Research On Terahertz Spectrum Characteristics And Parameter Extraction Algorithm Of Wood

In the electromagnetic spectrum, THz radiation refers to the electromagnetic radiation whose oscillation frequency is around 1 THz (1 THz=1012 Hz). Because of its perspectivity, security, Spectral resolution and many other properties, THz technology has many important application in spectroscopy, imaging, nondestructive detection and many other fields. However, due to some factors which restrict THz technology, THz radiation has been called the THz gap of electromagnetic spectrum in a very long period of time. In contrast, the microwave and the infrared radiation on both sides of THz wave have been already widely used in spectrum, imaging, communication, detection and many other fields.THz-TDS and THz imaging are two important ways and means of the practical application of THz technology and play crucial roles in the development of THz technology. This thesis studies the applications of THz technology in the Forest and Wood industry, mainly studies the extraction principle of THz absorption spectrum parameters (refractive index, absorption coefficient and birefringence) and the extraction algorithm of timber optical parameters in THz range, using transmissive THz time-domain spectroscopy system. The contents of the study mainly focus on the following three aspects:(1) Based on the model of extracting material optical parameters which Was proposed by T.D.Dornet, the thesis studies the principles and the methods of extracting timber optical parameters (refractive index and absorption coefficient) from THz time-domain waveform and discusses how to get the other physical parameters (birefringence) of timber. Since the timber optical parameters are basic data for wood characterization and some other researches, to get timber optical parameters in the THz range will be helpful for better understanding the interaction mechanism of THz wave and timber, studying the propagation characteristics of THz wave in the wood and laying the foundation for the identification of timber species.(2) By using the birefringence properties of wood, we demonstrate the behavior of spruce as a birefringent element (quarter-and half-waveplate) for frequencies in the far infrared. In addition, it studies the determination of the priority fiber orientation within the wood through the measurement of birefringence. The research may be applied to oriented strand board, paper products and other industries. For example, in Oriented Strand Board (OSB) industry, we can measure and control fibre orientation and density, which will improve OSB strength and produce significant cost savings.(3) The thesis also studies THz imaging technology. It lays the foundation for the detection of inner defects of timber. If we can test and diagnosis the hidden defects within the timber before processing nondestructively and get the information of their locations and sizes exactly, it will be expected to improve the quality and the value of wood products.Terahertz technology to achieve efficient utilization of the forest and timber resources has practical significance.