Abstract
The one-step modification of a commercial RFID sensing tag is demonstrated using polydimethylsiloxane-based thin-film chemistry to construct reusable passive RFID sensors for changes in the dielectric properties of electrolyte solutions as a function of concentration. The effects of PDMS film thickness were characterized as a function of RFID sensor code value. The output sensor code of the RFMicron RFM2100-AER wireless flexible moisture sensor (taken between 800 and 860 MHz) was compared with the readings taken when the tag was dry and when the tag had a water deposition on the sensor area. The effect of the direct application of liquid water on the tag was to alter the capacitance presented to the integrated chip which auto-tunes to correct for the reactance. By varying the thickness of the PDMS film between the interdigitated sensor and deposited liquid, the sensitivity of the tag to a high dielectric medium could be controlled. Aqueous salt solutions were tested on a 500-μm-thick film. It was found that the sensing platform could be used as a means of measuring the concentration of various salt solutions within the range 0–2 M and in turn could be used as a passive UHF RFID dielectric measuring tool. The measurement capability of the platform was subsequently demonstrated using a reduced frequency range (845–865 MHz).
Highlights
W IRELESS chemical sensors (WCSs) are an area of communications that have recently experienced a large increase in interest [1], [2]
The most common wireless platforms integrated into chemical sensors are Bluetooth (34%) [1] and Radio Frequency Identification (RFID) (23%) [2]
Cheaper disposable alternatives for monitoring in the pharmaceutical industries manufacturing process have been proposed as affordable, disposable sensors require single use manufacture [13]. Another approach taken with wireless chemical sensors is to modify pre-existing RFID tags and change the functionality by way of the addition of a chemically sensitive material
Summary
Abstract— The one-step modification of a commercial RFID sensing tag is demonstrated using polydimethylsiloxane-based thin-film chemistry to construct reusable passive RFID sensors for changes in the dielectric properties of electrolyte solutions as a function of concentration. The effects of PDMS film thickness were characterized as a function of RFID sensor code value. By varying the thickness of the PDMS film between the interdigitated sensor and deposited liquid, the sensitivity of the tag to a high dielectric medium could be controlled. It was found that the sensing platform could be used as a means of measuring the concentration of various salt solutions within the range 0–2 M and in turn could be used as a passive UHF RFID dielectric measuring tool.
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