| Since RF MEMS devices and MEMS systems can meet the requirements of small volume, high reliability and low cost in the air communication field, and have the advantages of enhancing robustness and substantially reducing power consumption, they have their unique competitive capabilities in the application of air communication equipments. However, with the wide application of MEMS devices and systems, the electromagnetic interference (EMI) problems have become increasingly prominent. How to increase the shielding effectiveness (SE) and of MEMS devices and systems by electromagnetic shielding design is one of the most important things in the process of MEMS technology development.In the"Eleventh Fives"advanced project --- Light Air Communication Node, we are asked to design an L/C/X-Band MEMS Antenna System. Among the MEMS devices adopted, RF MEMS switches produce electromagnetic radiation (EMR) and affect the circuits and devices around inside the system. Besides, EMR is produced when the whole system start working, which would affect the normal operation of other airborne equipments. So it's necessary to analyze the electromagnetic shielding of RF MEMS switches and MEMS systems, but no such document about it has been published.The general design of the L/C/X-Band MEMS Antenna System is presented first. By analyzing the electromagntic environment of the system, the top 5 most serious interference sources are found: MEMS antenna, switching power, PCB, RF MEMS switches, the whole system. When the interference reasons and suppression methods of all the 5 sources are analyzed, RF MEMS switches and the whole system are confirmed as the main research objects.The electromagntic model and EMR environment of a DC-contact RF MEMS series switch and a capacitive RF MEMS shunt switch are described subsequently. It is affirmed that the EMR of DC-contact RF MEMS series switches is just 0.01W, which is so weak that the em shielding can be ignored. While the electromagntic shielding is necessary for Capacitive RF MEMS shunt switches because it radiates electromagntic wave in discharging stage, the highest electric field intensity of which reaches 1.5×10~3 V/M. Selecting appropriate shielding materials and analyzing the em shielding of it, the SE is obtained through shielding simulation, which is above 60 dB.At last, the paper predicts the external EMR inference of the whole system, detecting that the interference margin is positive number, which means EMR inference is produced. So it is necessary to be eletromagnetic shielded. After investigating various light and wide-frequency shielding materials, it is found that carbon nano-tube shielding material can meet the light-weight and L/C/X-band requirements of the system. The size requirements of slot and vent are calculated when the structure of the shielding case is designed. The SE is above 30 dB after being simulated, which meets the engineering demand. |
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