Research On The Response Characteristic Of Ultra-wideband Electromagnetic Detection Of Shallow Target Using Finite Difference Time Domain Method

Ultra-wideband electromagnetic wave has the advantage of high frequency bandwidth, high resolving power, its echo can take abundant characteristic information of the detected target, so it is widely used in target detection and identification domain. Being limited to the power of ultra- wideband impulse source and the problem of electromagnetic compatibility, ultra- wideband electromagnetic detection is mostly used in shallow target detection field and short distance detection field at present.In this paper, the response characteristic of ultra-wideband electromagnetic detection of shallow target is simulated numerically based on Finite Difference Time Domain Method, separately researching the detection of target embedded in the wall and subsurface target det- ection, analyzing the effect of the character of impulse source, the character of target, the soil condition and so on. The achievements are obtained as follows.1. Based on time domain Maxwell equations, the basic theory of Finite Difference Time Domain Method of the three-dimensional cartesian coordinates is introduced in detail, and the validity of FDTD method is verified by researching on radialization of linetype electric current in free space.2. Based on theory of Finite Difference Time Domain Method, instituting the flow of programme, then program using MATLAB 7.0.1 software. The programme is verified by researching on radialization of linetype electric current in free space and radialization of electric dipole separately, numerical solutions are consistent with analytic solutions well, the validity and the correctness of the programmme are validated.3. By analyzing the waveform and frequency of different impulse, we find that modulated Gaussian pulse is a suitable impulse as UWB transmit signal. Then, the response characteristic of ultra-wideband in different walls and the response characteristic of the target detection embeded in wall is simulated numerically. Physical phenomena such as reflection, refraction, diffraction and the change of propagation in different material walls were obserbed. Also, we obtained the conclusion that in shallow target detection field, the higher of pulse's carrier frequency and the narrower of pulse's width, the higher of the resolving power.4. Applied FDTD method to the research on ultra-wideband electromagnetic detection of subsurface target. The ultra-wideband wave in different depth of earth indicated that ultra- wideband pulse is only suitable for subsurface target detecting field. Through the exploration toward different material target in different soil, we find that detection and identification of ultra-wideband signal are closely linked with target characteristic and soil surroundings. In the part of subsurface pipe detection, the pipe depth we calculated in this paper is completely settle for precision need. Also, we obtained the conclusion that the wider the pipe's width, the stronger the echo, the easier the detection. The tube width scarcely has any effect on pipe exploration, and that, we can primary judge the pipe's material based on the shape and amplitude of the echo.