Experimental demonstration of a high-frequency forward scattering acoustic barrier in a dynamic coastal environment

2010 ◽  
Vol 127 (6) ◽  
pp. 3430-3439 ◽  
Author(s):  
Karim G. Sabra ◽  
Stephane Conti ◽  
Philippe Roux ◽  
Tuncay Akal ◽  
William A. Kuperman ◽  
...  
Keyword(s):  
High Frequency ◽  
Coastal Environment ◽  
Forward Scattering ◽  
Experimental Demonstration

Modern and Holocene microbial mats and associated microbially induced sedimentary structures (MISS) on the southeastern coast of Tunisia (Mediterranean Sea)

2020 ◽  
pp. 1-21
Author(s):  
Rached Lakhdar ◽  
Mohamed Soussi ◽  
Rachida Talbi
Keyword(s):  
Spatial Distribution ◽  
High Frequency ◽  
Depositional Environment ◽  
Microbial Mats ◽  
Coastal Environment ◽  
Tidal Dynamics ◽  
Very High Frequency ◽  
Intertidal Zones ◽  
Sedimentary Structures ◽  
Very High

Abstract On the southeastern Tunisian coastline, very diverse living microbial mats colonize the lower supratidal and intertidal zones, and locally may extend into the upper infratidal zone. The interaction between the benthic cyanobacteria and their siliciclastic substratum leads to the development of several types of microbially induced sedimentary structures (MISS). The mapping of the microbial mats has allowed the identification of the types of MISS that characterize the different segments of the coastal environment. The modern microbial mats have been compared with those recorded at the top of the Holocene deposits, which are composed of biodegraded microbial black mats alternating with white laminae made of clastic and evaporitic sediments, indicative of very high frequency cycles of flood and drought. A hypothetic profile showing their occurrences along the different areas bordering the coastline is proposed as a guide for the reconstruction of the ancient depositional environment. The roles of tidal dynamics, storms, and climate in controlling their genesis and spatial distribution, are discussed and highlighted. The modern MISS of southeastern Tunisia are compared with their equivalents that are well documented through the different geological eras.

Kirchhoff Approximations for the Forward-Scattering Target Strength of Underwater Objects

2019 ◽  
Vol 28 (01) ◽  
pp. 1950008
Author(s):  
Chuanlin He ◽  
Yi Zheng ◽  
Xu Xiang ◽  
Yuanliang Ma
Keyword(s):  
High Frequency ◽  
Mode Coupling ◽  
Forward Scattering ◽  
Target Strength ◽  
Kirchhoff Approximation ◽  
Prolate Spheroids ◽  
Cylinder Method ◽  
Kirchhoff Integral ◽  
Numerical Approaches ◽  
Acoustic Approximation

Kirchhoff approximations for the forward-scattering target strength of underwater objects are developed by combining Babinet’s principle and the Kirchhoff integral, where theoretical formulations and a numerical implementation are given in detail. The Kirchhoff approximation is found to be a high-frequency physical acoustic approximation. The forward-scattering target strength versus frequency and the spatial angles for spherical objects, prolate spheroids and the Benchmark Target Strength Simulation Submarine (BeTSSi-Sub) model are obtained by the Kirchhoff approximation and compared with results from theory, the deformed cylinder method (DCM) and the boundary element method (BEM). The Kirchhoff approximation shows considerable agreement with the theoretical and numerical approaches in a region of [Formula: see text] from the rigorous forward-scattering direction. The forward-scattered field contour and the corresponding directivity for the BeTSSi-Sub model are also calculated as a demonstration. Mode coupling caused by the simulated target is clearly revealed. The results indicate that the Kirchhoff approximation can predict the forward-scattering target strength of complex underwater objects.

scholarly journals The Use of the Reassignment Technique in the Time-Frequency Analysis Applied in VHF-Based Passive Forward Scattering Radar

Sensors ◽  
2020 ◽  
Vol 20 (12) ◽  
pp. 3434
Author(s):  
Marek Płotka ◽  
Karol Abratkiewicz ◽  
Mateusz Malanowski ◽  
Piotr Samczyński ◽  
Krzysztof Kulpa
Keyword(s):  
High Frequency ◽  
Real Life ◽  
Forward Scattering ◽  
Kinematic Parameters ◽  
Very High Frequency ◽  
Digital Video Broadcasting ◽  
Time Frequency ◽  
Video Broadcasting ◽  
Airborne Target ◽  
Very High

This paper presents the application of the time-frequency (TF) reassignment technique in passive forward scattering radar (FSR) using Digital Video Broadcasting – Terrestrial (DVB-T) transmitters of opportunity operating in the Very High Frequency (VHF) band. The validation of the proposed technique was done using real-life signals collected by the passive radar demonstrator during a measurement campaign. The scenario was chosen to test detection ranges and the capability of estimating the kinematic parameters of a cooperative airborne target in passive FSR geometry. Additionally, in the experiment the possibility of utilizing FSR geometry in foliage penetration conditions taking advantage of the VHF band of a DVB-T illuminator of opportunity was tested. The results presented in this paper show that the concentrated (reassigned) energy distribution of the signal in the TF domain allows a more precise target Doppler rate to be estimated using the Hough transform.

Readiness of SiC MOSFETs for Aerospace and Industrial Applications

2016 ◽  
Vol 858 ◽  
pp. 894-899 ◽  
Author(s):  
Ljubisa Stevanovic ◽  
Peter A. Losee ◽  
Stacey Kennerly ◽  
Alexander Bolotnikov ◽  
Brian Rowden ◽  
...  
Keyword(s):  
High Frequency ◽  
Cost Savings ◽  
Industrial Applications ◽  
Motor Drive ◽  
Device Performance ◽  
Reliability Testing ◽  
Experimental Demonstration ◽  
Solar Inverter ◽  
Improved Performance ◽  
Reliability And Robustness

This paper highlights ongoing efforts to validate performance, reliability and robustness of GE SiC MOSFETs for Aerospace and Industrial applications. After summarizing ruggedness and reliability testing performed on 1.2kV MOSFETs, two application examples are highlighted. The first demonstrates the 1.2kV device performance in a prototype high frequency 75kW Aviation motor drive. The second highlights the experimental demonstration of a 99% efficient 1.0MW solar inverter using 1.7kV MOSFET modules in a two-level topology switching at 8kHz. Both applications illustrate that SiC advantage is not only in improved performance, but also in significant system cost savings through simplifications in topology, controls, cooling and filtering.

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