Efficient ultrasound transmission and focusing through acoustic barriers are crucial for advancing highresolution imaging, targeted therapy, and acoustic manipulation. However, impedance mismatch and the geometric complexity of practical barriers, particularly stiff solids such as metal or bone, lead to strong reflections, wave-front distortion, and substantial energy loss. This work introduces an acoustic metamask that enhances transmission and enables flexible focusing through a stiff, curved barrier. The patterned surface structure of the metamask enables strong acoustic-solid coupling, where incident ultrasound excites resonant Lamb modes, and these guided modes subsequently reradiate the energy into the surrounding medium. This process mitigates impedance mismatch and enhances transmission, while the patterned structure simultaneously enables phase-modulated wave control for focusing. Full-wave simulations of curved brass shells reveal that the proposed metamask achieves a peak focal intensity over 2 orders of magnitude greater than that of a bare barrier, while maintaining 58.5% of the intensity observed in the barrier-free case and simultaneously producing a subwavelength focus. Our findings further demonstrate that the metamask design adapts to barriers with nonuniform thickness and complex geometries, enabling flexible multifocal control through stiff barriers. By utilizing the patterned structure to enhance acousticsolid coupling, the design conceptually transforms the barrier into a functional acoustic device, facilitating efficient ultrasound transmission through acoustically opaque structures without requiring physical openings. The work establishes a design framework for wave manipulation through complex media, with broad potential implications for therapeutic ultrasound, nondestructive evaluation, and other advanced acoustic technologies.

Acoustic black hole (ABH) structures provide an efficient means of concentrating elastic-wave energy, yet their functionality is often constrained by static geometries and limited integration with other wave-control mechanisms. Here, we present a reconfigurable ABH metastructure that combines ABH-induced energy concentration with topological interface states, enabling strongly enhanced and tunable low-frequency vibration localization. The metastrucutre integrates an ABH base with tunable local resonators, enabling active control of the spectral response. By arranging the unit cells in a Su–Schrieffer–Heeger configuration, the system supports robust topological interface states characterized by strong localized vibrations and markedly enhanced displacement amplitude. Numerical simulations and experimental measurements demonstrate that the proposed ABH metastructure achieves substantially stronger elastic energy localization at the interface, compared with wedge-shaped or uniform base designs. Furthermore, spatial reconfiguration of the resonators allows broadband tuning of the interface-state frequency and enables the realization of gradient metastructures supporting multiple, spatially separated interface states, yielding a topological rainbow trapping effect. This reconfigurable platform extends the functionality of ABH structures and provides a versatile approach for adaptive elastic wave manipulation, with potential applications in high-sensitivity sensing and vibration energy harvesting.

Wave manipulation involves harnessing and tailoring wave properties to meet specific requirements, driving advancements across a wide range of scientific, industrial, and technological fields. A critical aspect of wave manipulation is directivity control, which has broad applications in areas such as underwater communication, non-invasive medical diagnosis, and targeted audio delivery. This review introduces various methods for achieving directional sound propagation, including both conventional techniques and emerging approaches based on acoustic artificial structures. It highlights how these methods, particularly those utilizing engineered artificial materials, control acoustic wave behavior to enable directional sound emission and transmission, with illustrative examples demonstrating their principles and practical applications. Finally, the review addresses the challenges of achieving broadband, low-frequency, and adaptive control of acoustic waves, while outlining potential future research directions in directional sound manipulation.

The ability to focus light beyond the diffraction limit has been a long-standing challenge in optical science. Although many innovative techniques have been developed, ranging from near-field scanning optical microscopy to super-resolution and plasmonic approaches, these methods often rely on complex configurations and expensive setups. In this study, we propose a way for optical hyper-focusing by simply placing a gold nanoparticle on a silicon/gold multilayer metamaterial. In our configuration, the gold nanoparticle generates a localized plasmon resonance hotspot, exciting high-wave vector electric fields that propagate through the Si/Au multilayer. These fields progressively focus at the bottom interface, forming focal spots tens of nanometers in diameter across a high-loss propagation zone (∼100 nm). An optimal spot size of 44 nm and an intensity 4.5 times that of the incident light are observed at a wavelength of 780 nm using a 160 nm gold nanoparticle, surpassing both diffraction limits and the nanoparticle geometric size. This work provides insights into how multilayer metamaterials can be utilized to achieve sub-wavelength light confinement and optical hyper-focusing, opening possibilities for advanced optical applications in super-resolution imaging, nano-optics, and integrated photonic devices.

