Thermal camouflage and cloaking can transform an actual heat signature into a pre-controlled one. A viable recipe for controlling and manipulating heat signatures using thermal metamaterials to empower cloaking and camouflage in heat conduction is demonstrated. The thermal signature of the object is thus metamorphosed and perceived as multiple targets with different geometries and compositions, with the original object cloaked.

Full control and manipulation of heat signatures: cloaking, camouflage and thermal metamaterials.

The recently introduced transformation-electromagnetics techniques provide a new methodology for designing devices that possess novel wave-material interaction properties. They are based on the form invariance of Maxwell's equations under coordinate transformations. These methods provide an extremely versatile set of design tools that employ spatial-coordinate transformations, where the compression and dilation of space in different coordinate directions are interpreted as appropriate scalings of the material parameters. The most famous transformation-optics device is the cloak of invisibility. However, a wide variety of other devices are also possible, such as field concentrators, polarization rotators, beam splitters, beam collimators, and flat lenses. In this paper, an overview of transformation-electromagnetics device design techniques is presented. The paper begins by introducing the underlying design principle behind transformation electromagnetics. Several novel transformation-based device designs are then summarized, starting with electromagnetic cloaks that have spherical shell or cylindrical annular shapes, More general cloaking designs of noncircular annular geometries are treated, and the application of cloaking to RF/microwave antenna shielding is also discussed. Following this, device designs that employ transformations that have discontinuities .on the domain boundary are presented. Unlike those used for cloaks, this type of transformation is capable of modifying the fields outside of the device. Examples of this type of transformation-electromagnetics device are presented, which include flat near-field and far-field focusing lenses, wave collimators for embedded sources (e.g., antennas), polarization splitters and rotators, and right-angle beam benders.

Transformation Electromagnetics: An Overview of the Theory and Applications

Inspired by recent demonstrations of metasurfaces in achieving reduced versions of electromagnetic cloaks, we propose and experimentally demonstrate source illusion devices to manipulate flexural waves using metasurfaces. The approach is particularly useful for elastic waves due to the lack of form invariance in usual transformation methods. We demonstrate compact and simple-to-implement metasurfaces for shifting, transforming, and splitting a point source. The effects are measured to be broadband and robust against a change of source positions, with agreement from numerical simulations and the Huygens-Fresnel theory. The proposed method is potentially useful for applications such as nondestructive testing, high-resolution ultrasonography, and advanced signal modulation.

Source Illusion Devices for Flexural Lamb Waves Using Elastic Metasurfaces.

Broadband and Broad-Angle Low-Scattering Metasurface Based on Hybrid Optimization Algorithm

http://ieeexplore.ieee.org/iel5/5176125/5187315/05187596.pdf

Geometrical Theory of Diffraction for Electromagnetic Waves

We experimentally demonstrate the first metamaterial "illusion optics" device - an "invisible gateway" by using a transmission-line medium. The device contains an open channel that can block electromagnetic waves at a particular frequency range. We also demonstrate that such a device can work in a broad frequency range.

Experimental realization of a broadband illusion optics device

We experimentally demonstrate the first metamaterial "illusion optics" device--an "invisible gateway" by using a transmission-line medium The device contains an open channel that can block waves at a particular frequency range We also demonstrate that such a device can work in a broad frequency range

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Experimental realization of a circuit-based broadband illusion-optics analogue.

A novel active terahertz imaging scheme based on the combination of fan-beam scanning and aperture synthesized reconstruction techniques is presented. In the horizontal direction, high resolution is obtained by the narrow side of the fan-beam based on real aperture focusing with special pillbox-like quasi-optics. In the vertical direction, high resolution is achieved by the aperture synthesized focusing techniques based on the broad side of the fan-beam. Appropriate focusing algorithms are proposed both for the single-frequency 2-D case and wideband 3-D imaging. With a 0.2-THz heterodyne transceiver, a prototype imager is developed and proof-of-concept experiments are performed. The experimental results on the resolution, specular reflection, and concealed threat objects detection are given in detail, which demonstrate the performance of the proposed imaging scheme and its potential application for fast personnel screening.

Terahertz Aperture Synthesized Imaging With Fan-Beam Scanning for Personnel Screening

Transformation optics is extended to the design of two-dimensional (2D) cloaks with non-conformal inner and outer boundaries. General and explicit expressions of the transformed medium parameters are derived, which are of the utmost importance in a cloak design procedure. A 2D cloak with irregular and non-conformal boundaries is designed as an example. Full-wave simulations combined with Huygens' Principle are applied to verify the invisibility of the cloak to external incident waves. All the theoretical and numerical results verify the effectiveness of the proposed method. The generalization in this Paper highly improves the flexibilities for cloak design.

Two-dimensional electromagnetic cloaks with non-conformal inner and outer boundaries.

In this paper, the wave equation based on phase shift migration technique is extended for terahertz 3-D imaging with quasi-optical transceivers. An analytical expression of the reconstructed 3-D point-spread function for targets under the illumination of a terahertz Gaussian beam was derived with this reconstruction technique. The quantitative relationship between the imaging quality and the parameters of the transmitted Gaussian beam was obtained, which provides a good criterion to be followed when designing the terahertz quasi-optical transceivers in the imaging systems. Moreover, the spatial sampling criterion was derived strictly which is also quantitatively related to the parameters of the transmitted Gaussian beam. Simulation results with fairly good agreement were given to verify the theoretical results derived in this paper. Finally, a monostatic prototype imager with a Gaussian beam transceiver was designed for the proof-of-principle experiments in 0.2-THz band. The 3-D imaging results of different targets and a mannequin with concealed threat objects were given to demonstrate the theoretical results obtained in this paper and the effectiveness of the 3-D terahertz image reconstruction for security applications.

Chao Li

Papers

Experimental realization of a broadband illusion optics device

Experimental realization of a circuit-based broadband illusion-optics analogue.

Terahertz Aperture Synthesized Imaging With Fan-Beam Scanning for Personnel Screening

Two-dimensional electromagnetic cloaks with non-conformal inner and outer boundaries.

Three-Dimensional Image Reconstruction of Targets Under the Illumination of Terahertz Gaussian Beam—Theory and Experiment