Geometrical considerations in the control and manipulation of conductive heat flux in multilayered thermal metamaterials

Abstract

We indicate the fundamental rationale underlying the control of temperature and the manipulation of thermal flux, with reference to a multilayered composite material. We show that when the orientation of the layers in the composite is physically rotated with respect to a constant temperature gradient, there would then be a corresponding introduction of off-diagonal components in the thermal conductivity tensor and thermal anisotropy is induced. The consequent bending of the heat flux lines is found to depend on both the (i) composite rotation angle, as well as the (ii) ratio of the thermal conductivities of the constituent materials.

Analytical investigations on the thermal properties of microscale inorganic light-emitting diodes on an orthotropic substrate

“…[4][5][6][7][8][9] When such µ-ILEDs are integrated with the biological tissue, the heat dissipation in the substrate is uniform in all directions and the maximum temperature increase in the tissue is located at the substrate/tissue interface. The recent work on thermal metamaterials, [10][11][12] consisting of layered metal and polymer materials, shows that the heat flow can be guided to yield orthotropic thermal conductivities along in-plane and off-plane directions. This orthotropic feature provides a novel route to further reduce the adverse thermal response of µ-ILEDs by controlling the heat dissipation along the in-plane directions much more than that along the off-plane direction (to the tissue).…”

“…Let k 1 and k 2 denote the thermal conductivity of layered material 1 and material 2 in the substrate, respectively. The effective thermal conductivity along x, y and z directions of the substrate can be obtained by 10 k substrate…”

“…The thermal conductivities are 0.2W/m/K, 0.17W/m/K and 237W/m/K for SU8, PDMS and Aluminum. 10 The thicknesses of the encapsulation layer and substrate are 7µm and 2mm, respectively. The in-plane dimension of the encapsulation and substrate is 12mm×12mm with the side surfaces adiabatic.…”

A concept of heat dissipation coefficient for thermal cloak based on entropy generation approach

“…14 Different multi-layers cloaking schemes with large gradient of thermal conductivities was reported. [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] A 2D micro-structured thermal cloak has been fabricated and experimentally demonstrated. 15 The thermal conductivity in the distorted coordinates [16][17][18][19][20] and the mechanism of predefined heat flux paths are further researched.…”

“…15 The thermal conductivity in the distorted coordinates [16][17][18][19][20] and the mechanism of predefined heat flux paths are further researched. [21][22][23][24] Considering the difficulty in fabricating a 3D cloak, the study of 3D thermal cloaks has a late start. Xu and co-workers 25 designed an ultrathin 3D thermal cloak on the basis of Ref.…”