Group velocity dispersion curves estimation based on joint processing of sound pressure and vertical particle velocity.

It is difficult to separate and estimate the intersected group velocity dispersion curves for different normal modes when the frequency is lower than the cutoff frequency of water column. To address this issue, an estimation method based on the joint processing of sound pressure (P) and vertical particle velocity (Vz) is proposed in this paper. Theoretical analysis shows that the amplitudes of P and Vz corresponding to the nth normal mode exhibit a complementary relationship in the certain frequency band, providing a theoretical basis for the method.

Line spectrum tracking method in transformed signal space for underwater moving targets in low signal-to-noise ratio environment.

Line spectrum tracking is an essential signal-processing method for underwater passive detection. However, its performance is often seriously degraded due to signal fluctuation, especially in low signal-to-noise ratio scenarios. In this paper, based on signal space transformation and hidden Markov model, a signal trajectory tracking method is proposed for underwater moving target detection and parameter estimation.

Geoacoustic inversion using very-low-frequency modal interference characteristics.

This paper presents a modal-based geoacoustic inversion method adapted for a very-low-frequency leaky waveguide. It is applied to air gun data collected by a seismic streamer during the multi-channel seismic exploration experiment in the South Yellow Sea. The inversion is carried out by filtering the waterborne and bottom-trapped mode pairs from the received signal and comparing the modal interference features (waveguide invariant) to replica fields.

Very low frequency three-dimensional beamforming for a miniaturized aperture acoustic vector sensor array.

In this Letter, a three-dimensional beamforming method is proposed for a miniaturized aperture acoustic vector sensor (AVS) array. This method extracts the multipole modes using the AVS array, and then synthesizes the desired beam pattern according to the relation between multipole modes and spherical harmonics. Compared to the spherical harmonics decomposition of the sound field method, the proposed method achieves comparable array gain with higher white noise gain when the distance of adjacent elements d and the wavelength λ satisfy 0.

A Linear Piezoelectric Actuator Using "A-Shaped" Structure.

A new design of linear piezoelectric actuator using "A-shaped" structure was proposed, designed, fabricated, and tested. By fusion design of the piezoelectric transducer and the mechanical structure, the proposed actuator only uses the first bending vibration of the center piezoelectric transducer to work. Frequency degeneration is no longer needed, which enables the actuator to adjust its structural parameters according to the application conditions.

A theoretical model of the intermittent contact of piezoelectric actuator based on Greenwood-Williamson theory.

A theoretical model of the intermittent contact mechanism of linear piezoelectric actuator was proposed, in which the microscopic characteristics of the contact surfaces were taken into account. Greenwood-Williamson (GM) theory was involved for the first time to describe the microscopic characteristics of the contact surfaces in which the contact surfaces were considered as random rough surfaces that were composed of large amounts of asperities and the heights of the asperities conformed to a Gauss distribution. The developed theoretical model gives an insight into the influence of the microscopic properties, as well as the macroscopic and material properties on the output performance of the actuator, which may provide guidance for the design of such type of piezoelectric actuator.

Passive Detection of Ship-Radiated Acoustic Signal Using Coherent Integration of Cross-Power Spectrum with Doppler and Time Delay Compensations.

Passive sonar is widely used for target detection, identification and classification based on the target radiated acoustic signal. Under the influence of Doppler, generated by relative motion between the moving target and the sonar array, the received ship-radiated acoustic signals are non-stationary and time-varying, which has a negative effect on target detection and other fields. In order to reduce the influence of Doppler and improve the performance of target detection, a coherent integration method based on cross-power spectrum is proposed in this paper.

A Passive Source Location Method in a Shallow Water Waveguide with a Single Sensor Based on Bayesian Theory.

Bayesian methodology is a good way to infer unknown parameters in a marine environment. A passive source location method in a shallow water waveguide with a single sensor based on Bayesian theory is presented in this paper. The input of a Bayesian inversion algorithm is received different normal mode impulse signals, which are separated and extracted with a warping transformation from received broadband impulse signals.

Extracting the time domain Green's function from ocean ambient noise using acoustic vector sensors.

A function that closely resembles the two-point time-domain Green's function (TDGF) representing the time delays associated with multipath between the two sensors can be recovered by correlating the noise field measured by two sensors. Here, a technique for extracting the TDGF from ambient ocean noise using acoustic vector sensors is presented. Experimental results suggest that the averaging time to extract TDGF is greatly reduced if sound pressure sensors (hydrophones) are replaced by acoustic vector sensors.

Estimating the delay-Doppler of target echo in a high clutter underwater environment using wideband linear chirp signals: Evaluation of performance with experimental data.

A chirp signal is a signal with linearly varying instantaneous frequency over the signal bandwidth, also known as a linear frequency modulated (LFM) signal. It is widely used in communication, radar, active sonar, and other applications due to its Doppler tolerance property in signal detection using the matched filter (MF) processing. Modern sonar uses high-gain, wideband signals to improve the signal to reverberation ratio.