#bap rfid

As always, the #savagecircuits irc chat inspires me with different topics that people talk about.  The latest one that caught my eye was about RFID chips, and placing them in pets - dogs, cats, mice!  And in turn creating an affordable RFID reader as a midpriced one is nearly 500 dollars.  So I thought I'd look into what RFID is and how complex the systems are that make up its components.

RFID is short for Radio Frequency Identification. There are three main components to this technology: Tags/Labels, Interrogators/Readers, and the software required.

RFID tags/chips:

Passive - No battery therefore no power source.  These require an external electromagnetic field to initiate a signal transmission.

Active - On-board battery that can transmit signals once an external RFID reader has been successfully identified.

Battery Assisted Passive - These have a small battery on-board that is activated when in the presence of an RFID reader but has a significantly higher forward link capability providing greater range.

Each tag contains at least two parts:

Integrated circuit: Stores / processes information, modulates / demodulates a RF signal

Antenna: Receives and transmits the signal

RFID Readers:

Fixed RFID - If the reader reads tags in a stationary position - it's called fixed RFID.  These have specific interrogation zones so when a tag goes into its bubble, the tag is read.

Mobile RFID - If the reader is mobile when the reader reads tags, it's called mobile RFID.  For instance, hand-held readers, or ones mounted on moving cars.

For passive tags, there are two basic methods of communication between reader and tag but for both methods, these readers put out a variable range AC magnetic fields that the passive RFID tag use for both power and as a communication medium:

Load modulation and inductive coupling in the near field: This magnetic field induces a voltage in the antenna coil of the RFID tag, which in turn powers the tag.  Each time the tag draws energy from the RFID reader's magnetic field, the RFID reader itself can detect a corresponding voltage drop across its antenna leads.  The tag can then communicate binary information to the reader by switching ON and OFF a load resistor to perform load modulation.  When the tag performs load modulation, the RFID reader detects this action as amplitude modulation of the signal voltage at the reader's antenna.

Backscatter modulation and electromagnetic coupling in the far field: Passive RFID tag draws energy from the electromagnetic field of the RFID reader. However, the energy contained in the incoming electromagnetic field is partially reflected back to the RFID reader by the passive tag antenna. The precise characteristics of this reflection depend on the load (resistance) connected to the antenna.  The tag varies the size of the load that is placed in parallel with the antenna in order to apply amplitude modulation to the reflected electromagnetic waves, thereby enabling it to communicate information back to the RFID reader via backscatter modulation.

For battery assisted passive tags, they use an on-board battery to provide power to communication and support circuits, such as temperature and shock monitoring. 

Although they have an on-board power source, BAP RFID tags do not use it to directly generate RF electromagnetic energy.  Rather, these tags typically use backscatter modulation and reflect electromagnetic energy from the RFID reader to generate a tag response similar to that of standard passive tags.

Moreover, the antenna contained in a BAP RFID tag is dedicated to backscatter modulation and there is no dependence on the semi-passive RFID tag antenna to be a reliable conduit of power for the tag.  Therefore, the antenna can be optimized to make most efficient use of the backscatter technique and provide far better performance than purely passive RFID tag antenna designs.

For active RFID tags, for example, a beaconing active RFID tag - a short message payload containing the unique identifier of the RFID tag is emitted at pre-programmed intervals. This interval is programmed into the tag by the tag owner or user, and it can be set appropriately depending on how often tag updates are required.

Anddd that's it for now :p.  I know there's A LOT more but the circuits are still a bit complex for me yet.  Maybe one day!

http://www.cisco.com/en/US/docs/solutions/Enterprise/Mobility/wifich6.html#wp1053545