RFID That Works

Radio Frequency (RF) Tags

RF tags have two main components:

A small silicon chip containing a unique identification number.

An antenna - typically a flat, metallic, conductive coil - that can send and receive radio waves.

The small size of these components results in a tiny, flat label or tag that can be embedded in or attached to items including CDs, DVDs, books and magazines.

The tags fall into three groups:

1. Passive Tags

Passive tags have no internal power supply and are active only when a reader is nearby to power them.

The antenna in a passive tag is designed both to collect power from the incoming signal and transmit its own information back to the reader.

Depending on the size and design of the antenna, the transmission range of passive tags is only up to a few metres.

Having no onboard power, these tags can be small and are relatively inexpensive to produce. But they do require a strong signal from a reader in order for it to scavenge enough power to receive and send a signal.

2. Active Tags

Active tags have an internal power source that powers the chip and broadcasts the response signal.

As a result, these tags can incorporate more memory in the microchip, can be read at higher speeds and - more importantly - at greater distances (up to hundreds of meters). A larger battery also means the tag itself is bigger.

These tags are considerably more expensive to produce and are most commonly used by the defence, shipping and mining industries.

3. Semi-Active/Semi-Passive Tag

These tags carry onboard power for the digital logic on the microchip, but – like passive tags - use "harvested" power for communication.

They operate at high speeds and over greater distances, but have relatively shorter lives than other tags, are slightly more fragile and are expensive to produce.

Semi-active/semi-passive tags are used in Australia for freeway toll invoicing (eg. CityLink).