Novel techniques for microwave imaging using the time reversal finite difference time domain method



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In recent years, microwave imaging technology has elicited considerable interest. Its remarkable properties make it attractive for various applications, including security, medical, and through-wall imaging. In this dissertation, novel microwave imaging techniques using the time reversal finite difference time domain (TR-FDTD) method are presented and validated through simulation and experimental work. TR-FDTD is a numerical method based on the solutions to the time-dependent Maxwell’s curl equations, which are represented by discrete formulas in time and space under a time reversal scheme to reconstruct images from previously captured data. To overcome the vulnerability of microwave frequencies to environmental noise, we introduce new TR-FDTD imaging techniques that incorporate signal correlation processing to minimize the corrupting effect of noise on the quality of reconstructed images. In a near-field microwave through-wall imaging test case, we use a planar grid to collect the signals scattered from an area of interest and then process them with a correlation operation before applying the TR-FDTD algorithm to construct images of desired planes in the computational domain. Our simulations as well as experiments in the presence of strong environmental noise show that the proposed technique successfully produces clear images, while the results of the standard TR-FDTD method are unrecognizable. We apply the same technique, instead using noise waveforms as the source signals, similar to source signals used in noise radar, in order to develop an anti-jamming microwave imaging approach that provides immunity to adversary interference. We demonstrate the method’s potential through the successful reconstruction of images in a test case involving a dielectric object behind a wall. Additionally, we investigate the lateral and range resolution of the TR-FDTD method and show that it is capable of superior range resolution, far exceeding that typically achievable in other radar imaging techniques. Based on this result, we introduce a microwave tomography (MWT) technique using the TR-FDTD method. We validate the performance of this technique by simulation of imaging scenarios with single and multiple objects. Finally, we present a technique for high-speed microwave imaging based on the TR-FDTD method and validate its applicability through simulation.



Microwave imaging, Time reversal, FDTD method, Noise waveforms, Microwave tomography, High speed imaging