Experimental verification of acoustic wave focusing of sonic black holes

Broadband acoustic wave-focusing sonic black holes (SBHs) has recently been demonstrated numerically via topology optimization. Here, we present the first experimental characterization of an SBH-based wave-focusing structure. We design and fabricate a custom rectangular impedance tube to measure the transmission coefficient and to characterize the internal acoustic pressure distribution inside SBHs using a laser scanning vibrometer. Additionally, we experimentally investigate the effect of geometric asymmetry on the wave-focusing performance of SBH devices. The results show good agreement with numerical predictions and confirm the intrinsic acoustic wave-focusing behavior of SBH waveguides. Although both symmetric and asymmetric designs exhibit broadband transmission, their internal pressure fields differ significantly, demonstrating that broadband transmission does not necessarily correspond to enhanced acoustic wave focusing. These findings highlight the potential advantages of SBH configurations for improved acoustic wave sensing and facilitate practical applications that require improved detection of weak signals.