Transmission method in C, L, M and U ranges
There are different transmission method used in C, L M and U ranges. Transmission method in BIS C is Amplitude modulation. The response of data carrier as a modulated 455KHZ frequency.
BIS L or M , the transmission method used is Inductive coupling.
The reader send a magnetic field to the tag which induces a voltage in the coil of the tag. The power consumed by the tag is seen as voltage drop on the internal resistance of the reader's antenna.
BIS U , the transmission method is Electromagnetic Backscatter coupling.
The reader send an electromagnetic field to the tag and power the tag. This energy is reflected back to the reader. Backscatter is reflecting the wave back to the reader and putting a signal inside that reflected wave. The tag switches its coil on and off to send data to the reader.