RFID Principle
3 parts：
1. tag(RF card)：it is composed of coupling elements and chips, including built-in antenna.3. antenna：transmit RF signal between tag and reader.
The basic workflow：
1. The reader sends a certain frequency of RF signal,than induced current generated when RF card enters the working area of transmitting antenna and RF card activated；
2. RF card sends information through the built-in antenna；
3. the system receives the carrier signal sent from the RF card then transmitted to reader via antenna regulator,the reader demodulates and decodes the signal and sends it to the main system for relevant processing；
4. the main system judges the validity of the card according to the logical operation,and make corresponding treatment and control for different settings.
