy-concentrated signal to a specific location, and the transmission direction can be freely adjusted, and it is particularly necessary to build a safe, flexible, and highly controllable underwater acoustic vortex communication system. There are fewer studies on off-axis vortices. One study combined the 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 the cost and the system flexibility was poor. To solve this problem, some studies have constructed a directional off-axis acoustic vortex by introducing a phase delay in the traditional planar sensor ring array, which greatly reduced the complexity of the system. However, the change of the vortex center requires recalculation of the phase of the sound source array, and the adjustability and flexibility are still poor. Summary of the Invention

[0004] In order to address the deficiencies of the above-mentioned prior art, the present invention proposes a directional transmission device for acoustic OAM signals, in order 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 object, the present invention adopts the following technical solutions:

[0006] The directional transmission device of an acoustic OAM signal of the present invention is characterized in that it comprises: a phased array circuit, a planar sector 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. The signals are then processed by a low-pass filter and a broadband power amplifier, 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 the propagation axis according to the received sinusoidal signal;

[0009] The sawtooth lens is nested on 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 a;

[0010] After the OAM target acoustic beam is linearly focused and phase-modulated in the sawtooth lens, the modulated OAM target acoustic beam is output and deflected onto 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] Two gradient lenses are placed at equal intervals in a direction perpendicular to the surface of the planar sector transducer array and at a distance d from the sawtooth lens, 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, is phase modulated again, and is further deflected at the fixed angle to propagate away from the propagation axis, ultimately outputting 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 controlled to achieve directional transmission of the acoustic OAM signal.

[0014] The directional transmission device for acoustic OAM signals described in the present invention is also characterized in that, based on 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.

[0015] Furthermore, according to the base angle α of the sawtooth lens, the phase modulation function of the sawtooth lens is designed using formula (1): , which is used to perform line-focused 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 formula (2): , and is used to phase modulate the Bessel OAM acoustic beam;

[0019] (2)

[0020] In formula (2), b1 is the gradient phase change rate of the first gradient lens, and b1∈[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 as follows: , to change the phase modulation effect between the first and second gradient lenses:

[0023] Step a: After adjusting the rotation angle of the first gradient lens to θ1, use formula (3) to design the phase modulation function of the first gradient lens: :

[0024] (3)

[0025] Step b: After adjusting the rotation angle of the second gradient lens to θ2, use formula (4) to design the phase modulation function of the second gradient lens: :

[0026] (4)

[0027] 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. :

[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 a 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 solution can generate a vortex center at any position on a two-dimensional plane simply by rotating the two lenses at any angle, significantly simplifying 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 existing technology, 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, it has broad application prospects and can meet diverse communication needs.

[0034] 4. This invention achieves higher signal transmission efficiency and longer transmission distances, resolving the severe signal attenuation issue in existing technologies and thereby improving the reliability and stability of underwater acoustic communications. This provides important technical support for the development of future underwater detection, monitoring, and communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of the entire transmitting system of a directional acoustic OAM signal transmitting device of the present invention, wherein: 1─ phased array circuit, 2─ planar sector transducer array, 3─ sawtooth lens, 4─ first gradient lens, 5─ 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 distances 1, 2, and 3 from left to right. Figure 2 (b) in the figure shows the phase distribution of the OAM signal 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 positions 1, 2, and 3 from left to right. Figure 3 (b) in the figure shows the phase distribution of the OAM signal at angular positions 1, 2, and 3 from left to right.

[0038] Figure 4 The acoustic field distribution diagram of the OAM signal with topological charge l = 1–4 generated by the first and second gradient lenses in the present invention at a fixed rotation angle; wherein, Figure 4 (a) in the figure 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) in the figure shows the phase distribution of OAM signals with topological charges 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 entire transmitting system includes: a phased array circuit, a planar sector 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, it outputs N initial phase-controllable sinusoidal signals to the planar sector transducer array. The number of sector transducers is M, and the sector angle of each sector 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 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 a. 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.

