Near field Radio Frequency Identification Technologies

This category depends upon the faraday’s principle of magnetic induction for the process of the coupling between the single reader and the series of tag. As a reader is able to pass a large amount of alternating current from the cross section of the reading coil. This also results varying the alternating magnetic field relatively in its cross section locality. When a tag is placed who's cross sectional are is small relatively  and also the smaller coil then the alternating voltage is induced  across it terminal. When this induced voltage is processed through rectification process and is connected to a capacitor bank then a large reservoir of the charge is accumulated through it. which is used to provide the power to the series of tag chip.

Series of tags which use near field coupling transfer the data to the previous  reader with the help of  using load modulation method. As all the current which is drawn through the series of tag coil gradually will provides the increment in poor  magnetic field. This poor magnetic field opposes the main advanced reader’s series of field. The testing coil can predicts this at a small incremental of current which is passing from it. This passing current is directly proportional to the combined. The principle used for this purpose is same as used for that of power transformers.

 As in the transformer effect the primary and secondary coils are connected magnetically not electrically. When the magnetic field through the primary winding increase through specific level then the secondary winding acquires this magnetic field. And it behaves the same role as the tag for the reader. The reader monitors this signal and recovers it. This recovering is done by changing the value of the current. Different types of modulation encodings are established which are based at the complete number series of registers and of ID bits.

Near-field coupling is completely a best technique to implementing practically a number of passive radio frequency identification system. With its advantages the narrow field also has some disadvantages and restrictions. The periodic range used  for  this purpose is approximately c/2πf. In this periodic approximation c shows a constant value which is also called  speed of light. Where f represents  the frequency. So when the frequency of increases automatically then the measuring distance decreases upon which the field coupling is depending.

 Moreover a specific limitation is required for the energy which is existing as the induction. This induction is the function of distance. It is connected with the reader coil. In this case the dropping factor for the magnetic field is near 1/r3. In this factor the r is representing the value of distance between or the separation of the tag and the reader. It is along the direction of center line. This center line is mutually perpendicular to plane of coil. In this case more ID bits are also required.

By the way the near field radio frequency communication system also has some restrictions and limitations physically. For this purpose the range used is near about c/2πf and it has magnetic effect.