Fig. 2: Design of acoustic tunnels with tunable acoustic paths.
From: Ultra-broadband illusion acoustics for space and time camouflages
a Schematic diagram of a curved tunnel with a varying cross-section. The gray portion represents the solid structure. A magnified view is displayed in the top-right corner. Arrows indicate the incidence and transmission of waves. b Simulated acoustic pressure field distributions that vary with the ratio of \(h/w\), corresponding to the phase shift \(\Delta \phi=0,\,{{{{\rm{\pi }}}}},\,2{{{{\rm{\pi }}}}}\). c Phase shift \(\Delta \phi\) and transmittance \({\left|t\right|}^{2}\) under normal incidence as a function of \(h/w\). Vertical gray dotted lines indicate the cases with \(\Delta \phi={{{{\rm{\pi }}}}},\,2{{{{\rm{\pi }}}}}\). d Equivalent relative refractive index \({n}_{r}\) as a function of \(h/w\) and the frequency \(f\).
