Near-Field Wireless Sensing of Plastics and Papers Using Frugal Peel-Off Passive Tag

This article presents a novel frugal approach of testing plastics and papers using a near-field microwave sensing technique with a peel-off tag. The proposed sensing technique involves two electrical entities: the sensor, which may be regarded as a reader, and a disposable tag. The reader is a modified design of a gap-coupled microstrip line (GCML) sensor, while the passive tag is a standard double-ring complementary split-ring resonator (CSRR) engraved on a commercially available copper foil using laser printing techniques. A detailed numerical study is presented for the engineered sensing methodology, showing the effect of the sample height, sensing distance, bending angle, and inclination. Empirical formulas associated with the dielectric properties of the sample under test are also given. The errors associated with a possible air gap between the peel-off tag and the sample, as well as the relative positioning of the tag and the reader, are analyzed while also considering the bending of the tag. Finally, the sensor is fabricated on a 1.5-mm-thick Rogers RT5880 laminate, and several standard samples are prepared to experimentally check the validity of the approach. The sensor provides a transmission bandwidth (BW) of 1.9 GHz with a typical insertion loss (IL) of 1 dB and a reflection loss of 20 dB. The tag engraved on the frugal peel-off copper foil is used for sensing various dielectric materials by placing it on planar and curved surfaces. The simulation and measured results are found to be in close agreement. The proposed scheme is found to be reliable and cost-effective also for the testing of microwave substrates. It provides robust results for the wireless sensing of objects located within a range of 10 mm from the reader.