Reconfigurable Multi‐Band Perfect Absorption Using a GST‐Integrated Metamaterial

Most phase‐change materials (PCMs), including Ge 2 Sb 2 Te 5 (GST), exhibit limited refractive index modulation in the visible range, resulting in only minor spectral shifts upon phase transition. In this work, we mitigate this limitation by employing a design strategy based on mode redistribution and critical coupling theory to realize pronounced spectral reconfigurability. A tunable multilayer metamaterial perfect absorber incorporating GST is numerically designed and optimized using COMSOL Multiphysics for the visible to near‐infrared range (400–850 nm) under normal incidence. The absorption response is governed by a phase‐dependent redistribution of resonant mode engineering and a controlled matching between loss and radiation, rather than by simple refractive‐index‐driven resonance shifts. Numerical results demonstrate near‐unity absorption exceeding 99.996% at multiple wavelengths in both the amorphous and crystalline states, with a distinct multi‐peak reconfiguration upon phase transition. The proposed GST‐based absorber mitigates the common limitations of visible‐range designs and offers a robust platform for reconfigurable photonic and optoelectronic applications.