We investigate the presence of topological gaps in a twist-modulated quasiperiodic, locally resonant metastructure. This work considers an elastic plate featuring a square lattice of resonators modulated by a twisted potential, which renders the formation of moir & eacute; superlattices within a single resonant layer. This setup provides a platform to explore the topological properties of the emerging 2D quasiperiodic patterns. Our theoretical simulations reveal a fractal-like spectrum dependent on the twist angle and bandgaps characterized by nonzero topological invariants reminiscent of the 4D quantum Hall effect. The model is then physically implemented in a LEGO (R) metastructure with reconfigurable resonators whose heights can be independently adjusted according to the twist angle. The experimentally observed bandgaps and fractallike spectrum are supported by finite element simulations, confirming the appearance of topological gaps in the 2D quasiperiodic lattices. This twist-induced quasiperiodic metastructure serves as a convenient platform to explore diverse topological phenomena inspired by twistronics and quasiperiodic patterning without multilayered fabrication requirements.

We investigate the dynamics of acoustic waveguides with time-varying Helmholtz resonators and the ensuing wave propagation features. We focus on the numerical modeling of such a system with emphasis on the time-varying dispersion properties and emerging wave phenomena due to slow time modulation. We show that a propagating wave packet experiences a transformation that preserves the wavenumber content, resulting in frequency conversion that follows the time evolution of the dispersion bands. The conditions for such a transformation to be “adiabatic” are derived analytically, which allows the identification of the limiting modulation speed required to avoid undesired reflections or mode conversions. The predictions from the dispersion investigations are confirmed by time-domain numerical simulations, which illustrate the possibilities for frequency conversion and temporal signal compression or decompression of impinging signals. The framework presented herein may open new avenues in the context of time-varying phonic waveguides, with possible applications in communication, sound isolation, and frequency conversion.

This talk describes recent progress on quasiperiodic and quasicrystalline metamaterial research done by the group. While the vast majority of metamaterials are based on periodic designs based on a repeating unit cell, quasiperiodic and quasicrystalline metamaterials break the periodicity paradigm and open new interesting possibilities. The first category is based on modulations of the properties of inclusions of otherwise periodic lattices, such as point masses, springs, resonators, or stiffeners, that are given by a deterministic non-periodic pattern. In the second case, quasicrystalline materials are based on rotational symmetries which are forbidden in periodic materials, such as 5,7,8, and 10-fold rotational symmetries. The investigation of the dynamics of such materials reveals intriguing properties such as topological bandgaps and localized vibration modes that can be manipulated by a few key parameters, and wave directionalities enabled by higher order rotational symmetries that expand the behavior known to be possible in periodic metamaterials. The talk will summarize the progress done in the area, including a large number of numerical and experimental investigations.

The twist angle between a pair of stacked 2D materials has been recently shown to control remarkable phenomena, including the emergence of flat‐band superconductivity in twisted graphene bilayers, of higher‐order topological phases in twisted moiré superlattices, and of topological polaritons in twisted hyperbolic metasurfaces. These discoveries, at the foundations of the emergent field of twistronics, have so far been mostly limited to explorations in atomically thin condensed matter and photonic systems, with limitations on the degree of control over geometry and twist angle, and inherent challenges in the fabrication of carefully engineered stacked multilayers. Here, this work extends twistronics to widely reconfigurable macroscopic elastic metasurfaces consisting of LEGO pillar resonators. This work demonstrates highly tailored anisotropy over a single‐layer metasurface driven by variations in the twist angle between a pair of interleaved spatially modulated pillar lattices. The resulting quasi‐periodic moiré patterns support topological transitions in the isofrequency contours, leading to strong tunability of highly directional waves. The findings illustrate how the rich phenomena enabled by twistronics and moiré physics can be translated over a single‐layer metasurface platform, introducing a practical route toward the observation of extreme phenomena in a variety of wave systems, potentially applicable to both quantum and classical settings without multilayered fabrication requirements.

