Figure 2
From: Emission Enhancement of Sound Emitters using an Acoustic Metamaterial Cavity
Effective medium analysis of single and double-walled metamaterial slabs.
(a) The perforated metamaterial can be viewed as a single slab using the effective medium theory when the incident wavelength is much larger than the unit cell (0th mode condition). Then effective medium parameters such as effective refractive index neff and effective impedance Zeff can be used to characterize the transmission and reflection coefficients. Variation of (b) neff and (c) Zeff with respect to the flange length (w) for the single slab metamaterial calculated using acoustic numerical retrieval scattering method18,19 is as shown. Increases in the refractive index and impedance are achieved by an increased path length when w is increased. (d) The double metamaterial slab can also be viewed as a single slab where the effective material parameters arise by coupling between the metamaterial-gap-metamaterial. Calculated (e) effective refractive index and (f) effective impedance of single and double metamaterial slab for frequencies between 100 and 1600 Hz are as shown. The single slab behave as resistive component having only a real component of the effective impedance, while the double slab behave as LC components having both real and imaginary components between 1060 Hz and 1600 Hz.
