Ungrounded Lightning Surge Protection Device for Wireless Sensor Networks Node in the Wilderness

The maintenance free remote monitoring character of wireless sensor networks (WSN) node in the wilderness demands ungrounded lightning surge protection. In this paper, a protection device with functions of low frequency surge cutting off and RF signal passing is designed, in which discharge circuit consists of three-level surge by-pass circuit, the antenna outer conductor and the circuit board copper clad. The current capacity, the start time and the output voltage meet the requirements of surge protection for weak current device. The discrete components that undertake protective effect were involved in impedance matching calculation. The parameters of discrete components were estimated and adjusted constantly at test stage to insure the inserted protection device impedance matching with the node RF transceiver module and antenna. The experimental results show that the node with the ungrounded protection device can pass the fourth level surge immunity experiments and have run of 49 months in Xinjiang coal fire area outdoor monitoring site.