Hangzhou Institute of Applied Acoustics

Text Correction [...]

Distributed optical fiber acoustic sensing (D-FOAS) has become an important branch of optical fiber acoustic sensing. Compared with typical fiber optic hydrophones, D-FOAS offers advantages of low cost and large aperture , but also suffers from the significant drawback of high system self-noise. In recent years, the performance of D-FOAS technology has significantly improved, and extensive application research has been conducted internationally. It is anticipated that D-FOAS can be applied in areas such as marine target detection, environmental monitoring and inversion, and underwater acoustic communication.

This paper proposes a complex fast recursive least-squares (FRLS) channel-estimation algorithm for single-carrier electromagnetic (EM) communications across the seawater–air interface, where severe attenuation and multipath cause strong SNR fluctuations. By redesigning the input-data structure and using forward–backward joint estimation, FRLS reduces the per-iteration complexity from the quadratic cost of classical RLS to a linear form (14L + 20 operations per iteration, where L is the channel length). Simulations under representative one- to three-path channels show that FRLS achieves the lowest steady-state mean-square deviation (MSD) at low SNR, outperforming LMS, IPNLMS, RLS, and PRLS. Offshore experiments further validate the practicality: after MMSE equalization, FRLS yields higher OSNR and improves the BER distribution, demonstrating an effective accuracy–complexity trade-off for hardware-constrained cross-medium EM links.

Research on active sonar systems (ASS) is gradually shifting from high-frequency to low-frequency operations. To address the challenges of narrow working bandwidth and low transmission efficiency in low-frequency hydroacoustic transducers (LHT) for acoustic-electric conversion, a variable LC-type impedance matching network (VLCM) is proposed. This network aims to enhance both the operational bandwidth and filtering performance of the system. Additionally, a wide-bandwidth parameter optimization model (WPOM) based on an inverter utilizing sinusoidal pulse width modulation (SPWM) is introduced. This model aims to achieve a broader operational bandwidth, minimize fluctuations, and alleviate potential harmonic issues resulting from resonance. Given the multi-constraint and multi-objective nature of the model, an optimization algorithm based on Non-dominated Sorted Multi-component Search (NSMS) has been developed. Finally, simulations and experimental comparisons are conducted to evaluate the system's performance under wide bandwidth conditions. The results demonstrate that the proposed VLCM significantly improves transmission performance and stability without introducing harmonic distortion.

Aiming at the load swing problem caused by helicopter airframe motion, wind disturbance, and load characteristic changes during the hoisting and recovery process of aircraft winches, this paper conducts a series of studies on anti-swing control strategies. Based on the Lagrange equation, a mathematical model of load swing incorporating helicopter six-degree-of-freedom motion, fluid resistance, and wind influence was established. A fuzzy adaptive PID-based anti-swing control method was designed. Load swing characteristics under different operating conditions were analyzed via the MATLAB simulation platform, and the effectiveness of the proposed control method was verified through experiments. Simulation results indicate that this control method can significantly suppress the swing amplitude and enhance the safety and stability of the recovery process. The research findings hold important theoretical value and engineering guiding significance for the optimal design of aerial winch systems.

In this Letter, a simplified expression of the vertical dimension narrowband interference pattern in deep water direct arrival zone is theoretically derived. The correlation between the vertical dimension interference pattern and source depth is analyzed, and the depth span corresponding to a complete interference cycle (interference period) is derived theoretically. A source depth estimation method is proposed based on matching the vertical interference pattern calculated from the data with theoretical predictions. The effectiveness of the theoretical approach in predicting the vertical interference pattern and effectiveness of the proposed depth estimation method are verified by experimental data.

The waveform recovery of underwater acoustic signals under strong interference is a challenge. The steered minimum variance (STMV) method, which has high convergence in the adaptive methods, is difficult to achieve rapid convergence under a large-aperture array, leading to distortion of the output waveform. In this paper, a method based on steered sample covariance matrix (ST-SCM) sparse reconstruction is proposed, which improves the similarity between the recovery waveform and the signal waveform under strong interference. In the proposed method, a sparse representation of the ST-SCM is derived using a shared dictionary matrix for different frequencies, achieving a high convergence performance while avoiding multi-frequency calculation. The simulated results demonstrated that the proposed method provides an improved performance in signal wave recovery compared to the CBF and the STMV method under a large-aperture receiving array.