An ultra-thin triple-band metamaterial absorber (MA) is proposed in the microwave region, which is composed of a periodic array of three rotated square rings (RSRs) and a continuous metal film separated by only 1 mm dielectric substrate. The fabricated MA exhibits three experimental absorption peaks at 4.88 GHz, 7.88 GHz, and 11.32 GHz with the corresponding absorption rates of 98.8%, 96.5%, and 95.9%, which shows an excellent agreement with the simulated results. The triple-band MA is polarization-insensitive at the normal incidence. Finally, the multi-reflection interference theory is introduced to interpretate the absorption mechanism. The calculated absorption rates of the improved unit cell for the strongly coupled MA coincide well with the simulated results at wide angles of incidence for both transverse electric (TE) and transverse magnetic (TM) waves.
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