Origami acoustics: using principles of folding structural acoustics for simple and large focusing of sound energy

Abstract

Fixed in spatial distribution, arrays of planar, electromechanical acoustic transducers cannot adapt their wave energy focusing abilities unless each transducer is externally controlled, creating challenges for the implementation and portability of such beamforming systems. Recently, planar, origami-based structural tessellations are found to facilitate great versatility in system function and properties through kinematic folding. In this research we bridge the physics of acoustics and origami-based design to discover that the simple topological reconfigurations of a Miura-ori-based acoustic array yield many orders of magnitude worth of reversible change in wave energy focusing: a potential for acoustic field morphing easily obtained through deployable, tessellated architectures. Our experimental and theoretical studies directly translate the roles of folding the tessellated array to the adaptations in spectral and spatial wave propagation sensitivities for far field energy transmission. It is shown that kinematic folding rules and flat-foldable tessellated arrays collectively provide novel solutions to the long-standing challenges of conventional, electronically-steered acoustic beamformers. While our examples consider sound radiation from the foldable array in air, linear acoustic reciprocity dictates that the findings may inspire new innovations for acoustic receivers, e.g. adaptive sound absorbers and microphone arrays, as well as concepts that include water-borne waves.

Architected Origami Materials: How Folding Creates Sophisticated Mechanical Properties

“…For example, rigid‐folding of Miura‐ori sheet can arrange the attached inclusions into square, hexagonal, rectangular, and asymmetrical patterns, thus significantly tailor and frequency spectrum of the corresponding acoustic bandgaps . Such and similar features have been utilized for noise mitigation, wave guiding and focusing …”

Adaptive acoustic energy delivery to near and far fields using foldable, tessellated star transducers

“…This means that reflections can occur, such that the free field assumption is not strictly valid. Secondly, the paths from the transducers to field points can be blocked by other facets when folded, such that acoustic shadows can influence directivity [35]. While BEM takes into account such acoustic phenomena, the analysis must adopt more ideal assumptions for Rayleigh's integral solution that neglect these factors.…”

“…Building upon this inspiring framework of engineering design, the authors have recently introduced a concept of acoustic beamfolding, wherein the tessellated surfaces of the Miura-ori origami fold pattern serve as the substrate for acoustic transducers [35,36]. Acoustic beamfolding therefore is a class of MSP that guides sound energy via the topological reconfiguration of the foldable Miura-ori-inspired arrays.…”

“…Contrasting this attention, when deploying ultrasonic waves, such as for medical diagnostics and treatment, a common need is to focus acoustic energy at strategic points in space, often in the near field of the transducers and arrays. In this perspective, the analysis put forward in the previous works [35,36] is applicable only for the prediction of sound pressure radiation to points in the acoustic far field. Therefore, a modeling methodology able to characterize both near and far field acoustic energy delivery from tessellated acoustic transducers is needed to begin uncovering opportunities for a more generalized guiding of acoustic energy via foldable, tessellated transducers.…”

“…The unfolded square shape of the Star transforms into three-dimensions by folding, although the tessellation is not flat foldable. Along with the focus on this new constituent comes the opportunity to establish new analytical procedures that facilitate prediction of near field sound energy delivery, which was not previously undertaken [35,36].…”