Wireless communications technologies are becoming such enmeshed parts of daily life that
radio-frequency identification (RFID) antennas and electronic devices are forming multi-function systems within the range of a single person’s body. When equipped with the proper antennas, passive RFID devices can even provide invaluable sensing functions for medical purposes, such as heart-rate and breathing-rate monitoring, as well as for stimulating the nervous system to achieve pain relief.
Such RFID-technology-based body-area systems consist of passive RFID tags and an RFID reader. The RFID reader transmits a wireless RF signal that activates the tags; it also encourages a response signal or backscatter wave from the RFID tag related to the condition of the monitored organ or body part. A wide range of frequencies are used for RFID applications, from as low as 13.56 MHz for monitoring simple activities to 26.5 through 40.0 GHz for smart skins and Internet of Things (IoT) applications. The design and format of the RFID antenna will depend on the operating frequency range and the intended functions of the RFID tags, especially when matching the impedance of any RFID semiconductor devices incorporated in the RFID tags.
Miniaturization is a key goal in the design of antennas for RFID tags. Perhaps as important for any wearable device, the antennas must support long-term safety against their radiated electromagnetic (EM) fields and comply with guidelines established by leading international safety organizations. A number of fabrication methods have been developed for safe, reliable RFID antennas, including e-thread embroidery on fabric substrates, inkjet printing on flexible substrates such as paper and plastics, and screen-printing of conductive polymer thick films on fabric substrates.
As the researchers note in their review of different RFID tag antennas, the markets for wearable and implantable RFID devices is growing at a phenomenal rate for applications such as smart homes, healthcare, and child monitoring across the commercial, military, and industrial sectors. Many applications are already in use, but the number of potential future applications for RFID-based tracking/monitoring using both worn and implanted devices is motivating much design work into smaller and more efficient RFID antennas on different substrates.
See “RFID Antennas for Body-Area Applications,” IEEE Antennas & Propagation Magazine, Vol. 60, No. 5, October 2018, pp. 14-25.