Breaking the barriers: advances in acoustic functional materials

Abstract

Acoustics is a classical field of study that has witnessed tremendous developments over the past 25 years. Driven by the novel acoustic effects underpinned by phononic crystals with periodic modulation of elastic building blocks in wavelength scale and acoustic metamaterials with localized resonant units in subwavelength scale, researchers in diverse disciplines of physics, mathematics, and engineering have pushed the boundary of possibilities beyond those long held as unbreakable limits. More recently, structure designs guided by the physics of graphene and topological electronic states of matter have further broadened the whole field of acoustic metamaterials by phenomena that reproduce the quantum effects classically. Use of active energy-gain components, directed by the parity-time reversal symmetry principle, has led to some previously unexpected wave characteristics. It is the intention of this review to trace historically these exciting developments, substantiated by brief accounts of the salient milestones. The latter can include, but are not limited to, zero/negative refraction, subwavelength imaging, sound cloaking, total sound absorption, metasurface and phase engineering, Dirac physics and topology-inspired acoustic engineering, non-Hermitian parity-time synthetic active metamaterials, and one-way propagation of sound waves. These developments may underpin the next generation of acoustic materials and devices, and offer new methods for sound manipulation, leading to exciting applications in noise reduction, imaging, sensing and navigation, as well as communications.

The Present and Future Role of Acoustic Metamaterials for Architectural and Urban Noise Mitigations

“…By adjusting the geometrical size and shape of structures, acoustic metamaterials can be used for noise attenuation purpose over a specific pre-designed and tunable frequency range. The fundamental concept of acoustic metamaterials is extensively discussed in previously published review articles [26][27][28][29][30][31][32][33][34][35][36]. In this article, we have explored the viability of acoustic metamaterials for architectural and urban noise mitigation applications.…”

Programmable Acoustic Metasurfaces

“…Metasurfaces, as a two‐dimensional (2D) equivalent of bulk metamaterials, have attracted numerous research efforts in recent years due to their powerful ability to control classical waves such as electromagnetic, acoustic, and elastic waves. In acoustics, metasurfaces offer a new paradigm for manipulating wave propagation, engineering acoustic wavefront, and realizing various interesting functions including acoustic cloaking, holographic rendering, and acoustic communication . These functions are enabled by the fundamental subwavelength building blocks (unit cells) of metasurfaces.…”

Nonlinear one-way edge-mode interactions for frequency mixing in topological photonic crystals

“…2e, apart from the gap of C = 1, other gaps with C = −1, −2, 2, 3 are typically narrow and appear at high frequencies, so designing setups where these gaps are wide and are formed at low frequencies is particularly relevant from experimental point of view. Last but not least, the concept of topology-protected nonlinear frequency mixing is universal in that it applies not only to photonics, but also to plasmonics [32][33][34][35], phononics [36][37][38], magnonics [39][40][41], and metamaterials [42,43], thus we expect that our work will generate a broad impact.…”