Dielectric characterization of wood and wood infiltrated with ceramic precursors

Wood has an anisotropic microstructure with 50–80 vol.% porosity, which we show is detectable by dielectric measurements. The dielectric properties of various types of wood were measured as a function of the grain orientation of the wood. The grain structure consists of wood fibers and void space in an arrangement containing longitudinal and radial pores. Measurements were conducted parallel to the longitudinal, radial and tangential directions of the wood structure at frequencies ranging from 200 Hz to 10 MHz. Significant differences were observed between the three directions. These differences were attributed to the arrangement of the pores and accounted for in two new mixing-rule equations. A series of wood samples was infiltrated with a ceramic precursor to introduce silica into the cell walls. The dielectric properties of these samples were then measured and compared to those of the original wood to see how the silica infiltrated the wood microstructure. Understanding how the wood structure affects the dielectric properties is important, as wood is becoming a mold material for making porous ceramics.