An integrated bifunctional metamaterial perfect absorber for high-efficient broadband absorption and narrowband refractive index detection

Metamaterial absorbers have been extensively investigated for broadband light harvesting and narrowband sensing, but integrating both into one compact device still remains challenging. In this work, we propose a bifunctional metamaterial absorber (BMA) based on zirconium nitride (ZrN). The device consists of periodically arranged ZrN concentric-ring arrays on a silicon dioxide (SiO2) spacer with an Au film underneath for broadband absorption, and ZrN-based four-by-four square-grid arrays on the opposite side of the Au substrate for narrowband refractive index sensing. Numerical simulations show that the broadband mode achieves an average absorptivity of 97.48% over the wavelength range of 800 to 2,300 nm, while the narrowband mode exhibits a near-perfect absorptivity at 948.1 nm with a bandwidth of 23.14 nm, delivering a sensitivity of 1,015.62 nm RIU-1. Electric field distributions and impedance analyses indicate that the absorption behavior arises from the couplings of localized surface plasmon resonances, multipole resonances, and Rayleigh Anomalies (RAs). Parametric studies demonstrate that the broadband absorption maintains high absorptivity in a wide wavelength range, whereas the narrowband resonance systematically shifts as the varying structural parameters. These results not only highlight the importance of integrating light harvesting and refractive index sensing in a single design, but also pave the way for incorporating multiple functionalities into one compact device for broad applications.