Permittivity measurements of materials during heating by microwaves

Among experimental designs used to study microwave heating from a fundamental point of view, a simple robust and low-cost device is proposed to measure the permittivity of a test sample during irradiation. It works at 2450 MHz and its basic component is a six-port implemented in a rectangular waveguide. Before using the six-port as a reflectometer, without moving mechanical parts, the diode detectors of the six-port and the six-port itself are calibrated together with a sliding short circuit. The calibration takes into account all the unwanted reflections inside the device. The device was used with an applicator made for rod-shaped samples. To check it, measurements were made on water, lucoflex and polytetrafluoroethylene. An example of the type of results that can be obtained is given for moistened sand.