Acoustic focusing has extensive applications in medical ultrasound and nondestructive detection. The recent rapid development of acoustic metamaterials and metasurfaces has provided various mechanisms for designing advanced focusing lenses. However, the realization of acoustic focusing lenses with ultrabroad bandwidth still remains a challenge. To overcome it, ultrabroadband acoustic focusing lens based on phased unit cells composed of different numbers of same V‐shaped meta‐atoms is theoretically proposed and experimentally realized. By using eight types of unit cells, the fractional bandwidth of the acoustic lens can reach about 1.12 with a high focusing performance. Moreover, based on two types of unit cells with a phase difference of π, the fractional bandwidth of the focusing lens still reaches about 0.76 with the same criteria, showing a high robustness characteristic. The proposed acoustic focusing lenses have the advantages of ultrabroad bandwidths, simple fabrication and assembly, and high robustness, which provide diverse routes to construct ultrabroadband sound devices for medical ultrasound and nondestructive detection.

No abstract

The technique of sound insulation has a wide range of potential applications in environment noise control and architectural acoustics. The rapid development of acoustic artificial materials has provided alternative solutions to design sound insulation structures. However, the realization of single-layer planar structures with bidirectional acoustic insulation (BAI) and unidirectional acoustic insulation (UAI) still poses a challenge. Here, we report the theoretical and experimental realization of two types of single-layer phased array lenses which presents the characteristics of broadband BAI and multi-channel UAI. Both types of lenses consist of 12 mode-conversion phased units which are composed of two types of unit cells (I and II) with an opposite phase and a step waveguide. Based on the phase regulation, the designed phased unit can realize the mode conversion between the zero-order and first-order waves and asymmetric sound manipulation, which enables multi-functional sound insulations. Based on the desired theoretical phase profiles, two types of lenses with BAI and UAI are realized for the incidence of the zero-order wave, and their fractional bandwidths can reach about 0.28 and 0.37, respectively. More interestingly, the UAI effect can be reversed for the incidence of the first-order wave. The proposed lenses based on the mode-conversion phased units have the advantages of single-layer planar structure, multi-functional sound insulation, and broad bandwidth, which have wide application prospect.

With the rapid development of semiconductor technology, highly integrated circuits (ICs) and future nano-scale devices require large diameter and defect-free monocrystalline silicon wafers. The ongoing innovation from silicon materials is one of the driving forces in future micro and nano-technologies. In this work, the recent developments in the controlling of large diameter silicon crystal growth processes, the improvement of material features by co-doping with the intend-introduced impurities, and the progress of defect engineered silicon wafers (epitaxial silicon wafer, strained silicon, silicon on insulator) are reviewed. It is proposed that the silicon manufacturing infrastructure could still meet the increasingly stringent requirements arising from ULSI circuits and will expand Moore's law into a couple of decades.