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

In the wilderness, the use of wireless sensor network (WSN) nodes because of their maintenance-free remote-monitoring characteristic demands ungrounded lightning surge protection. This paper proposes a design of a protection device with functions of low-frequency surge cutting off and radio-frequency (RF) signal passing. In this device, the discharge circuit consists of a threelevel surge by-pass circuit, an outer conductor antenna, and a copper-clad circuit board. The current capacity, start time, and output voltage meet the requirements of surge protection for a weak current device. Discrete components that provide the protective feature were involved in calculating impedance matching, and the parameters of these components were estimated and adjusted constantly at the test stage to ensure that the impedance of the inserted protection device matches with those of the node RF transceiver module and antenna. The experimental results show that the node with the ungrounded protection device can pass fourth-level surge immunity experiments and run for 49 months at the outdoor monitoring site in the Xinjiang coal fire area.