Harvesting for Scattering Bluetooth-Signals between Battery-less Transponder and Mobile Telephones

This work studies harvesting of electromagnetic energy from intentionally generated wireless signals (RF signal) as a power supply for a battery-less transponder in the 2.4 GHz ISM Band. The transponder (back-)scatters the incident RF signal by reflecting and modulating such that it is receivable by a Bluetooth Low Energy (BLE) receiver of a mobile telephone. This scattering includes signal modulation with a 4 MHz frequency shift of the incident signal and frequency shift keying for information transmission. Modulation is controlled by a low energy micro-controller, which receives its operational energy from a RF harvesting circuit that accumulates energy from the incident RF signal. In contrast to our previously used continuous wave transmitter, the present work studies the feasibility of using the BLE transmitter of a further mobile telephone for providing the incident RF signal. This approach requires dealing with the intermittent nature of practical wireless communication, which motivates us to use features of the BLE Standard version 5.0, namely the extended advertizing messages and their periodic re-transmissions. Our experiments involve a specifically designed code sequence, which generates a quasi-continuous wave signal of approx. 2 ms duration, which provides the basis for the transponder's scattering process. Thus, by using energy and waveform of a RF signal from a transmitting mobile telephone we achieved wireless communication from a battery-less transponder to a separate receiving mobile telephone, which encourages further endeavors in this direction.