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Plasmonic metasurfaces supporting collective lattice resonances have attracted increasing interest due to their exciting properties of strong spatial coherence and enhanced light-matter interaction. Although the focusing of light by high-numerical-aperture (NA) objectives provides an essential way to boost the field intensities, it remains challenging to excite high-quality resonances by using high-NA objectives due to strong angular dispersion. Here, we address this challenge by employing the physics of bound states in the continuum (BICs). We design a novel anisotropic plasmonic metasurface combining a two-dimensional lattice of high-aspect-ratio pillars with a one-dimensional plasmonic grating, fabricated by a two-photon polymerization technique and gold sputtering. We demonstrate experimentally multiple resonances with absorption amplitudes exceeding 80% at mid-IR using an NA = 0.4 reflective objective. This is enabled by the weak angular dispersion of quasi-BIC resonances in such hybrid plasmonic metasurfaces. Our results suggest novel strategies for designing photonic devices that manipulate focused light with a strong field concentration.

As a unique kind of artificial periodic composite materials, phononic crystals have attracted the wide attention in recent years. Unremitting efforts have been made to investigate the potential existence of phononic bandgaps, which can be used to manipulate the propagation of acoustic/elastic waves. This paper proposes a new topology optimization algorithm to achieve the optimised bandgap structures of 3D phononic crystals based on fixed-grid finite element method (FEM) and evolutionary procedure. The maximum normalised gap ratio obtained is as large as 97% between the 12th and 13th order of bands, with the optimised structure of tungsten carbide spheres embraced in epoxy matrix. Symmetric unit cells for simple cubic (SC) lattice are presented for the specified bandgaps to validate the effectiveness of the proposed optimization algorithm for designing 3D phononic bandgap crystals. Meanwhile, the proposed topology optimization represents structures with clear topologies and smooth boundaries.

With the availability of multi-material additive manufacturing , topology optimization of a multi-material structure and the selection of candidate materials become increasingly important. This paper aims to develop a new multi-material topology optimization algorithm and propose the guidelines for the selection of candidate materials from the database. The multi-material design variables and their inequality relationship are built on volume fractions of multiple materials within each element. The multi-material design variables are relaxed and multiple floating projection constraints simulate their discrete constraints by pushing design variables towards 0 or 1. Meanwhile, their inequality relationship is enforced by their variation limits. The proposed multi-material topology optimization algorithm can be applied to the compliance minimization problem constrained by a single mass or multiple volumes, as demonstrated in numerical examples. This paper mainly focuses on a single mass constraint, and 2D and 3D numerical examples systematically demonstrate that an optimized design under a mass constraint achieves a lower compliance when more materials appear in the final design simultaneously. Furthermore, we establish an approach to predict the inclusion or exclusion of a material from the final design, and propose the conditions for the co-existence of candidate materials, which guide users to select candidate materials from the database.

Cylinders are the most widely used pneumatic components in pneumatic systems. It is of great significance to study the energy distribution and energy loss of energy consumption in the process of pneumatic systems. This paper establishes an analytical model of cylinder operation process. By introducing the concept of effective energy and air power and applying MATLAB/Simulink software simulation, The energy distribution and energy loss of the cylinder are calculated separately, and the main factors affecting the energy loss of the cylinder are analyzed. Finally, the experimental results are compared with the simulation results, and the theoretical model of energy distribution and energy loss of the cylinder presented in this paper is verified, it is of great significance to study the energy saving of cylinder.

Higher-order topological insulators (TIs) develop the conventional bulk-boundary correspondence theory and increase the interest in searching innovative topological materials. To realize a higher-order TI with a wide passband of one-dimensional (1D) and two-dimensional (2D) transportation modes, we design three-dimensional non-trivial and trivial sonic crystals whose combination mimics the Su–Schrieffer–Heeger model. The topological boundary states can be found at the interfaces, including the zero-dimensional corner state, 1D hinge state, and 2D surface state. The fabricated sample with the bent two-dimensional and one-dimensional acoustic channels exhibits the multidimensional sound propagation and verifies the mode transition among the complete bandgap, hinge mode, and surface mode. The bandwidth of the single-mode hinge state achieves a large relative bandwidth of 9.1% in which sound transports one-dimensionally without significant leak into the surfaces or the bulk. The higher-order topological states in the study pave the way for sound manipulation in multiple dimensions.

In this work, a helical structure with three spiral channels is employed to build the coding units of metalenses, which can provide high transmission efficiency with an arbitrary phase shift compared to air. The helical unit with the phase shift of π is used as logical unit 1, and the hollow tube filled with air is regarded as logical unit 0. By arranging these logical units in specific sequences, acoustic metalenses can achieve wave-field manipulation like acoustic focusing and splitting. The focusing efficiency as high as 41.5% is achieved. Meanwhile, the genetic algorithm is applied to seek the optimal arrangement of the bipartite units for 3D sound focusing. Simulations and experiments are conducted to demonstrate the proposed coding metalenses for molding the acoustic wave field in the desired manners.