Passive Wireless UHF RFID Antenna Label for Sensing Dielectric Properties of Aqueous and Organic Liquids

The in situ wireless sensing of dielectric properties for organic aqueous solutions with a wide range of relative permittivities is presented. The use of a UHF passive label antenna design attached to either clear borosilicate glass bottle or petri plate is proposed and which allows for the unobtrusive, safe monitoring of the liquid solutions. The meandered dipole antenna (with a parasitic loop matching component) frequency is highly reliant on the chosen container as well as on the liquid present within, and adjusts with shifting dielectric properties. Tested solutions of high relative permittivity (such as water) along with low permittivity, lossy liquids (such as xylene) presented distinctive frequency characteristics with read distances of up to 7 meters for each type of container tested. The sensor was also able to detect ‘unknown’ solutions and determine the dielectric properties by utilizing standard curve analysis with an accuracy of ± 0.834 relative permittivity and ± 0.050 S·m-1 conductivity (compared to a standard dielectric measurement system available on the market). With the accuracy known, tuning the design to fit any necessary frequency is possible as a means to detect specific changes in any one liquid system. This sensor is a possible candidate for discreet real-time monitoring of liquid storage containers and an alternative for low-cost bulk liquid dielectric property identification which could be implemented in areas requiring, constant, or remote monitoring as needed

A passive UHF RFID pH sensor (smart polymers for wireless medical sensing devices)

A functionalised variant of polydimethylsiloxane (PDMS) was applicated atop an RFMicron RFM2100-AER UHF RFID tag and used in a series of depositions of pH buffer solutions, to observe changes in a sensor code generated by the tag. Averaged values of the sensor code data were used between 800-860MHz from 8-20dBm to compare pH buffers between 8.8 and 7.2 which consistently showed a significant degree of change in averaged sensor intensity readout. pH buffers outside the effective buffering range did not show a significant difference in averaged sensor code intensity

Miniature on skin passive UHF RFID antenna sticker

Passive Radio Frequency Identification (RFID) in recent years has been more widely suggested for medical use with different types of wearable antenna designs. However, wearable passive RFID technology has always been limited by a few key constraints (primarily size) when trying to overcome the variable human body's dielectric properties to produce a high read range antenna design. Here we present an on skin passive RFID antenna design, three centimetres in diameter with a read range near two meters on the human body. With slight adjustments to the polyutherane thickness, the original sticker design can negate the difference between the variable human body dielectric properties within subject groups with only slight loses in antenna read range. It was more cost effective to vary the thickness of the breathable polyutherane used as the tag substrate to achieve a resonance within the European UHF RFID frequency range (as well as to increase the read range capability) than to redesign the antenna. Most variability was seen in subjects with high muscle to fat ratio; if the subject was highly muscular then the antenna polyutherane layer was increased to accommodate the increase in the subject's dielectric properties. This has led to a single passive RFID antenna design (two different polyutherane thicknesses) that can accommodate most people as a wearable design with numerous possible applications