Data sharing 3 Multidir Plate from Omnidirectional flexural invisibility of multiple interacting voids in vibrating elastic plates.

In elasticity, the design of a cloaking for an inclusion or a void to leave a vibrational field unperturbed by its presence, so to achieve its invisibility, is a thoroughly analysed, but still unchallenged, mechanical problem. The ‘cloaking transformation’ concept, originally developed in electromagnetism and optics, is not directly applicable to elastic waves, displaying a complex vectorial nature. Consequently, all examples of elastic cloaking presented so far involve complex design and thick coating skins. These cloakings often work only for problems of unidirectional propagation, within narrow ranges of frequency, and considering only one cloaked object. Here, a new method based on the concept of reinforcement, achieved via elastic stiffening and mass redistribution, is introduced to cloak multiple voids in an elastic plate. This simple technique produces invisibility of the voids to flexural waves within an extremely broad range of frequencies and thus surpassing in many aspects all existing cloaking techniques. The proposed design principle is applicable in mechanical problems ranging from the micro-scale to the scale of civil engineering. For instance, our results show how to design a perforated load-bearing building wall, vibrating during an earthquake exactly as the same wall, but unperforated, a new finding for seismic protection.

在弹性力学领域，为内含物或孔洞设计隐身（cloaking）装置，使振动场不受该对象存在的扰动，从而实现其隐身效果，这是一个得到充分研究但仍未被完全攻克的经典力学问题。最初在电磁学与光学领域提出的“隐身变换（cloaking transformation）”理念，无法直接适用于具备复杂矢量特性的弹性波。因此，目前已公开的所有弹性隐身方案均涉及复杂的设计与厚包覆层。此类隐身装置往往仅能在窄频范围内针对单向传播的弹性波生效，且仅能实现单个被隐身对象的隐身效果。本研究提出一种基于增强理念的新方法，通过弹性刚度增强与质量重分布，实现弹性板内多个孔洞的隐身。该简易技术可使弹性板内的孔洞在极宽的频率范围内对弯曲波实现隐身，在诸多性能维度上优于现有所有隐身技术。所提出的设计原则适用于从微观尺度到土木工程尺度的各类力学问题。例如，本研究成果展示了如何设计带孔承重建筑墙体，使其在地震作用下的振动特性与完整无孔墙体完全一致，为抗震防护领域提供了全新的研究发现。