A microwave method for measuring moisture content, density, and grain angle of wood
U.S. Dept. of Agriculture, Forest Service, Forest Products Laboratory, 1985 - House & Home - 9 pages
The attenuation, phase shift and depolarization of a polarized 4.81-gigahertz wave as it is transmitted through a wood specimen can provide estimates of the moisture content (MC), density, and grain angle of the specimen. Calibrations are empirical, and computations are complicated, with considerable interaction between parameters. Measured dielectric parameters, however, correlate uniquely and repeatably with MC over a range of MC at least as great as 100 percent of the dry weight of the wood. Grain angle can be deduced reliably when the specimen thickness and MC are great enough to introduce sufficient dielectric anisotropy to appreciably depolarize the incident wave. At present, the apparatus and techniques are very complex, but the principles developed by this research show the method to be feasible for nondestructive testing of lumber as it is produced. Keywords include: Microwave transmission, Homodyne, Nondestructive testing, Moisture content, Density, and Grain angle. (Author).
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100 Moisture content 12 PERCENT 300-Hz modulation amplitude and/or thick anisotropy Apparatus and Methods Basswood constant Loss tangent constant of Douglas-fir CONTENT Dielectric constant correlation density and MC depolarization index Dielectric constant Loss dielectric properties diode Douglas-fir parallel electromagnetic wave elliptically polarized Figure frequency function of moisture grain angle Grain direction homodyne detector horn antenna imaginary incident polarization incident wave James and Hamill King and Yen line method James linearly polarized loss factor Loss tangent Dielectric MC levels measurements microwave beam MOISTURE CONTENT Dielectric nondestructive Numbers parallel and perpendicular Parallel Parallel Perpendicular Parallel Perpendicular Perpendicular PERCENT MC PERCENT MOISTURE CONTENT phase change phase shift polarization angle Power loss Red oak reduction reference signal reflected energy reflected wave reflecting dipole slotted line method specimen material specimen thickness speed of propagation spinning dipole structural tangent Dielectric constant transmission loss transmitted beam transmitted wave two-dimensional dielectric tensor unit thickness White pine wood