Development of packaging and products
for use in microwave ovens
Chapter 20: Modelling of excitation in domestic microwave ovens
Abstract: The present Chapter is concerned with modelling of excitation in real life microwave ovens. This is in extension to Chapter 18, where the computational model is truncated within the waveguide connecting the oven to the source, and the actual source is represented by the fundamental waveguide mode, assumed to have a well-defined frequency (or frequency range) and amplitude. In the first major part of this Chapter we summarise the uncertainties associated with the frequency spectrum of signals generated by magnetrons in domestic ovens. We further show how those uncertainties can be taken into account in deterministic modelling of the oven scenarios. Specifically, we propose an efficient time-domain approach, which allows one to generate load heating patterns and to calculate the overall oven efficiency in a single simulation performed in response to a Gaussian pulse whose spectrum mimics that of the magnetron. In the final part, we refer to new oven design perspectives associated with solid state sources and discuss several modelling regimes that make such design work easier and faster.
Examples illustrated and referred in the Chapter:
Pulse_spectrum

Simulation projects and results of a simple microwave cavity with sandwich. Simulation scenarios allow investigating:
- Spectrum of the power available from the source obtained for excitation with a Gaussian pulse, depending on the width of 3dB bandwidth of the pulse.
- Distribution of energy density dissipated in the sandwich over the pulse duration, depending on the width of 3dB bandwidth of the pulse.
- Value of energy available from the pulse and energy dissipated in the sandwich over the pulse duration, depending on the width of 3dB bandwidth of the pulse.
FD-Monitors

Simulation project and results of a simple microwave cavity with sandwich showing the usage of frequency domain monitors (FD-Monitors) for obtaining distribution of power dissipated in a sandwich. FD-Monitor allow calculating space distributions of power dissipated in a sandwich at several frequencies (Fig. 20.6) during excitation with one pulse (from a single EM simulation).
Oven_with_sandwich

Simulation projects and results of a simple microwave cavity with sandwich, fed by two sources placed on the opposite walls of the cavity, working simultaneously. Simulation scenarios consider the sources excited in phase and out of phase allowing for investigating the dependence of relative phase shift between sources on the effective distribution of power dissipated in the sandwich.
Oven_with_potato

Simulation projects and results of a simple microwave cavity with potato, fed by two sources placed on adjacent walls, working simultaneously. Simulation scenario allows for changing the phase shift between the two sources and observing the dependence of the reflection characteristic obtained for each source independently (accounting for interference from the second source)  on the relative phase shift between them (Fig. 20.15).