Electronic Tags - Materials, Technologies and Applications

Topics Covered

Background

Market Growth and Prospects

Ruminary Tagging of Livestock

Crime Prevention

The Counterfeit Goods Market

Potential Areas of Use for Electronic Tags

Types of Electronic Chips and How They Work

Electronic Tag Compatibility

Polymer Technology for Electronic Tags

Ceramic Coatings for Electronic Tags in Harsh Environments

Electronic Tag Differentiation

The Cost of Electronic Tags

Materials Technologies for Electronic Tags

Hybrid Technologies

Magneto-Acoustic Resonance Technology

Summary

Background

Electronic tagging is an emerging market, and awareness is growing internationally of the efficiencies and cost savings that can be achieved by adopting these new tag technologies. For example, the queuing times at many alpine resorts last ski season were significantly reduced by the introduction of a lift pass that operates as a chipped radio frequency proximity tag, replacing the unwieldy ‘slot-card on a string’ previously used. The tag transmits information on ticket validity and activates the turnstile as a skier passes through it.

Market Growth and Prospects

Indeed, electronic tagging is one of the world’s fastest growing market sectors. Global shipments of radio frequency identification tags are projected to increase from US$890 million to US$2.5 billion by 2005. This 24% growth per annum is, in part, being driven by the introduction of new legislation. For example, in the EU and some Australian states it is expected that before 2005, new laws will require livestock to be tagged for health traceability, which could help to control the spread of diseases such as foot and mouth. Market growth is also being assisted by innovations in tagging technologies and by the smart materials packaging of the tags themselves. For example, livestock tags, which are currently attached to ears or injected, could be replaced with new, ‘ruminary tags’ being developed to be swallowed and remain inside an animal.

Ruminary Tagging of Livestock

Injected tags can cause discomfort to the animal, and both ear and injected tags are prone to loss and damage. Ruminary tags provide a smart packaging solution. Transponders and microchips are embedded within a bolus (a rounded cylinder with typical dimensions for sheep and cattle of 7cm long and 2cm in diameter). The packaging of the tag is designed so that it is biocompatible and can withstand the harsh environment of the animal's rumen. The electronics are typically embedded in resin and encased in a ceramic shell. From large-scale tests, which have been performed on both sheep and cattle it appears that the tags are easy to swallow, remain within the animal without any apparent discomfort and continue to operate throughout the animal’s life. Attempts to remove the tags from live animals were unsuccessful, which may make them ideal for tamper-proof identification of thoroughbred horses.

Crime Prevention

Following the events of 11 September, airport management applications such as paging, tracking of freight, luggage and passengers for improved security and efficiency is an area that is receiving increased attention. The application of tagging technologies in crime prevention is seen as a key area of importance by the UK Government and is the subject of a £5.5 million ‘Chipping of Goods’ initiative aimed at demonstrating how property crime can be reduced through electronic tagging. Initial projects include the embedding of anti-theft ID chips into boat structures and the tagging of packaging for products such as mobile phones, spirits and jewellery for logistic tracking and authentication through the supply chain. This enables counterfeit protection by encrypted unique IDs for goods or batches of goods, hindering unlicensed and black market sales. The technique also allows the verification of postal shopping returns and returns on rented goods.

The Counterfeit Goods Market

Currently, the global counterfeit goods market is valued at £200 billion (accounting for around 10% of world trade), with £2 billion in lost trade in the UK alone. There are up to 100,000 job losses per year in the EU as a direct result. In response, electronic article surveillance is an area in which the tagging market is growing rapidly. More than six billion tag units for electronic article surveillance were sold in 2000 within the EU to combat shoplifting and the corresponding loss of ~10% in profits.

Potential Areas of Use for Electronic Tags

Other areas in which tagging may help prevent crime include personnel access security tagging and document authentication. Smart tags may also provide a means of storing information such as prices, sell-by dates, sources and maintenance logs, and can be used in retail, farming (e.g. dairy tagging) or hospitals (e.g. storing patient information or providing the basis for prosthesis databases). Also, the multiplexing of tags can enable product ‘handshaking’, with a variety of applications in which a matching of two products is required. Examples include security clearance for withdrawal or photocopying of certain documents, for monitoring of product refill compliance, and in various interactive games and toys.

Types of Electronic Chips and How They Work

The nature of the application will determine the type of system that is most suitable, table 1. Electronic tags may be chipped (active or passive) or chipless (passive) in nature. Active tags contain an internal power source (frequently a lithium battery) and, as such, can have a much longer range (typically tens of metres) than passive tags (typically under one metre), which rely on the power provided by the transceiver itself. Passive tagging systems measure differences in the attenuation of radio waves caused by changes of the electromagnetic properties of the tag. In the case of a passive chipped tag, a memory chip receives its power from the output current rectified from the tuned electrical resonant circuit. The chip shorts out the circuit in a time varying pattern by opening and closing a transistor switch according to the data stored in its memory. The cost of the application specific integrated circuitry within the chip adds significantly to the cost of the product, particularly if the number of tags produced is much less than 100,000. For chipped tags, research activities are underway in the areas of low-cost battery and reduced-cost chip manufacturing technologies.

Table 1. The selection of a tagging system for a given application is determined by considering requirements and performance criteria and minimising the cost of the tag system. Typical performance requirements are tabulated.

Data Capacity

The amount of information each tag needs to store

Range

Whether the tag can be scanned, or needs to be read remotely

Transfer rate

How quickly the tag needs to be read

Re-writeability

Whether the tag needs to be read/write or read only

Size and orientation
Robustness

Ease of integration and lifetime

Environmental Issues

Such as disposability

Electronic Tag Compatibility

The packaging and compatibility of tags with existing products is also important when selecting the most appropriate tagging system. For example, tags intrinsic to garments need to be flexible. Anti-counterfeit and security tags for brand named items such as shoes need to be ideally embedded inside the item and able to withstand manufacturing conditions. Tags that operate near metallic materials need to be designed to operate at sufficiently low frequencies or high powers to avoid problems associated with screening.

