28 RFID Systems Active, Semi-passive and Passive RFID Tags

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1 28 RFID Systems Although bar codes and bar code readers have been used for some time to provide quick computer based identification, the technology needed to support these systems is older and in many cases limiting. Radio frequency identification (RFID) tags are intelligent devices that can be attached to or implanted in almost anything and are being used to track products through the supply chain. RFID tags are an improvement over bar codes because the tags have read and write capabilities. Data stored on RFID tags can be changed, updated and locked (Bonsor and Fenlon 2014). RFID was originally developed for short-range product identification, typically covering the 2 mm - 2 m read range (Ruiz-Garcia 2011). In agriculture RFID tags have been used for some time to track beef cattle from birth to consumption (Ruiz-Garcia 2011). In recent years RFID tracking applications have expanded to include most manufactured products, with many manufacturers using the tags to track the location of each product they make from the time it is made until point of sale (Wang, et al. 2007). Other similar applications of RFID tags include tracking of: vehicles; airline passengers; Alzheimer s patients; and pets (Bonsor and Fenlon 2014). RFID technology has been widely accepted for a well-structured traceability system. These devices have also been used to monitor animal behaviour in mid-size outdoor pens, such as in a feed-lot; however, newer RFID hardware that is fitted with various sensors have extend the range of application (Ruiz-Garcia 2011). There are commercial active and semi-passive tags that can collect temperature, humidity, vibration, light, ph and concentration of various gases, such as acetaldehyde or ethylene (Ruiz-Garcia 2011). RFID tags have also been added to transportation devices like highway toll passcards and public transport key-cards (Bonsor and Fenlon 2014). Because of their ability to store data so efficiently, RFID tags can tabulate the cost of tolls and fares and deduct the cost electronically from the amount of money that the user places on the card (Bonsor and Fenlon 2014) Active, Semi-passive and Passive RFID Tags RFID tags can be categorised as active, semi-passive and passive. Active and semipassive RFID tags use internal batteries to power their circuits. An active tag also uses its battery to broadcast data to a reader, whereas a semi-passive tag relies on the reader to supply its power for broadcasting (Bonsor and Fenlon 2014). Active and semi-passive tags usually broadcast in the frequency range between 850 to 950 MHz; however the exact frequency is variable and can be chosen to avoid interference with other electronic devices including other RFID tags and readers.

2 346 RFID Systems Passive RFID tags rely entirely on the reader for power. These tags are read from up to 6 meters away (Bonsor and Fenlon 2014). Passive tags have lower production costs than active or semi-passive tags and are often manufactured to be disposable. Another way of categorising RFID tags depends on how data is stored on the tag. These are defined as: read-write, read-only and WORM (write once, read many) (Bonsor and Fenlon 2014). As the names imply, read-write tags can be used almost like a USB thumb drive with data being added to or overwritten at any time. Readonly tags cannot be changed from their originally installed data. WORM tags can have additional data (like another serial number) added once, but they cannot be overwritten (Bonsor and Fenlon 2014) Animal Tracking Systems Agricultural systems have been using RFID for many years to track the movement of livestock. Australia pioneered the implementation of a mandatory RFID identification system, developing its own individual whole-of-life traceability program for livestock called the National Livestock Identification Scheme (NLIS) (Ruiz-Garcia 2011). The NLIS requires all calves to have RFID devices fitted, often as an ear tag or rumen bolus/ ear tag combinations, before leaving the property on which they were born (Ruiz- Garcia 2011). Animals are registered into a national data base, and their identity and movements are recorded by readers at sale yards, abattoirs, or on farms (Peck 2003). The data base can store information about: diseases and chemical residue status; market eligibility; lost, stolen or mortgaged cattle; and commercial value (Peck 2003). The United States Department of Agriculture (USDA) established the National Animal Identification System (NAIS) in 2005 as a voluntary program (Ruiz-Garcia 2011). It provides registration and tracking of Camelids (llamas and alpacas), cattle, bison, Cervids (deer and elk), Equines, Goats, Poultry, Sheep and Swine (Ruiz-Garcia 2011). Other countries, including: Argentina, Brazil, Canada, Japan, Mexico, the United Kingdom, New Zealand, and several European Union countries have also implemented national RFID based herd registries (Peck 2003). Other animals such as domestic pets have also been injected with RFID chips to allow quick identification of ownership for stray animals. There are however some concerns about the use of these chips: research from as far back as 1996 shows that these implants can cause cancerous tumours in lab rats and mice (Lowan 2007). Specifically, the implants caused sarcomas, which affect body tissue. No studies have proven yet that cancer can form in animals other than lab rats and mice, and it s still too early to tell what effects the chips can have on humans. No negative health effects have been linked to the radio waves emanating from RFID chips. Despite this evidence, or lack thereof, other disadvantages of human chipping may outweigh its advantages.

