Quartz Crystal Microbalance Based UVA and UVC Sensor

We propose a novel ultraviolet (UVA and UVC) sensing technique based on parallel resonance frequency ( ${f}_{\text {p}}$ ) changes of a ZnO film-coated quartz crystal microbalance (QCM). A thin ZnO film was coated on a 5 MHz AT-cut QCM using RF magnetron sputtering technique. Impedance analyser measurement indicated that the parallel impedance and frequency changed upon exposure to the UV. Further, an oscillator circuit was designed to excite the ZnO coated QCM (ZnO-QCM) at ${f}_{p}$ and changes in ${f}_{p}$ ( $\Delta {f}_{p}$ ) upon exposure to UVA (365 nm) and UVC (265 nm) were measured. For each value of intensity, ZnO-QCM exhibited a repeatable, stable, and distinctive change in $\Delta {f}_{p}$ . From multiple trials of experiments, we discovered that the rate of change in $\Delta {f}_{p}$ values for the first 10 s of measurement was unique for each intensity and overall showed linear characteristics. Our experiments and results indicate that UVA and UVC can be detected at a resolution of 1 mW.cm $^{-{2}}$ and 0.01 mW.cm $^{-{2}}$ , respectively. Also, a single ZnO-QCM as the sensing element was sufficient to detect both types of UV. The proposed method is envisioned to have broad industrial and domestic applications ranging from water purification to disinfection where UV radiation is crucial.