Study On Design, Optimization And Experiment Of Multilayered Thermal Cloak

As a new-type technology of heat management proposed recently, thermal metamaterials have attracted more and more attentions and thermal cloak is a typical case. Thermal cloak has enriched the cloak technologies, but it is in the start stage. The biggest bottleneck is the requirement of inhomogeneous, anisotropic and locally singular medium. Multilayered structure composed of isotropic constituents is a feasible choice to implement the thermal cloak, but this approximation method is restricted by simple shapes, monotonous design method, massive constituents. In order to implement thermal cloaking technology, it is important to conduct in-depth research into the theoretical design, experimental preparation and test of multilayered thermal cloak.Firstly, the approximation method of designing multilayered two-dimensional(2D) cylindrical thermal cloak is extended to design the multilayered structures of 2D cylindrical ones with cross-sections of ellipse and more complex shapes. According to the numerical simulations, the thermal cloaking effects of multilayered thermal cloaks are close to that of the perfect ones. The extended approximation method has provided an effective way for realizing thermal cloak with complex shape.Secondly, to overcome the monotony of design method, implicit transformation method is adopted to design the 2D cylindrical thermal cloak without knowledge of the coordinate transformation in advance. Two indexes are defined to quantify the thermal cloaking performance. Nonlinear coordinate transformations with different forms are established to design the multilayered structures. Results of heat-transfer simulations show that thermal cloaking performances of multilayered structures are directly influenced by the form of coordinate transformation which determines the distributions of heat flows in the cloak region. Through the active changing of form of coordinate transformation, the thermal cloaking performance of multilayered structure can be controlled and optimized. Two improved multilayered structures of 2D cylindrical thermal cloak are proposed, and both have good thermal cloaking performance.Finally, to reduce the number of constituents needed, multi-goal optimization is conducted to improve the multilayered structure of 2D cylindrical thermal cloak. A multilayered cloak with only six constituents and excellent performance is obtained. This multilayered cloak is prepared with six constituents found in existing material library and is tested under uniform heat flows. Experimental results show that the prepared multilayered cloak has good thermal cloaking effect both in steady state and in transients but its cloaking performance is dependent on working time. Furthermore, we find that higher convection significantly limits effectiveness of the heat flow control region, which means that the multilayered cloak may be better implemented in smaller surface area microelectronics applications where conduction is the dominant mode of heat transfer.