Improving absorption performance of resonant metamaterials using self-complementary shapes

In electromagnetics, self-complementary antenna shapes possess a frequency-independent characteristic due to their particular shape. Based on this concept, this paper investigates the potential applications of self-complementary shapes for sound absorption to broaden the bandwidth and enhance the performances of resonators without altering the sizes and resonance frequencies. Self-complementary shapes, such as log-periodic planar tooth and log-spiral shapes, are used to demonstrate the effectiveness of our approach in enhancing the absorption bandwidth and performance of a resonator. Such shapes improve the absorption performance up to 58 % compared to a resonator with an equivalent circular area when the opening area is reduced, whereas they exhibit weak performance for wide opening areas. Numerical and experimental analyses are conducted to verify their performances and to investigate the effect of the materials inside the backing cavity, neck length, opening size, and geometry on absorption. By extending the use of frequency-independent antenna shapes as sound-absorbing structures, this approach overcomes the inherent limitations of resonant metamaterials to achieve an enhanced sound absorption for various applications.