Simulation of cut off characteristics of 2.45 GHz microwave inside the open-ended conductor cylindrical pipe

For a realtime measurement of moisture contents and temperature profiles of a sample inside a microwave oven, Sensors and open-ended pipes are equipped to the microwave system, allowing to measure those parameters from other ends of the pipes. The main role of the pipes is to reduce the microwave wave from leaking out to the environment and the interference with measuring equipment. In this research, a model of a microwave system with five installed pipes is simulated using COMSOL Multiphysics. The microwave cavity is modelled to be a cube with equal lengths of 33 cm. A pipe with diameter of 1.5 cm is installed on the top of the microwave and the other four pipes with diameter of 2.5 cm are installed at the bottom. The system is designed so that an infrared sensor can be attached to one end of the top pipe to measure temperature and a load cell is equipped under the bottom four pipes to measure the moisture content. The simulation result shows an exponential decay of electric field norm along the pipes away from the microwave chamber. For the pipes with diameters of 1.5 cm and 2.5 cm, the microwave wave is reduced to virtually zero at the distance of 3 cm and 4 cm away from the chamber, respectively.