Passive vs Active RFID Tags

RFID is a wireless system which can be mounted or attached to a product, animal or a human being by using a minuscule microchip which transfers data using radio waves. The data is beamed out through the device which is termed as a RFID tag to a reader which may be in the line of sight or several meters away. The RFID tags essentially comprise an electronic circuit for storing and processing data and an antennae for transmitting the signals. The tag's antennae pick up the signals from the RFID reader and returns the signal with some additional information like a unique serial number or customized information. The technology is increasingly being used in enterprise supply chain management for inventory tracking and asset management.

There are two varieties of RFID tags available, known as the active and passive tags. While the active tags with their batteries or by using solar power can transmit data to the reader autonomously, the passive tags in the absence of a battery, require external sources of power to provoke signal transmission.

Differences between Active and Passive RFID Tags

Differences in the Technical Characteristics
Passive tags contain an integrated chip or circuit to absorb radio frequency waves from reader's signals and to send and receive data, low frequency or high frequency antennae and a plastic or mylar substrate which holds the pieces of the tag together. Since there is no battery, the power is supplied by the reader which draws the radio waves through the antennae forming a magnetic field. This allows the supply of the power to the tag which is restricted to the field of the reader. On the other hand, an active tag which is substantially larger than a passive tag features two additional components, an on board power supply and on board electronics. The power supply to an active tag is through battery although some may be solar power driven. The on board electronics consisting of sensors, microprocessors and I/O units are powered by the on board power which enables it to transmit the data to the reader on its own. With a continuous availability of tag power, the required signal strength from the reader to the tag is lower than what is required for a passive RFID tag. Also, the available signal strength is higher from a tag to a reader in an active tag.

Communication Range
Since passive RFID tags are constrained by the need for strong signals to power the tag and the small amount of power to respond to the reader, the communication range of a passive tag is limited to 3 meters or less. Active tags do not have the constraint of power and can thus transmit to as far as 100 meters or more.

Data Storage
Although both these varieties of RFID tags can dynamically store data, active RFID tags have large read and write data storage almost 128 kilobytes and sophisticated data search and access capabilities. In a passive RFID, the data storage is less then 128 bytes with no search capabilities or data manipulation features.

Sensor Capabilities
While active RFID tags are able to continuously monitor and record sensor input, passive tags are able to monitor and record sensor input only when the tag is powered by the reader.

Multi-Tag Collection
Since the communication range of a passive RFID tag is limited to 3 meters or less, it can collect 100 or so tags, at the range from only a single reader. In contrast, an active tag can collect more than 100 tags from a seven acre region using a single reader.

Although an active RFID tag has significantly more advantages as compared to a passive RFID, it is costlier and bigger in size. Therefore an organization's choice for a particular RFID tag would depend on the application of RFID in the organization and their budget.