Interesting question. The answer depends on which tags are used—and, more importantly, which goods are being tagged. Generally speaking, companies have been employing ultrahigh-frequency (UHF) EPC Gen 2 RFID tags on cases of goods stacked on pallets, though high-frequency (HF) tags are also used. UHF tags provide the read range needed to read a tag on a pallet as it goes through a wide dock door.
At UHF frequencies, radio waves bounce off metal and are absorbed by water. Metal also detunes all RFID antennas if they come in direct contact with the metal. So if you are using generic UHF RFID tags on RF-friendly products, such as paper towels or apparel, you will often read the tags on 100 percent of cases or items. But if the cases contain cans or bottles of water, the read rate could be only about 60 percent, because only tags on cases on the outside of the pallet can be read.
Tags designed to work in the presence of metal or water can improve read rates, but the reality is that it is next to impossible to read passive UHF tags on a case of water or canned soup buried in the center of a pallet. Most companies have found they can work around this issue by reading tags on cases as they are being placed on or removed from a pallet.
—Mark Roberti, Editor, RFID Journal
How Can I Track Locations Indoors? »