Implementation and wireless readout of passive UHF RFID strain sensor tags based on electro-textile antennas

Sensing capabilities embedded in a passive UHF RFID tag provide a battery-free wireless sensor equipped with a digital identifier. We present an RFID strain sensor tag based on a stretchable antenna made of conductive fabrics. To create an efficient antenna for the sensor tag, we use non-stretchable and highly conductive copper-coated fabric to form the main antenna body and join a section of stretchable conductive fabric by means of sewing with conductive thread. We test wirelessly two different sensors with 1 cm and 3 cm stretchable sections and characterize them in terms of the maximal sensor readout distance and the response of its backscatter strength to the antenna elongation. Our results show that the percentage change in the backscatter strength is in approximately linear relation with the antenna elongation.