Application Cases

【Overview】
In this study, the Aigtek ATA-L4 underwater acoustic power amplifier was used to build an experimental system for laser-based underwater acoustic angle-of-arrival (AOA) measurement. A refined model of the integral response of the acousto-optic effect was developed to investigate its influence on angular resolution. Based on this model, a joint estimation method for high-resolution AOA measurement was designed. Simulation and experimental results demonstrate that the theoretical model achieves high accuracy over a wide frequency range of 25 kHz to 75 kHz, with deviations between predicted and measured values of less than 5%. Furthermore, the joint estimation method enables high-resolution AOA measurement, achieving an average root mean square error (RMSE) as low as 0.14°. This research is expected to lay a theoretical foundation for high-resolution AOA acoustic vector sensor technology and promote its further development.

Experiment Name: Laser-Based Underwater Acoustic Angle-of-Arrival Measurement

Research Direction: Laser-based underwater acoustic sensing, laser-based physical aperture expansion

Experimental Content:
The acousto-optic response mechanism of laser-induced acoustic measurement is a spatial integration effect of acoustic waves along the laser propagation path under far-field conditions. This special response mechanism, combined with conventional array signal processing methods, can significantly improve the angular resolution of direction-of-arrival (DOA) estimation. Far-field acoustic signals were generated in an anechoic water tank, and the laser-induced acoustic DOA estimation method was experimentally tested. The resolution of two algorithms was compared and analyzed.

Testing Equipment:
ATA-L4 underwater acoustic power amplifier; underwater acoustic transducer; sensors, etc.

Experimental Procedure:

Figure: Schematic Diagram of the Experimental Test System

1. The laser-induced acoustic device and the underwater acoustic transducer were placed at specified depths underwater, and the distance between them was adjusted to satisfy the far-field plane wave condition.

2. A signal generator was used to generate a pulse signal at a specified frequency, which was amplified by a specified gain using the ATA-L4 underwater acoustic power amplifier and then applied to the underwater acoustic transducer to generate acoustic signals.

3. The laser-induced acoustic device received the acoustic signals and calculated the angle information of the sound source.

4. The position was adjusted using a high-precision rotary stage, rotating the sensor from -6° to +6° (in 0.5° steps) in both the xoy and xoz planes to simulate the angular displacement of the sound source in elevation and azimuth. The sound source was triggered to emit 30 sinusoidal pulse sequences (each sequence containing 10 oscillation cycles at 75 kHz).

5. The sensor received the signals, and each pulse was processed to obtain 30 independent angle estimates at each rotation position for statistical error quantification.

Experimental Results:

Figure 1: Comparison of angle estimation performance between the coarse estimation and joint estimation methods.

Figure 1(a) and (b) show the error bars for elevation changes, while Figure 1(c) and (d) show the results for azimuth. As shown in Figure 1(a–b), the joint estimation solutions (blue markers) are closely clustered around the theoretical reference value (yellow dashed line), whereas the coarse estimation (red markers) exhibits significant deviations (maximum > 3°) in Figure 1(b) and (d). Although the coarse method occasionally achieves improved accuracy at specific angles (e.g., ±4°), its overall inconsistency contrasts sharply with the robustness of the joint method.

Figure 2: Estimation results of the two methods for a sound source located in the sidelobe region (corresponding to the 7°–15° range in Figure 13).

The joint estimation method exhibits a significant inherent bias, with its estimation results showing a U-shaped distribution. This anomaly occurs because the method erroneously maps the sidelobe radiation intensity to the main lobe direction. In contrast, although the coarse estimation method exhibits persistent random fluctuations, its results are generally linearly correlated with the true values. Therefore, the joint estimation method is not suitable for use in the sidelobe region. This technical challenge can be addressed by two different approaches: shortening the acousto-optic interaction length extends the main lobe coverage area at the expense of angular resolution, or improving the joint estimation algorithm to prioritize coarse estimation weighting in the sidelobe region, thereby mitigating azimuth bias through spatial confidence redistribution.

Advantages of Aigtek Amplifiers in This Application:

1. High voltage and high power drive capability – Ensures the penetration and signal-to-noise ratio of acoustic signals under far-field plane wave conditions.

2. Wide frequency coverage and pulse fidelity – Accurately reproduces the time-frequency characteristics of sinusoidal pulse sequences.

3. Multiple adjustable output impedance settings and real-time monitoring – Adapts to transducer load characteristics, ensuring measurement repeatability under precise rotation angles.