[0043] After the OAM target acoustic beam is linearly focused and phase-modulated in a sawtooth lens, the modulated OAM target acoustic beam is output and deflected onto 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, the phase modulation function of the sawtooth lens is designed using formula (1) according to the base angle α of the sawtooth lens. , which is used to perform line-focused 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 thicker, the phase compression method is used to compress the sawtooth lens and design the sawtooth lens into 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] Two gradient lenses are placed at equal intervals in a direction perpendicular to the surface of the planar sector transducer array and at a distance d from the sawtooth lens. The interval between the two gradient lenses is also d. Since spherical waves will have a divergence effect, setting the interval too large will affect the beam quality of the Bessel OAM beam. Setting the interval too small will increase the reflection and refraction effect between the first and second gradient lenses. Therefore, d is set to 1 mm, and the rotation angle range of the two gradient lenses is set to [-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. It then enters the second gradient lens for phase modulation again and is further deflected at a fixed angle to propagate away from the propagation axis, ultimately outputting 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 formula (2): , and is used to phase modulate the Bessel OAM acoustic beam;

[0050] (2)

[0051] In formula (2), b1 is the gradient phase change rate of the first gradient lens, and b1∈[2π / 100, -2π / 10]. The principle of phase compression is also used in the design and processing of the first gradient lens. The thickness of the first gradient lens is compressed to form a thin lens, thereby reducing the attenuation of acoustic waves propagating through 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 controlled 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: The first gradient lens can only shift the OAM signal by a fixed distance ∆d. By changing the rotation angle θ1, the angular position of the acoustic OAM signal can be controlled. After adjusting the rotation angle of the first gradient lens to θ1, the phase modulation function of the first gradient lens is designed using formula (3): :

[0056] (3)

[0057] Step b: After adjusting the rotation angle of the second gradient lens to θ2, use formula (4) to design the phase modulation function of the second gradient lens: :

[0058] (4)

[0059] Step c: Assume θ1 = -θ2 and use formula (5) to determine the combined phase modulation effect of the first gradient lens and the second gradient lens after rotation. :

[0060] (5).

[0061] In formula (5), the combined effect of the first gradient lens and the second gradient lens after rotation is equivalent to a gradient phase equal to For the gradient lens, there is a cosine function relationship between the gradient size and the rotation angle θ1.

[0062] The range is [0,2b1]. Changing θ1 can adjust the distance between the acoustic OAM signal and the center of the observation surface, such as Figure 2 shown.

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

[0064] The range is [0,2b2], 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 completing the control of the distance between the acoustic OAM signal and the center of the observation surface and the azimuth position, the topological charge of the acoustic OAM signal can be controlled by changing the excitation sinusoidal signals of different sectors of the planar sector transducer array. 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 emission device of the present invention combines active phase control with passive phase modulation, employing a gradient lens design to deflect acoustic waves along 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 location within a two-dimensional plane. This method not only simplifies the lens manufacturing process but also offers significant advantages in cost and flexibility, demonstrating broad application prospects.

Claims

1. A directional transmission 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. The signals are then processed by a low-pass filter and a broadband power amplifier, 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 the propagation axis according to the received sinusoidal signal; The sawtooth lens is nested on 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 a; After the OAM target acoustic beam is linearly focused and phase-modulated in the sawtooth lens, the modulated OAM target acoustic beam is output and deflected onto 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; Two gradient lenses are placed at equal intervals in a direction perpendicular to the surface of the planar sector transducer array and at a distance d from the sawtooth lens, 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, ultimately outputting 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 controlled 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 formula (1): , which is used to perform line-focused 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 3, characterized in that: According to the generalized Fresnel law, the phase modulation function of the first gradient lens is designed using formula (2): , and is 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 acoustic OAM signals according to claim 4, characterized in that: Phase modulation function of the second gradient lens Phase modulation function with the first gradient lens same.

6. The directional transmission device for acoustic OAM signals according to claim 4, 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 formula (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, use formula (4) to design the phase modulation function of the second gradient lens: : (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 method for designing a directional emission device for acoustic OAM signals according to claim 1, wherein: The coverage range of the acoustic OAM signal is any position within a circle with a radius R extending outward from the propagation axis.

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