Multiple-frequency perfect absorption by hybrid membrane resonators

Besides generating their own perfect absorption bands, the primary hybrid resonances of a hybrid membrane resonator (HMR) consisting of a decorated membrane resonator (DMR) backed by a cavity can also provide strong assistance for weak resonances to create secondary hybrid resonances and multiple-frequency perfect absorption by forming a low impedance region between the primary hybrid resonances. The weak resonances can be introduced by placing another DMR in front of a HMR or by using a DMR with an off-centered platelet in an HMR. In one such sample, five perfect absorption bands within the range of 200–1000 Hz are experimentally observed with minimum reflection values ranging from 1.2% to 7%.