RFID inductive coupling
RFID inductive coupling is used for what are termed “vicinity coupled” cards. RFID inductive coupling is defined in ISO 15693 standard, although not all RFID inductively coupled tags need conform to this standard.
In terms of operation, inductive coupling is the transfer of energy from one circuit to another via the mutual inductance between the two circuits. For RFID inductive coupling to be used, both the tag and the reader will have induction or “antenna” coils. When the tag is placed close enough to the reader the field from the reader coil will couple to the coil from the tag. A voltage will be induced in the tag that will be rectified and used to power the tag circuitry.
To enable data to be passed from the tag to the reader, the tag circuitry changes the load on its coil and this can be detected by the reader as a result of the mutual coupling.
RFID inductive coupling is a near field effect. Accordingly the distance between the coils must be kept within the range of the effect – normally this is taken to be about 0.15 wavelength of the frequency in use.
RFID inductive coupling is normally used on the lower RFID frequencies – often LF, i.e. below 135 kHz or at 13.56 MHz.
The choice of the best form of RFID coupling will depend upon the intended application. Capacitive RFID coupling is used for very short ranges, inductive RFID coupling for slightly longer ranges and RFID backscatter coupling or RFID backscattering is normally used where longer distances are needed.