Application Cases

Introduction

Underwater acoustic beamforming technology relies on discrete array structures composed of a limited number of transducers to achieve precise sound source localization through spatial sampling and filtering. However, the spatial sampling characteristics of arrays are prone to spatial aliasing issues. When the element spacing exceeds half a wavelength, ghost images exhibit levels comparable to those of real sources, making source direction difficult to distinguish. Moreover, the physical size limitations of array elements make it difficult to satisfy the Nyquist sampling interval required for high-frequency signals. Existing research has partially alleviated aliasing effects through algorithmic optimization methods such as moving arrays, compressive frequency-differential beamforming, and spherical array spatial aliasing mode modeling, but has not fundamentally solved the problems arising from the discrete sampling mechanism. Although acousto-optic Doppler beamforming technology avoids spatial aliasing through continuous-aperture laser sensing, its optical path is complex and dependent on fixed reflection points, making it unsuitable for constrained underwater environments. Therefore, introducing a continuous integral sensing mechanism based on the acousto-optic deflection effect into the underwater acoustics field to break through the sampling limitations of traditional discrete arrays, fundamentally eliminate spatial aliasing, and expand high-frequency operating bandwidth has become a critical technical problem urgently requiring resolution in this field.

This study represents a technological breakthrough in the direction of beamforming and sound source localization within the broad category of underwater acoustics applications. Its core connections are manifested as follows: it inherits the fundamental demands of underwater acoustics for target detection, localization, and identification, yet completely overturns the traditional sensing architecture that relies on discrete transducer arrays. By utilizing the acousto-optic deflection effect, a laser beam serves as a continuous, gap-free virtual sensor array to integrate acoustic field information, fundamentally circumventing the inherent bottleneck of spatial aliasing caused by element spacing limitations in underwater acoustic arrays, thereby extending the anti-aliasing effective bandwidth to 20–80 kHz. This method demonstrates superior performance over conventional beamforming in core underwater acoustic application scenarios such as underwater target detection, high-resolution sound source localization, and three-dimensional DOA estimation. Meanwhile, by leveraging optical path extension and enhancement technology, it resolves the challenges of underwater miniaturization and integration, and verifies the feasibility of acousto-optic sensing in complex shallow-sea environments. This research is not a simple improvement to underwater acoustic signal processing algorithms; rather, it provides an entirely new technical pathway for underwater acoustic sensing and beamforming, transitioning from "discrete electronic arrays" to "continuous optical arrays," and holds significant importance for advancing underwater acoustic detection toward high-frequency, high-resolution, and aliasing-free development.

Research Direction

Acousto-Optic Deflection Effect Modeling,Spatial Aliasing Suppression Mechanism,Spatial Aliasing Suppression Mechanism,Optimization of Acousto-Optic Interaction Length and Angular Resolution,Optimization of Acousto-Optic Interaction Length and Angular Resolution,Anti-Multipath Interference Double-Layer Laser Structure

Experimental objective

The underwater acousto-optic beamforming method (AODB) utilizes the continuous integration of acoustic signals by laser to replace the discrete summation performed by a limited number of transducers in traditional array structures, thereby fundamentally resolving the spatial aliasing problem in beamforming. To verify this characteristic, beamforming experiments were conducted in an anechoic water tank across the frequency range of 20 kHz to 80 kHz. The effectiveness and superiority of the AODB method were validated through experimental comparative analysis against conventional array beamforming methods in terms of MSL and resolution.

Testing equipment

Tektronix MDO3104 Signal Generator,Aigtek ATA-L4HF Power Amplifier,CT30 Transducer,CT60 Transducer,RHSM-10 Spherical Hydrophone,633 nm Wavelength Laser (HL63193MG),532 nm Wavelength Laser,Position Sensitive Detector (PSD),Underwater Turntable,Anechoic Water Tank.

Experimental process

1. The experiments were conducted in an anechoic water tank measuring 20 m × 10 m × 8 m (anechoic coefficient ≥ 98%, for sound waves > 2 kHz). The acousto-optic beamforming system was placed 12 meters from the sound source to receive underwater acoustic signals and output them for computational processing.

