Understanding RFID
Technology Limits

By Ted Twietmeyer
Much has been said about the miracle abilities of tracking chip technology. It is widely claimed to track people and items, and it's time to set the record straight. As someone who has designed and built miniature transmitters, I can tell you there are many exaggerations about this technology. I'll leave the tech talk out of this as much as possible to make it more readable.
There are basically 3 types of technologies:
1. PASSIVE - These are found in rental tape labels ("Be Kind Please Rewind") and other similar labels. Also, a small strip inserted into the spine of a library book operates the same way. These are activated and deactivated with a powerful magnet on the checkout counter. All of these function by using a resonant circuit to operate at one particular radio frequency. When this type of label passes through a portal's radio frequency field, a sensitive receiver connected to the portal detects the resonance of a particular label and sounds the alarm. Since these receivers are very sensitive, and sometimes other unrelated objects can trip the alarm, too. These devices do NOT have any ID chips, and are intended only as an alarm to detect an object of value being removed from a given area. These are also used inside the white plastic clips used in stores to prevent shoplifting, as well as inside the packages of some products. This is also similar to the strip found embedded in today's currency.
Range - There is no real range to this type of RFID other than inside a portal or near a wand that can power it and read it. This device cannot transmit any signals on it's own, contrary to public rumor.
2. SEMI-PASSIVE - These are the type of interest to Wal-Mart and others. This consists of a small chip connected to an antenna. The simple chip contains a simple power rectification circuit, a few bytes of memory to store a serial number and very small transmitter circuit. This is also the same type used in the implantable chips for humans and animals. The chip is powered by an external field such as a wand or a portal. Once powered up by receiving energy from the small antenna (such as the tiny coil inside the Digital Angel device) the transmitter circuit operates and transmits the serial number. A receiver detects the signal from the device and sends the data to a computer. Don't be fooled by press release pictures from Hitachi and other companies that show how tiny the chip is. A antenna is always required for it to work - which is hundreds of times larger than the chip.
Range - As these devices can only use a very small percentage of the RF energy from the field that powers them, and distance is limited to a few feet. It is virtually impossible for someone at the street to point an antenna at your home and detect an RFID device. The reason: radio frequency energy falls off the square of the distance in BOTH directions, just like light from a flashlight. This also includes the RF power used to power the device. Power transmitted from the device is measured in microwatts or less which therefore limits range. Data collision is a problem, too. This occurs when more than one device attempts to transmit it's data at the same time. It is one of the engineering problems being worked on for the proposed shopping portals in stores. When fully implemented, you will wheel your shopping cart through past a portal and it will automatically read all the items in the cart.
3. ACTIVE - This is where RFID becomes seriously intrusive. This consists of systems such as Northstar and similar "help" systems used in vehicles, and covert hidden technology used in cordless, speakerphones and cell phones. This was illustrated in the film "Enemy of the State." Most of the technology shown in the film is real or is possible. Active technology far surpasses transmitting only serial numbers - these devices can be silently activated by intelligence agencies via satellite command signals. Not only can agencies determine where you are on the globe, but they can also to listen in on your conversations at will. The movie was wrong about flushing a tracking device and showing it still working. Even if it survives immersion in water, it will quickly become undetectable. This is caused by the shielding of the water, the metal shielding of the sewer pipe and/or earth around the pipe even if made of PVC. Active technology requires use of a battery or other power source to transmit with sufficient power over distance. This is also why it works so well with cordless and cell phones. People should be more concerned about the current use of this technology in vehicles and telephones. Rather than passive or semi-passive devices described above which are much more limited and cannot eavesdrop.
Personally, I don't support any spying or surveillance of people. This always leads to a paranoid state of mind, like that endured by the people of East Germany for decades. But with this new technology - it has the potential to be far worse than anything the Stasi organization imagined and it will be far more invasive.
Tracking people and objects clearly implies mistrust, and has little or nothing to with preventing terrorism.



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