Materials based on minimal surface geometries have shown superior strength and stiffness at low densities, which makes them promising continuous-based material platforms for a variety of engineering applications. In this work, it is demonstrated how these mechanical properties can be complemented by dynamic functionalities resulting from robust topological guiding of elastic waves at interfaces that are incorporated into the considered material platforms. Starting from the definition of Schwarz P minimal surface, geometric parametrizations are introduced that break spatial symmetry by forming 1D dimerized and 2D hexagonal minimal surface-based materials. Breaking of spatial symmetries produces topologically non-trivial interfaces that support the localization of vibrational modes and the robust propagation of elastic waves along pre-defined paths. These dynamic properties are predicted through numerical simulations and are illustrated by performing vibration and wave propagation experiments on additively manufactured samples. The introduction of symmetry-breaking topological interfaces through parametrizations that modify the geometry of periodic minimal surfaces suggests a new strategy to supplement the load-bearing properties of this class of materials with novel dynamic functionalities.

The acoustic properties of an acoustic crystal consisting of acoustic channels designed according to the gyroid minimal surface embedded in a 3D rigid material are investigated. The resulting gyroid acoustic crystal is characterized by a spin-1 Weyl and a charge-2 Dirac degenerate points that are enforced by its nonsymmorphic symmetry. The gyroid geometry and its symmetries produce multi-fold topological degeneracies that occur naturally without the need for ad hoc geometry designs. The non-trivial topology of the acoustic dispersion produces chiral surface states with open arcs, which manifest themselves as waves whose propagation is highly directional and remains confined to the surfaces of a 3D material. Experiments on an additively manufactured sample validate the predictions of surface arc states and produce negative refraction of waves at the interface between adjoining surfaces. The topological surface states in a gyroid acoustic crystal shed light on nontrivial bulk and edge physics in symmetry-based compact continuum materials, whose capabilities augment those observed in ad hoc designs. The continuous shape design of the considered acoustic channels and the ensuing anomalous acoustic performance suggest this class of phononic materials with semimetal-like topology as effective building blocks for acoustic liners and load-carrying structural components with sound proofing functionality.

The discovery of topological gapless phases challenges the perception that topological features necessarily require a bandgap, expanding the understanding of topological phases of matter in various realms including electric, photonic, and phononic systems. The progress on 3D topological gapless states in elastic and acoustic systems is still in its early stages of formulation and design. We here investigate 3D acoustic gyroid crystals supporting symmetry-enforced gapless surface states in minimal surface-based structures. The inherent chirality and morphology of gyroid surfaces enable the implementation of 3D acoustic crystals hosting symmetry-enforced Dirac points and topologically gapless surface states. The associated fourfold degeneracy is protected by the nonsymmorphic space group featuring a combination of screw symmetry and glide reflections. The presence of gapless surface arcs relies on band structure calculations conducted using finite element simulations, while preliminary experimental results on additively manufactured samples validate their occurrence in the proposed gyroid surfaces. With the continuous development in additive manufacturing techniques, the presented surface-based framework provides a platform to explore a variety of topological wave physics phenomena in 3D load-bearing, continuum materials of potential engineering relevance, among which superior acoustic absorption may be particularly promising.

We investigate the dynamics and topology of metastructures with quasiperiodically modulated local resonances. The concept is implemented on a LEGO beam featuring an array of tunable pillar-cone resonators. The versatility of the platform allows the experimental mapping of the Hofstadter-like resonant spectrum of an elastic medium, in the form of a beam waveguide. The non-trivial spectral gaps are classified by evaluating the integrated density of states of the bulk bands, which is experimentally verified through the observation of topological edge states localized at the boundaries. Results also show that the spatial location of the edge states can be varied through the selection of the phase of the resonator's modulation law. The presented results open new pathways for the design of metastructures with functionalities going beyond those encountered in periodic media by exploiting aperiodic patterning of local resonances and suggest a simple, viable platform for the observation of a variety of topological phenomena.

Improving photosynthesis and light capture increases crop yield and paves a sustainable way to meet the growing global food demand. Here we introduce a spectral-shifting microphotonic thin film as a greenhouse envelope that can be scalably manufactured for augmented photosynthesis. By breaking the intrinsic propagation symmetry of light, the photonic microstructures can extract 89% of the internally generated light and deliver most of that in one direction towards photosynthetic organisms. The microphotonic film augments lettuce production by more than 20% in both indoor facilities with electric lighting and in a greenhouse with natural sunlight, offering the possibility of increasing crop production efficiency in controlled environments.

