Hydrogen sensor based on metasurface in a palladium film with a hole array

Hydrogen energy finds extensive applications in transportation, power generation, and other sectors. However, due to its small molecular size and wide explosive concentration range (4%–75%), highly sensitive monitoring devices are essential for ensuring safety. We investigate a novel hydrogen sensor based on a palladium (Pd) metasurface. This sensor utilizes a silicon dioxide (SiO2) substrate coated with a precisely controlled thickness of Pd film. Five rectangular air holes in one unit with gradient dimensions are etched, forming periodic metasurface units. Leveraging Pd's hydrogen absorption property —where hydrogenation (PdHx) alters refractive index— the study employs finite difference time domain (FDTD) simulations to calculate the transmittance difference (ΔT) before hydrogen absorption and after absorbing 4% H2 (lower explosive limit concentration). ΔT serves as the sensitivity metric. Simulation results indicate that the incident polarization being perpendicular to the gradient structure exhibits superior performance with its peak located within the visible light spectrum. The polarization along the gradient is the primary factor influencing sensing performance, while the polarization perpendicular to gradient has a limited effect. ΔT can reach to 10% with 4% of H2 concentration changing. It is so easy to observe H2 through ΔT. This sensor combines high sensitivity with electromagnetic interference resistance, meeting safety monitoring requirements for hydrogen storage and transportation scenarios.