The first considerations concerning the use of RFID are factors that can impact reliability.
A basic RFID system will include am RFID tag and an RFID reader. The tag is comprised of an embedded electronic chip that is used to store information and an antenna that is used to transmit. A reader, which can be stationary or mobile, is used to capture information contained in a radio wave.
There are 2 general classes of RFID tags. These are active and passive.
Active means that the RFID tag utilizes an internal power source (battery) to power the chip and transmit information outward.
Passive tags have no internal power source and require access to an energy wave in order to operate. RFID readers function by emitting an energy wave. When a tag is within range, the wave excites the chip, causing it to wake and transmit the information contained in it.
This information then rides the wave back to the reader, where it is stored and processed. The system depends upon the energy wave reaching the tag and the chip in turn releasing information that must ride the wave back to the reader.
Various sources of interference can interrupt this cycle and cause the technology to fail. A few common sources of interference are water and metal. Water is known to absorb RF signals while metal is known to deflect them.
For this reason (among others), the first step in the process is to conduct what is known as a site survey.