Metalenses are instruments that manipulate waves and have exhibited remarkable capabilities to date. However, an important hurdle arises due to the severe hampering of the angular response originating from coma and field curvature aberrations, which result in a loss of focusing ability. Herein, we provide a blueprint by introducing the notion of a wide field-of-hearing (FOH) metalens, designed particularly for capturing and focusing sound with decreased aberrations. Employing an aberration-free planar-thin metalens that leverages perfect acoustic symmetry conversion, we experimentally realize a robust wide FOH capability of approximately 140^∘in angular range. Moreover, our metalens features a relatively short focal length, enabling compact implementation by reducing the aperture-to-hearing plane distance. This is beneficial for space-efficient source-tracking sound sensing. Our strategy can be used across various platforms, potentially including energy harvesting, monitoring, imaging, and communication in auditory, ultrasonic, and submerged environments.

Beyond conservative systems, altering the wave propagation frequency emerges as a crucial factor across diverse physical domains. This Letter presents a demonstration of bidirectional asymmetric frequency conversion-either upward or downward-depending on the excitation direction, surpassing conventional unidirectional mechanisms. We numerically and experimentally demonstrate its practical realization in a model system of cylindrical granular crystals with intrinsic local resonance coupling. This novel wave transport mechanism arises from the interplay of nonlinear contact, spatial asymmetry, and coupled local resonance. In particular, we show that local resonance coupling induces wavenumber-dependent wave dynamics, including frequency conversion. Given that this local resonance exemplifies avoided crossings (i.e., strong coupling), this Letter may inspire studies on nonlinear systems supporting material or structural resonance.