3 Environmental Sensor Applications Environmental Sensor Applications RFID has great potential for very low cost environmental sensing. The sensor can be integrated either in the chip or simply as an antenna on an RFID tag that directly responds to the environmental parameter of interest. Antenna-based sensory RFID tags utilise the influence of the physical or chemical parameters of interest over the matching coefficient of the tag antenna (Gao 2013). Recalling the Friis Transmission Equation, which was Equation (26.57) from chapter 26, the coupling between the RFID reader and the tag antenna, will depend on the matching coefficient (t) between the antenna and the remainder of the tag s circuitry (or structure). If the tag antenna is designed to change this coefficient in proportion to the environmental parameter of interest, then the tag antenna can be used to as a sensor (Bhattacharyya, et al. 2011, Gao 2013). For example, an antenna can be printed onto a very thin substrate. If this substrate directly responds to moisture, the matching coefficient the antenna to the substrate changes as a function of moisture; therefore the response of the antenna tag to the RFID reader s electromagnetic fields will change as the substrate s moisture status changes. This passive antenna system (i.e. the RFID tag) is simple, can be mass produced at extremely low cost, needs no power supply and can provide accurate moisture data as the RFID reader passes nearby. The trade off in this type of data acquisition is that measurements are only made when the RFID reader passes over the passive antenna tag. The advantage of this kind of system is that the sensors cost a few cents each and can be regarded as expendable after the sensing project has been completed. An interesting application of this type of system may be for high resolution monitoring of soil moisture for irrigation scheduling. Thousands of passive RFID antennae, printed on a biodegradable moisture sensitive substrate, such as paper, could be deployed across a paddock and regularly read by a passing RFID reader to determine site specific soil moisture deficit. This data could be used to provide high resolution irrigation application. Once the irrigation season was finished, these sensors could effectively be ploughed in during preparations for the next crop and new passive sensors deployed. A slightly more sophisticated, and expensive, approach to RFID data acquisition is to use a microchip system that incorporates: an RF power harvesting system; some kind of ultra low power sensor circuitry; a small amount of processing power to summarise the data; some rewritable memory; and a high efficiency capacitor that acts as a very fast charging, rechargeable power supply (Sample, et al. 2007). As the RFID reader passes over these sensors they harvest electrical energy from the reader s electromagnetic fields and store this energy as electrical charge on the high efficiency capacitor. Over time, as the charge on the capacitor is depleted, the sensor circuitry captures and condenses data about the environmental parameter of interest and stores this summarised data as the equivalent of an ID code in the rewritable memory. Upon the next pass of the RFID reader, this summarised data is transferred to the

4 348 RFID Systems reader for further processing and the capacitor is recharged for the next sequence of data acquisition. This strategy utilises near field communication systems Near Field Communication Near Field Communication (NFC) allows wireless data exchange at very close range. More precisely, NFC is a set of technical specifications and standards for transferring information between two objects via the inductive coupling of radio frequency fields at MHz (McHugh and Yarmey 2014). NFC was developed from radio-frequency identification (RFID) standards. The primary distinction between NFC and other RFID technologies, however, is its operating range: typically within 3 to 5 cm (McHugh and Yarmey 2014). Among many potential applications, Near Field Communication (NFC) technology has been developed for credit cards. Some credit cards have NFC chips embedded in them and can be tapped against NFC payment terminals instead of being swiped through a magnetic reader. Near Field Communication devices can also read passive RFID tags and extract the information stored in their memory (Bonsor and Fenlon 2014), as described above. Like RFID systems, the NFC implant chips can be either active or passive. In passive communication, only one device (the initiator) actively generates a radio frequency field, to which the other object (the target) responds by modulating the initiator s field (McHugh and Yarmey 2014). A passive target is energised by the magnetic field generated by the initiator (McHugh and Yarmey 2014). In both active and passive modes, NFC data exchange is based on a half-duplex system, where one device must receive while the other is transmitting. Data exchange can be at a rate of 106, 212, or 424 kbps; 848 kbps is available in some NFC-enabled devices but is not yet standardized (McHugh and Yarmey 2014). As a result, NFC is significantly slower than other wireless communication technologies such as Bluetooth and Wi-Fi, and most applications of NFC involve transfer of very small amounts of data (McHugh and Yarmey 2014), usually is a summarised form. References Bhattacharyya, R., Floerkemeier, C., Sarma, S. and Deavours, D RFID tag antenna based temperature sensing in the frequency domain. Proc. RFID (RFID), 2011 IEEE International Conference on Bonsor, K. and Fenlon, W How RFID Works. 27th August, 2014, howstuffworks.com/ Gao, J Antenna-Based Passive UHF RFID Sensor Tags. Unpublished thesis. Mid Sweden University, Department of Electronics Design Lowan, T Chip Implants Linked to Animal Tumors. The Washington Post.

5 References 349 McHugh, S. and Yarmey, K Near Field Communication: Recent Developments and Library Implications. Synthesis Lectures on Emerging Trends in Librarianship. 1(1): Peck, C Around The ID World. BEEF. 40(4): Ruiz-Garcia, L THE ROLE OF RFID IN AGRICULTURE. Journal of Current Issues in Media & Telecommunications. 3(1): Sample, A. P., Yeager, D. J., Powledge, P. S. and Smith, J. R Design of a Passively-Powered, Programmable Sensing Platform for UHF RFID Systems. Proc. RFID, IEEE International Conference on Wang, L.-C., Lin, Y.-C. and Lin, P. H Dynamic mobile RFID-based supply chain control and management system in construction. Advanced Engineering Informatics. 21(4):