Study On Responses Of Buildings To Microwave Pulses

The study on responses of buildings to microwave illumination is significant for the application of high power microwave technology, wireless communication technology, radar detection technology and electronic equipment hardening technology against intensive electromagnetic pulses. The responses of buildings to microwave pulses are researched using theoretical analysis, computational simulation and experimental investigation in the paper. The main content and research results are summarized as follows:Firstly, the transmission characteristics of electromagnetic wave penetrating the surface of the wall, the propagation characteristics in the wall and the propagation attenuation characteristics of electromagnetic wave penetrating the wall are analyzed by the plane wave theory. They are numerically compared by adopting different parameters such as polarization, incident angle, dielectric permittivity, conductivity, tangent of dielectric loss angle and frequency. The conclusions are summarized as:The larger the incident angle, conductivity and the tangent of dielectric loss angle are, the larger the attenuation constant is, and in addition, in the wall the attenuation constant changes much more obvious by employing different values of the above parameters at higher frequencies.With the increasing of the incident angle, the power transmission coefficient of the parallel polarization increases at first and then decreases. When the conductivity is not zero, the complete transmission of the parallel polarization disappears. With the increasing of the incident angle, the power transmission coefficient of the perpendicular polarization decreases. With the increasing frequency, the power transmission coefficient increases slowly and then rises rapidly and eventually tends to a constant.There exists the resonance phenomenon when the electromagnetic wave penetrating the wall. The resonant frequency is ?m=m/(2d(με)1/2). The larger theσor tanδis, the less obvious of the resonance phenomenon. The propagation attenuation of the electromagnetic wave penetrating the wall consists of the transmission attenuation of electromagnetic wave penetrating the surface of the wall and the propagation attenuation in the wall. On the one hand, when the dielectric permittivity is smaller, at the low frequency the propagation attenuation is mainly determined by the transmission attenuation of electromagnetic wave penetrating the surface of the wall; at the high frequency the propagation attenuation is mainly determined by the propagation attenuation in the wall. On the other hand, when the dielectric permittivity is larger, the propagation attenuation is mainly determined by the transmission attenuation of electromagnetic wave penetrating the surface of the wall.The propagation attenuation characteristics of homogeneous plane wave penetrating the wall are analyzed applying the theory of Modal Transmission-Line (MTL) and numerical simulation. These results are in accordance with the results of theoretical analysis. Meanwhile the propagation attenuation characteristics of electromagnetic wave penetrating the periodic wall such as brick wall and walls structure are studied using the above methods. The results are not rigorously the same but the trend of the two results is similar. The MTL method is more effective and has less computational cost.In order to obtain the electrical properties of the wall structures, the relative permittivity and tangent of dielectric loss angle of the brick was measured by using the closed resonant cavity. The results show that the relative permittivity is about 3 and the tangent of dielectric loss angle is in the order of 10-3. The propagation attenuation of microwave at 1.5 GHz penetrating the wall of a building is measured to be 14 dB.Finally, according to the building structure and the results of the experimental measurement, the 3D simulation of microwave pulses propagating, reflecting and transmission in a building is carried out to obtain the response characteristics of the building to microwave pulses. The distribution of the electric field in the building is measured under the illumination of high power microwave pulses. Compared with the simulation results, the experimental studies on response for buildings to microwave pulses result in the following conclusions:1) For narrow-band modulated square pulses with different incident angles, the size of the field enhancement region is in the direct proportion to the size of region illuminated by microwaves directly through the fixed windows and doors.2) The field amplitude in the area behind windowsills reduces significantly in the propagation direction of microwave pulses.3) With the perpendicular incident to the window, the pulses width has little influence upon size of field enhancement region and the maximum value of electric field to a certain extent.4) For narrow-band modulated square pulses with shorter rise time and fall time, the effect of field superimposition is stronger and the maximum value of electric field can reach 7.94 dB.5) The microwave pulses width is widened in the building due to the reflection of the walls.