Estimating lumber strength with radio frequency scanning

The amount of lumber graded by machine stress rating (MSR) has continued to increase since the development of the technology in the early 1960s. Accuracy of lumber strength estimation by X-ray method is reported to be equal to that of MSR. This study examined whether lumber specific gravity and strength can be accurately estimated with radio frequency waves if the moisture content influence in a signal passed through the lumber thickness can be eliminated. Strength of a radio frequency signal passed through the lumber thickness was measured at 6.35 mm intervals along the length of lumber central axis. A linear regression predictive equation was estimated relating modulus of rupture (MOR) to measured signal voltage. Correction for the influence of moisture content on MOR resulted in a predictive equation with an R2 of 0.59. Validation results based on the developed equation gave an R2 of 0.67. The results indicate potential for accurate radio frequency estimation of MOR if adequate correction for moisture content influence is performed.