Sari Merilampi

The characterization of electrically conductive silver ink patterns on flexible substrates

Electrically conductive silver ink patterns were produced by the screen printing method. Paper, fabrics and plastics were used as the substrate materials. The electrical properties of the samples were characterized by sheet resistance measurement as a function of curing temperature and curing time. The mechanical properties of the samples were characterized by cross hatch adhesion test, bending test and tensile test. Depending on the process parameters and materials, the sheet resistance of the printed conductive patterns varied between 0.04 Ω/□ and 0.13 Ω/□. The curing temperature appeared to have a significant effect on the sheet resistance. In all cases sheet resistance decreased as a function of curing temperature. Adhesion between the substrates and the conductive patterns appeared to be good. The result of the bending test indicated that the resistivity of the silver ink patterns increased as a function of the bending cycle process. The results of the tensile and electrical tests showed that with the screen printing method it is possible to produce highly stretchable electrically conductive patterns for practical applications.

Chip Impedance Matching for UHF RFID Tag Antenna Design

Passive UHF RFID tag consists of a microchip attached directly to an antenna. Proper impedance match between the antenna and the chip is crucial in RFID tag design. It directly influences RFID system performance characteristics such as the range of a tag. It is known that an RFID microchip is a nonlinear load whose complex impedance in each state varies with the frequency and the input power. This paper illustrates a proper calculation of the tag power reflection coefficient for maximum power transfer by taking into account of the changing chip impedance versus frequency.

The Effect of Conductive Ink Layer Thickness on the Functioning of Printed UHF RFID Antennas

In this study, the effect of the conductive ink layer thickness on the performance of printed ultra-high-frequency (UHF) radio-frequency identification (RFID) tag antennas was investigated. A simple quarter wave dipole tag for European UHF RFID frequencies was designed to be tested in this study. All the tags were made by using screen-printing technique. Three different thicknesses for the ink layer were used. Performance of the tags was analyzed by the measurement of threshold and backscatter power. The results show that it is possible to produce RFID tag antennas by screen printing and it is possible to optimize the tag performance by adjusting the thickness of the electrically conductive layer. The results show how the performance characteristics deteriorated when the thickness of the printed ink layer was reduced. However, it was also shown that thin ink layers can be used in some applications and cost savings can be achieved in this way. It is therefore important to recognize these effects on the performance.

Embedded wireless strain sensors based on printed RFID tag

Purpose – The purpose of this paper is to develop a wireless strain sensor for measuring large strains. The sensor is based on passive ultra high‐frequency radio frequency identification (RFID) technology and it can be embedded into a variety of structures.Design/methodology/approach – Silver ink conductors and RFID tags were printed by the screen printing method on stretchable polyvinyl chloride and fabric substrates. The development of the strain‐sensitive RFID tag was based on the behavior of the selected antenna and substrate materials. Performance of the tags and the effect of mechanical strain on tag functioning were examined.Findings – The results showed that large displacements can be successfully measured wirelessly using a stretchable RFID tag as a strain‐sensitive structure. The behavior of the tag can be modified by selection of the material.Research limitations/implications – New tag designs, which are more sensitive to small levels of strain and which have a linear response will be the subje...

Analysis of electrically conductive silver ink on stretchable substrates under tensile load

Electrical conductors were printed by the screen printing method on stretchable PVC substrates and on fabrics. Polymer thick film silver ink was used as the conductive medium. The electrical performance and the structure of the ink film were investigated in unloaded conditions and under strain. In addition, the ink film morphology was examined. The goal of this study was to provide information for developing a strain sensor for large strain levels using the materials under investigation. An additional aim was to assist the integration of electronics into other structures. The results showed that strain sensitive structures can be made using the materials selected for this study and these materials provide an opportunity to develop strain sensors. The structures also tolerated large strain levels and thus they can be integrated into other materials which are exposed to strain.

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.

Analysis of Silver Ink Bow-Tie RFID Tag Antennas Printed on Paper Substrates

In this study, polymeric silver inks, paper substrates, and screen printing were used to produce prototype Bow-Tie tags. Because of increasing interest in applying passive UHF-RFID systems in paper industry, the Bow-Tie antenna used in this study was designed to work through paper. The maximum reliable read ranges of the tags were measured thorough stacked paper and also in air. The analysis and functioning of the antenna design are also discussed. All inks and paper substrates were suitable as antenna material and the prototype tag antennas had good reading performance. The maximum reliable read ranges were quite the same as for copper and aluminum tags studied elsewhere. This means that printed UHF tags are competitive solutions for the identification of simple mass products.

Printed passive UHF RFID tags as wearable strain sensors

Strain measurements could be utilized in monitoring human bodily functions and movements. Cost effective and low maintenance wearable sensors are needed in this field. The goal of this paper was to produce wearable strain sensors based on UHF RFID technology and the behavior of the materials which were utilized in prototypes. Two tag geometries were compared. Polymer thick film silver ink was used as the conductive medium. The tags were fabricated by screen printing the ink on stretchable PVC and on fabric substrates. Performance of the tags and the effect of mechanical straining on tag functioning was examined. The prototypes tolerated large strain levels. The results showed that the behavior of the UHF RFID tag strain sensor is dependent on the material behavior under strain as well as the tag antenna geometry. These offer various possibilities in strain measuring.

Mobile exergames for preventing diseases related to childhood obesity

Childhood obesity and physical inactivity are well-known problems which are typically related with videogames. The goal of this study is to develop digital games which motivate children and adolescents to exercise more, instead. The games are realized in such way that no special game consoles are required. The games can be played with a regular computer while mobile phones and heart rate monitors are used as the game controllers. Thus the games can also be played from a public screen in schools, for example, thus offering new exercising possibilities among youngsters. In this study, two exercising games (exergames) are presented and their ability to motivate youngsters is examined by group studies. The results indicate that the developed exergames are suitable in school environment. It is concluded that the games were found engaging and they motivated players to exercise. This indicates a positive effect of exergames in prevention of diseases which are related to childhood obesity and physical inactivity.