Techniques for high resolution imaging of wood structure: a review

High resolution imaging of wood requires the development of measurement techniques for nondestructive characterization of this material. The techniques, ranging from ionizing radiation to thermal techniques, microwaves, ultrasonics and nuclear magnetic resonance, provide excellent means of obtaining information about the internal structure of wood. High resolution images of wood structure can be obtained from a complete set of projections of relevant physical parameters such as x-ray attenuation, ultrasonic velocities, dielectric properties, etc. In this article the criterion selected for the description of the measurement techniques is the wavelength of the radiation which interacts with wood. The most relevant technique for the imaging of the cross section of the specimen under test will depend upon the particular application and material being studied: trees, logs, timber and wood-based composites.