Thin film based flexible current sensor using a micropatterned Cu coil

This paper reports a novel thin film based flexible clamp-on type current sensor with 250 turns micropatterned Cu coil (line / space = 50 μm / 105 μm) formed by through-holes and flexible printed circuits (FPC) technologies for wireless sensor networks. Using flexible electronics techniques, microvias and fine stripe Cu patterns could be formed around 60-mm-long and 14.5-mm-wide permalloy film sandwiched between 40-mm-lomg and 20-mm-wide polyimide films with a high precision. Since the sensor has high flexibility, it can be used by winding the cable and drastically reduce the installation space. Furthermore, it can construct wireless sensor networks without external power supply because wireless nodes can drive by utilizing the secondary current generated in the coil of the sensor by the behavior of current transformer. Coil resistance between contact pads was about 241 Ω. The output voltage (V_o) changed linearly with variation of the value of primary current (C_p) in the 0 to 20 A range. C_p-F_o sensitivity was about 39.4 mV/A. The sensor can be fabricated by roll-to-roll FPC mass production facility because it is developed using only FPC technology.