RADIO FREQUENCY RADIO FREQUENCY IDENTIFICATION AND ITS READER IDENTIFICATION AND ITS READER

CIRCUITCIRCUIT

RFIDRadio-frequency identification (RFID) is an automatic

identification method using radio waves.

RFID is a technology that incorporates the use of

electromagnetic or electrostatic coupling in the radio

frequency (RF) portion of the electromagnetic spectrum to

uniquely identify an object, animal, or person.

RFID is also called dedicated short range communication.

Other Auto-ID-Technologies:Bar CodeSmart CardsBiometrics (e.g. fingerprint)

Special Characteristics of Radio Communication:

No physical contactNo line-of-sight

Components of RFIDComponents of RFID1. Tag.

2. Reader.

3. Reader antenna.

4. Host and software system.

TagAn RFID tag is a device that can store and transmit data to

a reader in a contact less manner using radio waves.Each tag contains a unique code that facilitating the

identification process & is known as EPC (Electronic Product Code).

Types Active tag

Passive tag

Passive RFID TagsPassive RFID TagsNo on-board power source (for example, a battery)

Uses the power emitted from the reader to energize itself

and transmit its stored data to the reader

Reader always communicates first, followed by the tag.

Smaller than an active tag.

It has a variety of read ranges starting with less than 1

inch to about 10 feet (3 meters approximately).

Cheaper compared to an active or semi-active tag.

Active tagHas on-board power source .

No need for reader's emitted power for data transmission

A tag always communicates first, followed by the reader.

High Read Range

System overviewSystem overview

Communication between transponder - reader

RFID backscatter coupling

RFID inductive coupling

Inductive CouplingAn inductively coupled transponder (tag) comprises of an

electronic data carrying device, usually a single microchip and a large area coil that functions as an antenna.

The reader's antenna coil generates a strong, high frequency electro-magnetic field, which penetrates the cross-section of the coil area.

By induction, a voltage is generated in the transponder's antenna coil.

Used in Short range communication (< 1m).

Backscatter couplingCommunication between reader and tag (long range).

Reader sends a signal (energy) to a tag, and the tag responds by reflecting a part of this energy back to the reader.

A charge device such as a capacitor contained in the tag makes this reflection possible.

The capacitor gets charged as it stores the energy received from the reader.

As the tag responds back, it uses this energy to send the signal back to the reader. The capacitor discharges in the process.

Reader antennaLinear Polarization (dipole antennas) - the electromagnetic

wave propagates entirely in one plane (Vertical or Horizontal) in the direction of the signal propagation. This is the best wave propagation when the tag orientation is known and fixed.  

Circular Polarization (helix, patch): This is best to use when tag orientation is unknown, but you lose at least 3dB when compared to a linear polarized antenna.

Quadrifilar antenna Radiation from the quadrifilar antenna is circularly polarized. Comprises of two bifilar helical loops oriented in a mutually

orthogonal relation on a common axis.

The terminals of each loop are fed 180° out of phase, Used in aircrafts, LEO satellites.

Quadrifilar Helix Antenna in RFID Composed of four helical elements that are fed at each port

with equal amplitude and phased at 0°, 90°, 180°, and 270° respectively.

The helical elements are bottom fed at the ground plane. Gain of 5.4 dB . Bandwidth of 900-930 MHz.

RFID Helix antenna

Quadrifilar Helix Antenna in RFID

References

Garret I. McKerricher and Jim S. Wight ” Design of a Shaped Beam RFID Reader Antenna” in IEEE 14th International Symposium on Antenna Technology and Applied Electromagnetics [ANTEM] and the American Electromagnetics Conference [AMEREM], 2010.