Verification of wood permittivity spectra using the Kramers ??? Kronig relation

Spectra of the complex permittivity of spruce (Picea obovata), obtained by capacitor, resonator and free space techniques in the frequency range 100 kHz - 500 GHz are presented. Data from the literature containing information about the permittivity spectra of these wood, are presented. Kramers-Kronig relation can be used to adjust the measurements of the complex permittivity subject to the availability of experimental data in three important regions of the spectrum: near zero frequency, in the anomalous dispersion region and near the optical range.