Experimental Apparatus for Measuring Ultralow Thermal Conductivity Structures

Abstract

Ultralow thermal conductivity materials play an important role in many applications such as space exploration and thermal insulation. One of the primary challenges in studying heat conduction in these materials is performing basic thermal conductivity measurements, because even a small amount of steady heating results in enormous temperature increases. While methods do exist to measure the thermal conductivities of macroscopic materials, these techniques are difficult to apply to the microscopic samples that are the only samples available for some materials. In this thesis, we describe an optical, non-contact experimental system for measuring ultralow thermal conductivities. The system we designed and built is a modified pump-and-probe system. With this system, we will be able to measure a sample as small as tens of microns without having physical contact between the tester and the sample. Different from a traditional pump-and-probe method, we used a pump laser with a very low repetition rate of a few hundred Hz, which can efficiently reduce the steady heating, and at the same time the transient heating is still enough to give a measurement result. In the following chapters, we will first discuss the background of this thesis, including a brief introduction to the manufacture of the nano-lattice and the principles of the pump-and-probe method. Then we will go through some calculations done during the design process of the apparatus. Finally, we will present the test results from the experiments and compare them against the simulation.