a system for the detection of knots and voids in wood or lumber employs opposed arrays of capacitor plates . the presence of knots and / or voids is detected based on changes in the dielectrical response produced in the electrical fields defined by the opposed capacitor plate arrays . a software system delineates specific knot and void defects determined . wood or lumber strength can further be estimated by comparing a sensed dielectric value in a clear portion of the lumber or wood with an established dielectric response value for wood of known density . employing an appropriate correlation factor the relative wood density , coupled with knot / void location and size , permits an estimate of over all wood strength .