Figure 3
From: Feasibility of backscatter RFID systems on the human body
Link budget of a backscatter RFID system. Link budget of a backscatter RFID system: In the forward link, the reader transmits RF power and data to the tag. The RFID tag consists of an antenna and a microchip. The power received by the tag antenna is PTag=|S21|2PTX,Reader. The power absorbed by the chip is PChip=τ PTag, where τ is the power transmission coefficient of the tag. In the backward link, the tag responds to the reader by modulating the backscattered signal. The received power at the reader can be written as PRX,Reader=|S12|2η PTag, η is the modulation efficiency of the tag.