This paper details the design, fabrication and testing of flexible textile-concealed Radio Frequency Identification (RFID) tags for wearable applications in a smart city/smart building environment. The proposed tag designs aim to reduce the overall footprint, enabling textile integration whilst maintaining the read range. The proposed RFID filament is less than 3.5 mm in width and 100 mm in length. The tag is based on an electrically small (0.0033 λ 2 ) high-impedance planar dipole antenna with a tuning loop, maintaining a reflection coefficient less than −21 dB at 915 MHz, when matched to a commercial RFID chip mounted alongside the antenna. The antenna strip and the RFID chip are then encapsulated and integrated in a standard woven textile for wearable applications. The flexible antenna filament demonstrates a 1.8 dBi gain which shows a close agreement with the analytically calculated and numerically simulated gains. The range of the fabricated tags has been measured and a maximum read range of 8.2 m was recorded at 868 MHz Moreover, the tag’s maximum calculated range at 915 MHz is 18 m, which is much longer than the commercially available laundry tags of larger length and width, such as Invengo RFID tags. The reliability of the proposed RFID tags has been investigated using a series of tests replicating textile-based use case scenarios which demonstrates its suitability for practical deployment. Washing tests have shown that the textile-integrated encapsulated tags can be read after over 32 washing cycles, and that multiple tags can be read simultaneously while being washed.

Reliable UHF Long-Range Textile-Integrated RFID Tag Based on a Compact Flexible Antenna Filament.

Spiral resonator loaded S‐shaped folded dipole dual band UHF RFID tag antenna

Platform tolerant dual‐band UHF‐RFID tag antenna with enhanced read range using artificial magnetic conductor structures

A meandered tag antenna is proposed for dual band operation in UHF (Ultra High Frequency) range at f1 = 866 MHz and f2 = 912 MHz. Initially, the proposed tag consists of folded dipole configuration with extended meandered arms to achieve single resonating band. The inverted L-shaped stub is embedded at the lower arm of the folded dipole to introduce additional resonance and realize the dual band operation at desired resonant frequencies. The proposed tag’s impedance is optimised to match conjugately to the RFID IC (Alien Higgs-4). The proposed dual-band tag is designed and simulated using CST microwave studio. The tag prototype is fabricated and is experimentally characterised to verify its impedance matching with respect to the employed RFID IC. The read range performance of the fabricated tag prototype is measured experimentally by placing the proposed tag on different type of objects like wood, fibre, plastic etc. validating its environment tolerance capability. The proposed tag is found to perform well in all the presented scenarios. The proposed tag is compact with volumetric size of dimensions 1920 mm3 and exhibits measured read range of 5.5 m and 5.8 m at 866 MHz and 912 MHz.

Compact Meandered Folded-Dipole RFID Tag Antenna for Dual Band Operation in UHF Range

Textile Ultra High Frequency (UHF, 865–868 MHz) Radio Frequency Identification (RFID) devices meet difficulties from connection of solid chips and textile antennas. In this work, three electro-textile interfaces integrated with the corresponding textile UHF-RFID antennas as the solutions are proposed and compared. The simulated and measured impedance curves of the corresponding antennas are all close and the radiation performance (realized gain) are designed to be near (about 1.4 dBi). According to the Friis formula, the simulated and measured read ranges of the interfaces with the corresponding antennas in air are obtained (all above 4.5 m). For reliability validation, mixed use feasibility tests are implemented and the results show the read ranges of each interface used on other two designs have tolerable read range decrease (< 2 m but all above 3.41 m).In addition, the read ranges of the designs on body are all above 2.05 m. Due to the small sizes of the interfaces, stable performance on body and good reliability, the proposed interfaces solutions are proved feasible. 

Experimental comparison of three electro-textile interfaces for textile UHF-RFID tags on clothes

A novel compact and highly efficient dual-polarized horn-like antenna is presented. It exploits a radiating aperture that is fed by four smaller waveguides via a quad-furcated junction. The antenna also comprises the full feed network for the feed waveguides including an integrated 4-way orthomode power divider. Design principles are described in detail and illustrated by means of an example involving an antenna with aperture size of 2.6<inline-formula> <tex-math notation="LaTeX">$\lambda _{0} \times 2.6\lambda _{0}$ </tex-math></inline-formula> (<inline-formula> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> the wavelength at the central frequency of operation) intended primarily for Geostationary Orbit (GEO) satellites. The antenna feed was designed to comply with the Additive Manufacturing rules and exhibits aperture efficiency levels close to the theoretical maximum ones over the entire transmit Ku band (10.7 – 12.75 GHz), while at the same time its profile is highly compact (6.4<inline-formula> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula>). The measured results of a prototype 3D-printed in Selective Laser Melting (SLM) verified experimentally the calculated high aperture efficiency (over 90%). The total antenna feed attains return loss > 19 dB and maximum cross-polarization isolation (XPI) > 24 dB over a bandwidth of 18%. In light of the favorable electrical performances and compact size, the proposed solution constitutes an appealing alternative to profiled (or spline) horns for satellite antenna systems used either as reflector feeds or direct radiating arrays.

