Yu-Gui Peng

Tomography enables volumetric visualization of internal structures with high fidelity, which has transformed diverse fields of science and engineering. Ultrasound tomography, in particular, provides radiation‐free, real‐time, and low‐cost imaging. Conventional linear and planar array designs typically impose inherent limits on aperture, coverage, and resolution, hindering accurate imaging of deep structures. Here, we present an active and programmable circular meta‐array of 2048 channels integrated with cylindrical acoustic lenses, generating a wide‐angle point‐source radiation in plane and a thin flat sound‐sheet beam out of plane. This configuration delivers omnidirectional homogeneous coverage and dynamic focusing, allowing comprehensive full‐matrix echo acquisition. Based on the circular meta‐array, subwavelength resolution ultrasonic images (∼0.8λ) are obtained with delay multiply and sum reconstruction. Extending to the volumetric tomography, the acoustic system reconstructs complex 3D objects and resolves human soft tissues and musculoskeletal structures. Our work provides a versatile platform for ultrasound tomography and opens an avenue for various advanced applications in biomedical imaging and therapeutic monitoring.

Flat bands have emerged as a cornerstone of contemporary condensed matter physics, with promising applications in photonic and phononic crystals that have garnered significant attention. In three-dimensional (3D) crystals, flat bands can be realized through Landau levels (LLs) induced by synthetic magnetic fields with crystal lattice distortions, forming partially flat bands that nevertheless become dispersive around the boundaries and surfaces. However, the realization of ideal non-dispersive LLs in 3D systems remains elusive thus far. Here, for the first time, we propose a general model to generate all-flat bands (AFBs) in 3D systems and experimentally demonstrate the exotic wave-matter interactions with 3D acoustic Fock-state lattices. Notably, this framework can be generalized to other wave systems, such as photonics and electronics. Our findings not only resolve controversies regarding the existence of non-dispersive LLs, but also advance the explorations of flat bands and quantized physics in classical wave systems, providing new possibilities for high-Q detection and energy harvesting applications.

Acoustic tweezers harness the mechanical effects of ultrasound to achieve contact-free manipulation of micro/nanoparticles. In acoustofluidics, standing-wave tweezers were widely adopted for particle trapping and translation due to their facile implementation and on-chip integrability. However, those conventional standing-wave fields, typically generated by transducer pairs, exhibit limited manipulation flexibility owing to their simplistic field configurations. Here, we demonstrate topological mass transport along arbitrarily designed trajectories by constructing localized and tunable standing-wave fields based on valley interface states. Precise phase modulation of incident waves enables efficient particle conveyance through continuous displacement of standing-wave pressure nodes or antinodes, leveraging the radiation forces from topologically protected standing waves in scattering systems. Experimental results confirm that such topological tweezing and circulating effect enables robust mass transport, showing antibackscattering characteristics and immunity against various structural defects such as sharp corners or cavities. Our work establishes a foundational paradigm for investigating the radiation forces in topological acoustic fields and advances the development of acoustofluidics technologies.

The exploration of non-Hermitian effects is essential for advancing both the theoretical understanding and practical applications of fundamental physics, and has garnered significant attention in the past few decades. The non-Hermitian skin effect (NHSE), when combined with other physical mechanisms, enables flexible and intriguing manipulation of wave transport. Recent theoretical study demonstrates that a distinctive non-Hermitian Hamiltonian with real eigenvalues can be constructed, enabling the emergence of the selective skin effect. Here, we verify that the selective non-Hermitian skin effect can be induced by cooperative interaction between the skin effect and localization modes, characterized by a reinforced skin state in the zero mode. With delicately designed parameters, we further visualize the selective NHSE via full-wave simulations and experiments in acoustic ring lattices. Our results enrich the perspectives of non-Hermitian effects research and expand the avenues for wave manipulation, offering insights into potential acoustic device applications such as energy harvesting and sensing.

Overcoming the diffraction limit has been a long-lasting pursuit for researchers owing to the great potential it offers in going beyond the fundamental resolution restriction in imaging processes. In acoustics, meta-lenses have been a promising way to achieve sub-wavelength imaging, the practical application of which, however, has been limited by expensive material manufacturing, complex system setup, and material loss. Here, we propose a set of procedures equivalent to a virtual super-lens that selectively amplifies the evanescent wave components in the measured acoustic field spectrum, thereby enabling super-resolution imaging without any auxiliary setups or purposely designed super-lens. The proposed virtual super-lens is experimentally verified by considering the imaging of an irregularly shaped sample with sub-wavelength features. We further demonstrate the robustness of the high-quality imaging performance remains acceptable with some environment background noises. In the light of the simple experimental setup involved, our proposed method is flexible and can be readily applied to various practical imaging scenarios.