scholarly journals Low‐frequency underwater acoustic waves from an ice plate‐edge leaky Rayleigh wave

1987 ◽  
Vol 81 (S1) ◽  
pp. S10-S10
Author(s):  
Jacques R. Chamuel
Keyword(s):  
Rayleigh Wave ◽  
Acoustic Waves ◽  
Low Frequency ◽  
Plate Edge ◽  
Underwater Acoustic ◽  
Leaky Rayleigh Wave

Resonator-based reflective metasurface for low-frequency underwater acoustic waves

2020 ◽  
Vol 128 (5) ◽  
pp. 055305
Author(s):  
Zhong Chen ◽  
Fei Yan ◽  
Mehrdad Negahban ◽  
Zheng Li
Keyword(s):  
Acoustic Waves ◽  
Low Frequency ◽  
Underwater Acoustic

Tunable underwater acoustic metamaterials via quasi-Helmholtz resonance: From low-frequency to ultra-broadband

2021 ◽  
Vol 118 (7) ◽  
pp. 071904
Author(s):  
Mingyu Duan ◽  
Chenlei Yu ◽  
Fengxian Xin ◽  
Tian Jian Lu
Keyword(s):  
Low Frequency ◽  
Acoustic Metamaterials ◽  
Underwater Acoustic ◽  
Helmholtz Resonance

scholarly journals Design and implementation of a jellyfish otolith-inspired MEMS vector hydrophone for low-frequency detection

2021 ◽  
Vol 7 (1) ◽  
Author(s):  
Renxin Wang ◽  
Wei Shen ◽  
Wenjun Zhang ◽  
Jinlong Song ◽  
Nansong Li ◽  
...  
Keyword(s):  
Structural Parameters ◽  
Low Frequency ◽  
Directivity Pattern ◽  
Stress Distributions ◽  
Strong Response ◽  
Underwater Acoustic ◽  
Frequency Detection ◽  
Vector Hydrophone ◽  
Shock Resistance ◽  
Marine Applications

AbstractDetecting low-frequency underwater acoustic signals can be a challenge for marine applications. Inspired by the notably strong response of the auditory organs of pectis jellyfish to ultralow frequencies, a kind of otolith-inspired vector hydrophone (OVH) is developed, enabled by hollow buoyant spheres atop cilia. Full parametric analysis is performed to optimize the cilium structure in order to balance the resonance frequency and sensitivity. After the structural parameters of the OVH are determined, the stress distributions of various vector hydrophones are simulated and analyzed. The shock resistance of the OVH is also investigated. Finally, the OVH is fabricated and calibrated. The receiving sensitivity of the OVH is measured to be as high as −202.1 dB@100 Hz (0 dB@1 V/μPa), and the average equivalent pressure sensitivity over the frequency range of interest of the OVH reaches −173.8 dB when the frequency ranges from 20 to 200 Hz. The 3 dB polar width of the directivity pattern for the OVH is measured as 87°. Moreover, the OVH is demonstrated to operate under 10 MPa hydrostatic pressure. These results show that the OVH is promising in low-frequency underwater acoustic detection.

Methods to isolate retrograde and prograde Rayleigh-wave signals

2019 ◽  
Vol 219 (2) ◽  
pp. 975-994 ◽  
Author(s):  
Gabriel Gribler ◽  
T Dylan Mikesell
Keyword(s):  
Rayleigh Wave ◽  
Time Domain ◽  
Fundamental Mode ◽  
Poisson Ratio ◽  
Low Frequency ◽  
Wave Dispersion ◽  
Low Frequencies ◽  
Retrograde Motion ◽  
Mode Identification ◽  
Time Frequency

