Independent dual-band metamaterial absorber with large frequency ratio based on Helmholtz resonators

We propose a dual-band metamaterial absorber with large frequency ratio, comprising periodic laminated metal–dielectric pyramids cascaded with a Helmholtz resonator array. Specifically, the metal–dielectric pyramids achieve over 90% broadband absorption from 16.6 to 19 GHz while remaining transparent at lower frequencies to the Helmholtz resonator array. Conversely, the Helmholtz resonator array exhibits 99.9% absorption at 2.88 GHz, simultaneously serving as a natural ground for the pyramids. By cascading these two structures, our design achieves independent dual-band absorption with a center-frequency ratio exceeding 6 and no spurious absorption peaks between the bands, paving the way for the development of more advanced multifunctional energy-harvesting devices.