The identification system operates on the principle of modulated backscatter. The reader sends a continuous unmodulated radio frequency (RF) signal, which is received by the tag (transponder). The tag encodes its data by altering the strength of the signal (amplitude modulation) it reflects back to the reader. A mirror operates in a similar fashion to a tag except a mirror reflects light instead of RF energy. A mirror reflects different colors or frequencies of light. The tag, functionally similar to the mirror, will reflect different radio frequencies. This capability to operate at multiple frequencies is extremely important when tags are mounted on containers that travel internationally. Each country to which a container can travel has its own limitations on allowable radio frequencies and power levels. There is not one single radio frequency that can be used in every country. Therefore, a single tag mounted on a container must have the capability to be read at different frequencies and power levels. Amtech's tags have this unique ability, and this system is the only system that meets the current ISO 10374 standard for container identification.
There are two types of Amtech Transportation Tags, Beam Powered and Battery Powered. The Beam Powered Transportation Tag does not contain a battery. It must get all of the energy needed to operate its internal circuitry from the reader's RF signal. Because of this constraint, its maximum range with a 2 watt 915 MHz reader RF source is approximately 20 feet, and its normal operating range is 12 feet. The Battery Powered Transportation Tag contains a battery to operate the tag's internal circuitry. Once this battery is installed in the tag, the tag's internal circuitry will operate continually whether or not the tag is being read. There is enough energy in this battery to operate the tag continually for 15 years, but since the battery's chemicals deteriorate over time, the expected battery life is approximately 10 years. The Battery Powered Transportation tag has a maximum range with a 2 watt 915 MHz reader RF source of 200 feet, and its normal operating range is 60 feet. This tag's ranges will decrease at lower reader RF power levels and at higher reader RF frequencies.
Because the railways do not need long read ranges, the AAR standardized on Amtech's AT5110 Beam Powered Tags. Amtech's Battery Powered Tag meets the ISO identification standard for containers.
The tags can store up to 120 bits of user data and be programmed in the field. This feature is extremely important to the railways since they want to encode rail car information into the tag immediately before mounting the tag on the car. Information the AAR specified to be encoded in the tag includes the rail car owner's code, car number, number of axles, bearing type, and length. Tags can be reprogrammed in the field up to 10,000 times.