SUMMARY Estimating shear wave velocity with depth from Rayleigh-wave dispersion data is limited by the accuracy of fundamental and higher mode identification and characterization. In many cases, the fundamental mode signal propagates exclusively in retrograde motion, while higher modes propagate in prograde motion. It has previously been shown that differences in particle motion can be identified with multicomponent recordings and used to separate prograde from retrograde signals. Here we explore the domain of existence of prograde motion of the fundamental mode, arising from a combination of two conditions: (1) a shallow, high-impedance contrast and (2) a high Poisson ratio material. We present solutions to isolate fundamental and higher mode signals using multicomponent recordings. Previously, a time-domain polarity mute was used with limited success due to the overlap in the time domain of fundamental and higher mode signals at low frequencies. We present several new approaches to overcome this low-frequency obstacle, all of which utilize the different particle motions of retrograde and prograde signals. First, the Hilbert transform is used to phase shift one component by 90° prior to summation or subtraction of the other component. This enhances either retrograde or prograde motion and can increase the mode amplitude. Secondly, we present a new time–frequency domain polarity mute to separate retrograde and prograde signals. We demonstrate these methods with synthetic and field data to highlight the improvements to dispersion images and the resulting dispersion curve extraction.

Realizing high-efficiency low frequency sound absorption of underwater meta-structures by acoustic siphon effect

2021 ◽  
pp. 2150319
Author(s):  
Li Bo Wang ◽  
Cheng Zhi Ma ◽  
Jiu Hui Wu ◽  
Chong Rui Liu
Keyword(s):  
Absorption Coefficient ◽  
Sound Absorption ◽  
High Efficiency ◽  
Physical Mechanism ◽  
Low Frequency ◽  
Area Ratio ◽  
Underwater Acoustic ◽  
Element Simulation ◽  
Average Absorption Coefficient ◽  
New Perspective

The underwater acoustic siphon effect is proposed in this work, which aims to reveal the basic physical mechanism of high-efficiency sound absorption in meta-structures composed of multiple detuned units. Furthermore, the influence of the area ratio on the underwater acoustic siphon effect is then investigated by finite element simulation (FES) and theoretical calculation. On this basis, a meta-structure with the maximum absorption coefficient of almost 100% and average absorption coefficient of 80% at 600–1400 Hz is achieved. The underwater acoustic siphon effect could provide a better understanding of high-efficiency sound absorption and offer a new perspective in controlling underwater noises.

Studies on the interaction of low‐frequency acoustic signals with the ocean bottom

Geophysics ◽  
1979 ◽  
Vol 44 (12) ◽  
pp. 1922-1940 ◽  
Author(s):  
Salvatore R. Santaniello ◽  
Frederick R. DiNapoli ◽  
Robert K. Dullea ◽  
Peter D. Herstein
Keyword(s):  
Acoustic Waves ◽  
Grazing Angle ◽  
Low Frequency ◽  
Propagation Loss ◽  
Ocean Bottom ◽  
Computer Technique ◽  
Quantitative Evidence ◽  
Ocean Sediment ◽  
Wave Models ◽  
Processing Techniques

Understanding the mechanisms by which the ocean sediment redirects impinging sound back into the ocean is necessary in developing propagation models for sonar performance prediction. The Naval Underwater Systems Center (NUSC) has (1) conducted controlled, self‐calibrating acoustic measurements where the ocean bottom interacted signal is isolated in time for analysis, (2) developed deconvolution processing techniques to aid in describing the impulse response of the ocean sediment, and (3) performed modeling to study the interaction of acoustic waves at the ocean bottom. This paper presents a synopsis of studies showing the necessity of considering the refraction of sound by the ocean sediment when predicting low‐frequency propagation loss. Constructive interference between nonplanar wave sediment refracted sound and sound reflected by the ocean‐sediment interface and subbottom layering can cause negative values of bottom loss when using plane‐wave models to interpret measured data. These models cannot account for all possible acoustic arrivals at a receiver. In addition, for a given frequency and constant ocean bottom grazing angle, bottom loss can be dependent upon both processing bandwidth and source/receiver depth. Deconvolution has aided in time resolution of signals that make up the bottom‐interacted signals. Resolution of these signals aids in interpreting results. A modeling effort utilizing the Fast Field Program (a computer technique for evaluating the field integral by the fast Fourier transform) provides quantitative evidence for the necessity of accounting for the refraction of sound by subocean sediments to interpret properly low‐frequency propagation loss measurements.

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