Advanced Product Tags for Recycling Steven Saar Electrical Engineering, Princeton University Princeton, NJ 08544 USA
[email protected] Abstract Capacitive or inductive radio-frequency tags could be used to support the recycling of batteries and other products. Both types of tags can be used on metal and nonmetal products in some circumstances, although range and operability can be limited..
Valerie Thomas Princeton Environmental Inst., Princeton University Princeton, NJ 08544 USA
[email protected] circuits by direct printing, could reduce the cost of radio frequency tags considerably [1, 2]. Radio frequency tags are already used in a number of applications, including baggage tracking at airports, automatic highway tolling, and personnel identification.
Keywords Recycling, RFID, tags.
A typical radio frequency tagging system consists of a
RADIO FREQUENCY TAGS
reader, a tag, and a data processing system. The reader
Low-cost radio frequency tags are now available from a
has radio circuitry to communicate with a tag, a micro-
number of companies (Figure 1). Some have batteries
processor, a memory, and an antenna. Most passive ra-
that allow operation at long ranges, but for low cost and
dio frequency tags are inductive; the tag antenna and the
low maintenance, tags have been developed that do not
reader antenna are loops of conductive material. When
have batteries (“passive” tags). Manufacturers envision
the reader sends a signal to interrogate the tag, current in
that these tags could replace UPC bar codes and become
the reader antenna creates an alternating magnetic field,
the standard label for all products. Current prices for
which in turn induces current in the tag antenna. The
radio-frequency tags are about 25¢. In the longer term,
tag modulates this signal with the stored information,
new technologies, including fabrication of integrated
and returns the modulated signal back to the reader.
Figure 1. RFID tags. Left: An inductive tag from Texas Instruments, showing the conductive loops around the tag. Center: A capacitive tag from Motorola showing the printed black antennas; the chip is underneath the black square in the middle. Right: An inductive tag from Microchip. All of the tags are flexible and about 5 cm on a side.
In capacitive tag technology the electric fields are ca-
within the next several years. This would be more than
pacitively coupled to and from a reader and tag. The tag
sufficient for many waste management applications.
consists of conductive ink that can be printed with standard printer technology onto an ordinary sheet of paper.
Interference from Metal
The chip is under the black square in the center of the tag [3]. There are two different types of capacitive tag readers: monopole readers and dipole readers. Monopole readers allow for great flexibility in the orientation of the tag, but require that one of the tag’s two antennas be grounded in order for the tag to operate effectively. Dipole readers
Although there is no question that radio frequency tags can operate well on paper and plastic packaging, their operation on or near metal needs to be considered more carefully because the metal can alter the electromagnetic fields by which the tags operate.
have less orientation flexibility, but don’t have any antenna grounding requirements.
Both inductive and capacitive tags can operate on products containing metal such as batteries. Capacitive tags operate
The FCC permits the operation of these sorts of radio devices at 125 kHz, 13.56 MHz, 900 MHz and 2.45 GHz. Lower frequencies penetrate some materials better, but higher frequencies provide higher data rates. Universal application of product tags will require standardization of label formats.
Researchers at MIT propose a 96-bit
scheme with an 8-bit header and three data partitions [4].
well on batteries with no modifications, with range roughly equal to their operation in free space. The inductive tags also operate well (Figure 2), although they need to be specially tuned if they are to be installed on a battery or other metal-containing object in order to maximize the read range. The metal in the object decreases the inductance of the circuit in the tag, which changes the circuit’s resonance frequency. Tuning the tag involves increasing either the inductance or capacitance of the tag’s circuit in
LIMITATIONS OF RADIO FREQUENCY TAGS
order to restore the original resonance frequency.
Although radio frequency tags are rapidly improving, they do have limitations. The key issues are read range and interference from metal objects.
Range Range is affected by a number of factors, including the power and size of the reader antenna, the system frequency, and the size of the tag. Currently available passive tag systems have ranges of less than one meter. Developments in wireless technology and low-power CMOS (complementary metal oxide semiconductors) suggest that the range could possibly increase to up to several meters
Figure 2. Passive radio-frequency reader (rear) and tag on battery (front), demonstrating that inductive tags can be read through a battery.
ucts. However, our tests indicate that reading tags through an unopened metal truck is well beyond the currently available technology.
