Realizing directional acoustic signal transmittance and reception robust against surrounding noise and competing signals is crucial in many areas such as communication, navigation, and detection for medical and industrial purposes. The fundamentally wide-angled radiation pattern of most current acoustic sensors and transducers displays a major limitation of the performance when it comes to precise targeting and probing of sound particular of interest in human speaking and hearing. Here, it is shown how topological acoustic valley transport can be designed to enable a unique beamforming mechanism that renders a superdirective needle-like sound radiation and reception pattern. The strategy rests on out-coupling valley-polarized edge states, whose beam is experimentally detected in the far-field with 10° width and a sound-intensity enhancement factor ≈10. Furthermore, anti-interference communication is proposed where sound is received from desired directions, but background noise from other directions is successfully suppressed. This type of topological acoustic antenna offers new ways to control sound with improved performance and functionalities that are highly desirable for versatile applications.
Metamaterial absorbers have recently been developed to act as efficient sound absorption components of subwavelength dimensions. However, the working frequency has so far been mainly limited to a single narrow band. Here, we demonstrate a multiband quasi-perfect absorber constructed by a double-channel Mie resonator (DMR) in a unique configuration. By attentively tuning the leakage factor to match the loss factor at multi-order monopolar and dipolar resonances of DMR simultaneously, a series of absorptive peaks with near-unity absorptances have been achieved in both numerical simulation and the experimental measurement. Our approach gives a simple platform for extending the response of metamaterial devices from the single band to the multiband without superimposing resonant elements in multiple configurations, which allows us to envision acoustic devices with versatile applications.
Detection of weak sound signals masked by strong noise background remains challenging in acoustic science and engineering. The major bottleneck of advancing this technology is the limited directivity and sensitivity of ordinary acoustic sensors. Here, we engineer acoustic metamaterials with a near-zero-index (NZI) in the form of a low-profile planarized acoustic antenna for combined highly directive-sensitive detection. The detectable incident angle can be substantially narrowed down by the directional selectivity of NZI acoustic metamaterials, while the detected pressure can be enhanced by deeply tunneling compression at the sound radiation vent. Magnification of signal amplitude more than 18 dB with a half-power beam width of mainlobe less than 5° is demonstrated both numerically and experimentally, which overcomes the detection limit of conventional acoustic sensing systems.
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