DSDS 16
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Browsing DSDS 16 by Subject "'Electrical and Electronic Engineering not elsewhere classified'"
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Item Open Access Accurate, fast and stable solver for electromagnetic scattering of absorbing layer materials(Cranfield University, 2016-12-06 11:26) Dély, AlexandrePoster presentation at the 2016 Defence and Security Doctoral Symposium. The boundary element method is an efficient and flexible tool for the modelling of scattering of electromagnetic waves by conducting and penetrable objects. It finds applications in the solution of forward and inverse problems in e.g. radar footprint determination, stealth technology, and imaging for diagnostics and security. To model scattering by objects that are for almost perfectly conducting, the classic equations are augmented with a so called impedance boundary condition (IBC). The IBC specifies a relationship between the electric field and the magnetic field on the surface of the scatterer, or equivalently between the magnetic and electric currents. IBC applications are numerous: especially they are well suited to simulate metals coated by a dielectric/absorbing layer which is the base of stealth technologies. In this contribution, an IBC enabled electric field integral equation will be introduced that can provide accurate results in linear time complexity at arbitrarily low frequency. The starting point of this work is the classic IBC formulation. Unfortunately, this suffers from low frequency and dense grid breakdowns. This means that the accuracy of the solution deteriorates and/or the computation time increases, when the frequency is low and/or when the number of unknown of the problem is high, because the iterative solvers used to solve the linear system require more iterations. The new IBC-EFIE introduced in this work does not suffer from these problems and can deliver highly accurate solutions at arbitrary frequency in near linear computational complexity. The formulation is based on quasi Helmholtz decomposition techniques and multiplicative preconditioners and yields a system whose condition number is independent of both the frequency and the discretization density.Item Open Access Passive Bistatic Radar Detection Using Non-Stationary Transmitters of Opportunity(Cranfield University, 2017-01-12 09:50) Ghazalli, Nasyitah3MT presentation at the 2016 Defence and Security Doctoral Symposium.Passive Bistatic Radar (PBR) systems use non-cooperative illuminations of opportunity to detect, localise and track targets. They have attracted a lot of interest in recent years because 1) they can be operated and deployed at a relatively low cost 2) they are difficult to detect and hence allow covert operations in a hostile environment and 3) because of the proliferation of illuminators of opportunity.Various illuminators of opportunity from analogue signal sources to digital ones, have been studied and exploited in recent years, and these include commercial broadcast systems, cellular base stations and local area networks. The aim of this research is to investigate the potential of PBR target detection in the presence of non-random signals emitted by a moving transmitter of opportunity and without the use of a reference channel. Typical transmitters of opportunity could be, for example, satellites carrying a SAR system. This research will include a study of the waveform properties, an assessment of target tracking performance and a set of experimental trials to demonstrate the feasibility of the proposed solution.Item Open Access Searching for High Density Material in Cargo Containers Using Gravity Gradiometry(Cranfield University, 2017-02-06 09:34) Leahy, DavidPoster presented at the 2016 Defence and Security Doctoral Symposium.Imaging cargo containers at ports in this country is an important task, especially if they are being checked for possible fissile material. Some detection methods cannot be used as they are too destructive. A possible alternative is the use of gravity gradiometry - a non-destructive sensing technique which can provide better resolution than straightforward gravity readings, with the trade-off being less penetration power. The resulting inverse problem becomes an underdetermined system of linear equations. This poster looks at applying both a level set method and a genetic algorithm. In its simplest form a level set method uses a level set function to define two distinct regions based on the sign of the function at each point, the boundary being where the function is zero. It then uses a gradient-based iterative method to allow the shape to deform (including splitting and merging) to better fit the data. I explore the use of the colour level set method, which uses more than one level set function to describe many domains. Genetic algorithms are methods which draw inspiration from the process of natural selection using steps such as crossover and mutation. By limiting the population size and by use of a reparameterisation the algorithm can work at the speed required for the time-constraints we have. Both methods have their strengths and weaknesses when applied to this real-life problem. Crown copyright.