Thesis(MScEng)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: The SQUID-NMR technique has been increasingly recommended by many researchers
as holding a lot of potential, and it is believed it will become an invaluable
tool for non-destructive evaluation in the future. Most of its potential is yet to be
exploited. Non-destructive quality control of food products is one of the applications
where such a system is being tried.
Much of the progress that has been made in improving such a system to the present
degree of user friendliness and cost effectiveness shows that, with more effort, it
would be possible to implement the technology for on-line sorting, and possibly to
reduce it down to hand-held devices.
The goal was to investigate the feasibility of the internal fruit quality measurements
using the NMR technique, and to develop a SQUID system suitable for SQUID-NMR
application, intended for a later integration in a full SQUID-NMR system.
A working dc SQUID was manufactured on an YBCO (Y Ba2Cu3O7 ) thin film
deposited on a 10 mm x 10 mm MgO substrate. The SQUID was made of microbridge
Josephson junctions, patterned by using the double resist laser lithography
method, implemented during the course of this manufacturing process. The test of
the SQUID showed a non-hysteretic current-voltage characteristic. Under the action
of bringing a magnet closer to the SQUID under test, and then retracting it, the
modulation of the I-V curve was observed. The critical current of the SQUID was
20 A and the resistance was 5.5
A series of experiments were performed on destructive measurements of the sugar
content in table grapes using NMR, in order to evaluate the feasibility of this technique.
The total sugars(TSS) measurements of the same samples were carried out
by refractometry, chosen as a conventional method for validation. The NMR measurements
were evaluated to be 5.4% precise and have an accuracy of 9.3% relative
to the refractometry measurements.
A further series of experiments were carried out on a high-Tc SQUID-NMR system. A high correlation coefficient (0.85) of the increasing values of the T1 and T2 relaxation
times to the decreasing concentration of sugar (sucrose) in water was obtained.
Non-destructive measurements T1 and T2 in table grapes suggested a possible prediction
of sugar content in table grapes from the values of T1 or T2. This technique also
presented many advantages compared to the conventional high field NMR technique,
such as the fast measurements that do not require spectral processing, the ease of
sample preparation, and its non-destructive nature. / AFRIKAANSE OPSOMMING: Die SQUID-NMR tegniek word al hoe meer aanbeveel deur navorsers oor die
groot potensiaal, en dit beloof om in die toekoms van onskatbare waarde te wees in
nie vernietigende evaluering. Die potensiaal moet grotendeels nog ontgin word, en
die nie vernietigende kwaliteitsbeheer van voedselprodukte is een van die toepassings
wat hier getoets word.
Die vooruitgang tot dusver om die stelsel te verbeter wat die gebruikersvriendelikheid
en koste-effektiwiteit betref, toon dat met effens meer moeite dit moontlik
sal wees om die tegnologie aan te pas vir lynsortering van vrugte, en om dit dalk
ook as handtoestel beskikbaar te stel. Die vooruitgang tot dusver om die stelsel te
verbeter wat die gebruikersvriendelikheid en koste-effektiwiteit betref, toon dat met
effens meer moeite dit moontlik sal wees om die tegnologie aan te pas vir lynsortering
van vrugte, en om dit dalk ook as handtoestel beskikbaar te stel.
Die doel is om die uitvoerbaarheid van interne vrugtekwaliteit metings deur hierdie
tegniek te ondersoek en om ’n SQUID stelsel te ontwikkel wat gepas is vir SQUIDNMR
toepassing, met die doel om dit later in ’n volledige SQUID-NMR stelsel te
kan integreer.
’n Werkende GS-SQUID is vervaardig op ’n YBCO dunfilm wat op ’n 10 mm x
10 mm MgO substraat gedeponeer is. Die SQUID is van mikro-brug Josephson aansluitings/
voegvlakke, waarop in die loop van die vervaardigingsproses ’n patroon m
et dubbelweerstand laser litografie neergelê is. Toets van die SQUID het ’n niehisterese
stroom-spanning as kenmerkend getoon. Die nader bring en terugtrekking
van ’n magneet het gelei tot waarneming van die modulasie van die I-V kurwe. Die
kritieke stroom van die SQUID was 20 A en die weerstand was 5.5 ohm. ’n Reeks eksperimente is uitgevoer oor vernietigende metings van die suikerinhoud
van tafeldruiwe met gebruik van NMR, om die gangbaarheid van hierdie tegniek te
evalueer. Totale suikers (TSS) metings van dieselfde monsters is uitgevoer deur refraktometrie,
wat gekies is as gebruiklike metode vir geldigheidsbepaling. Die NMR
metings is as 5.4% presies/noukeurig evalueer, en met ’n akkuraatheid van 9.3%
teenoor die refraktometrie metingsyfers.
’n Verdere reeks eksperimente is uitgevoer op ’n hoë-Tc SQID-NMR stelsel. ’n
Hoë korrelasiekoëffisiënt van 0.85 van die toenemende waardes van T1 en T2 ontspantye
teenoor die afname in konsentrasie van sukrose in water is waargeneem.
Nie-vernietigende metings van T1 eb T2 in tafeldruiwe het gelei tot die moontlikheid
van gebruik van hierdie tegniek om suikerinhoud van tafeldruiwe te voorspel.
Die tegniek het ook baie voordele getoon in teenstelling met die gebruiklike hoëveld
NMR tegniek, onder andere dat hierdie metings vinniger is, nie verdere verwerking
van die spektrum benodig nie, die maklike voorbereiding van die monsters en die
nie-vernietigende aard van die proses.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/71801 |
| Date | 12 1900 |
| Creators | Nturambirwe, Jean Frederic Isingizwe |
| Contributors | Perold, W. J., Opara, L., Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering., Stellenbosch University. Faculty of Agrisciences. Dept.of Horticulture |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | Unknown |
| Type | Thesis |
| Format | 141 p. : ill, |
| Rights | Stellenbosch University |
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