Resonant tunneling of acoustic waves through a double barrier consisting of two phononic crystals

We present the acoustic analog of resonant tunneling through a double barrier in quantum mechanics. Pairs of identical phononic crystals, in both 2D and 3D, were assembled and separated by a uniform spacer, forming a resonant cavity. The ultrasonic transmission exhibits resonant peaks at frequencies inside the band gaps, where ultrasound tunneling through each phononic crystal occurs. On resonance, the measured group time is large and even predicted to increase exponentially with the thickness of the crystals in the absence of absorption, while off resonance very fast speeds are found.