Bifunctional metamaterials with simultaneous and independent manipulation of thermal and electric fields

Abstract

Metamaterials offer a powerful way to manipulate a variety of physical fields ranging from wave fields (electromagnetic field, acoustic field, elastic wave, etc.), static fields (static magnetic field, static electric field) to diffusive fields (thermal field, diffusive mass). However, the relevant reports and studies are usually conducted on a single physical field or functionality. In this study, we proposed and experimentally demonstrated a bifunctional metamaterial which can manipulate thermal and electric fields simultaneously and independently. Specifically, a composite with independently controllable thermal and electric conductivity was introduced, on the basis of which a bifunctional device capable of shielding thermal flux and concentrating electric current simultaneously was designed, fabricated and characterized. This work provides an encouraging example of metamaterials transcending their natural limitations, which offers a promising future in building a broad platform for manipulation of multi-physics field.Usually, the realization of physical functionality means to manipulate and control the relevant physical fields in a desired way. To accomplish such a goal, various structures and geometries are designed based on available materials. However, the capacity and functional diversity are usually limited by the material it is made of. As a result, some desirable properties seem impossible to achieve with materials available at present. For example, a material with independently controllable thermal and electric conductivity is difficult to come 2 by. Once such material becomes available, numerous intriguing possibilities will be opened up and myriad novel applications will find their way into our life.The rapid development of metamaterials is beginning to bring such a bright future ever closer to us. Metamaterials actually are composites consisting of well-arranged subwavelength inclusions that can be considered as "effective" material. Compared with conventional materials which are synthesized at the molecular level, the novel conception of metamaterials are capable of tailoring material properties at a subwavelength level. What is more interesting, metamaterials derive their properties not from materials used in the process of fabrication, but from their designed structures. With all these novelties, metamaterials possess numerous exotic properties and promise many applications. Over the past years, metamaterials were widely used in manipulation of physical fields ranging from electromagnetic wave, [1][2][3] acoustic wave, [4] elastic wave [5] to matter wave. [6] Recently, metamaterial was introduced to control fields such as static magnetic field, [7][8][9][10][11] dc electric field, [12][13][14] thermal field, [15,16] electrostatic field [17] and diffusive field. [19][20] However, bifunctional or multifunctional metamaterials are rarely reported and studied. It is interesting to explore the possibility of creating novel metamaterials to achieve independently controllable thermal and electric cond...

Geometrical effects on the concentrated behavior of heat flux in metamaterials thermal harvesting devices

“…The heat transfer process for such thermal harvesting devices [11][12][13][14][15][16][17][18][19][20][21][22][23] can be presented by the rigorous theoretical model 8,9,16,24 as shown in Fig. 1.…”

“…κ 0 is the thermal conductivity of the surrounding. The profile of a thermal harvesting device [14][15][16][17][18][19][20][21][22][23][24][25] based on a spatial transformation can be separated into three parts including the background (Part I), concentrating region (Part II), and central region (Part III). In this view, heat transfer properties in the entire system can be deduced by rigorously solving the conduction function of the three parts under certain boundary conditions.…”

“…The form invariance of the heat diffusion equation after coordinate transformation led to the extension of TO to the thermal field to guide the design and experiments of thermal TO devices including thermal cloaks, [7][8][9][10][11][12][13] concentrators, [14][15][16][17][18][19][20][21][22][23][24][25] rotators, 26 camouflage, 27 and diodes. 28 With thermal TO devices, an active and efficient control of thermal energy can be achieved with a pre-designed profile and reasonable arrangement of metamaterials.…”

“…To realize local heat harvesting, alternative composite materials with a wedge-like structure (e.g., spoke, fan, and sensu) were widely adopted in previous studies. [14][15][16][17][18][19][21][22][23] The feasible method for fabricating a thermal concentrator is reversing the conductivity components 15 in the transformational domain, i.e., keeping the radial component considerably larger than the azimuthal component. Based on this concept, theoretical 3D thermal harvesting cells 16 have been demonstrated by employing naturally available materials with tunable anisotropy.…”

“…Furthermore, a type of dual-function thermal metamaterial was proposed by employing homogeneous isotropic materials and shape-memory alloys for realizing automatic switching between a thermal cloak and concentrator. 19 In recent years, TO-based thermal harvesting devices were extended to attain convergent heat transfer 33 via rotation and compression transformations, to design multifunctional metamaterials, [20][21][22][23] which manipulated Laplace fields (thermal and electric) 22 simultaneously, and to fabricate tunable unit-cell thermal shifters 34 by considering the heat flux bending 35,36 in the material layers. To concentrate the heat flux more effectively, the influence of conductivities 24 was investigated, and it showed that a larger conductivity ratio of the radial and azimuthal components ensured a better harvesting performance.…”