A new antenna, designed on a polyethylene terephthalate (PET) substrate and implemented by inkjet printing using a conductive ink, is proposed as a passive tag antenna for UHF radio frequency identification (RFID). The operating bandwidth of the proposed antenna is very large since it encompasses all worldwide UHF RFID bands and extends well beyond at both edges. Moreover, it has a very simple geometry, can be easily tuned to feed many of the commercial RFID chips, and is very robust with respect to realization tolerances. The antenna has been designed using a general-purpose 3-D computer-aided design (CAD), CST Microwave Studio, and measured results are in very good agreement with simulations. The proposed passive RFID tag meets both the objectives of low-cost and size reduction.

The robustness of wearable antennas to the human body proximity can be improved by properly placing the radiating element over a ground plane, or by shaping the ground plane, on the basis of the antenna electric and magnetic energy density distributions, aiming to confine the electric energy density in specific regions far from the antenna border. The effectiveness of the above design criterion has been assessed through both numerical analysis and experimental measurements, by optimizing the position of the radiating element of a wearable grounded UHF RFID tag operating at the ETSI band (865-868 MHz), with respect to its ground plane. A flexible tag characterization and performance evaluation platform is used to measure the tag sensitivity as a function of the antenna-body distance.

A novel wearable textile dual-band antenna configuration based on a substrate integrated waveguide (SIW) cavity is presented. The miniaturization of the antenna is achieved by exploiting the magnetic field symmetry of a square SIW cavity, reducing its size to 1/8 of the full square cavity with an eighth-mode SIW configuration. This solution is applied to the design of a wearable dual-band antenna for Long Range (LoRa) applications. The antenna operating frequency covers both the UHF LoRa bands, the European (863-870 MHz) and the North American (902-928 MHz). The proposed design provides a low-cost and compact antenna, which is easy to fabricate and ensures a very good isolation and robustness with respect to the human body proximity. The commercial software CST Studio Suite has been used for the antenna design and simulations. A prototype has been fabricated and the measured results are in good agreement with numerical simulations.

This paper presents a compact AMC structure used as a shielding element for a generic wearable RFID tag at UHF frequencies for on-body applications, with an overall footprint limited to an area of only 0.03 λ ₀ ² (41.4 mm × 82.8 mm). Thanks to the isolation provided by the AMC planar structure, the tag antenna gain and reading range are increased of about one order of magnitude in comparison with the case of a conventional tag attached to the human body. The designed antenna is platform tolerant, with a very good robustness and isolation with respect to the human body, exhibiting a high reliability. The AMC structure is implemented on a thin, flexible and biocompatible high permittivity silicon-doped dielectric substrate, with apertures both in the substrate and in the ground plane to allow skin transpiration. Therefore, the presented device can be effectively used also as an epidermal antenna, allowing the “on-skin” sampling of the most typical health parameters. The presented configuration has been designed using CST Studio Suite. A prototype has been fabricated and fully characterized, and measured results are in very good agreement with simulations.

The robustness of wearable UHF-band ungrounded antennas with respect to body-coupling effects is addressed. Two different configurations of single-layer antennas, with different energy density distributions, are presented, and a design criterion to improve their performance with respect to the antenna-body separation is derived. Through an analysis of the antenna electric and magnetic energy density distributions, it is shown that the degradation of the antenna performance due to the proximity of the human body can be reduced if the electric energy density is confined in specific regions far from the antenna border. The proposed design criterion has been validated by numerical simulations and experimental measurements.