Single-Sided Microwave Near-Field Scanning of Pine Wood Lumber for Defect Detection

Defects and cracks in dried natural timber (relative permittivity 2–5) may cause structural weakness enhanced warping beams. For a pine wood beam (1200 mm × 70 mm), microwave reflection (S11) transmission (S21) measurements using cavity-backed slot antenna on the surface showed variations caused by imperfections defects wood. Reflection at 4.4 GHz increased (>5 dB) above major knot evident when E-field was parallel to grain. Similar results were observed for air cavities, independent of depth from surface. The presence metal bolt an hole S11 2 dB. In comparison, 6 dB screw centered cavity. A kiln-dried sample saturated with water increase its moisture content 17% 138%. Both perpendicular difference more than 15 open saw-cut water-saturated beam. insertion brass plate created 7 rise measurement (p < 0.0003), while there no significant variation orientation. By measuring coefficient, it possible detect location crack through change magnitude without noticeable (<0.01 GHz) resonant frequency. These offer simple, single-frequency non-destructive testing method situ, one or plane faces are accessible direct contact.