An Inkjet Printed Chipless RFID Sensor for Wireless Humidity Monitoring

TL;DR

This paper introduces a low-cost, inkjet-printed chipless RFID humidity sensor that uses a finite Artificial Impedance Surface to detect humidity levels via frequency shifts with high accuracy.

Contribution

The work presents a novel, printable RFID humidity sensor based on AIS with high Q nulls, capable of accurate humidity detection through frequency shift analysis.

Findings

Frequency shift up to 270MHz for humidity change from 50% to 90%

High measurement accuracy with low error probability at 10% RH discrimination

Fabrication using inexpensive inkjet printing on coated paper

Abstract

A novel chipless RFID humidity sensor based on a finite Artificial Impedance Surface (AIS) is presented. The unit cell of the AIS is composed of three concentric loops thus obtaining three deep and high Q nulls in the electromagnetic response of the tag. The wireless sensor is fabricated using low-cost inkjet printing technology on a thin sheet of commercial coated paper. The patterned surface is placed on a metal backed cardboard layer. The relative humidity information is encoded in the frequency shift of the resonance peaks. Varying the relative humidity level from 50% to 90%, the frequency shift has proven to be up to 270MHz. The position of the resonance peaks has been correlated to the relative humidity level of the environment on the basis of a high number of measurements performed in a climatic chamber, specifically designed for RF measurements of the sensor. A very low error probability of the proposed sensor is demonstrated when the device is used with a 10% RH humidity level discrimination.