Numerical modeling of an enhanced very early time electromagnetic (VETEM) prototype system

In this paper, two numerical models are presented to simulate an enhanced v ery early time electromagnetic (VETEM) prototype system, which is used for buried-object detection and environmental problems. Usually, the VETEM syst em contains a transmitting loop antenna and a receiving loop antenna, which run on a lossy ground to detect buried objects. In the first numerical mod el, the loop antennas are accurately analyzed using the Mettled of Moments (MoM) for wire antennas above or buried in lossy ground, Then, Conjugate Gr adient (CG) methods, with the use of the fast Fourier transform (FFT) or Mo M, are applied to investigate the scattering from buried objects. Reflected and scattered magnetic fields are evaluated at the receiving loop to calcu late the output electric current. However, the working frequency for the VE TEM system is usually low and, hence, two magnetic dipoles are used to repl ace the transmitter and receiver in the second numerical model. Comparing t hese two models, the second one is simple, but only valid for low frequency or small loops, while the first modeling is more general. In this paper, a ll computations are performed in the frequency domain, and the FFT is used to obtain the time-domain responses. Numerical examples show that simulatio n results from these two models fit very well when the frequency ranges fro m 10 kHz to 10 MHz, and both results are close to the measured data.