Applying Metamaterial-Based Repeater in LC Passive Wireless Sensors to Enhance Readout

Inductor-capacitor (LC) passive wireless sensors allow for a continuous, real-time monitoring for various parameters of interest in situations, where wired connections are difficult or even impossible. However, geometrical constraints reduce the magnetic coupling between the sensor and the readout coil, resulting in a limited interrogation distance. Here, we propose a left-handed metamaterial as a repeater to enhance the readout of the LC passive wireless sensors. The left-handed metamaterial consists of double-side square spirals and possesses negative relative permeability. The operating frequency of the left-metamaterial is designed adjustable to cover the frequency spectrum of the sensor. By monitoring the relative humidity as an example, we have demonstrated that the readout distance with the left-handed metamaterial can achieve nearly 1.8 times as long as that without metamaterial, while keeping their signal strength and sensitivity the same. Overall, this strategy through the metamaterials-based repeaters represents an effective approach for enhancing the readout.