Non-destructive testing of solid wood plate using variable permittivity plate capacitor

A variable permittivity capacitance measuring method is proposed in this paper for solid wood plate defects detection. A fast and non-contact NDT is realized by measuring the difference of capacitances between the plates with and without defects. Theoretical and simulation analysis are firstly presented to validate this method, then two wood samples with knots and holes are tested. There are 0.1059pF(2.73%), 0.0841pF(2.18%) and 0.0576pF(1.50%) positive mutations of capacitance for the first sample at its three knots; while there are 0.0074pF(0.20%), 0.0171pF(0.47%), 0.0262pF(0.72%) and 0.0383pF(1.1%) negative mutations of capacitance for the second sample with one, two, three and four holes respectively, which demonstrates that the mutation of capacitance value increases with the defects' size. This new method is more suitable for the online processing and production, which is able to identify and locate the wood defects effectively and accurately.