Passive tags refer to RFID tags which are powered solely by the RFID interrogator. The interrogator emits a radio frequency (RF), which powers the silicon chip on the tag when it is within range of the RF field. When the power to the silicon chip on the tag meets the minimum voltage threshold it require to turn on, the silcion chip can then send back information on the same RF wave. Range is usually limited to several meters.
Active tags refer to RFID tags which have their own power source, so they can recieve a weaker signal from the interrogator (i.e. be further away), and the power source on the tag boosts the return signal. These types can have ranges of many tens of meters and even hundreds of meters, but cost more becasue of their size and sophistication. Battery life can also limit the life of the tag.
Semi Passive tags refer to tags with a power source (usually a laminar, flexible, low cost battery) which can be used for on tag sensing (e.g. temperature), but not to boost range.
- Read only tags contain a unique licence plate number which cannot be changed
- WORM Write Once Read Many - enables users to encode tags at the first instance of use, and then the code becomes locked and cannot be changed
- Read/write allows for updated or new information to be written to the tag
Read only tags can be the cheapest, because they often require the least amount of memory, but they rely on an infrastrucutre and readily available database to retrieve useful information. Where this is not possible, read/write tags, whcih are more expensive (but do not need large infrastructure) and often used. In many cases these functionalities are combined with segmented memories.
RFID tags come in a range of shapes and sizes. The following are the most common:
- Label: The tag is a flat, thin, flexible form
- Ticket: A flat, thin, flexible tag on paper
- Card: A flat, thin tag embedded in tough plastic for long life
- Glass bead: A small tag in a cylindrical glass bead, used for applications such as animal tagging (e.g. under the skin)
- Integrated: The tag is integrated into the object it is tagging rather than applied as a separate label, such as moulded into the object
- Wristband: A tag inserted into a plastic wrist strap
- Button: A small tag encapsulated in a ruggesdised, rigid housing