Polymer Technology for Electronic Tags

An emerging materials technology that may impact on the production of tag electronics is plastic electronic technology. An advantage of the ‘all-polymer’ transistor is its intrinsic flexibility and potential low cost compared with silicon chips. However, key problems with this technology include relatively low switching speeds, which limits the data transfer rates, and the operational lifetime of such transistors.

Ceramic Coatings for Electronic Tags in Harsh Environments

Advances in materials research may also enable the deployment of tags in a broad range of more hostile environments. For example, developments in ceramic coatings and SiC-based semiconductor ‘technologies may enable the use of tags that can survive high manufacturing or operating temperatures, such as those found in clay kilns or attained in aircraft engine components.

Electronic Tag Differentiation

Research is also active in antenna design methods and software development, for example in the development of tag differentiating ‘anti-collision’ protocols to enable unique identification in which a number of tags are within range of the transceiver). Antennas can be designed to respond well to a specific frequency and a transceiver design can allow for specific tag directionality or, by paying a power penalty, can allow the read/write of tags with any orientation.

The Cost of Electronic Tags

The cost of a chipped active tag may be more than US$2, with a chipped passive tag costing around US$ 1. However, chipless tags may cost only a few US cents. Emerging chipless tags provide an opportunity to address requirements that may not need the high ranges or data capacities of chipped tags, but in which the line-of-sight requirement of conventional barcodes is not practical, for example in hidden anticounterfeit tags.

Materials Technologies for Electronic Tags

Many chipless tags use magnetically soft materials with large, non-linear, magnetic permeabilities, such as the melt-spun Co68Fe4Mo2Si16B10 amorphous ribbon produced by Vacuumschmelze GmbH. The material is sometimes incorporated into a tuned antenna circuit or can be used in a stand alone form, acting like ‘transformer cores’ in large transmit-receive coil systems. Simple yes/no harmonic labels of this kind change their harmonic radio frequency response through a change in the permeability profile of the soft material. The soft magnetic materials are magnetically coupled to a rewriteable ‘semi-hard’ magnetic under-layer. This under-layer can be made to change its magnetic state on the application of an external field. Consequently, this causes a change in the permeability profile of the soft material. Therefore, an external field can be used to write yes/no information to the tags. In general, it is found that the most sensitive response to changes in permeability is in the second harmonic of the tag’s response. The so-called ‘Barkhausen effect’ in which very rapid changes in magnetisation in certain types of material can lead to large transmitted signals is a potential refinement to this technology. Harmonic tag manufacturers are also investigating the possibility of using arrays of harmonic tags, each tuned to a different frequency, to store multi-bit information.

Another magnetic technology, which is closely related to bar-codes is used in magnetic swipe cards in which information is stored as a series of bits on a semi-hard magnetic strip as a binary magnetic code. Readers pick up stray fields as the card is moved past a magnetic sensor. Although improved sensors may allow ‘proximity’ measurements of several millimetres, the range is likely to remain limited to less than a couple of centimetres.

Hybrid Technologies

An interesting technological hybrid between swipe cards and resonant tags is available from Cambridge-based Flying Null Ltd. Magnetic information is stored as a series of soft magnetic bits. Bits that are in a high magnetic field are inactive (their permeability is low) whereas bits in a low magnetic field are active and can be detected by the harmonic resonance field. An external field is applied by the reader, which is zero only in a very small region of space. As this null region is scanned, bits are triggered and measured (as with a barcode). Typically, several tens of bits can be stored in a few centimetres and can be read at a range of a few centimetres.

Magneto-Acoustic Resonance Technology

Another emerging tagging technology based on magnetic material response is magneto-acoustic resonance. A strip of foil with one free end is set resonating in an oscillating magnetic field, figure 1. The foil is made from magnetostrictive material, i.e. a material that undergoes a physical deformation on the application of a magnetic field. The tag is again written to in a ‘yes/no’ fashion via a semi-hard magnetic material, which can supply an additional static field. Sufficient static field causes the resonance to be damped out i.e. the change of state of the semi-hard material causes a change in the mechanical resonant properties of the magnetostrictive material. Therefore, the process of magnetising the semi-hard material can be used to write yes/no information to the tags. It is possible to extend this technology by writing complex magnetic patterns on the semi-hard layer and detecting the resultant higher harmonic resonance frequencies. It has been estimated that such tags containing 64 bits of information can be produced at around 50 US cents each.

Figure 1. At the heart of resonant tags is a magnetostrictive strip (dark grey). The strip is suspended above a semi-hard magnetic ribbon (light grey). The strip is fixed along one edge to the plastic retainer (white). An oscillating magnetic wave emitted from coils, causes the megentostrictive strip to resonate according to the state of the semi-hard magnetic material.

Summary

Research in the field of electronic tagging is very active, with companies investing in the development of intellectual property in order to establish themselves as leaders in this new market. It is expected that there will substantial rewards for the early market entrants, with low cost, multi-bit tagging technologies. Without a doubt, currently well guarded technologies will emerge imminently, enabling a range of applications. These developments will provide us with the easier, cheaper, quicker storage and retrieval of product information, which can only help to protect both our commercial and individual interests. A new information revolution is dawning.

 

Primary author: George J. Tomka

Source: Materials World, Vol. 10 no. 5, pp. 12-15May 2002.

 

For more information on this source please visit The Institute of Materials, Minerals and Mining.

 

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