:<math> \varepsilon (\omega) = \varepsilon_\infty + \sum_{p=1}^N \dfrac{\Delta \varepsilon_p}{1 + j\omega \tau_p}, \quad \Delta \varepsilon_p = \varepsilon_{sp} - \varepsilon_\infty </math>
where <math>\varepsilon_{\infty}</math> is the value of the permittivity at infinite frequency, <math>\tau_p</math> is the relaxation time corresponding to the p''th'' pole having the unit of seconds, and <math>\varepsilon_{sp}</math> is the value of the static permittivity (at DC) corresponding to the p''th'' pole. <math>\Delta \varepsilon_p = \varepsilon_{sp} - \varepsilon_{\infty}</math> represents the change in permittivity due to the p''th'' pole. Water has a Debye pole with parameters τ<sub>p</sub> = 9.4×10<sup>-12</sup> s, ε<sub>sps</sub> = 81 and ε<sub>∞</sub> = 1.8. In this example, we consider a laterally infinite slab of water with a finite thickness of 6mm. A periodic unit cell with lateral periods of 3mm along both X and Y directions are assumed.
Figure 1 shows the geometry setup for the periodic unit cell of the water slab in [[EM.Tempo]]. The top and bottom domain walls are assumed to be convolutional perfectly matched layers (PML). The periodic structure is excited using a normally incident plane wave source.