Thesis (MScEng (Electrical and Electronic Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Flanged coaxial probes are widely used to conduct accurate, broadband permittivity measurements
of various dielectric materials. A metrology study, discussed in [1], revealed that
small perturbations in measured permittivity data, are due to escaping common-mode (CM)
current that propagates onto exposed VNA feed cabling. This is not considered in published
permittivity extraction algorithms, like the National Institute of Standards and Technology
(NIST) full-wave code that assumes an infinite flange radius. To characterise this effect we
validate a finite volume time domain (FVTD) CST simulation model of an SMA coaxial
probe, by probing sensitive E-fields in a metallic shielding cylinder, placed around it.
For this process, electro-optic (EO) E-field sensors are considered and a Mach-Zehnder
type sensor is designed. Manufacturing difficulties discontinues this approach, but the revisited
extended centre conductor E-field probing technique proves successful. The technique
entails a high dynamic range, two-port VNA measurement. Through CST we gain
knowledge of the physics behind the CM-problem and the behaviour of fields around the
coaxial probe. Different shielding environments are simulated to establish their ability to
impede CM-current coupling onto measurement cabling.
To study the CM-effect on extracted permittivity results, the investigation is extended
to Short-Open-Load (SOL) calibrated face-plane measurements of dielectric solids. A CST
model, which considers escaping CM-energy, is used to generate open circuit (OC) calibration
coefficients and to serve as an independent extraction method. We inspect the effect
of different shielding environments and through CST, extract accurate permittivity results
for e00, to a degree not previously achieved for such systems. This allows comment on the
infinite-flange-radius assumption of the NIST method and proves the significance of the
CM-effect. / AFRIKAANSE OPSOMMING: Geflensde koaksiale probes word algemeen in die praktyk gebruik om akkurate, wyeband
permitiwiteitmetings van diëlektriese materiale te verrig. ’n Studie wat in [1] bespreek
word, dui aan dat klein verskynsels in gemete resultate, verband hou met gemene-modus
(GM) stroom, wat ontsnap en teenwoording is aan die buitekant van onbeskermde voerkabels.
Hierdie verkynsel word nie deur huidige volgolf ekstraksie-algoaritmes, soos die van
NIST wat ’n onëindige flensradius aanvaar, in ag geneem nie. Om die GM-effek te karakteriseer,
verifieer ons ’n eindige-volume tyd-gebied CST simulasiemodel, deur sensitiewe
metings binne ’n silidriese metaalskerm, wat om so ’n probe geplaas word.
Vir hierdie meting word elektro-optiese E-veld probes eers oorweeg. In gevolg word
’n Mach-Zehnder-tipe probe ontwerp, maar vervaardigingsprobleme en tyd-oorwegings
kniehalter hierdie benadering. Heroorweging van die verlengde koaksiale sentraalgeleier,
E-veld-probe tegniek, wat hoë dinamiese bereik twee-poort netwerkanaliseerder metings
behels, slaag uiteindelik in hierdie doel. CST maak dit nou moontlik om die GM stroomprobleem
te simuleer en spesefieke veldgedrag te kan waarneem. Verskillende afskermingsmetodes
se vermoë om GM-koppeling na kabels te beperk word ondersoek.
Die GM studie word uitgebrei na SOL-gekalibreerde, flensvlakverwysde permitwiteitmetings
van diëlektriese vastestowwe. ’n CST model, wat GM stroom in ag neem, word
gebruik om oopgeslote kalibrasiekofisiënte te genereer en dien ook as ‘n alternatiewe permitiwiteit
ekstraksiemetode. Die effek van die verskillende afskermingstegnieke word ondersoek
en deur die CST metode te gebruik, word ’n aansienlike verbetering in akkuraatheid
van e00 waardes verkry. Dit regverdig kommentaar oor die aannames wat in die NIST
metode gemaak word en beklemtoon die belangrikheid om GM stroom in ag te neem.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/5425 |
| Date | 12 1900 |
| Creators | Rossouw, Daniel Johannes |
| Contributors | Reader, H. C., University of Stellenbosch. Faculty of Engineering. Dept. of Electrical and Electronic Engineering. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 87 p. : ill. |
| Rights | University of Stellenbosch |
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