Thermal Conduction Measurements of Materials using Microwave Energy

Abstract

ABSTRACTWe have developed a new technique to measure the thermal conductivity of materials using microwave energy. A thermal wave is induced in a material of unknown thermal conductivity using a pulse of microwave energy. This energy is incident on one side of the material. The corresponding temperature rise of the opposite side of the material is measured. The thermal diffusivity of the material can then be determined in the same way as ‘laser flash’[1]. Some of the advantages of the microwave system are the relatively low cost of the magnetron compared to the high energy laser, easily variable pulse length, and accurate measurement of the reflected energy.The microwave system consists of a 2.45 GHz magnetron that is pulse modulated to energies as high as 10 J. A typical pulse lasts for 1 ms with rise and fall times of 10µs. This is achieved by a high voltage source (5 – 8 kV at 1 – 2 A), switched by a high power, rf transmitting tube connected in the filament circuit of the magnetron.