Dual band complementary metamaterial absorber in near infrared region

Abstract

In this paper, we present the dual band absorption characteristics of complementary metamaterial absorber in near infrared (1.3–2.5 μm) region. The dual band absorption is caused by two distinct resonance mechanisms—electrical resonance and cavity resonance. Electrical resonance occurs in the metal layer—top complementary metamaterial and the cavity resonance occurs in the spacer cavity formed between the top complementary metamaterial and bottom metal reflector layers. In order to elucidate the resonant mechanisms and study the effects of geometrical variations on both the resonant absorption behaviours, two sets of experiment were performed. It was seen that with increasing complementary metamaterial pattern dimension, the electrical resonance absorption peak showed a blue shift, while the cavity resonance showed a slight red shift. However, on the other hand, for the increase in spacer thickness, the cavity resonance peak showed a strong red shift, while the electrical resonance peak remained uninfluenced. The reason for these geometrical dependencies, for both resonances, is conceptually analysed. Furthermore, the design was optimized to attain single absorption band by engineering the cavity and electrical resonances to be at the same wavelength. The single absorption band was successfully realized, however, the peak wavelength showed a red shift from the electrical resonance as in dual band absorber case. The reason for the shift was further explored to be caused due to the strong coupling of electrical and cavity resonances. This approach of utilizing different resonant mechanisms for absorption at different wavelengths provides the means to achieve multiband absorbers, using a simple design and low cost fabrication process.