The measurement of radio frequency complex permeability of thin round wires

Stuart, Thomas (Thomas Edward Walter) (2003-04)

Thesis (PhD)--University of Stellenbosch, 2003.

Thesis

ENGLISH ABSTRACT: This thesis is concerned with the measurement of the complex permeability of thin round wires at radio frequencies. This is of interest as such wires are used in various applications, such as absorbing chaff. Iron and nickel alloys are also used for their good tensile properties but have an undesired electromagnetic effect which needs to be characterised. Although little work has been done in this field in recent decades it remains a relevant problem. In this thesis the advantages of accurate wide-band measurements performed by automatic network analysers are applied to the field. The measurement system is a closed coaxial transmission line with a short circuit termination. The centre conductor is the wire of interest. The surface impedance of the wire is related to complex permeability and is measured using low-loss transmission line approximations applied to half-wavelength resonances. The loss associated with complex permeability is separated from conductivity by a D.C. conductivity measurement. A full wave analysis of the coaxial mode was performed and compared to measured values. The maximum error of the propagation constant was found to be 31% at the highest frequencies and was primarily due to length uncertainties. By varying parameters expected error bands around the measured permeability were found. These bands are of the order 1 and demonstrate that the system is sufficiently robust. The measurement of the permeability of two non-magnetic wires was performed and a relative permeability of 1 was found, demonstrating the correct working of the system. A steel wire was measured and compared to measurements found in literature. The permeability dropped as frequency rose as was expected, and an acceptable comparison to other measurements was made as there is no verification standard. Thus a simple measurement system that takes advantage of calibrated automatic network analyser measurements has been developed and demonstrated to work with sufficient accuracy.

AFRIKAANSE OPSOMMING: In hierdie tesis word die meting van die komplekse permeabiliteit van dun ronde drade by radio frekwensies ondersoek. Hierdie drade word in verskeie toepassings gebruik, waaronder dié van absorberende materiale. Nikkel- en ysterallooie word ook vir hul goeie breekkrageienskappe gebruik. In laasgenoemde gevalle moet die ongewenste elektromagnetiese effekte wat voorkom, gekarakteriseer word. Hoewel baie min werk in onlangse dekades gedoen is, bly die meting van die komplekse permeabiliteit 'n relevante probleem. In hierdie tesis word die voordele van akkurate wyeband metings, soos geneem deur 'n outomatiese netwerk analiseerder, toegepas in dié veld. Die meetopstelling is 'n geslote koaksiale transmissielyn, kortgesluit aan een end. Die middel geleier is die draad van belang. Die oppervlak impedansie van die draad is verwant aan die komplekse permeabiliteit, en word gemeet deur die gebruik van lae verlies transmissielyn benaderings, soos toegepas op halfgolf resonante frekwensies. Die verlies wat met die komplekse permeabiliteit geassosieer word, word van die geleidingsvermoë onderskei deur 'n G.S. meting van die geleidingsvermoë. 'n Volgolf analise van die koaksiale mode is uitgevoer en met gemete waardes vergelyk. 'n Maksimum fout van 31% by die hoogste frekwensie is in die voortplantingskonstante gevind. Hierdie volg primêr uit onsekerhede in lengte. Deur die parameters te varieer kon 'n verwagte foutband rondom die gemete permeabiliteit gevind word. Hierdie bande is van die orde 1 waaruit volg dat die stelsel 'n genoegsame robuustheid toon. Die komplekse permeabiliteit van twee nie-magnetiese drade is gemeet en 'n relatiewe permeabiliteit van 1 is gevind. Hierdie bevestig die korrekte werking van die stelsel. 'n Staal draad is opgemeet en met gepubliseerde meetresultate vergelyk. Soos verwag, verminder die permeabiliteit met 'n verhoging in frekwensie. Hoewel geen verifiëringstandaard beskikbaar is nie, is 'n aanvaarbare vergelyking met ander metings gemaak. Die produk van die navorsing is 'n metingstelsel wat, met behulp van 'n gekalibreerde outomatiese netwerk analiseerder, aanvaarbare akkuraatheid in die meting van die komplekse permeabiliteit van dun ronde drade by radio frekwensies kan verkry.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/53657
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