2. The underwater acoustic signals were generated by a Tektronix MDO3104 and amplified by an Aigtek ATA-L4HF power amplifier, which drove CT30 (20–40 kHz) and CT60 (40–80 kHz) transducers respectively to emit underwater acoustic signals at specified frequencies, simulating underwater sound sources.

3. Eighteen RHSM-10 hydrophones arranged in a linear array with 30 mm spacing constituted the conventional beamforming system, which collected underwater acoustic signals at the same location and performed beamforming computational processing.

4. The underwater acoustic signals in the 20 kHz to 80 kHz range collected by both AODB and conventional beamforming were analyzed, and two-dimensional beamforming maps were plotted. The resolution and maximum sidelobe level (MSL) of both methods were also analyzed.

5. 

Figure1 Experimental system for

AODB. (a) Schematic diagram of the

experiment. (b) AODB. (c) Instrument

diagram of the experiment.

Figure2  Schematic diagram of underwater beamforming measurement

using the AODB. (a) Beamforming

based on orthogonal laser beams. (b)

Beamforming using a horizontal laser.

Experimental results

  This study validates the effectiveness of the proposed acousto-optic deflection beamforming technology in underwater acoustics through experiments conducted in an anechoic water tank and shallow-sea environments. The experimental results demonstrate that: at an acousto-optic interaction length of 17 cm, the system achieves aliasing-free beamforming across the 20–80 kHz frequency band, with angular resolution improving as frequency increases and the maximum sidelobe level remaining at extremely low levels throughout. The beam deflection amplification module extends the optical path by 1000 mm, improving sensitivity by approximately 18 dB. The 633 nm laser exhibits higher acoustic signal response amplitude than the 532 nm laser. The dual-beam orthogonal configuration successfully achieves three-dimensional direction estimation (azimuth and elevation angles) of the sound source, and can still acquire clearly distinguishable acoustic signals in turbid shallow-sea water. Comparative experiments with a conventional 18-element hydrophone linear array show that AODB achieves comparable resolution to the traditional method at a 0° angle of incidence, but significantly outperforms it at large angles of incidence (30° and 60°). Moreover, in the high-frequency band (>50 kHz), it completely suppresses the ghost images and localization failures that occur in conventional beamforming, with a maximum sidelobe level far below that of the traditional method (which approaches 0 dB). These results prove that by replacing discrete element summation with continuous optical integration, this technology fundamentally resolves the spatial aliasing problem, providing a reliable new pathway for high-frequency underwater acoustic detection.

Figure3 Comparison of resolution and

MSL of AODB and line array beamforming in simulation and actual measurements, respectively. (a) The

resolution in the simulation results. (b)

The MSL in simulation results. (c) The

resolution in an anechoic pool actual

measurement. (d) The MSL in the

anechoic pool actual measurement.

Figure4  The result of underwater AODB.

The effectiveness of the amplifier in this experiment

1. Amplify the low-voltage excitation signal output from the signal generator into a high-power electrical signal to drive the underwater transmitting transducer to generate acoustic waves of sufficient intensity.

2. Cooperate with CT30 (20–40 kHz) and CT60 (40–80 kHz) transducers to cover different frequency bands respectively, supporting broadband sound source emission requirements from 20–80 kHz.

3. Provide stable high-power output to ensure that the sound source satisfies far-field plane wave conditions in both anechoic water tank and shallow-sea environments, establishing a reliable acoustic field for beamforming experiments.

4. Work synergistically with the signal generator and transducers to form a complete sound source emission chain, providing standard sound source excitation for verifying the spatial aliasing suppression performance of the AODB system.

Application fields

Underwater Target Detection and Localization,Marine Environmental Monitoring and Ocean Acoustic Observation,Underwater Communication and Acoustic Networking,Port Security and Critical Waters Surveillance,Underwater Structural Health Monitoring and Non-Destructive Evaluation.