(1) inductive coupling. Transformer model, coupled with space high-frequency alternating magnetic field, is based on the law of electromagnetic induction, as shown in the following figure.
inductive coupling
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(2) Electromagnetic backscattering coupling: radar principle model, the emitted electromagnetic wave is reflected after hitting the target, and carries back the target information at the same time, based on the spatial propagation law of electromagnetic wave.
Electromagnetic backscattering coupled RFID reader
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Just like the principle of radio, radio frequency tags and readers must be modulated to the same frequency to work. Low frequency, high frequency and ultra-high frequency correspond to different frequencies of RF. LF stands for low frequency radio frequency, about 125KHz, HF stands for high frequency radio frequency, about 13.54MHz, UHF stands for ultra-high frequency radio frequency, and there is a 2.4G microwave reader in the range of 850 to 9 10MHz.
Inductive coupling mode is generally suitable for short-distance RFID systems working at medium and low frequencies. Electromagnetic backscattering coupling method is generally suitable for long-distance radio frequency identification system working at high frequency and microwave.