The Forward Simulation And Inversion Imaging Of The Ultra Wide Band Electromagnetic Method

In this dissertation, a new detect method was proposed which use ultra-wideband(UWB) electromagnetic pulse to detect underground targets or through-the-walldetection, so it was called UWB electromagnetic method. It combines transientelectromagnetic field theory, very narrow pulse signal transmission technology, high-speed sampling techniques, UWB antenna and signal processing technology andother subjects of research, the result of simulation is accurate, noninvasive, highresolution and penetrating depth etc. Many basic theoretical issues have been studiedin-depth in this dissertation, such as the UWB electromagnetic waves in lossy media, the dissemination of energy distribution, Resolution and penetrating depth, therelationship between pulse width or bandwidth and the Echo of effectivelyinformation and so on. The high-resolution survey research was carried out to detectthe media under the ground with UWB electromagnetic pulse. We used limited-areaof aperture antenna, feed into the high power and very narrow pulses. In this way, wecan improve the penetrating depth and resolution at one time.The numerical simulation of the theoretical model for arbitrary complex mediaunderground and through the walls to detect life was carried out which used thehigh-order finite-difference time-domain (FDTD) method, the result revealed thelaw of the electromagnetic pulse dissemination and the impulse responsecharacteristics of objectives in complex media. The inversion method of conductivityand permittivity simultaneously reconstructing for UWB electromagnetic method wasproposed in this dissertation.The main contribution of this dissertation can be summarized as follows:1. Combined the time domain convolutional PML with high-order FDTD tosimulate the UWB electromagnetic radiation field of limited-area of aperture antenna, developed the 3D electromagnetic simulation of high-order FDTD software which cancarry out numerical simulation for arbitrarily complex of underground lossy media. 2. Improved the convolution method in iterative formula of CPMLabsorption boundary conditions, proposed piecewise linear convolution PML(PCPML) absorption boundary approach, and further improved the absorptioneffect of the boundary.3. Discussed the narrow radiation pulse of limited area of aperture antennatransmission and energy density characteristic of the spatial distribution in uniformlossy media space with frequency domain analytic method and the time domainFDTD method respectively, revealed the nature law of electromagnetic flux densityslow decay for the first time, and corrected the misunderstand about electromagneticmissile for the moment, evaluated objectively the applied value of electromagneticmissile used in explorating earth4. Simulated the UWB electromagnetic wave filed of arbitrary complexitymodel, the transmission of UWB electromagnetic wave in several typical undergroundmodel and through the walls to detect the human body model can be shown directly, explained the interaction mechanism of electromagnetic wave in lossy mediaunderground. Analyzed the antenna parameters and electrical parameters on theperformance of the radiation field, and then discussed the resolution and depth ofUWB electromagnetic detection method. It can provide theoretical guidance for thepractical work of UWB electromagnetic method.5. The inversion method of conductivity and permittivity simultaneouslyreconstructing for UWB electromagnetic method was proposed in this dissertation.Using the improved time-domain limited memory BFGS quasi-Newton constrainedinversion method and nonlinear conjugate gradient method approximate inversionmethod to reconstruct permittivity and conductivity of the model in the same time, and completed the UWB electromagnetic double-parameter inversion and developedthe corresponding inversion software.6. Studied the rapid imaging methods of UWB electromagnetic detectmethod which based on time-domain waveform matching filter method of probabilityimaging, and achieved the single or multiple objects with the probability imagingsuccessfully.