Development of a radiation-safe CW-THz roll-to-roll monitoring system using UTC-PD emitter and ZBD for industrial metal-particle coatings

Abstract We demonstrate a compact, radiation-safe continuous-wave terahertz (THz) system for in-line industrial monitoring. The system integrates a high-efficiency uni-traveling-carrier photodiode emitter and a zero-bias detector into a single robust monitoring system for roll-to-roll manufacturing. Its efficiency was validated by monitoring platinum (Pt) catalyst loading in hydrogen-fuel-cell electrodes. Critically, the THz transmission showed a strong linear correlation with conventional X-ray fluorescence measurements, not only for dried films ( R 2 = 0.957) but also for the as-coated wet slurry ( R 2 = 0.804). This result confirms the feasibility of non-destructive, real-time quality control before the energy-intensive drying process, offering a practical solution for material savings and process optimization in advanced manufacturing.