Radio Frequency IDentification (RFID) stores and retrieves data using devices called RFID tags: objects attached to or incorporated into a product, animal or person which communicate with an RFID reader or interrogator. This book proposes a linear two-port model for an N-stage modified-Greinacher full wave rectifier, predicting the overall conversion efficiency at low power levels where the diodes are operating near their threshold voltage. Included is an experimental procedure to measure how impedance modulation in the tag affects the signal at the reader, and a useful tool for choosing the most appropriate impedances.