Near Field Coupled Wireless Microwave Sensor

This paper presents a wireless planar microwave sensor operating at industrial scientific and medical (ISM) frequency for the detection of dielectric materials. The microwave sensor consists of a reader (ground defected microstrip coupled line) and a passive tag where a complementary split-ring resonator (CSRR) is made on the commercially available copper-foil. The CSRR is a peel-off type tag that is excited using the near field of microstrip coupled transmission line. The near field coupling, the low-cost passive tag design, and the high sensitivity (~250 MHz change per unit change in dielectric constant) make the proposed sensor wireless, cost-effective, and reliable.