Effects of Metal Plane in LC Passive Wireless Sensors

Inductor-capacitor (LC) sensors have advantages in situations where wired connections are impossible in harsh environments. Due to the wireless mutual coupling, the LC sensor can resist most external influence brought by the ambient objects, even when they are in the propagation path. However, the metals can shield electromagnetic waves, which affects the signal readout. A metal plane is added at the back of the LC sensor to study the interrogating change. A simulation and an equivalent circuit are demonstrated to give a theoretical analysis. Then, experiments are conducted to conclude that the metal plane will shift the resonant frequency of the LC sensor to be greater and weaken the Q factor of the LC sensor.