To maximize utilization of our forest resources, detailed knowledge of wood property variation and the impacts this has on end-product performance is required at multiple scales (within and among trees, regionally). As many wood properties are difficult and time-consuming to measure our knowledge regarding their variation is often inadequate as is our understanding of their responses to genetic and silvicultural manipulation. The emergence of many non-destructive evaluation (NDE) methodologies offers the potential to greatly enhance our understanding of the forest resource; however, it is critical to recognize that any technique has its limitations and it is important to select the appropriate technique for a given application. In this review, we will discuss the following technologies for assessing wood properties both in the field: acoustics, Pilodyn, Resistograph and Rigidimeter and the lab: computer tomography (CT) scanning, DiscBot, near infrared (NIR) spectroscopy, radial sample acoustics and SilviScan. We will discuss these techniques, explore their utilization, and list applications that best suit each methodology. As an end goal, NDE technologies will help researchers worldwide characterize wood properties, develop accurate models for prediction, and utilize field equipment that can validate the predictions. The continued advancement of NDE technologies will also allow researchers to better understand the impact on wood properties on product performance.

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The sound speed of wood is related to important wood quality properties such as the microfibril angle of the S2 layer in the cell wall, stiffness, and shrinkage propensity. Measuring the sound speed of seedling stems has benefits to the forestry industry, potentially enabling early selection of trees that yield better quality wood. A nondamaging longitudinal-wave time-of-flight (LWToF) acoustic technique was used to determine the sound speed of 10 cm long sections of 2-year-old Pinus radiata D. Don seedlings. The measured sections were harvested and acoustic resonance used to determine the sound speed of the sections before and after the bark was removed and after the remaining xylem was dried. A linear relationship between the acoustic resonance sound speed of the dry xylem and the LWToF sound speed of the seedling stem was found (R2 = 0.89). To demonstrate a potential application using the LWToF acoustic technique, it was used as a tool for investigating the effect of various applied stresses on wood properties of a clone of P. radiata. The LWToF sound speed measurements of phytohormone stressed stems were significantly lower than the control stems, indicating the negative impact on stiffness and shrinkage propensity imposed by this treatment.

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Abstract-A microwave Focused Beam transmission measurement is identified as a good candidate for fast, accurate and affordable industrial wood testing. In this paper, the transmission measurement setup, in its various forms, is applied to the measurement of wood properties, considering wood as an anisotropic, heterogeneous, multiphase dielectric. The depolarization of a linearly polarized plane wave in an anisotropic media is considered first. It is used for grain angle detection for arbitrary grain inclination in three-dimensional space. A good correlation with visually inspected grain angle values is obtained. A scattering experiment is performed, measuring the transmission through the wood when the transmitting and the receiving antenna axes are at the right angle. The results indicate that the annual ring arrangement strongly influences the scattering in the sideways direction, while other investigated parameters (defects, gradual density variation, bulk density) show poor correlation with measured scattering coefficient.

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