Battery Assisted Passive (BAP) RFID Tags are also called as Semi-Passive RFID Tags or Semi-Active RFID Tags. Semi-Passive RFID Tags operate similarly to passive RFID tags. However, Semi-Passive RFID Tags contain a battery that enables longer reading distance and also enables the tag to operate independently of the reader. One example is a data logger tag, which can take sensor readings automatically and run a real-time clock.

Semi-Passive RFID tags are the tags with a low-power source (usually a low cost battery) which can be used for on tag sensing, but not to boost range. It is important to understand that the communication in semi-passive tags is still completely passive; no power is transmitted – the tag simply reflects back some of the power emitted by the RFID reader.

Like passive, Semi-passive RFID tags do not contain any radio transmitter circuit, but simply reflect back a small fraction of the power, which is emitted by the RFID reader. Semi-passive RFID uses an internal power source to monitor environmental conditions (thermal, shock, etc.), but requires RF energy transferred from the reader/interrogator similar to passive tags to power a tag response.

Advantages of Semi-Passive RFID over Active RFID

EPC compatibility

The primary advantage of a semi-passive RFID tag over active RFID is that it can be used with existing passive RFID infrastructure. Since both passive RFID and semi-passive RFID use a backscatter mechanism to communicate with the reader, a passive RFID reader does not need to distinguish between these two types of tags.

Lower Tag Cost

Since a semi-passive RFID tag does not require a radio transmitter circuit, the cost of the electronic tag chip can be less than that of an active RFID tag. However, single chip solutions are now available for both, and the difference in cost is small relative to the cost of the battery, for example.