Harvesting Data Streams for Scattering between Battery-less Transponder and Mobile Telephones

This work studies RF (radio frequency) harvesting of electromagnetic energy from intentionally generated RF signals in the 2.4 GHz ISM band as power supply for a battery-less (back-)scattering transponder. In addition to such a transponder, our implementation uses two regular, unmodified mobile telephones, the first one for transmitting WLAN (Wireless Local Area Network) signals and a quasi-continuous Bluetooth (BLE) advertising signal, the second one for receiving the scattered signals from the transponder. The transponder accumulates energy from the incident WLAN and BLE signals for powering a micro-controller, which in turn controls the scattering and modulating of the incident BLE signal. The scattering process applies a 4 MHz frequency translation and frequency shift keying for information transfer such that the scattered signal is detectable by the BLE receiver of the second mobile telephone. The present study implements the WLAN signals as data stream and examines the coexistence of this data stream and the BLE advertising signals as well as the effects of alternative data transfer protocols and different WLAN transmission frequencies. Results show that the User Datagram Protocol (UDP) provides high duty cycle transmissions at an operational range of approx. 2 cm without interfering the scattering process. Thus, the UDP data stream enables an improved wireless power transfer from the transmitting telephone to the battery-less transponder, which enables a significant range extension and encourages further endeavors in this direction.