Tiiti Kellomaki

Towards Washable Wearable Antennas: A Comparison of Coating Materials for Screen-Printed Textile-Based UHF RFID Tags

(Radio frequency identification) RFID tags integrated into clothing enable monitoring of people without their conscious effort. This requires tags to be an unnoticeable part of clothing and comfortable to wear. In this study, RFID antennas were screen printed on two different fabrics, six different coating materials for the (integrated circuits) ICs were applied, and the reliability of these RFID tags was tested with moisture and laundry tests. Generally, glue-type coating materials were easier to handle and could be spread precisely. All the tags were operational immediately after the coatings were applied, and five of the coating materials were seen to protect the IC from detaching in the laundry. It was found that the uneven fabric surface caused discontinuities and breaks in narrow conductors, and thus hard coatings may also be needed to keep the tag from breaking in laundry.

Wearable antennas for FM reception

The effect of human body on wearable 100 MHz antennas is studied by measurements. At that frequency, the body is very thin compared to the wavelength, but about half a wavelength tall. Antenna performance is most affected by the posture of the antenna wearer, second matter being antenna position on body. Physical traits of the wearer have only a slight effect on the antenna performance. A ¿13 dBi gain was achieved by the constructed dipole-like antennas, and letting one¿s arms hang down reduces this by 5 to 15 dB. Most of the power delivered to the antennas is absorbed by the human body, but some is radiated not only by the antenna but also by the body. Wearable antennas need to be shortened by 15 to 25 % from the free-space length to achieve the desired resonance frequency.

Design approaches for bodyworn RFID tags

Bodyworn tags are a challenging application for radio frequency identification (RFID) systems. The importance of this application will increase in the future due to emerging novel wireless identification and sensor systems. In this paper, a literature survey of wearable RFID tag antennas is presented. One-layer and multilayer tags are compared. The body effect on antenna parameters is analysed. Based on the findings, guidelines for wearable tag antenna design are given. As an example of a bodyworn tag, a meandered dipole is presented.

Effects of bending GPS antennas

The effect of antenna bending on return loss, impedance bandwidth, and radiation pattern is studied, taking four antennas as examples. These include a patch, slot, inverted-F, and dipole antenna. Some of them exhibit circular polarization and one is broadband. Impedance is seen to be fairly constant regardless of bending, though if circular polarization is excited by careful antenna shaping, the circular polarization and corresponding resonance are easily lost. The axial ratios of all examined antennas degrade quickly with decreasing bend radius. Linearly polarized antennas are more tolerant to bending effects, though their polarization may twist and main lobe direction change.

On-Body Performance of a Wearable Single-Layer RFID Tag

The effects of the human body on a wearable radio frequency identification (RFID) tag at 866 MHz are presented. We concentrate on the effect of the varying antenna-body separation distance on the antenna properties. The results of the three-dimensional radiation pattern measurements are presented. A 6-m read range, -6 dBi realized gain, and 12% antenna efficiency are achieved when this antenna is worn on the body.

Analysis of Circular Polarization of Cylindrically Bent Microstrip Antennas

When circularly polarized (CP) microstrip antennas are bent, the polarization becomes elliptical. We present a simple model that describes the phenomenon. The two linear modes present in a CP patch are modeled separately and added together to produce CP. Bending distorts the almost-spherical equiphase surface of a linearly polarized patch, which leads to phase imbalance in the far-field of a CP patch. The model predicts both the frequency shifting of the axial ratio band as well as the narrowing of the axial ratio beam. Uncontrolled bending is a problem associated especially with flexible textile antennas, and wearable antennas should therefore be designed somewhat conformal.

Bendable plaster antenna for 2.45 GHz applications

A plaster antenna for 2.45 GHz applications is presented. Measurement results for different use cases are given, and bending effects are examined. The proposed structure exhibits a 6 dBi on-body gain, and covers the 2.4-2.5 GHz ISM band in all use cases. The effect of bending the antenna on the SAR has been investigated by simulations. The antenna is suitable for medical applications.

Magnetic and electric antennas close to the body

Thin single-layer antennas for plaster-like sensor applications at 2.4 GHz are presented. Measurements show that the antennas are operational when placed at a 0.3 mm distance from the body. Magnetic dipole performs the best in the immediate proximity of the body.

Snap-on buttons in a coaxial-to-microstrip transition

Commercial snap-on buttons are used in a coaxial-to-microstrip transition. The reflection properties of the transition are examined in time and frequency domains. Snap-on buttons are usable in wearable antenna connections in a frequency range up to three gigahertz.

Snaps to Connect Coaxial and Microstrip Lines in Wearable Systems

Commercial snaps (clothing fasteners) can be used to connect a coaxial cable to a microstrip line. This is useful in the context of wearable antennas, especially in consumer applications and disposable connections. The measured S-parameters of the transition are presented, and an equivalent circuit and approximate equations are derived for system design purposes. The proposed connection is usable up to 1.5 GHz (10 dB return loss condition), and the frequency range can be extended to 2 GHz if a thinner, more flexible coaxial cable is used.