Optimizing microwave transmission into a water-filled high-pressure reactor

Microwave energy transmission from a coaxial line into a water-filled high-pressure reactor through a sapphire window is investigated numerically at 2.45 GHz. The FDTD method is implemented in cylindrical co-ordinates to compute the normalized electric field along the coaxial line and to extract reflection coefficients. The magnitude of reflection coefficient |Γ| measured for a window of diameter 25.4 mm and thickness 6.35 mm is 0.7268 for water at 25°C. This parameter is reduced to a minimum value of 0.5627 using a movable PTFE sliding slug inside the coaxial feed. A parametric study of the effect of varying window diameter or window thickness on |Γ| is also undertaken. The results obtained indicate that the return loss from the reactor is minimized when the window diameter is 23 mm and that it falls slowly with decrease in window thickness.