Figure 2. Photograph and mechanical schematic of the effective material element.

A photograph of the assembled element is shown second from the bottom of (a) along with membrane and perforated paper samples and a US 1-cent coin for scale. The membrane is 0.125 mm thick and the paper is 0.45 mm thick with 3.1 mm-diameter circular holes. The membrane and the paper are separated by a 5.9 mm-thick air cavity using an aluminum holder. The mechanical schematic shown in b describes the behaviour of the effective material element in the long-wavelength limit as a membrane with a mass M_m and bending stiffness k_m, an air cavity with stiffness k_a and air masses in the holes of a plate with mass M_h.