Abstract
In this thesis, the application of NMR to the characterization and imaging of wood, and to wood in living trees, is investigated in two parts. The first part characterises wood using advanced two dimensional (2-D) NMR measurements. The second part presents a novel portable magnet, purpose built for the imaging of living trees in-situ. The NMR relaxation parameters (T1 and T2) of the wood water components are established using standard one dimensional (1-D) procedures. Generally, three T2 components are found in wood with values of 10-100’s μs (small cell wall pores), 1-8 ms (larger cell wall pores) and 10’s ms (lumen cavities). There are also three T1 components: a few ms (cell wall pores), 10’s ms (latewood lumen) and -100ms (earlywood lumen). Information on these components is furthered by application of the 2-D T1-T2 correlation experiment. T1-T2 spectra show that at T2 times of a few ms (cell wall pores), there are two components which have different relaxation times: 12ms (peak C) and 85ms (peak B). Peak B is suggested to arise from exchange between peak C and lumen water. Another exchange peak (peak D) is identified at 0. 05ms T2 and 58ms T1 (data from spruce at 45% MC). Peaks B and D are further investigated by 2-D T2-T2 correlation experiments, allowing first estimates of the exchange times to be made. The time for exchange of water/ magnetisation between lumen and cell wall water was found to be 4. 6ms and between smaller and larger cell wall pores to be 21ms. Presentation of the Tree-Hugger forms the second part of this thesis. This portable magnet has been carefully designed to meet the specifications required to enable it to measure living trees in-situ. The magnet operates at the low field of 1.085MHz and has an open access design. It weighs 55kg and has three gradients (15kg each) which produce gradient fields in three orthogonal directions. The achievable field strengths are 6.7 G/cm, 7.1 G/cm and 10 G/cm in the x, y and z directions, respectively. The homogeneity of the magnetic field has been mapped in the x,z planar area and found to be 1750ppm over a distance of 120mm. The magnet has a workable open access solenoid probe with 180mm internal diameter. Pending improvement to this design, successful imaging has been carried out using a shielded solenoid with 130mm internal diameter. 2-D images of wood samples have been made using this probe with resolution of 1mm, although due to non uniformity in the sample, the visible resolution is between 1-2mm. In the 2-D images heartwood and sapwood regions are clearly defined, as is the central pith. The annual rings can be seen as they are distinguished by the higher signal intensity arising from the earlywood than the latewood. Three dimensional images have also been successfully made which show heartwood/sapwood regions as well as annual rings.