A new family of passive wireless RF harvesters based on R-C-Quartz oscillators

This work presents Resistor-Capacitor-Crystal (RC-Quartz) oscillators for use as passive amplification in RF energy harvesters. Quartz crystals can provide inductive reactance with extremely high quality factor (Q). This high Q inductive reactance coupled to a capacitor can provide the needed resonance for voltage amplification with minimal in-circuit losses. Detailed theoretical analyses of the condition precedents necessarily for voltage amplification of the R-C-Quartz foscillators are presented. RF harvesters based on this approach are realized and characterized for voltage sensitivity and efficiency. The circuits were realized on FR4 substrates with commercially available components. By using this approach, DC voltage sensitivity of 1.9 V and efficiency of 55% is measured for 1 μW (-30 dBm) RF input power at a frequency of ~13.56 MHz.