RECYCLING APPLICATIONS There are numerous environmental applications of product tags that are feasible with today’s technology. The tags could allow for detailed tracking of the recycling patterns of various products containing hazardous materials such as lead, mercury, and cadmium. Such products include batteries, electronics, and fluorescent lights. This sort of tagFigure 3. Capacitive tag on a metal can.
ging could provide valuable information for lifecycle research and management, make product reuse easier, and
Capacitive tags also operate well on metal products such as
simplify the product sorting process. Product tags have the
steel or aluminum cans (Figure 3). They can also be read
potential to make recycling easier for producers, consum-
through small metal objects, as long as the metal object is
ers, and recyclers, and to provide new approaches for envi-
not grounded. Both inductive and capacitive tags work
ronmental regulation.
well on fluorescent light bulbs (Figure 4). Consider, for example, the recycling of laptop computer batteries. A tag with a unique code could be attached to each laptop battery; the unique code would be listed in a database and would reference specific information about the battery, such as battery types, the manufacturer, and when the battery was sold. When the battery is returned for recycling, an electronic reader at the recycling plant would read the tag and automatically update the database to show when the battery was returned. In an initial program, the information could be used to evaluate use and recycling patterns. In a more developed program, the information could be used to reward customers who recycle Figure 4. Inductive tag on a fluorescent light.
their batteries. When the battery is returned to the recycling plant, the reader could identify the battery and auto-
These examples indicate that radio frequency tags can be
matically credit the customer’s account with cash or a dis-
used on metal products if the tags and tag-product connec-
count on future purchases.
tion are appropriately designed. Radio frequency tags can be read through a limited amount of metal or other prod-
Figure 5 shows a simple battery identifier that could be
ments in the technology. But a greater challenge will be
used for this application. In the figure, the reader is in-
the development of the physical, data, and institutional
stalled in a battery recycling box such as those currently
infrastructures to support the tag-mediated recycling of
used for battery collection in many stores. In an actual
products.
application, the reader might be installed at the central battery recycling facility, using a longer-range, higherpower reader. Alternatively, readers could be installed in stores in recycling bins as shown in Figure 5, and might provide users with coupons for in-store use.
Most of the commercial interest in product tags relates to their value for retailing and marketing, not environmental management. It is quite possible that products will soon be sold with these new types of tags for non-environmental uses. These non-environmental tags might also be used for environmental applications if two criteria are met. First, the tag must remain on the product throughout its lifetime. Second, the encoded tag information must be available to waste managers and consumers, not just to manufacturers and retailers.
ACKNOWLEDGEMENTS
Figure 5. A simple battery identifier. A reader installed inside the box reads the tag on the battery as the battery enters the box, and immediately knows what type of battery it is.
This work was supported by a grant from the New Jersey Commission on Science and Technology through the Multilifecycle Engineering Research Center at NJIT, as well as by an AT&T Foundation Industrial Ecology Fellowship. We thank Robert Pfahl and Grant Milner of Motorola and Dennis Johnson at Microchip Technology for discussions and for sample readers and tags, and we thank Home Depot and the Rechargable Battery Recycling Corporation for product samples. We thank Sigurd Wagner and David Saar for discussions, comments and encouragement.
REFERENCES Tags could allow recyclers to sort products automatically based on information from the tag. While automatic sorting may not lead to any increase in recycling rate, it could be one of the easiest near-term applications. Sorting of some recycled products is a labor-intensive and expensive process, a process which product tags could make cheaper and more reliable.
The widespread use of advanced tags for product lifecycle management will require lower tag costs and improve-
[1] Wagner, S., H. Gleskova, J. C. Sturm, and Z. Suo. 2000. “Novel Processing Technology for Macroelectcronics,” in Technology and Applications of Hydrogenated Amorphous Silicon. R. A. Street, ed. Springer, Berlin, pp. 222-251. [2] Fletcher, R. R. 1997. A Low-Cost Electromagnetic Tagging Technology for Wireless Identification, Sensing, and Tracking of Objects. MIT Master’s Thesis. [3] Motorola, Inc. 2000. BiStatix Technology: A White Paper. Version 4.1. http://www.motorola.com/smartcard/ [4] MIT Auto-ID Center. 2000. The Networked Physical World. December. http://auto-id.mit.edu MIT Auto-ID Center. MIT-AUTOID-WH-011. December.
