User:Michael Silverman/Radio Frequency Identification
Here the theory behind how RFID works from an electrical engineering perspective should be documented. The section should include equations and references while trying to be understandable to those without a degree in engineering.
Here all the major applications of RFID should be discussed. It should include how RFID chips have been implanted in dogs to confirm identification if they are lost and how they have been implanted in humans experimentally.
Here all the different protocols that have been approved as standards should be discussed. i.e. ISO standards.
Here all the issues surrounding security and privacy should be discussed. i.e. theft of information and tracking of persons.
Chipless and passive RFID tags are currently in development. There are chipless RFID tags commercially available based upon surface acoustic wave technology. However, these tags are of piezoelectric nature and cannot be implemented inside paper or plastic items.  The tags under development will be printable, which means the only material required for manufacturing is the copper or substrate material to which the layout will be printed on.
The new research being published is based around the application of resonance for identification encoding. When allowed to vibrate freely, every object has a natural or resonant frequency, the speed at which it vibrates. In electromagnetic engineering a circuit can have a resonant frequency which is related to how the energy is transferred inside the circuit.  In these tags a resonant frequency circuit is used to encode the identification number of the tag. When the reader emits a certain frequency and phase to these tags, a certain frequency and phase are transmitted back to the reader. The reader uses the difference in these two signals to decode the identification number of the tag. As the data is encoded in the frequency spectrum, the unique ID created is called a spectral signature.
Each tag has a unique physical layout which directly corresponds to a unique identification number. There are certain designs which have a predictable resonant frequency. By modifying dimensions such as the length and width of these designs we alter the resonant frequency.
One method to create resonance is a split ring resonator. The unique ID is created by varying parameters of the ring as well as the directions of the gaps. This circuit requires an antenna for transmitting (TX) and receiving (RX) information. The data is received from the reader into the RX antenna, passes through the resonator circuit and then is sent back to the reader through the TX antenna.  An ultra-wideband antenna is used for the TX/RX antennas because of the large bandwidth and broad radiation pattern. The RX and TX antennas are cross polarized to minimize interference. 
Spiral resonators are also used to create resonance. Here, each resonator encodes one bit of the number. A different stop resonance is created after each resonator to inform the reader it's moving onto the next bit. The phase information is used to encode and decode the data. A phase ripple at a certain frequency represents a logic “0” while its absence represents logic “1.” These tags have a single microstrip patch antenna for receiving and transmitting information. The signal scattered, or the electric field created from this antenna, is made up of two components. The first component, antenna mode scattering, is a function of the resonant radiation properties of the antenna. The second, structural mode scattering, is created by the currents on the surface of the antenna when it is conjugate matched. 
- Preradovic S, Balbin I, Karmakar NC, Swiegers GF (2009) Multiresonator-Based Chipless RFID System for Low-Cost Item Tracking. Microwave Theory and Techniques, IEEE Transactions on 57: 1411-1419.
- Preradovic S, Karmakar NC (2010) Design of Chipless RFID Tag for Operation on Flexible Laminates. Antennas and Wireless Propagation Letters, IEEE 9: 207-210.
- Chipless means the tag doesn’t need a microcontroller for any identification or processing purposes.
- Balbin I, Karmakar NC (2009) Phase-Encoded Chipless RFID Transponder for Large-Scale Low-Cost Applications. Microwave and Wireless Components Letters, IEEE 19: 509-511.
- Shrestha S, Balachandran M, Agarwal M, Phoha VV, Varahramyan K (2009) A Chipless RFID Sensor System for Cyber Centric Monitoring Applications. Microwave Theory and Techniques, IEEE Transactions on 57: 1303-1309.
- The Physics of Resonance (Accessed March 2011)
- Hyeong-Seok J, Won-Gyu L, Kyoung-Sub O, Seong-Mo M, Jong-Won Y (2010) Design of Low-Cost Chipless System Using Printable Chipless Tag With Electromagnetic Code. Microwave and Wireless Components Letters, IEEE 20: 640-642.