Design and Experiments of a Portable Seabed Integrated Detection Sonar

The integrated observation of seabed topography, sediment geomorphology and sub-bottom profile information is very important for seabed remote sensing and mapping. To improve the efficiency of seabed detection and meet the needs of portable development of detection equipment, we developed a portable seabed feature integrated detection sonar (PSIDS) with whcih a single sonar device can simultaneously detect the above three types of seabed information. The underwater transducer is mainly composed of the following three components: a parametric emission array as the sound source, a high frequency receiving linear array for multibeam echo signal collection, and a two-dimensional vector hydrophone for receiving the low-frequency sediment echo signal. Field experiments were conducted to validate the performance of the PSIDS on 11–17 January 2018 in Jiaozhou Bay, China. (1) PSIDS could perform the functions of both multibeam sonar and sub-bottom profiler; (2) The synchronously and integrated measurement of various seabed information was achieved by alternately emitting multibeam echo-sounding and sub-bottom profiling signal using parametric source. The detection results proved the feasibility and practicability of PSIDS to achieve multiple seafloor characteristics. PSIDS provides a new idea for developing integrated seabed detection sonar. In terms of convenience and data fusion, it is a good option to use this equipment for integrated seabed detection.

Research and Fabrication of Broadband Ring Flextensional Underwater Transducer

At present, high-speed underwater acoustic communication requires underwater transducers with the characteristics of low frequency and broadband. The low-frequency transducers also are expected to be low-frequency directional for realization of point-to-point communication. In order to achieve the above targets, this paper proposes a new type of flextensional transducer which is constructed of double mosaic piezoelectric ceramic rings and spherical cap metal shells. The transducer realizes broadband transmission by means of the coupling between radial vibration of the piezoelectric rings and high-order flexural vibration of the spherical cap metal shells. The low-frequency directional transmission of the transducer is realized by using excitation signals with different amplitude and phase on two mosaic piezoelectric rings. The relationship between transmitting voltage response (TVR), resonance frequency and structural parameters of the transducer is analyzed by finite element software COMSOL. The broadband performance of the transducer is also optimized. On this basis, the low-frequency directivity of the transducer is further analyzed and the ratio of the excitation signals of the two piezoelectric rings is obtained. Finally, a prototype of the broadband ring flextensional underwater transducer is fabricated according to the results of simulation. The electroacoustic performance of the transducer is tested in an anechoic water tank. Experimental results show that the maximum TVR of the transducer is 147.2 dB and the operation bandwidth is 1.5–4 kHz, which means that the transducer has good low-frequency, broadband transmission capability. Meanwhile, cardioid directivity is obtained at 1.4 kHz and low-frequency directivity is realized.

EFFECTS OF UNDERWATER LOW-FREQUENCY SOUND PROPAGATION THROUGH CONTINENTAL BARRIER

Обнаружены и исследованы подводный и донный низкочастотные акустические сигналы (400 Гц) от подводного источника излучения, расположенного относительно приемной системы по другую сторону перешейка мыса Шульца. Приемная система состояла из трехкомпонентного донного геофона и приемной акустической комбинированной системы, расположенной в толще волновода на глубине 9 м. Кратчайшее расстояние между источником и приемником через материковый барьер составляет ~ 1000 м. Азимутальный угол прихода сигнала продольных волн совпадает с геометрической линией, соединяющей источник и приемник. Прием поперечной и продольной волн осуществляется по различным ортогональным осям координат геофона. Направление прихода продольной волны в точку измерения близко к горизонтальному. Наличие поперечной волны в донном грунте позволяет предположить, что дно волновода представляет собой твердую жесткую поверхность. The present work studies the underwater and sea bottom low-frequency signals (400 Hz) emitted by the underwater transducer and detected by the receiver system located on the other side of the Schultz cape neck relative to the transducer. The receiver system consisted of a three-component bottom geophone and composite acoustical system immersed 9 m down the water column of the waveguide. The shortest distance between transducer and receiver through the continental barrier was ~1000 m. The azimuth angle of signal arrival corresponds to a geometrical line connecting a pair transducer/receiver. The reception of longitudinal and transverse waves was performed alongside different orthogonal axes of geophone coordinates. The direction of the longitudinal wave arrival at the reception point was close to horizontal. The presence of the transverse wave in the bottom soil suggests that the bottom of the waveguide represents a solid rigid surface.

Study on Underwater Performance of Underwater Transducer Manufactured by 1-1-3 Piezoelectric Composite

A novel kind of underwater transducer with trapezoidal matching layer manufactured by 1-1-3 piezoelectric composite has been proposed to improve the underwater performance of high frequency transducer. In this paper, the finite element method has been used to analyze the influence of the matching layer on the electrical properties of the composite materials and vibration displacement of the radiation area. Two kinds of underwater transducers with and without matching layers have been fabricated. The experimental results show that the transmission voltage response of the underwater transducer with matching layer reaches 169.4 dB at 360 kHz, and the receiving voltage sensitivity reaches-190 dB, the bandwidth is up to 70 kHz and the maximum sound source level is 208 dB. Comparing with transducer without matching layer, the transmission voltage response is increased by 3.8 dB. Meanwhile the sound source level is increased by 6 dB. The received bandwidth is increased by 1.45 times.