User:Michael Silverman/Radio Frequency Identification

Radio Frequency Identification (RFID) is a contactless identification system. It is similar to the bar codes of today however RFID does not require a direct line of site and multiple tags can be read simultaneously. The system has found widespread use in commercial, industrial, and governmental applications due to its low cost and flexibility. Radio frequency waves are used for communication between the transponder, or tag, and the interrogator, or reader. For a system there may be only one reader and thousands of tags. Thus, an important design characteristic is the power usage of the tags. Passive tags have no internal battery and are powered completely by the reader. For more complicated systems, there are battery powered tags which allow utilization of a microcontroller.

With an increased interested in incorporating RFIDs into items such as bank note and stamps, the future of RFID tags are passive, chipless and printable. Chipless means the tag doesn’t need a microcontroller for any identification or processing purposes.

Theory
Here the theory behind how RFID works from an electrical engineering perspective. Section should include equations and references while trying to be understandable to those without a degree in engineering.

Applications
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. They have also been implanted in humans experimentally.

Operating Protocols
Here all the different protocols that have been approved as a standard should be discussed. i.e. ISO standards.

Issues
Here all the issues surrounding security and privacy should be discussed. i.e. theft of information and tracking of persons.

The Future
A chipless and passive RFID tags are currently in developement. These tags also intend to be printable, which means the only component required is the copper or substrate material to which the layout will be printed on.

The new research being published is based upon the application of resonant frequency for identification encoding. Every object or system has a natural or resonant frequency, or speed at which it vibrates. In electromagnetic engineering a circuit can have resonant frequency which is related to how the energy is transferred throughout the circuit. In these tags a resonance frequency circuit is used to encode the identification number of the tag. When the reader emits a certain frequency and phase to these tags, the tags then reflect or transmit a certain frequency and phase 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 must have it's own unique physical layout which directly corresponds to it's 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. (insert picture of layout on the right). 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 receiving and transmitting antennas are cross polarized to minimize interference.

Spiral resonators are also used to create resonance. Here, each resonator encodes one bit of the overall 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 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.