Abstract:

The stress wave nondestructive testing （NDT） technique is developed quickly in the recent years. How to determine the appropriate number of sensors and allocate the sensors in order to improve the testing efficiency and accuracy is one of the common issues. Ten samples of four tree species with two kinds of defects collected from Heilongjiang Province are selected for the study. The results show that for trees with diameter ranging from 20～40 cm，at least 12 sensors are needed to ensure a high testing accuracy of roughly 90% of fitness and 0.1 of error rate. Ten sensors are suitable to tell the possible locations of defects and 6 sensors are sufficient to decide whether there are defects. With plane geometry and statistic analysis this study further discusses the impact of planar distribution of sensors on the percentage of minimum detectable defect size （MDDS）. The mathematical model developed in this study indicates the affecting factors and basic rules of the sensor planar allocation on testing results. Finally，it is concluded that a satisfied testing result could be achieved only if the sensors are distributed in uniformity by eyeballing.

Key words: wood nondestructive testing, stress wave, sensor quantity, planar distribution, testing results