I suspect this works off the Doppler effect with triangulation.
The device sends a ping for a certain tag, calculates the time (or distance) for a reply, then it "pings" two (or more) additional tags in the pile of luggage and then similar to GPS the device triangulates the position of the bags with in the pile and gives a location that is approximate to the bag in question. The more bags (RFID tags) in a pile, the more exact the location information would be.
Actuallly the RFID tag measurement is not doppler as the bandwidth of the reader is too narrow. Radio waves travel at the speed of light (300,000,000 meters/sec) which means discerning the time of arrival of tags a few feet apart would require picosecond measurment ability or 100 MHZ plus of IF processing bandwidth (The reader hardware is very narrowband). Rather it is likely an amplitude system that measures the signal increase as it gets closer and signal decrease as it moves further away.
Reader Comments (Page 1 of 1)
I LOVE THE CAPS LOCK KEY @ Apr 13th 2008 1:56AM
I suspect this works off the Doppler effect with triangulation.
The device sends a ping for a certain tag, calculates the time (or distance) for a reply, then it "pings" two (or more) additional tags in the pile of luggage and then similar to GPS the device triangulates the position of the bags with in the pile and gives a location that is approximate to the bag in question. The more bags (RFID tags) in a pile, the more exact the location information would be.
mike.westrick @ Apr 14th 2008 7:24AM
Actuallly the RFID tag measurement is not doppler as the bandwidth of the reader is too narrow. Radio waves travel at the speed of light (300,000,000 meters/sec) which means discerning the time of arrival of tags a few feet apart would require picosecond measurment ability or 100 MHZ plus of IF processing bandwidth (The reader hardware is very narrowband). Rather it is likely an amplitude system that measures the signal increase as it gets closer and signal decrease as it moves further away.
I LOVE THE CAPS LOCK KEY @ Apr 17th 2008 3:41PM
You are correct, to use Doppler you would need bags that were in motion. Attenuation would likely be the best method.