Equivalent Circuit Modeling of Wood at 12% Moisture Content
Keywords:Electrochemical Impedance Spectroscopy (EIS), electrical relaxation, contact resistance, corrosion test methods
AbstractElectrical impedance spectra (EIS) were collected from southern pine (Pinus spp.) wood equilibrated to 12% moisture content. Cylindrical graphite electrodes were embedded in the wood so that they met nearly end-to-end along a line parallel to the grain, and the EIS properties were characterized as functions of electrode spacing and electrode contact pressure at frequencies between 1 x 10-1 and 3 x 105 Hz. The data show a narrow distribution of relaxation times, which can be fit using a Debye model or, even better, a model with a constant phase element (CPE) in parallel with a resistor. The relaxation time is sensitive to contact pressure applied to the electrodes but not electrode spacing. The width of the CPE distribution is sensitive to electrode spacing but not contact pressure. On first inspection, the data suggest a finite contact resistance between wood and electrode, but further examination reveals that the "contact resistance" is an artifact caused by electrode fringe effects.
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