Tree Flaw Detection System Based On Electrical Resistivity Tomography

It is the most important for forest resources protection and the improvement of the utilization ratio of wood to detect the internal structure of the tree.The-state-of-art technologies for tree flaw detection mostly lead to damagement of trees,and most of non-destructive detection technologies can usually be used only in cut wood.Non-destructive detection technology which can be used on tree has been paid more and more attention in recent years.The application of resistance tomography technology in non-destructive detection on tree will be discussed in this paper and laboratory prototype of non-destructive tree detection device will be developed.Firstly,the positive problems of resistivity tomography will be briefly studied.The influence of the internal field conductivity on the boundary field voltage will be analyzed in the previous two chapters,which will provide the foundation for resistance tomography.Secondly,the dynamic resistance tomography imaging technology will be discussed in this paper,high speed and high precision back projection method will be applied to implement the contour imaging of the cross section of the resistances on tree.Through the research about input excitation and voltage measurement mode,an optimized weighting function has been achieved.The new weighting function performs well in removing star artifacts and improves the accuracy of reconstructed images.Then,non-destructive detection equipment based on electrical resistance tomography which can be used on tree will be designed and implemented in the next chapter.The device is divided into signal acquisition part and PC imaging part.In signal acquisition part,voltage controlled current source based on AD9850 is used to generate alternating exciting current.Switching conduction between different exciting electrodes and measuring electrodes is controlled by a signal gating module.The excitation signal is applied to the tested tree through the input electrode.Then the electrode signal collected from the measuring electrode is processed and amplified.Finally,the amplified electrode signal is input to the main control module by the ADC sampling module.The main control module stores and transfers the collected data to PC software to realize image reconstruction.Finally,non-destructive detection equipment based on resistance tomography will be applied on different immersing trees for reconstruction effect analysis.The image reconstruction results show that the device has good resolution for the internal defects of tested tree with different positions and sizes.The device is more sensitive to especially the small defect on tested tree and can meet the requirements of internal tree qualitative measurement.