Frequency selective wave beaming in nonreciprocal acoustic phased arrays

Abstract

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.

On-demand harmonic wave suppression in non-Hermitian space-time-periodic phased arrays

“…In the array's transmission mode, the scattering matrix S can be obtained from V out = SE T v for both PTand anti-PT-symmetric systems, with V out being a vector of the various harmonics in the output voltage signal. The scattering matrix can be defined as follows [27]: The amplitude C (h) and percentage energy E (h) % of the hth harmonic for (a) a PT-symmetric phase profile and (b) an anti-PT-symmetric phase profile. The different harmonics in each subplot are color coded to reflect the value of h. The yellow-shaded scenarios depict a suppression of the up-converted harmonic when the hermiticity ratio is equal to −1 for the PT-symmetric system and 1 for the anti-PT-symmetric one.…”

“…Lately, and inspired by recent progress in temporally-modulated phononic metamaterials, the notion of implementing a dynamic phase profile in a phased array, i.e. one that varies spatially along the length of the array but also simultaneously in time, has been shown to yield multiple beams which travel along different directions and within different frequency channels, representing small harmonic conversions of the fundamental and modulation frequencies [27,28] (see figure 1(a)). These space-time-periodic (STP) arrays are described using Hermitian Hamiltonians, which represent the dynamics of energy-conservative systems that support real-valued energy spectra.…”

Anomalous wavefront control via nonlinear acoustic metasurface through second-harmonic tailoring and demultiplexing

“…Engineered material systems have been widely used in controlling acoustic/elastic waves due to their unique and intriguing properties such as bandgap and ability to slow the wave speed, which leads to diverse applications, including vibration suppression systems 1,2 , energy harvesting devices 3,4 , topological insulators 5 and nonreciprocal wave propagation [6][7][8] .…”

Sound diffusion with spatiotemporally modulated acoustic metasurfaces

“…Modulation has also been employed as a means to mimic symmetry-breaking momentum bias present in fluid-flow 22 in order to create nonreciprocal acoustic and electromagnetic circulators [23][24][25] . Modulation has also been used in metasurfaces to induce nonreciprocal reflection and transmission of elastic and acoustic waves 21,26 as well phase shifting 27 , total power combining 28 , nonreciprocal scattering 29 , and the Doppler-like frequency shift of reflected optical waves 30,31 .…”