Low Frequency and High Frequency semi-active wireless sensors

Semi-active wireless sensors are wireless and batteryless sensors that obtain the required energy to power active electronic components such as a microcontroller core or an oscillator from the electromagnetic field generated by a base station. This paper focuses on wireless capacitive sensors that utilize load modulation in the low frequency (LF) to high frequency (HF) bands for communication. While HF offers the possibility to use air core loop antennas with only a few windings, lower frequencies have advantages with respect to penetration of conductive material. The influence of conductive material for different carrier frequencies is discussed and application examples for low and high frequency carriers are provided.