Sensing knots: Piezoelectric signatures of anatomical variation in wood

Abstract

This study aimed to investigate the influence of knots, as anatomical irregularities in wood, on piezoelectric properties. Smooth-grained and knot-containing specimens obtained from common ash, Scots pine, and white poplar were subjected to mechanical testing under varying loading conditions. The experimental parameters included a constant load level of 5000 N and loading up to maximum stress. Specimen dimensions were prepared as 20 & times; 20 & times; 60 mm(3) and 30 & times; 30 & times; 90 mm(3). In addition, tests were conducted considering both radial and tangential surface orientations to evaluate the influence of anatomical direction on piezoelectric performance. The measurements were conducted with Keithley 2002 8 & half;-digit high-performance multimeter under the specific loadings. The results demonstrated that knot presence had a statistically significant effect on the piezoelectric response, accounting for 78.29% of the total variance in V-rms values and resulting in a pronounced reduction in piezoelectric performance. Smooth-grained specimens exhibited higher piezoelectric voltage values, particularly under higher applied loading levels. Among the species tested, common ash consistently showed the highest V-rms values, highlighting the importance of anatomical integrity and mechanical resistance for efficient piezoelectric behavior, whereas Scots pine and poplar displayed markedly lower responses. Overall, the findings indicated that anatomical defects, particularly knots, governed the piezoelectric performance of wood, while variations in applied force, specimen size, and surface orientation were found to play a comparatively limited role.