A Flexible Printed Chipless RFID Tag for Concentration Measurements of Liquid Solutions

摘要

A fully inkjet-printed flexible chipless RFID tag is presented in this paper. It is based on a coplanar waveguide (CPW) coupled to a multiresonator circuit to encode the information in the frequency domain. Two cross-polarized ultra-wideband (UWB) antennas connected to the CPW receive and transmit the signals. Three spiral resonators are used to encode a 3-bit signature. The RFID tag is applied for the wireless concentration measurements of liquid solutions by characterizing the insertion loss response. Water/isopropyl alcohol solutions with different concentrations are measured wirelessly by the tag. A capillary tube is placed on one of the resonators to allow the interaction between the sensor and the solutions. By observations of the measurements, different parameters are used to quantify the sensitivity. The change of the insertion loss at the resonant frequency |ΔS_(21)| and the shift of resonant frequency |Δf_(res)| are used to analyze the water/isopropyl alcohol samples. A |ΔS_(21)| = 0.3dB/(20 vol%) and |Δf_(res)| = 30 MHz/(20 vol%) have been achieved by the sensor in the concentration range of [20, 80] vol% and [40, 99] vol%, respectively.