Ferrite-Less Frequency-Tuned Printed-Coil Resonator With Rear Metallic Plate for RFID Applications

Abstract

The communication distance of Radio Frequency Identification (RFID) system is affected by the environment. This study presents a compact ferrite-less frequency-tuned printed-coil (PC) resonator, which introduces the additional PC resonators as well as the tunable matching circuits to the coil-based antennas, to address the rear metallic effect and the impedance mismatch effect caused by the environment variation for RFID system. The tunable matching circuit using the proposed negative voltage generator achieves low power consumption of only 0.5 mW. The usefulness of the proposed technique is experimentally validated with the rear metallic plate and the interference of water. Measurements show that compared with the commercial PC resonator, the proposed technique reduces the gaps between the coil and the rear metallic plate from 2.9 mm to 1.1 mm when the detected distance is 4.1 mm and, furthermore, improves the detected distance of the system from 3 mm to 17 mm with the interference of water.