Acoustic Phased Arrays (APAs) are comprised of a set of electroacoustic transducers, each capable of augmenting an excitation signal with a distinct phase shift. The common sound pattern generated from all the transducers is amplified by constructive interference in desired directions and attenuated by destructive interference in others. As such, by controlling such prescribed phase shifts, a wide range of intriguing features can materialize ranging from beam steering, focusing, to acoustic levitation and holography with direct impacts on applications in nondestructive testing and ultrasound imaging. Although APAs have been around with successful implementation in several applications, their performance and dynamics thus far have been restricted by the fundamental reciprocity principles. Reciprocity of wave propagation in linear time invariant systems guarantees identical transmission of waves if the locations of the sender and receiver are interchanged. As a consequence, traditional acoustic phased arrays inevitably exhibit identical directivity patterns in radiation and reception and cannot communicate in duplex mode, i.e. simultaneously radiate and receive signals along the same frequency channel, a premise which would be highly favorable in radar and SONAR applications.

In this work, we introduce an actively controllable acoustic phased array with prescribed space-time modulation of phase shifts that break time-reversal symmetry. The modulations induce an artificial momentum bias along the length of array and enable phononic transition in both the momentum and energy spaces. It is primarily inspired and motivated by recent spurt of developments in the study of nonreciprocal metamaterials which realize one-way travel of waves in mechanical systems. In the proposed space-time acoustic phased array, the static phase shift between adjacent transducers is supplemented with a dynamic spatial and temporal periodic phase that travels along the array with a subsonic modulation speed. By leveraging the dynamic phase shift modulation, the space-time acoustic phased array is no longer bound by reciprocity constraints, and supports asymmetric directivity patterns in radiation and reception which can be tuned independently. Furthermore, due to time-reversal symmetry breakage, radiated and received signals can be desirably modulated to allow simultaneous operation in both modes and at the same frequency. Through theoretical and numerical investigations, we develop and verify a mathematical framework to characterize the underlying nonreciprocal phenomena and optimize the frequency conversion between the excitation and the acoustic wave fields. The space-time acoustic phased array is a relatively simple and effective analog approach in radar and SONAR signal processing that facilitates unprecedented control over sound waves and downsizing via duplex telecommunication.


A Linear Acoustic Phased Array for Nonreciprocal Transmission and Reception

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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