An RF Distance Sensor Utilizing Harmonic Signal from Rectenna for Power-Controlled Wireless Power Transmission System to Wearable Devices

We propose an RF distance sensor that utilizes the transmission wave itself for the distance measurement between the transmitter and an individual for power level management. The harmonic signal generated by a rectenna is used for the return signal. Since the frequency is different from the transmitted wave, the detector is not saturated by the transmitting wave and can thus be set to high sensitivity. We measured the propagation delay from the transmission timing to f received wave for the distance sensing. The time detector by utilizing an equivalent sampling technique suppressed the accuracy of a distance within ±3 cm.