When Tags Meet the
Real World"> The DOD will use two types of tags: passive, which requires the monitoring device to power the tag itself; and active, where the tag contains its own power supply. Passive tags are often powered by low-power microwaves, which convert the transmitted energy into power and reply with a weak radio signal. According to analysts, the problems will be that the shipping containers will be subjected to the harshest environments imaginable: snow, wind, rain, heat, and ambient moistureall bad news for the semiconductors in the tags and for wireless transmission.There can be basic logistical problems, according to Kara Romanow, an analyst at AMR Research Inc. For example, she pointed to Wal-Marts loading portal, which is approximately 14 feet wide, while passive RFID tags can only transmit 5 feet in any direction. The militarys supply-chain specifications are unknown. Reading the RFID tags on the outside of the pallet isnt difficult; identifying the central containers is, Abell observed. In both commercial and military environments, various materialsranging from meats and fishes to paper products, water and gasoline and the steel used by rotisserie ovens and riflesmay be bundled within a pallet, and all interfere in varying degrees with radio signals. Transmitting an RF signal through liquids and metal is especially difficult, Abell said. The DODs policy seeks to avoid this interference problem by excluding "bulk commodities" such as sand, gravel, or liquids, from its RFID tagging plan. In addition, the failure rate of current tag technology is a problem tags failure rates are an additional problem, Romanow said, pointing to a failure rate of as much as 30 percent. Moreover, the tags dont have to be checked just once, but monitored within several locations within the depot and at satellite hubs, Abell added. That means rechecking the tags under a variety of conditions, such as from the electrical interference generated by forklifts and conveyor belts. "To meet Wal-Marts performance requirements, you dont want to slow down a forklift or the identification device fastened to the driver," Abell said. "Hes going to need to read these things at his speed, like 10 to 15 MPH. You cant slow down their conveyor belt lines, either."
"A supply chain does not yield the ideal conditions of a laboratory," said Pete Abell, an analyst with The ePC Group Ltd., a consultancy assisting Wal-Mart with its RFID deployment.