Kaarle Jaakkola

Phase-Based UHF RFID Tracking With Nonlinear Kalman Filtering and Smoothing

In this paper, we present an UHF RFID location tracking system, which is based on measuring the phases of back scattered signals from RFID tag using multiple spatially distributed antennas at a single carrier frequency. The wavelength ambiguity of the phase measurements is resolved by using the extended Kalman filter (EKF) and the Rauch-Tung-Striebel (RTS) smoother, where the state includes the position, velocity and the phase offsets of antennas. The performance of the method is experimentally verified at 890 MHz using a commercially available RFID reader.

Ranging of UHF RFID Tag Using Stepped Frequency Read-Out

This paper presents a phase-based method for obtaining the distance of an RFID tag with unknown properties. The tags response is measured by the reader at several discrete frequencies at the threshold power of the tag. The dispersive properties of the modulated reflection coefficient of the tag are estimated from the measured power sensitivity and their effect is compensated in the distance estimation. The method is derived using a simple theoretical model for the tag and the performance of the method is experimentally verified at 860 MHz.

Applicability of Metallic Nanoparticle Inks in RFID Applications

Radio frequency identification (RFID) antennas for HF and UHF frequencies are ink-jet printed using commercially available silver nanoparticle ink. Quality factors of 5.3 and 9.4 are obtained for coil antennas targeted for 13.56 MHz when the printing and sintering process is repeated two and three times, respectively. The measured maximum effective aperture of the printed UHF antenna is only some decibels lower than that of an equivalent etched copper antenna and the maximum reading distance with 0.5 W (ERP) transmitted power is 3 m for continuous reading. These results suggest that obtaining a low enough series resistance for printed coils is challenging while printed RFID antennas for UHF do not set as strict requirements on conductivity. With a perfectly optimized structure, a UHF tag antenna printed in just one layer of ink can be practically equal in performance with the traditional etched copper and aluminum tags.

Monitoring environmental performance of the forestry supply chain using RFID

It is estimated that wood raw material worth of approximately @?5billion is wasted annually in Europe. The major reason for this is that the raw material is not used in the most efficient way as information needed regarding the wood raw material is not available throughout the supply chain. An automatic traceability system makes it possible to utilise raw material information efficiently throughout the forestry-wood production chain and to maximize the raw material yield, and to optimise and to monitor the environmental impact, by linking the relevant information to the traced objects. This paper describes novel RFID technology and traceability solutions that have been developed for the wood products industry. RFID-marking connects the physical objects with their database counterparts thus allowing automatic tracing of the objects. The architecture is needed to the dynamic and decentralised nature of the wood industry. The developed novel RFID based technology allows tracing of individual logs from the tree felling to the sawing of the logs at the saw mill. By combining the traceability and process information systems, new methods are enabled for analysing the performance of the supply chain. As an example, the environmental performance of a product can be traced and analysed even on an individual level. This means that not only the performance from the own production of a manufacturer will be accessible, but also the upstream processes that constitute the product value chain and the life cycle performance for the product leaving the manufacturer.

Antenna Effective Aperture Measurement With Backscattering Modulation

A scattering measurement method for antenna characterization is described. The antenna backscattering is modulated by an oscillator circuit. The modulation begins, when a known RF power is transferred to the oscillator circuit from the antenna. This enables the measurement of the effective aperture of the antenna, from which the antenna bandwidth and radiation pattern are obtained. A theory for antenna aperture measurement is developed using a simple circuit model for the antenna-oscillator system. A dipole and a PIFA with a reactive input impedance at the application frequency were measured. The antenna aperture was measured to an accuracy of 9%, and the measurements complied with simulated and measured references. The method provides simple and accurate bandwidth and radiation pattern measurements with the reactive load the antenna is designed to work with.

Backscattering-Based Measurement of Reactive Antenna Input Impedance

A scattering technique for measuring reactive antenna input impedance is described. The antenna scattering is measured with three different loads: an open circuit, a conjugate match, and a reactive match. The load reactances tune the antenna into resonance at the measurement band. Theory and error considerations are presented, as well as measurement results of two ultra high frequency radio frequency identification antennas. The measurements were performed in a gigahertz transverse electromagnetic mode cell. The measured impedances are within about 10% of the simulated values for a dipole-like antenna. The results of a planar inverted-F antenna are somewhat more complex, but also supported by the presented simulations and the coaxial impedance measurement results.

UHF RFID based tracking of logs in the forest industry

This paper describes a prototype of a UHF RFID based log marking and tracking system developed for the challenging four-season outdoor conditions in Scandinavia. The RFID system comprises of novel pulping compatible EPC Class 1 Generation 2 transponders, and of robust readers with novel performance boosting features. A wedge-shaped transponder is inserted into the log end with a special tool so that it is protected and held firmly in place by wood during the transportation and processing of timber. A robust EPC-compliant RFID reader featuring an adaptive RF front end was developed for use in a harvesting machine. Readability tests at saw mills with test logs using specially adapted commercial UHF readers show nearly a 100% readability for the transponders inside fresh moist logs.

Wirelessly Powered Sensor Transponder for UHF RFID

A transponder for UHF RFID with sensor interface for external capacitive sensors is described. The sensor interface consists of a capacitive voltage divider and a 10 bit successive approximation analog to digital converter. The power consumption is about 30 muWDC and the transponder is wirelessly powered with RF waves from the reader device. Wireless measurement of capacitance is demonstrated at a distance of 30 cm with 0.5 W erp transmission power. Low operation distance is mostly due to low efficiency of the rectifying Schottky-diodes in the particular BiCMOS process.

Low-Cost and Low-Profile Near Field UHF RFID Transponder for Tagging Batteries and Other Metal Objects

A new UHF RFID transponder solution especially designed for tagging batteries of portable devices is presented. The new transponder is a thin and low-cost label that can be read from the opposite side of the tagged object. This feature is based on utilizing the secondary currents induced on the metal object. The new transponder was first analyzed and optimized by electromagnetic simulations, and subsequently a small series of prototypes was fabricated. After finding the right dimensions by electrical measurements, a bigger series with the selected dimensioning was fabricated. With these prototypes a practical test of automatic sorting of batteries was run and the performance of the transponder in practice was evaluated by the yield of the test. In the test, yields of over 96 % were obtained, even though the reader setup was not optimized.

Challenges and Possibilities of RFID in the Forest Industry

Considerable added value in wood and timber production can be achieved via higher yield and quality of the wood products deriving from improved control of the production proc‐ esses. The key to improve the production is the identification of the individual wood items in order to utilise exact information of their properties. This can be realized by marking and tracking of tree trunks, logs and sawn wood products to allow the information associated with them to be collected and utilised in all stages of the value chain from forest to the wood product.