Acoustic phased arrays are capable of steering and focusing a beam of sound via selective coordination of the spatial distribution of phase angles between multiple sound emitters. Constrained by the principle of reciprocity, conventional phased arrays exhibit identical transmission and reception patterns which limit the scope of their operation. This work presents a controllable space–time acoustic phased array which breaks time-reversal symmetry, and enables phononic transition in both momentum and energy spaces. By leveraging a dynamic phase modulation, the proposed linear phased array is no longer bound by the acoustic reciprocity, and supports asymmetric transmission and reception patterns that can be tuned independently at multiple channels. A foundational framework is developed to characterize and interpret the emergent nonreciprocal phenomena and is later validated against benchmark numerical experiments. The new phased array selectively alters the directional and frequency content of the incident signal and imparts a frequency conversion between different wave fields, which is further analyzed as a function of the imposed modulation. The space–time acoustic phased array enables unprecedented control over sound waves in a variety of applications ranging from ultrasonic imaging to non-destructive testing and underwater SONAR telecommunication.
Acoustic phased arrays are capable of steering and focusing a beam of sound via selective coordination of the spatial distribution of phase angles between multiple sound emitters. Here, we propose a controllable acoustic phased array with space-time modulation that breaks time-reversal symmetry, and enables phononic transition in both momentum and energy spaces. By leveraging the dynamic phase modulation, the proposed linear phased array is no longer bound by the reciprocity principle, and supports asymmetric transmission and reception patterns that can be tuned independently. Through theoretical and numerical investigations, we develop and verify a mathematical framework to characterize the nonreciprocal phenomena, and analyze the frequency conversion between the wave fields. The space-time acoustic phased array facilitates unprecedented control over sound waves in a variety of applications including underwater telecommunication.
Neuromorphic computing was originally introduced in electronic circuits to mimic neuro-biological architectures. In these systems, a physical agent (e.g., an electromagnetic or acoustic wave) propagates through multiple layers of metasurfaces which are trained to perform a computational task (e.g., classification). Despite their potential, current neuromorphic metasurfaces rely on passive designs which limits their computational power to a single task. Furthermore, attempts to realize these systems in the context of mechanical wave propagation have been very scarce. This work presents a neuromorphic metasurface which is designed to exploit elastic wave scattering to realize a physical computing environment. Owing to the reconfigurable design of the chosen unit cell, the neuromorphic metasurface can be tuned to conduct multiple distinct classification tasks without the need for remanufacturing. The designed subwavelength metasurface cell will be used to train a customized neural network with constant weights (representing the elastic wave propagation between different layers of metasurface) and trainable activation functions (representing the phase modulation at each layer of metasurface). To perform distinct classification tasks, the trainable parameter in the activation function will be tuned accordingly. This work opens up new avenues in high performance mechanical computing.
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