Contributed editorial appearing in
Scientific Computing & Instrumentation 17:12, November 2000, pg. 14.
It has happened to most of us. We purchase a few sundries at the local department store, make a mad dash for the exit after enduring the interminable price checks and jammed register tapes, only to be assaulted by a blaring alarm. A quick check of the receipt, a swift waft of our parcel over a magnetic pad and we are finally on our way. Evidence that technology is making our lives more convenient? Most definitely.The problem lies not with the goal of each new technology. It is that we must survive the adolescent years of its development and implementation. As we enter this new age of informatics, we should remain ever cognizant of our targeted destination; the ability to measure all things in their natural habitat. If we could borrow an alien technology for scanning the identity, composition, state, and position of all things, then we could proceed to tackle the problem of how to manage, analyze, archive, and interpret the information. Since other star systems have not offered their assistance, humans have developed an elegant surrogate for our missing expertise; add something we can measure to the system and continue on to the next level of development. As our measurement prowess improves, we can decrease our dependence on the additives and measure things directly.
These additives are most often referred to as a "tag". In biochemical assays, the tag most often takes the form of a small, fluorescent molecule that is attached to a biological target of interest. The target is released back into its natural habitat, such as a cell, a test tube, or perhaps the blood stream. To locate the subsequent position of the "tagged" target, the entire sample is irradiated with light of appropriate frequency and the telltale glow from the tag is emitted in response. This process of irradiating the tag with a specific source frequency and the tag responding at a different frequency is the functional definition of a "transponder". This term was first associated with a tag that operated in the radio frequency range of the electromagnetic spectrum. Known as the Identification Friend or Foe (IFF) system, World War II aircraft were equipped with radio transponders that broadcast the identity of the aircraft in response to an encoded interrogation signal. Radio-frequency Identification (RFID) transponders are used extensively by modern commercial aircraft to provide air traffic controllers with identity, altitude, airspeed, and heading information.
Embraced by the retail industry to assist in the deterrence of shoplifting, the Electronic Article Surveillance (EAS) system uses a "1-bit" RFID tag that can respond as "functional" or "non-functional". These small, inexpensive tags are constructed of magnetic material in the shape of an induction-coil antenna. A low-power magnetic field operating around 125 kHz injects energy into the induction coil and the tag responds immediately at a different oscillation frequency, or the excitation field is pulsed and the detector senses the oscillation decay of the tag. When the magnetic orientation of the tag is scrambled by placing it on a magnetic pad, the tag is deactivated and no response is detected by the readers placed at the exit of the store. Unfortunately, the scrambling pad has a voracious appetite for the magnetic strips of customer credit cards.
To dissuade would-be thieves equipped with their own magnets, expensive inventory is often protected by microwave-frequency tags. These tags contain an oscillation antenna in the form of an integrated circuit and are not deactivated, but removed by a store employee at the time of purchase and reused. As we follow the response frequency of the tags from radio (kHz/MHz), through microwave (GHz), to visible (THz) frequencies, we transition from the realm of the traditional transponder to the Universal Product Code (UPC) symbol, a standardized barcode. Barcodes are visible-frequency transponders that return binary ones and zeros in response to a beam of visible light. They only cost as much as the ink used to print them and are used to report the price and manage store inventory. Barcode technology in general is omnipresent in the tracking of parcels and mail routing. Unfortunately, higher-frequency is not always better. Not many materials are transparent to visible light and therefore the barcode must reside on the outside of the object and be in close proximity of the reader.
The use of RFID transponders is finding broad application and acceptance in the public sector. The Mobil SpeedPass and Shell EasyPay systems both use magnetically coupled key ring transponders operating at 125 kHz that the customer waves in proximity of the reader inside the gasoline pump. The customer’s identity is recorded and the purchase is recorded on account. Toll roads are offering transponder tags that are placed inside the windshield of automobiles and are scanned at highway speeds as the automobile passes through a toll both equipped with the appropriate reader. Recent patents for smart appliances such as washing machines and dryers capable of reading transponders embedded in clothing and automatically adjusting temperature and cycles have been issued. Even though the ability to acquire data directly from every object in its native habitat remains science fiction, transponders permit us to bring the benefits of such technology into practice.
