Anizotropija lomnega količnika in absorpcijskega koeficienta lesa v mikrovalovnem področju

diplomsko delo

Jernej Kamenšek (Author), Nataša Vaupotič (Mentor)

Abstract

V diplomskem delu obravnavam anizotropijo lomnega količnika in absorpcijskega koeficienta lesa v mikrovalovnem področju. Najprej na kratko predstavim zgradbo lesa. Les sestavljajo lesna vlakna, ki so usmerjena povprečno v eni smeri. Zato je les anizotropna snov, kar pomeni, da so fizikalne lastnosti lesa v smeri vlaken drugačne kot pravokotno nanje. V diplomskem delu iz Maxwellovih enačb izpeljem, da se po lesu razširjata dve valovanji, redno in izredno valovanje. Redno valovanje se v vseh smereh razširja z enako fazno hitrostjo, medtem ko je za izredno valovanje fazna hitrost odvisna od smeri razširjanja. Največjo razliko lomnih količnikov lesa za izredno in redno valovanje imenujemo anizotropija lomnega količnika lesa. Razliko v absorpcijskih koeficientih izrednega in rednega valovanja pa imenujemo linearni dikroizem. Osrednji del diplomskega dela predstavljajo meritve anizotropije lomnega količnika in linearnega dikroizma smrekovega lesa v mikrovalovnem področju. Meritve sem opravil pri različnih debelinah in vlažnostih za smrekov les. Za merjenje linearnega dikroizma in anizotropije lomnega količnika lesa uporabimo transmisivno metodo. Med mikrovalovni oddajnik in sprejemnik vstavimo les in merimo tok na sprejemniku. Tok je odvisen od količine prepuščenega elektromagnetnega valovanja. Izmerjena vrednost za linearni dikroizem zračno suhega lesa, ki ima 10,8 % vlažnost, znaša (0,18-0,03) cm^(-1), medtem ko je vrednost linearnega dikroizma vlažnega smrekovega lesa s 33,0 % vlažnostjo nekoliko višja in znaša (0,6 -0,1) cm^(-1). Ob upoštevanju, da je linearni dikroizem odvisen od frekvence mikrovalov, se izmerjeni vrednosti absorpcijskih koeficientov dobro ujemata z vrednostmi iz literature. V zračno suhem smrekovem lesu sem s transmisivno metodo izmeril tudi največjo razliko med lomnima količnikoma izrednega in rednega valovanja, ki znaša 0,22-0,03. Pri primerjavi rezultata z vrednostmi iz literature je spet potrebno upoštevati, da je dielektričnost in s tem lomni količnik odvisen od frekvence elektromagnetnega valovanja. Ujemanje je v tem primeru slabše, vzrok za to je najverjetneje v stopnji vlažnosti in v temperaturi lesa.

Keywords

fizika;lomni količnik;les;absorpcija;koeficient;anizotropija;mikrovalovi;linearni dikroizem;transmisivna metoda;diplomska dela;

Data

Language:	Slovenian
Year of publishing:	2011
Source:	Maribor
Typology:	2.11 - Undergraduate Thesis
Organization:	UM FNM - Faculty of Natural Sciences and Mathematics
Publisher:	[J. Kamenšek]
UDC:	53(043.2)
COBISS:	18819080
Views:	3522
Downloads:	263
Average score:	0 (0 votes)
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Other data

Secondary language:	English
Secondary title:	ANISOTROPY OF INDEX OF REFRACTION AND ABSORPTION COEFFICIENT OF WOOD IN THE MICROWAVE REGION
Secondary abstract:	In the thesis the anisotropy of the index of refraction and the absorption coefficient of wood in the microwave region is discussed. First I briefly introduce the structure of wood. Wood consists of wood fibers that are on average oriented in one direction. Because of that wood is anisotropic material, which means that it's physical properties along the fibers are different than in the direction perpendicular to fibres. It follows from the Maxwell's equations that two waves, the ordinary and extraordinary wave can propagate trough wood. The ordinary wave propagates in all directions with the same phase velocity, while the extraordinary wave's phase velocity depends on the direction of propagation. The maximum difference between the refractive indices for the extraordinary and ordinary wave is called the anisotropy of the index of refraction. The difference in the absorption coefficients of the extraordinary and ordinary wave is called a linear dichroism. The central part of the thesis presents measurements of the anisotropy of refractive index and linear dichroism of spruce wood in the microwave region. I made measurements at different thicknesses and humidity of the spruce wood. For the measurement of the linear dichroism and anisotropy of the index of refraction in wood a transmissive method is used. Between the microwave transmitter and receiver we insert a piece of spruce wood and measure the electric current at the receiver. The electric current at the receiver depends on the absorption of the electromagnetic waves in the wood. The measured value of the linear dichroism of the air-dried wood with 10,8 % humidity is (0,18-0,03) cm^(-1), while the value of the linear dichroism of the moist wood with 33,0 % humidity is a bit higher and it equals (0,6-0,1) cm^(-1). Taking into account that the linear dichroism depends on the frequency of the microwaves, measured values of the absorption coefficients agree well with the values from the literature. I also measured the maximum difference in the refractive indices for the extraordinary and ordinary wave and found it equals to 0,22-0,03. When comparing the results with the values from the literature it is again necessary to note that the dielctric constant and the refractive index depend on the frequency of the electromagnetic waves. The agreement of the measured value and the values in the literature is not so good in this case, the reason for this is most likely in the level of humidity and temperature of the wood.
Secondary keywords:	anisotropy;microwaves;wood;index of refraction;absorption coefficient;linear dichroism;transmissive method;
URN:	URN:SI:UM:
Type (COBISS):	Undergraduate thesis
Thesis comment:	Univ. v Mariboru, Fak. za naravoslovje in matematiko, Oddelek za fiziko
Pages:	V, 44 f.
Keywords (UDC):	mathematics;natural sciences;naravoslovne vede;matematika;physics;fizika;
ID:	19682