Small square-shaped slot antenna for wearable passive UHF RFID tags

We present a slot antenna with the footprint size of 4 × 4 cm² (0.12λ × 0.12λ at 915 MHz) for wearable passive UHF RFID tags. In addition to the main radiating slot, cuts made into the surrounding conductor increase the antenna radiation efficiency and help to self-match the antenna impedance with the RFID microchip in the body-worn configuration. Antenna structure is uniplanar and optimised for a low-permittivity textile substrate. The measured attainable read range of the tag is 2.5 metres when affixed to the upper back of a test subject.