Novel thermal lens for remote heating/cooling designed with transformation optics

Shifty invisibility cloaks

We recently presented what we believe are new cloaking strategies [Bělín et al., Opt. Express27, 37327 (2019)10.1364/OE.27.037327], abstracted from the properties of an ideal-lens cloak that exists in theory only. Key to the cloaking strategies is that objects on the cloak's inside are imaged to its outside. In the simplest case, interior objects appear simply shifted, forming a "shifty cloak". Here we connect our work to several previous investigations of shifty cloaks and other shifty devices, designed using standard transformation optics, thereby bringing our cloaking strategies closer to experimental realization. We investigate to the best of our knowledge novel combinations of shifty cloaks, specifically Janus devices and optical wormholes. Finally, we demonstrate an experimental realization of a paraxial shifty cloak.

Effective medium theory for thermal scattering off rotating structures

Controlling heat transfer with artificial functional materials has been a promising route towards the efficient and smart utilization of thermal energy in modern society. At the macroscopic scale, thermal metamaterials have demonstrated versatile functionalities in manipulating thermal conduction. One major method is the effective medium theory, which provides a reliable approximation for the material parameters of the composite. Although most of thermal metamaterials use static components, recent devices with integrated moving parts are attracting great interest thanks to their high efficiency and flexibility. However, the effective medium theory for thermal scattering off such devices has not been well established, due to the fundamental difference between thermal convection and conduction. Here, we provide a thorough study on heat transfer through mechanically rotating structures. It is shown that the effective thermal conductivity of a rotating structure can be rigorously described in a complex plane. The analytical expressions of the effective thermal conductivity for structures with rotating multiple layers are formulated, which explicitly capture their influences on the surrounding temperature field. We validate the theory and numerically demonstrate the rotated and unrotated temperature distributions generated around a single structure. Our theory is expected to become a design recipe for novel thermal metamaterials and meta-devices.

Manipulating cell: flexibly manipulating thermal and DC fields in arbitrary domain

To extend the metamaterial applications on simultaneously regulating multiple fields with transformation optics, we propose a class of manipulative cell here to manipulate thermal and DC fields simultaneously in non-conformal angular schemes. Significant behaviors of thermal cloaking, electrical concentration, and related switched functions are numerically demonstrated with appropriate media. The findings not only present an efficient method for simultaneously manipulating various energy, but also break the limitation of structural profiles in the designs of bi-functional meta-device. Moreover, it may also provide references for efficient energy manipulation and management in conventional energy techniques.

Encrypted Thermal Printing with Regionalization Transformation

Artificially structured thermal metamaterials provide an unprecedented possibility of molding heat flow that is drastically distinct from the conventional heat diffusion in naturally conductive materials. The Laplacian nature of heat conduction makes the transformation thermotics, as a design principle for thermal metadevices, compatible with transformation optics. Various functional thermal devices, such as thermal cloaks, concentrators, and rotators, have been successfully demonstrated. How far can it possible go beyond just realizing a heat-distribution function in a thermal metadevice? Herein, the concept of encrypted thermal printing is proposed and experimentally validated, which could conceal encrypted information under natural light and present static or dynamic messages in an infrared image. Regionalization transformation is developed for structuring thermal metamaterial-strokes as infrared signatures, enabling letters of the alphabet to be written, paintings to be drawn, movies to be made, and information to be displayed. This strategy successfully demonstrates an extreme level of manipulation of heat flow for encryption, illusions, and messaging.

Arbitrarily shaped thermal cloaks with non-uniform profiles in homogeneous media configurations

We propose a novel class of "complete" arbitrary thermal cloaks through rotatory linear maps. Different from the conventionally circular and arbitrary shape cloaks, as well as the unconventionally non-continuous shape cloaks, the proposed cloaking performances are observed in non-uniformly structural devices. Four schemes are demonstrated with homogeneous media configurations, and expected cloaking behaviors are exhibited in the internal regions. Further investigations reveal that the proposed devices perform robustness on the thermal profiles. The findings may also open up a novel avenue to generally achieve novel behaviors in the fields of optics, electromagnetics, and so forth.

Translational illusion of acoustic sources by transformation acoustics

An acoustic illusion of creating a translated acoustic source is designed by utilizing transformation acoustics. An acoustic source shifter (ASS) composed of layered acoustic metamaterials is designed to achieve such an illusion. A practical example where the ASS is made with naturally available materials is also given. Numerical simulations verify the performance of the proposed device. The designed ASS may have some applications in, e.g., anti-sonar detection.

Control and design heat flux bending in thermal devices with transformation optics

We propose a fundamental latent function of control heat transfer and heat flux density vectors at random positions on thermal materials by applying transformation optics. The expressions for heat flux bending are obtained, and the factors influencing them are investigated in both 2D and 3D cloaking schemes. Under certain conditions, more than one degree of freedom of heat flux bending exists corresponding to the temperature gradients of the 3D domain. The heat flux path can be controlled in random space based on the geometrical azimuths, radial positions, and thermal conductivity ratios of the selected materials.

Remote cooling by a novel thermal lens with anisotropic positive thermal conductivity

A novel thermal lens that can achieve a remote cooling effect is designed by transformation thermodynamics. The effective distance between the separate hot source and cold source is shortened by our shelled thermal lens without any negative thermal conductivity. Numerical simulations verify the performance of our thermal lens. Based on the effective medium theory, we also propose a practical way to realize our lens using two-layered isotropic thermal media that are both found in nature. The proposed thermal lens will have potential applications in remote temperature control and in creating other thermal illusions.