Energy Efficient Enhancement in a 5.8 GHz Batteryless Node Suitable for Backscattering Communications

Abstract

This work presents a compact batteryless node architecture suitable with the backscattering communication (BackCom) approach. The key functional blocks are demonstrated at 5.8 GHz, making use of commercially available components involving a DC/DC step-up converter, a 3.3 V data generator, and an ASK backscattering modulator based on a single GaAs HEMT in a cold-FET configuration. The node integrates a patch antenna exhibiting a non-50 Ω optimal port impedance; the value is defined by means of a source pull-based optimization technique aimed at maximizing the DC/DC input current supplied by the RF to DC converter. This approach maximizes the node compactness, as well as the wireless power conversion efficiency. A prototype was optimized for the −5 dBm power level at the input of the RF to DC converter. Under this measurement condition, the experimental results showed a 63% increase in the harvesting current, rising from 145 to 237 μA, compared to an identical configuration that used a microstrip matching network coupled with a typical 50-Ω patch antenna. In terms of harvested power, the achieved improvement was from −13.2 dBm to −10.9 dBm. The conversion efficiency in an operative condition improved from 15% to more than 25%. In this condition, the node is capable of charging a 100 μF to the operative voltage in about 27 s, and operating the backscattering for 360 ms with a backscattering modulation frequency of about 10 MHz.