Radio waves are used to transfer data between the RFID tag and the read/write device (interrogator), which are tuned to the same frequency. The interrogator sends out a signal, which is received by all tags tuned to that frequency that are present in the RF field.
Tags receive the signal with their antennas, and selected tags respond by transmitting their stored data. The tag can hold many types of data about the item, such as its manufacturer, product number, serial number, configuration instructions, what time the item traveled through a certain zone, even temperature and other data provided by sensors.
The interrogator receives the tag signal with its antenna, decodes it and transfers the data to the host computer system.
RFID tags can be attached to virtually anything – from a semi tractor, to a pallet, to a case, to an item on a store shelf. If multiple tags are present in the field, more efficient RFID implementations have anti-collision algorithms, which determine the order of response so that each tag is read once and only once.