## 4 Results  
To analyze the resonance in the microwave chamber, the dependency of the distribution of the electromagnetic field strength \(H\) was calculated along the line in the \(Z\)-axis direction, as presented in Figure 5. Electromagnetic field strength \(H\) distributions are plotted as a function of both chamber's radius \(R\) and mesh parameter \(h_{max}\), presented in Figure 6. On the base of the results presented in Figure 6, the plots of resonant electromagnetic field strength \(H\) distributions are displayed in Figure 7.  
The presented results clearly indicate that meshing granularity \(h_{max}\) has a strong influence on the results of electromagnetic field strength \(H\) distribution on microwave chamber resonance. It should be highlighted that for different mesh granularity values of \(h_{max}\), resonance occurs for different positions on the line in the \(Z\)-axis of the resonant chamber. For mesh granularity \(h_{max}\) values between 8 mm and 20 mm, the parameter \(R\) varies from 170.25 mm to 171.00 mm.  
In addition, for higher mesh granularity \(h_{max}\), artefacts in the spatial distribution of maximal values of \(H\) occur. It can be observed in Figure 6 that for \(h_{max}=20\) mm, values of maximal \(H\) values near the centre of resonant chamber are smaller than near its edge. For smaller granularities (e.g., for \(h_{max}=8\) mm), the spatial distribution of values of amplitudes in the maxima of the \(H\) plot corresponds to the expected physical phenomena. Maxima of \(H\) values near the centre of the chamber are higher than near the edge of resonant chamber.  
The presented results may lead to significant confusion during modelling in the development of microwave resonant chambers for practical applications. The radius of the resonant chamber \(R\) is critical from a practical perspective; however, it is dependent on mesh granularity \(h_{max}\) in the model.  
Figure 8 presents the idea of overcoming this problem. It is evident that the required radius \(R\) of the resonant chamber is convergent to a given value as a function of mesh granularity parameter \(h_{max}\).  
Figure 5: A cross section of electromagnetic field strength distribution \(H\) inside the microwave resonant chamber; the value of electromagnetic field strength \(H\) was sampled along the white line (parallel to \(Z\) axis, 240 mm \(\leq z\leq\) 720 mm) for field analysis.  
Figure 6: Electromagnetic field strength \(H\) distributions dependent on chamber’s radius \(R\) and mesh granularity: (**a**) \(h_{max}\) = 8 mm, (**b**) \(h_{max}\) = 10 mm, (**c**) \(h_{max}\) = 12 mm, (**d**) \(h_{max}\) = 15 mm, (**e**) \(h_{max}\) = 20 mm.  
The results of modelling presented in Figure 8 clearly confirm that the required radius \(R\) of the microwave resonant chamber is equal to 170.75 mm. In addition, the influence of the accuracy of microwave resonant chamber dimensions on its effectiveness may be estimated from Figure 8.  
On the other hand, it should be indicated that a decrease of mesh granularity (connected with decreasing of parameter \(h_{max}\)) leads to an increase in the number of tetrahedral mesh elements in a third power proportion. As a result, reduction of the granularity of the model must be done carefully to avoid overcoming the computing power and memory resources of the available computer.  
In addition, the presented results clearly indicate that the height of the tetrahedral elements can be much bigger than the accuracy of estimation of the geometry of the resonant chamber. This effect relates to spatial averaging during the finite element method modelling. As a result, the efficient modelling of the microwave resonant chamber may be carried out with reasonable computing power and memory resources.