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Abstract-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.

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 subject for future work. Tag performance under cyclic loading and in a real environment will also be investigated. Future work relating the investigation of practical applications and the system designing for the strain sensor will also be required. Practical implications -Printing is fast and simple manufacturing process which does not produce much waste or material loss. The sensor is a new application of printed electronics. It also provides new opportunities for system designers. Originality/value -The paper provides a new kind of wireless strain sensor which can be integrated into many structures (i.e. clothes). The sensor is a new application of printed electronics and it is made from novel materials.

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An electrically conductive nanocomposite composed of thermoplastic elastomer and nanosized silver particles was developed. Nanosized silver particles were produced by the liquid flame spraying method. Nanocomposites were produced employing a batch mixing process in the melt state. The percolation curve and the minimum resistivity as a function of silver content were defined. A plasticized styrene block-copolymer was used as the matrix polymer. The results showed that the agglomeration of the silver particles has a major influence on the percolation threshold and the resistivity of the compound. With slightly agglomerated silver particles a percolation threshold with a silver content of 13-16 vol.% was achieved. The corresponding resistivity was 2.0 · 10 -1 X cm. With heavily agglomerated particles the resistivity is high (2.9 · 10 3 X cm), even with a silver content of 20 vol.%. With a low primary silver particle size (under 100 nm), the resistivity of the compound was high (5.6 · 10 5 X cm).