Johanna Virkki

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.

The effects of recurrent stretching on the performance of electro-textile and screen-printed ultra-high-frequency radio-frequency identification tags

Future welfare and healthcare applications require wearable radio-frequency identification (RFID) tags where the tag antenna is an integral part of clothing and endures repeated stretching. In this study, wearable passive ultra-high-frequency (UHF) RFID tag antennas were fabricated from silver-plated stretchable fabric and by screen printing them on non-conductive, stretchable fabric. The reliability of the tags was studied by stretching them repeatedly from the initial length of 10 cm to 13.5 cm, up to 200 stretching cycles. According to our results, the electro-textile tags achieved read ranges of 6.5 meters, also after the 200 harsh stretches. The screen-printed tags initially achieved read ranges of 9.5 meters and after the 200 stretches the read ranges were only 2.5 meters shorter, that is, still about 7 meters. These measurement results and the strengths and weaknesses of both types of wearable tags are discussed in this paper.

Experimental Study on the Washing Durability of Electro-Textile UHF RFID Tags

In this letter, we investigate the impact of washing on the performance of passive ultra-high frequency (UHF) radio frequency identification (RFID) tags based on dipole antennas fabricated from silver and copper fabrics. Initially, the tags achieved read ranges of 6 and 10.8 m, respectively, under the European RFID emission regulation. To assess the impact of washing on the performance of the tags, they were washed repeatedly in a washing machine and measured after every washing cycle. The silver fabric tag was found to be more durable without any coating and maintained a read range of over 2 m after 10 washing cycles. We also tested two conformal coatings to protect the tags from wear and tear during washing and found regular textile glue to be a promising conformal coating for both types of textile tags. Finally, we present simulation results to confirm the relationship between reduction in the antenna conductivity and the measured read ranges of the tags during the washing test.

A Selective Ink Deposition Method for the Cost-Performance Optimization of Inkjet-Printed UHF RFID Tag Antennas

A selective ink deposition method is proposed for fabricating inkjet-printed passive UHF RFID tag antennas with optimized cost-performance ratios. The deposition method is based on identifying areas with high surface current densities on a given tag antenna and applying additional silver nanoparticle ink onto such areas to increase tag read range. In this paper, the proposed method is experimentally verified by utilizing the method on a small dipole tag antenna. Several ink deposition schemes are created, and their read range performances and ink consumptions are presented.

Accelerated testing for failures of tantalum capacitors

This study focused on the use of accelerated testing to find out why tantalum capacitors fail. Stress effects of humidity, temperature, and ripple voltage were examined in different combinations. Results show that a standard 85/85 test with combined enhanced moisture and temperature does not result in failure of tantalum capacitors in 2500 h. However, with added ripple voltage, failures may occur in a relatively short time. High relative humidity and high temperature both affect water diffusion, but apparently increased ripple voltage in 85/85 testing causes tantalum capacitor characteristics to weaken and capacitors to fail. The paper elaborates on the possible reasons.

Testing the effects of temperature and humidity on printed passive UHF RFID tags on paper substrate

This article is an interesting substrate material for environmental-friendly printable electronics. In this study, screen-printed RFID tags on paper substrate are examined. Their reliability was tested with low temperature, high temperature, slow temperature cycling, high temperature and high humidity and water dipping test. Environmental stresses affect the tag antenna impedance, losses and radiation characteristics due to their impact on the ink film and paper substrate. Low temperature, temperature cycling and high humidity did not have a radical effect on the measured parameters: threshold power, backscattered signal power or read range of the tags. However, the frequency response and the losses of the tags were slightly affected. Exposure to high temperature was found to even improve the tag performance due to the positive effect of high temperature on the ink film. The combined high humidity and high temperature had the most severe effect on the tag performance. The threshold power increased, backscattered power decreased and the read range was shortened. On the whole, the results showed that field use of these tags in high, low and changing temperature conditions and high humidity conditions is possible. Use of these tags in combined high-humidity and high-temperature conditions should be carefully considered.

Embedding inkjet-printed antennas into plywood structures for identification and sensing

The embedding of radio frequency identification (RFID) tags into plywood boards will enable the identification and tracking of individual plywood boards and end products of plywood. Even more benefits can be achieved by adding sensing functions into these tags. We present tags that are embeddable inside plywood by direct inkjet-printing on pure birch veneer. The use of passive UHF RFID technology in the plywood industry is discussed, two tag antenna designs for plywood are presented and the tag fabrication procedures are described. Furthermore, tag performance measurement results from various setups are presented to verify the concept of embedding RFID and sensor antennas into plywood structures. Measurements show that tags printed on veneer and embedded inside 2 mm thick plywood board exhibited theoretical read ranges from 7.9 meters to 10.3 meters. The read ranges obtained meet the demands of the plywood industry and offer reliable identification even in challenging environments.

Automated Identification of Plywood Using Embedded Inkjet-Printed Passive UHF RFID Tags

The use of passive ultra high-frequency (UHF) radio frequency identification (RFID) integrated into plywood boards is proposed to enable the identification and tracking of individual plywood boards and end products of plywood. For the first time, tags are embeddable inside plywood by direct inkjet-printing tag antennas on pure birch veneer. The use of passive UHF RFID technology in the applications of plywood industry is discussed, two tag antenna designs for plywood are presented and the tag fabrication procedures are described. Furthermore, results from tag performance measurements performed in the authentic application environment as well as in anechoic conditions are presented and discussed. Measurements show that tags printed on veneer and embedded inside 2 mm thick plywood board exhibited theoretical read ranges from 7.9 to 10.1 meters. The read ranges obtained meet the demands of the plywood industry and offer reliable identification even in challenging environments.

Experimental Study on Brush-Painted Metallic Nanoparticle UHF RFID Tags on Wood Substrates

Due to an increasing interest to add functionality in various products, versatile electronics manufacturing methods are needed for numerous applications. In this letter, ultra-high-frequency (UHF) radio frequency identification (RFID) tag antennas manufactured by brush-painting directly on wood veneer substrate were examined. Silver and copper nanoparticle inks were used in antenna manufacturing. According to our measurements, brush-painted silver and copper nanoparticle UHF RFID tags showed read ranges of 5 and 3 m, respectively, even when embedded inside wood layers. These read ranges are sufficient for many applications, e.g., in construction and packaging industry, where wood is a common material. The novel manufacturing process, its applications, and the achieved tag performance results are presented in this letter.

Towards Washable Electrotextile UHF RFID Tags: Reliability Study of Epoxy-Coated Copper Fabric Antennas

We investigate the impact of washing on the performance of passive UHF RFID tags based on dipole antennas fabricated from copper fabric and coated with protective epoxy coating. Initially, the tags achieved read ranges of about 8 meters, under the European RFID emission regulation. To assess the impact of washing on the performance of the tags, they were washed repeatedly in a washing machine and measured after every washing cycle. Despite the reliability challenges related to mechanical stress, the used epoxy coating was found to be a promising coating for electrotextile tags in moist conditions.