UHF RFID Tags for On-/Off-Metal Applications Fabricated Using Additive Manufacturing

Radio frequency identification (RFID) tag design is generally focused specifically on either off-metal or on-metal configurations. In this letter, passive 2-D and 3-D RFID tags are presented, which perform similarly in both configurations. The tags operate in the industrial, scientific, and medical (ISM) RFID UHF bands (864–868 MHz and 902–928 MHz). A matching loop consisting of two parallel stubs to ground is used for impedance matching to a passive integrated circuit, which has −18-dBm sensitivity. A planar 2-D tag with a footprint of 13126.5 mm2 is first introduced, showing a simulated gain of approximately 3 dBi and a measured read range of 10 m (for 31-dBm transmit power from the reader) in both on-metal and off-metal conditions. The tag is miniaturized into a 3-D geometry with a footprint of 2524.25 mm2 (520% reduction) and achieves the same broadside simulated on-metal gain. The antennas are fabricated using a 3-D printed acrylonitrile butadiene styrene. The conductive layer is realized by microdispensing silver paste (Dupont CB028). A meshed ground configuration is explored in order to accomplish a 50% conductive paste reduction without disrupting the performance. The proposed tags are compared to commercially available tags as well as previously published tags in terms of read range and size. The tags in this letter present an improvement in terms of read range, gain, and area with respect to previous designs covering the ISM RFID UHF bands. Moreover, the performance of these tags is maintained in on- and off-metal conditions, achieving comparable performance and a reduction in volume of 11 482% with respect to the best tag reported.