Harvesting for Scattering Modulated RF-Signals Receivable by Mobile Telephones

This work studies electromagnetic energy harvesting as power supply for wireless (back-)scattering technology in the 2.4 GHz ISM Band. The scattering technology reflects and modulates an incident continuous wave (CW) signal such that the scattered signal is receivable by a Bluetooth Low Energy (BLE) receiver of a regular mobile telephone. The modulation performs a 4 MHz frequency shift of the incident CW signal combined with frequency shift keying for information transmission. The relative low range of frequency shifting allows a controlling of the modulation by a low energy micro-controller (MCU). The M CU receives its operational energy from an RF harvesting circuit, which accumulates and intermediately stores the energy of the incident CW signal. The M CU operates as signal generator and generates a modulation control signal by using its internal asynchronous components such as RC oscillator and counter, and uses an external 1 MHz crystal as time base for digitally changing the frequency of the oscillator in dependency of the information to be transmitted. Thus, the reception of unidirectional BLE advertising messages combines scattering technology and RF energy harvesting. Based on this technology, we achieved a 50 % power efficiency improvement at the transponder tag, i.e. 9.2 m W active mode power consumption, which is encouraging and promotes expectations of further progress in this direction.