Quad-Furcated Profiled Horn: The Next Generation Highly Efficient GEO Antenna in Additive Manufacturing

An experimental procedure for the accurate characterization of the impedance of balanced tag antennas for RFID applications is re introduced. The balanced devices that are characterized are modeledas two-port networks and their impedance is derived from network parameters, through a rarely used equation that is preferred because it accounts for the losses of non-reciprocal structures such as imperfect test fixtures or baluns. The measurements are conducted using a test fixture for the proper excitation of the balanced devices, and its effects are removed by shifting the measurement plane to the plane of the device under test. The accuracy of the proposed method is demonstrated through the measurement of the impedance of a balanced dipole antenna, and is complemented by the measurement of the RFID ASIC chip. The experimental characterization of the impedance of an RFID tag antenna constitutes a secure way to achieve conjugate matching between the two devices (i.e. the antenna and the RFID chip), and finally enhance the reading range of the RFID tags. Also, since RFID tags are designed to be placed directly on different surfaces, the proposed procedure is further evaluated by mounting the antenna onto two more surfaces.

Experimental characterization of the impedance of balanced UHF RFID tag antennas

This paper presents two designs of Orthomode Transducers (OMTs) tailored to the disruptive additive manufacturing (AM) technology. In particular, in this work we propose guidelines and rules which can be adopted for the efficient design and development of such broadband OMT components in vertical 3D-printing. The final objective relates to the creation of a generic framework which should enable any designer to realize OMT topologies following specific criteria dictated by both the limitations and flexibilities of the AM technology. The numerical models of a turnstile and Bøifot OMT achieve a 35% frequency bandwidth with a return loss better than 25 dB. The experimental characterization of a Ku-band Bøifot OMT verifies the high RF performance of the component as well as its efficient manufacturing. The designed and optimized OMTs are targeted for high-power applications and, therefore, we further provide the multipactor analysis performed to characterize their power handling capabilities.

Orthomode Transducers in Additive Manufacturing for Broadband and High-Power Applications

We present here the design and 3D-printing of Conformal Slotted Waveguide Antenna Arrays (CSWAA) in Ku-band. These solutions are appealing candidates for applications where 3-D Adaptive Electrically Scanned Array (AESA) antennas are employed in conformal surfaces, like airplanes, for beam-steering. First, a non-optimized antenna with a coaxial to ridged waveguide transition is designed and manufactured in Stereolithography (SLA). Then the antenna is later metallized and measured. The problematic aspects of the complex transition are further optimized by a second highly compact antenna concept which employs a direct coaxial feeding mechanism. The second and optimized CSWAA is fabricated in Selective Laser Melting (SLM) and is verified experimentally. Both numerical and measurement results show a close agreement. The proposed CSWAA presents return losses above 10 dB and realized gain above 14 dBi over a relative bandwidth of 8%.

On the Additive Manufacturing of Conformal Slotted Waveguide Antennas

|In this work we demonstrate the extended and generalized methodology for the design of Quad-Furcated Pro(cid:12)led Horns (Q-FPHs). Based on a design case of a 4 (cid:21) 0 (cid:2) 4 (cid:21) 0 Q-FPH, we extract the Generalized Scattering Matrix (GSM) of the enlarged quad-furcated discontinuity and provide analytical expressions for its multimode feeding. Next, the four feeding and the upper common waveguide sections are optimized accordingly through Mode-Matching (MM). The high aperture eﬃciency levels delivered by the methodology are veri(cid:12)ed by full-wave simulations of the optimized design case and compared to the state-of-the-art which is thereby rede(cid:12)ned.

C. K. Stoumpos

Papers

Quad-Furcated Profiled Horn: The Next Generation Highly Efficient GEO Antenna in Additive Manufacturing

Experimental characterization of the impedance of balanced UHF RFID tag antennas

Orthomode Transducers in Additive Manufacturing for Broadband and High-Power Applications

On the Additive Manufacturing of Conformal Slotted Waveguide Antennas

Generalized design methodology of highly efficient quad-furcated profiled horns with larger apertures