RFID Compatible Sensor Tags for Remote Liquid Sample Interrogation

In this paper, a passive harmonic generator based wireless sensor for long range interrogation of small liquid samples is demonstrated. A step by step method for development of the harmonic doubler based sensor is presented. Two different sensor designs are evaluated for liquid sensing. The first sensor is a T-line resonator coupled to patch antennas and harmonic doubler. The second sensor is a compact design in which a split ring resonator is directly coupled to a dipole antennas based diode doubler. The resonators are loaded by the liquid samples that in turn induce changes in reflected power from the tag. The sensors are evaluated for their remote interrogation capabilities of sensing different liquids under test. Liquid samples measured include mixtures of isopropyl alcohol-water, methanol-water and glucose-water samples. These mixtures provide a range of dielectric properties for the evaluation of the long range sensor. This sensor holds good for potential application in food safety, bio sensing and hazardous chemicals monitoring and detection.