Near-field measurements for wood anisotropy using cavity-backed slot antennas

Abstract

Wood is becoming a very important structural material for buildings because it is a renewable resource and has a very small carbon footprint. This paper reports an experimental study on the effect of annual rings on wood anisotropy measurements using near-field microwave scanning for Pine, Hemlock, Red Cedar, and Hardwood laminated wood beams. Transmission measurements show significant anisotropy (>10 dB) for Pine wood compared to Hemlock wood and Red Cedar wood for linear polarization. The effect of annual rings in guiding the transmitted signal through wood fibers is observed through transmission measurements. Microwave guidance in transmission disappears with increasing the moisture content (17%–138%) of the Pine wood sample. The study provides a novel, accurate, fast, low-cost structural-wood testing method based on cavity-backed slot antennas for transmission and reflection measurements.