Tunable nematic liquid crystal circular polarization converter for pesticide detection

A reflective circular polarization converter (CPC) based on dynamically tuned nematic liquid crystals (NLC) is proposed for high-quality (Q) detection of six pesticides. The converter configuration comprises a multi-armed semicircular copper ring resonator, a polyimide (PI) dielectric layer, an NLC tuning layer, an etched multi-armed semicircular copper layer, and a bottom PI substrate. Polarization state manipulation of incident electromagnetic waves is achieved by the multi-armed semicircular resonant element through electromagnetic coupling, efficiently converting right-handed circularly polarized waves into left-handed circularly polarized waves with a peak polarization conversion ratio exceeding 95%. Notably, the alignment of the NLC molecules can be reconfigured by the external electric field, enabling dynamic optimization of the sensing performance. In the absence of bias, the given CPC exhibits a sensitivity (S) of 72 GHz/RIU and an average Q of 35.11. Under an applied saturation bias voltage, although the S decreases to 32 GHz/RIU, the average Q factor increases markedly to 105.12. Compared with existing pesticide sensors, the proposed CPC achieves superior overall performance in both operational modes, together with a broad detection range and high environmental adaptability. Owing to these performance advantages, the CPC offers a powerful technological platform for food safety monitoring, contributing to enhanced health security in the consumption of agricultural products. The CPC represents a brand-new application field for NLC in fluid soft matter.