Acoustic metamaterials (AMMs) and phononic crystals (PCs) have garnered significant attention in recent years, as part of the collective driving force toward creating intelligent acoustic devices. Advancements in these fields have greatly enhanced the way we manipulate sound waves through transmission, reflection, refraction, absorption, diffraction, or attenuation. In the past decade, AMMs and PCs have enabled novel applications such as acoustic lensing, [1-3] cloaking, [4] levitation, [5] and holography. [6-8] While these exotic structures have been well explored through theoretical and numerical analysis, [9-13] their physical realization is an important topic that is rarely discussed. Considering the ubiquity of sound and the powerful capabilities of AMMs and PCs, the impact of these acoustic structures could be phenomenal. Across the full acoustic frequency spectrum, practical applications such as noise cancellation, [14] underwater detection, [15] medical imaging, [16] and energy harvesting [17,18] could benefit key sectors in our society like healthcare, well-being, environmental sustainability, and security. Moreover, AMMs and PCs can help to usher in next-generation technologies for personalized, immersive multisensory [19-22] experiences. The manipulation of sound can enrich the way we communicate and interact with our surroundings, not simply through audio, but also through tactile sensations. In the future, AMMs and PCs could be used in virtual reality (VR) setups, [23] compact wearable devices, and dynamic midair volumetric displays [24] that are controllable and capable of providing haptic feedback. [25] Beyond the notion that AMMs and PCs can replace phased arrays, they could readily complement one another for more precise control. In commercial devices, AMM and PC functionalities could even be combined together in different ways, e.g., transmissive and sound absorptive structures, for improved performance. To unlock the full potential of AMMs and PCs, it is therefore vital to ensure that practical, physical realization is pursued alongside theoretical investigation in the development of viable acoustic designs. Building an AMM or PC requires some form of fabrication or assembly or both. Fabrication refers to the technologies and processes used to manufacture an object, whereas assembly refers to the strategic amalgamation of parts for a constructive purpose.

Acoustic metamaterials (AMMs) and phononic crystals (PCs) have garnered significant attention in recent years, as part of the collective driving force toward creating intelligent acoustic devices. Advancements in these fields have greatly enhanced the way we manipulate sound waves through transmission, reflection, refraction, absorption, diffraction, or attenuation. In the past decade, AMMs and PCs have enabled novel applications such as acoustic lensing, [1][2][3] cloaking, [4] levitation, [5] and holography. [6][7][8] While these exotic structures have been well explored through theoretical and numerical analysis, [9][10][11][12][13] their physical realization is an important topic that is rarely discussed.Considering the ubiquity of sound and the powerful capabilities of AMMs and PCs, the impact of these acoustic structures could be phenomenal. Across the full acoustic frequency spectrum, practical applications such as noise cancellation, [14] underwater detection, [15] medical imaging, [16] and energy harvesting [17,18] could benefit key sectors in our society like healthcare, well-being, environmental sustainability, and security. Moreover, AMMs and PCs can help to usher in next-generation technologies for personalized, immersive multisensory [19][20][21][22] experiences. The manipulation of sound can enrich the way we communicate and interact with our surroundings, not simply through audio, but also through tactile sensations. In the future, AMMs and PCs could be used in virtual reality (VR) setups, [23] compact wearable devices, and dynamic midair volumetric displays [24] that are controllable and capable of providing haptic feedback. [25] Beyond the notion that AMMs and PCs can replace phased arrays, they could readily complement one another for more precise control. In commercial devices, AMM and PC functionalities could even be combined together in different ways, e.g., transmissive and sound absorptive structures, for improved performance. To unlock the full potential of AMMs and PCs, it is therefore vital to ensure that practical, physical realization is pursued alongside theoretical investigation in the development of viable acoustic designs.Building an AMM or PC requires some form of fabrication or assembly or both. Fabrication refers to the technologies and processes used to manufacture an object, whereas assembly refers to the strategic amalgamation of parts for a constructive purpose.

Conventional energy sources are continuously depleting, and the world is actively seeking new green and efficient energy solutions. Enormous amounts of acoustic energy are dissipated daily, but the low intensity and limited efficiency of current harvesting techniques are preventing its adoption as a ubiquitous method of power generation. Herein, a strategic solution to increase acoustic energy harvesting efficiency using a specially designed metamaterial is implemented. A scalable transmissive labyrinthine acoustic metamaterial (LAM) is designed, developed, and employed to maximize ultrasound (40 kHz) capture over its large surface area (>27 k mm2), which is focused onto a piezoelectric film (78.6 mm2), thus magnifying incident sound pressure by 13.6 times. Three different piezoelectric films – two commercial and one lab‐made nanocomposite film are tested with LAM in the acoustic energy harvesting system. An extraordinary voltage gain of 157–173% and a maximum power gain of 272% using the LAM compared to the case without the LAM are achieved. Multipoint focusing using holographic techniques, showcasing acoustic patterning to allow on‐demand simultaneous harvesting in separate locations, is demonstrated. Our versatile approach for high‐intensity acoustic energy harvesting opens future opportunities to exploit sound energy as a resource to contribute toward global sustainability.

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It is highly desirable to engineer multiple operational states in a single metamaterial device. Here, we present a powerful approach to transform a conventionally passive metamaterial into an actively reconfigurable metamaterial, using dynamic standalone unit cells, called dynamic meta-bricks. These 3D-printed meta-bricks comprise an actuatable internal magnetorheological elastomeric flap, designed for active ultrasonic (40 kHz) transmission and modulation. Computational assembly of dynamic and static meta-bricks generates controllable hybrid metamaterial stacks, within a composite metasurface. We demonstrate for the first time, dynamic acoustic levitation with a transmissive metasurface, showcasing that partial peripherally localised actuation, can enable full array operational dynamicity. Without re-assembly, actuating the dynamic meta-bricks shifts an acoustically trapped bead in mid-air in real-time, while maintaining acoustic levitation. This work uncovers the potential for strategic synergy between active and passive reconfigurability, opening novel possibilities to develop versatile, integrated, multifunctional metamaterials with enhanced degrees of freedom in design and control.