(a), (b) The real and imaginary parts of the DMR’s normalized surface impedance Z/Z₀, where Z₀ denotes the impedance of air, plotted as a function of frequency. They are seen to satisfy the total absorption requirements given by equation (5) at the hybrid resonance frequency, indicated by the intersection of the black curves with the blue dot-dashed line. Total absorption is confirmed experimentally, shown in (c). A sharp absorption peak, reaching 0.994, is seen. The solid and dashed arrows indicate the first eigenmode and the anti-resonance frequency of the DMR, respectively. Experimental results are shown by the red circles, and the black curves denote the theoretical predictions.