Compact folded square-loop antenna for reading near-field RFID tags in blood sample tracking system

Abstract

A highly compact (25 × 25 × 0.8 mm3) dual-band folded square-loop antenna is proposed for reading near-field RF identification (RFID) tags. The antenna has a strong and uniform magnetic field in the nearfield zone of the square loop. The side length of the square loop (∼λ/16) generates resonant frequencies in two conventional modes (0.5λ and 1.0λ). Experimental interrogation of a small RFID button tag attached to a blood sample collection tube showed that the antenna has a small interrogation zone (15 × 15 mm2), which avoids unnecessary interrogation. Experiments also showed that with an input power of 25 dBm, the antenna can tag at a distance of up to 40 mm, which confirmed its suitability for reading button-Type RFID tags attached to blood sample collection tubes and other specimen containers.