Cloaking and Holography Experiments Using Immersive Boundary Conditions

Abstract

We report the experimental realization of real-time and broadband acoustic cloaking and holography by manipulating wave fields through their boundary conditions. The method of immersive boundary conditions (IBCs) enables us to virtually replace part of a physical experiment with a virtual computational environment. By introducing a source surface enclosing the virtual environment and calculating the source strengths in real time, the wave field in the physical experiment can be controlled such that incoming waves are suppressed and transmissions through the arbitrary virtual domain are radiated in a desired manner. A one-dimensional experiment shows that scattering objects can be made undetectable without prior knowledge about the incident wave field. Moreover, virtual objects or media can be emulated where they are not present-even objects or media exhibiting properties that do not occur in nature. Our results provide useful insights into how to implement IBCs for dynamic cloaking and holography, suggesting that higher-dimensional experiments are feasible.

Real-Time Immersion of Physical Experiments in Virtual Wave-Physics Domains

“…In this way, the physical laboratory and scatterers placed within it can be considered as the unit cell of an infinitely periodic lattice, leading to a range of unusual and exotic wave phenomena [36]. When interchanging the recording and emitting surfaces of the physicovirtual laboratory, the presented methodology can also be used for broadband acoustic cloaking and holography [32,[37][38][39][40], as has been presented in 1D experiments in Börsing et al [27]. This could be used to conceal objects from acoustic waves or to create acoustic illusions in real time and for arbitrary incident wave fields.…”

“…(A3) at faster-than-real wavepropagation speed, so the total latency between physically recording the wave field on S rec and applying the required boundary conditions on S emt needs to be smaller than the shortest physical travel time between the surfaces. This makes the design of the extrapolation and control system particularly challenging and as a result, to date only onedimensional (1D) immersive wave experimentation has been achieved, for which only a few control sources and receivers are required and the extrapolation reduces to a trivial sum [26][27][28]. To achieve immersive wave experimentation in higher dimensions, a tailor-made low-latency control system is constructed, which allows the extrapolation from 800 simultaneous analog input channels to 800 simultaneous analog output channels at a sample rate of 20 kHz in no more than 200 μs.…”

Bi-functional Metasurface Polarizer for Reflected and Transmitted Waves

“…Conventional approaches to manipulate the polarization state of light using birefringent crystals and grating structures are subject to bulky waveplates [14][15][16] , thus the inherent defects of the conventional polarizers are large geometry and low efficiency in natural materials, which are difficult to meet in the current miniaturization of microwave and optical system integration. Metamaterials (MMs) are artificially engineered planar materials that typically with sub-wavelength periodic structures 17,18 , which exhibit EM properties not existed in nature, such as negative refraction 19,20 , perfect absorbers 17,21 , and electromagnetic cloaking 22,23 . Metasurface (MS) is a kind of two-dimensional MM, which not only possesses the exotic EM characteristics not existed in nature metamaterials, but also has the advantages of design, fabrication and integration compared to the MMs.…”

Elastic immersive wave experimentation: Theory and physical implementation

“…Furthermore, IWE alleviates the necessity of downscaling the samples under study, in turn reducing assumptions about frequency dependent wave phenomena, such as attenuation or dispersion [7][8][9]. Finally, the possibility to implement virtually any kind of boundary conditions, or virtual domains with arbitrary mechanical or acoustic properties (e.g., media with gain or negative constitutive parameters over a broad frequency range), offers new possibilities in the emerging fields of metamaterials [10,11], parity-time symmetry [12], as well as holography and cloaking [13,14]. Especially in these fields, the possibility to circumvent the difficulty of building materials with the desired properties will make practical realizations of theoretical proposals possible.…”