Study On The Coupling Of Microwave Pulses Into Monolayer And Nested Cavities Through Slots

The investigation of microwave pulse coupling into the metallic cavity through narrow slots is of interest to the application of HPM and the electromagnetic compatibility. We use the finite-difference time-domain (FDTD) method to investigate the linear coupling process of the microwave pulse into the rectangular cavity and the cylindrical cavity with narrow rectangular slots. The nested rectangular cavities and the nested cylindrical cavities with narrow rectangular slots are also considered in this paper.First, we investigate the coupling process of microwave pulse into the rectangular cavity and the cylindrical cavity with narrow rectangular slots. The phenomena of field enhancement, cavity modulation, and pulse width stretch are observed in the coupling processes. Especially, we find that there is still spectrum separation effect during the coupling process. In the case in which the electrical field of the microwave pulse is parallel to the short-side of the rectangular slot, we employ the coupling function method to investigate the internal distribution of the coupling microwave electrical fields of the two cavities, and find that the coupling electrical field in the plane, which is perpendicular to the short-side of the slot, decreases rapidly near the inner wall of the cavity. In addition, in the cross-sections of the cavities, the coupling electrical fields oscillate in a quasi-periodic manner, and the field amplitude is relatively uniform for the rectangular cavity than for the cylindrical cavity. The coupling electrical field is maximum around the centre of the cross-section in the case of the cylindrical cavity, and except for the regions around the slots, the coupling electrical field is much larger near the ends of the central axis for the cylindrical cavity than for the rectangular cavity. We also find that the value of the resonant peak (ηc) of the coupling system is mainly determined by the length of short-side of the rectangular slot. The resonant frequency of the coupling system (fc) decreases as the length of long-side of the rectangular slot increases. The influences onηc and fc caused by the thicknesses changing of the rectangular slot are very small. We find that the peak value of total energy of coupling wave inside the system increases as the area of the cross-section of slot increases, which is independent of the intensity of field enhancement inside the slot. In addition, we find that there are no enhancement and resonant effect inside triangular slots and circular slots. However, annular slots have obvious enhancement and resonant effect. It is may be mentioned that, we eliminate the cavity reflection by setting the absorbing boundary condition (ABC) on inner walls of the cavities to investigate the dependence of the resonant frequency on the system, and find that the resonant frequency of the system is not only determined by the dimension of the slot, but also by the process of microwave pulse refection inside the cavity.Secondly, we investigate coupling processes of microwave pulse into the nested rectangular cavities and the nested cylindrical cavities with narrow rectangular slots. Slot on outer cavity (Q1) is called the outer slot and slot on inner cavity (Q2) is called the inner slot. We find that the phenomenon of field enhancement appears near the outer slot and the inner slot. The outer slots of these two systems both have same main coupling pulse and field enhancement coefficient. Peak values of coupling fields inside inner cavities of above two systems are equal approximately. Compared with outer cavities and the single cavities that have same slot and volume under same incident pulse, the coupling wave inside Q2 are very weaker. Then, we calculate numerically the resonant peaks, the resonant frequencies and the maximum coupling function curves of the two systems. The investigative results show that the inner slots of the two systems make the coupling wave inside Q1 attenuate down at about 10dB. Moreover, we find that the peak values of the coupling electrical field at the centre of the outer slot and the coupling power on the cross-section of the outer slot show the property of degressive periodic fluctuation along with the distance between the centers of the outer slot and inner slot, and the period equals to the half-wavelength of carrier frequency of the incident wave. However, the peak values of coupling electrical field at the centre of the inner slot and the coupling power on the cross-section of the inner slot fluctuate rulelessly. In addition, the peak value of the coupling electrical field at the centre of the outer slot also shows the property of degressive periodic fluctuation along with the side-length of the cross-section of the rectangular cavities or along with the diameter of the cylindrical cavities, and the period equals to the wavelength of carrier frequency of the incident wave. Finally, we find that the coupling field and energy are mainly determined by the position of the inner slot of the nested cavities, and they are minimums when the position of the inner slot is optimized.