At these concentrations and at room temperature, the Pd-H system will be in the so-called αphase, characterized by hydrogen concentrations in the metal typically lower than ~1 at.%. To best model the optical properties of the palladium hydride phase, we therefore use the composition PdH 0.12 , corresponding to the lowest PdH x composition for which an accurate dielectric function is available in the literature. From Eq. 1, it is apparent that the highest FoM is obtained by finding an array configuration where the contributions from the LSPR (maximizing Δλ peak upon hydrogenation) and RA (narrowing FWHM) in their hybridized modes are optimized. The FoM exhibits ~10% variance from the best sensor, which indicates that a rather constant FoM can be achieved during the fabrication of the sensor.