Photoacoustic imaging, an acoustic imaging modality with potentially optical resolution in an optical turbid medium, has attracted great attention. However, the convergence of wavefront optimization and raster scanning in computational photoacoustic imaging leads to the challenge of fast mapping, especially for a spatial resolution approaching the acoustic deep-subwavelength regime. As a sparse sampling paradigm, compressive sensing has been applied in numerous fields to accelerate data acquisition without significant quality losses. In this work, we propose a dual-compressed approach for photoacoustic surface tomography that enables high-efficiency imaging with 3D spatial resolution unlimited by the acoustics in a turbid environment. The dual-compressed photoacoustic imaging with single-pixel detection, enabled by spatially optical modulation with synchronized temporally photoacoustic coding, allows decoding of the fine optical information from the modulated acoustic signal even when the variance of original photoacoustic signals is weak. We perform a proof-of-principle numerical demonstration of dual-compressed photoacoustic imaging, that resolves acoustic sub-acoustic-wavelength details with a significantly reduced number of measurements, revealing the potential for dynamic imaging. The dual-compressed concept, which transforms unobtrusive spatial difference into spatio-temporal detectable information, can be generalized to other imaging modalities to realize efficient, high-spatial-resolution imaging.

Photon scattering imposes a fundamental restriction on optical imaging in turbid media. In this work, we propose a compressive-sensing-based photoacoustic imaging modality that allows single-shot tomography with a single detector in a scattering medium. The nonuniform optical speckle grains created in the diffusive regime, which act as a conventional drawback of optical modality, are used to generate ultrasound locally. The photoacoustic signals from spatial positions can be well extracted from a superimposed signal via introduction of locally modulated time delays. Taking advantage of the compressed measurement assisted by the acoustic mask, we demonstrate a theoretical compressed framework of three-dimensional photoacoustic surface tomography with a broad field of view after one-time optical illumination. This approach can increase the photoacoustic imaging efficiency greatly and reveals the potential for dynamic imaging in optically diffusive media.

The discovery of topological phases of matter, initially driven by theoretical advances in quantum condensed matter physics, has been recently extended to classical wave systems, reaching out to a wealth of novel potential applications in signal manipulation and energy concentration. Despite the fact that wave propagation in many realistic media (metals at optical frequencies, polymers at ultrasonic frequencies) is inherently dispersive, topological wave transport in photonic and phononic crystals has so far been limited to ideal situations and proof-of-concept experiments involving dispersionless media. Here, we report the first experimental demonstration of topological edge states in a classical water wave system supporting highly dispersive wave propagation, in the intermediate regime of gravity-capillary waves. We use a stochastic method to rigorously take into account the inherent dispersion and devise a water wave crystal insulator supporting valley-selective transport at topological domain walls. Our measurements, performed with a high-speed camera under stroboscopic illumination, unambiguously demonstrate the possibility of valley-locked transport of water waves.

To improve the focused ultrasonic beam induced by laser phased array (LPA), the superiority of an improved LPA distribution with conjunction of geometric attenuation and directivity functions of the stimulated ultrasonic beams are investigated theoretically instead of only considering the directivity function. Numerical simulations for the generation of focused longitudinal waves in the thermoelastic regime were implemented to reveal the advantages of the improved LPA design. It is shown that the amplitude of the focused beam increased by 42.1%, and the rise time reduced by 25.0%, as well as spatial sizes narrowed by 50.6% and 41.9% in longitudinal and transverse directions, respectively. In addition, the thermal expansion superposition caused by adjacent laser pulses, which deteriorates the focusing features of the focused beam, should be avoided by setting proper spacing of LPA.

As an essential necessity for fundamental study and a broad variety of technological applications, it is important to control the propagation of acoustic waves and select their particular wavefronts. This work is to achieve effective wavefront shaping of acoustic waves along specific paths in strongly scattering media including phononic periodic structures and random media. In the phononic crystal, a kind of artificial phononic structures, wavefront shaping, and super-resolution imaging have been achieved by designing the geometry and material parameters. Furthermore, the confocal technique of the optical beam and acoustic beam has been improved to achieve sub-wavelength imaging in random media with strongly scattering. The presented results of wavefront shaping have implications for tailoring phonon dynamics in scattering media, which offers further possibilities of controllable acoustic waves in complex materials and enlightens the interaction of multi-physics fields.