Broadband Impedance Modulation Via Non-Local Acoustic Metamaterials

Causality of linear time-invariant systems inherently defines the wave-matter interaction process in wave physics.This principle imposes strict constraints on the interfacial response of materials on various physical platforms.A typical consequence is that a delicate balance has to be struck between the conflicting bandwidth and geometric thickness when constructing a medium with desired impedance,which makes it challenging to realize broadband impedance modulation with compact structures.In pursuit of improvement,the over-damped recipe and the reduced excessive response recipe are creatively presented in this work.As a proof-of-concept demonstration,we construct a metamaterial with intensive mode density that supports strong non-locality over a frequency band from 320 Hz to 6400 Hz.Under the guidelines of the over-damped recipe and the reduced excessive response recipe,the metamaterial realizes impedance matching to air and exhibits broadband near-perfect absorption without evident impedance oscillation and absorption dips in the working frequency band.We further present a dual-functional design capable of frequency-selective absorption and reflection by concentrating the resonance modes in three frequency bands.Our research reveals the significance of over-damped recipe and the strong non-local effect in broadband impedance modulation,which may open up avenues for constructing efficient artificial impedance boundaries for energy absorption and other wave manipulation.