General three-dimensional thermal illusion metamaterials

Thermal illusion aims to create fake thermal signals or hide the thermal target from the background thermal field to mislead infrared observers,and illusion thermotics was proposed to regulate heat flux with artificially structured metamaterials for thermal illusion.Most theoretical and experimental works on illusion thermotics focus on two-dimensional materials,while heat transfer in real three-dimensional(3D)objects remains elusive,so the general 3D illusion thermotics is urgently demanded.In this study,we propose a general method to design 3D thermal illusion metamaterials with varying illusions at different sizes and positions.To validate the generality of the 3D method for thermal illusion metamaterials,we realize thermal functionalities of thermal shifting,splitting,trapping,amplifying and compressing.In addition,we propose a special way to simplify the design method under the condition that the size of illusion target is equal to the size of original heat source.The 3D thermal illusion metamaterial paves a general way for illusion thermotics and triggers the exploration of illusion metamaterials for more functionalities and applications.

Multiple control of thermoelectric dual-function metamaterials

Thermal metamaterials based on transformation theory offer a practical design for controlling heat flow by engineering spatial distributions of material parameters,implementing interesting functions such as cloaking,concentrating,and rotating.However,most existing designs are limited to serving a single target function within a given physical domain.Here,we analytically prove the form invariance of thermoelectric(TE)governing equations,ensuring precise controls of the thermal flux and electric current.Then,we propose a dual‐function metamaterial that can concentrate(or cloak)and rotate the TE field simultaneously.In addition,we introduce two practical control methods to realize corresponding functions:one is a temperature‐switching TE rotating concentrator cloak that can switch between cloaking and concentrating;the other is an electrically controlled TE rotating concentrator that can handle the temperature field precisely by adjusting external voltages.The theoretical predictions and finite‐element simulations agree well with each other.This work provides a unified framework for manipulating the direction and density of theTE field simultaneously and may contribute to the study of thermal management,such as thermal rectification and thermal diodes.

Thermal Magnifier and Minifier

For thermal conduction cases,one can detect the size of an object explicitly by measuring the temperature distribution around it.If the temperature is the only signature we can obtain,we will give an incorrect judgment on the shape or size of the object by disturbing the distribution of it.According to this principle,in this article,we develop a transformation method and design a dual-functional thermal device,which can create a thermal illusion that the object inside it ＂seems＂ to appear bigger or smaller than its original size.This device can functionally switch among magnifier and miniGer at will The proposed device consists of two layers：the cloak and the complementary material.A thermal cloak can make the internal region thermally ＂invisible＂ while the complementary layer offsets this effect.The combination leads to the illusion of magnification and minification.As a result of finite element simulations,the performances of the illusions are confirmed.