Demonstrating crystal optics using microwaves on wood targets

Anisotropy of wood in the microwave region

“…The samples of wood were boards of different wood types and thicknesses (table 1). Different thicknesses of spruce boards were obtained by appropriately clamping together two triangular-shaped pieces of spruce wood as suggested in the paper by Perkalskis and Freeman [2].…”

“…A number of anisotropic properties of wood were reported, for example, thermal conductivity, thermal expansion, absorption of water, etc [1]. As wood is transparent for microwaves, one can expect that also the optical properties of wood in the region of microwave frequencies would reveal anisotropic properties [2,3]. Indeed the anisotropic properties of wood in the microwave region are used in technological processes for measurements of the water content in some sorts of wood [1].…”

“…The interference and diffraction [4], Bragg reflection, evanescent absorption [5] and other phenomena [6,7] are discussed during lectures or studied in the laboratory. In spite of an intensive literature search, we were able to find only one study of the anisotropic properties of wood for educational purposes [2]. Perkalskis and Freeman presented a simple but effective means for demonstrating the anisotropic properties of crystals by using microwaves and wood targets.…”

“…The aim of this contribution is to present a set of experiments that can easily be used for demonstration purposes or for laboratory work in undergraduate courses. Based on the findings in [2,3], our experiments allow for quantitative measurement of the anisotropy in the absorption (linear dichroism) and the birefringence of wood. As the structure of wood in general is macroscopically anisotropic, wood can serve as a model for demonstration of anisotropic optical properties in crystals in the visible region.…”

Examining Young s modulus for wood

“…Since wood is symmetric about any plane containing the fibre axis and any plane perpendicular to the fibre axis, the simple axial symmetry about the wood fibre axis allows a clear visualization of the anisotropic physics. Anisotropic properties of wood can readily be used to demonstrate the underlying principles in electric polarization physics [1] (dielectric permittivity and electric resistivity), in optics [2] (birefringence) and in thermal expansion [3] (thermal resistivity).…”