Characterisation of the dielectric properties of rhinoceros tissue using computer simulation and physical tissue phantom models

Van Zyl, Floris Johannes (2017-12)

Thesis (MEng)--Stellenbosch University, 2017.

Thesis

Introduction: Understanding the electromagnetic behaviour of in-vivo devices within rhinoceros tissue will aid existing tracking and anti-poaching endeavours and provide new insights into rhinoceros physiology and environment. The simulation and agar models proposed in this project allow the investigation of electromagnetic propagation by in-vivo and ex-vivo devices without the need for surgery. Computer simulation and agar phantom models of rhinoceros tissue based on approximated dielectric properties are designed and evaluated. Methods: Since the dielectric properties of rhinoceros tissue have not been documented, the conductivity and permittivity of the skin, fat, muscle, blood and other organs were approximated by means of a meta-analysis that includes animals with similar physical properties. Alternative dielectric properties of the skin (epidermis, dermis and fat) were calculated based on previously reported mechanical measurements and chemical composition. Recipes using salt, sugar and agar were designed to match the dielectric properties of each tissue within the Industrial, Scientific and Medical (ISM) frequency band by applying previously reported mathematical models. Various phantom models were designed and produced to measure the power efficiency of an in-vivo transmitter to an ex-vivo receiver for two types of antenna. Results: The average error between the measured and theoretically predicted dielectric values was 6.22% when measured over all recipes and 4.49% for the 2.4 GHz group specifically. The specific absorption rate (SAR) within the various tissues complied with international standards. The findings indicate that the planar inverted-F antenna (PIFA) implanted in the chest of the rhinoceros is the optimal combination in terms of power efficiency, when communication with an ex-vivo receiver attached to the hind leg of the rhinoceros is considered. The power efficiency of the PIFA was seen to improve by 16 dbm when a 10 mm air gap between the antenna and phantom was introduced. Signal penetration through the hide of the rhinoceros is possible, but communication from an in-vivo transmitter located in the back, chest or neck to an ex-vivo receiver on the hind leg is not ideal for the specified antenna size and power constraints. All practical results were compared with corresponding simulation models and found to agree to an acceptable degree. The comparability between the agar and simulated rhinoceros flank models was 67.38% when regarding the efficiency between the transmitting and receiving antennas. Discussion: The simulation and agar models have been demonstrated to be in substantial agreement with respects to the power efficiency of in-vivo and ex-vivo antennas. It is therefore concluded that both models represent a good basis for the design of in-vivo and ex-vivo sensors for the rhinoceros. The comparability between the simulation and agar models might be improved by including more real-world mitigation factors to the computer models. Further validation can be performed in future by analysis of the dielectric properties of actual rhinoceros tissue.

Inleiding: `n Begrip van die elektromagnetiese gedrag van in-vivo toestelle binne renoster weefsel, kan bestaande opsporings en anti-stropery ondernemings bevorder en terselfdetyd nuwe insig in die biologiese funksionaliteit en omgewing van renosters verskaf. Die simulasie en agar modelle wat in hierdie projek voorgestel word, kan opsporings en monitor projekte bevoordeel deur `n middel te verskaf om in-vivo en ex-vivo toestelle te toets, sonder die noodsaaklikheid vir chirurgie. Hierdie projek stel rekenaar simulasies en agar modelle van renoster weefsel voor, wat op benaderde diëlektriese eienskappe gebaseer is. Metodes: Aangesien die diëlektriese eienskappe van renoster weefsel nog nie gemeet of gedokumenteer is nie, is die permitiwiteit en geleidingsvermoë van die vel, vet, spier, bloed en ander organe deur middel van `n meta-analise van diere met soortgelyke fisiese eienskappe aan renosters, benader. Alternatiewe diëlektriese eienskappe van die vel (epidermis, dermis en vet) is bereken met behulp van meganiese metings en chemiese samestellings wat alreeds in die literatuur bekend gestel is. Resepte van sout, suiker en agar is bereken om met die diëlektriese eienskappe van elke tipe weefsel in die industriële, wetenskaplike en mediese frekwensie band ooreen te stem, deur die wiskundige modelle wat alreeds in die literatuur voorgestel is, toe te pas. Verskeie modelle is ontwerp om die doeltreffendheid van die kragoordarg tussen `n in-vivo transmitter en `n ex-vivo ontvanger van twee tipes antenna pare te meet. Resultate: Die gemiddelde fout tussen die gemete en teoretiese waardes was 6.22% vir al die resepte en 4.49% vir die 2.4 GHz groep. Die spesifieke absorpsie koers binne die verskeie weefsel tipes, het aan internasionale standaarde voldoen. Die bevindinge het aangedui dat `n planêre omgekeerde-F antenna wat in die bors van die renoster geïmplanteer is, die optimale ontwerp is om met `n ex-vivo ontvanger op die agterpoot van die renoster te kommunikeer in terme van die doeltreffendheid van kragoordrag. Die kragoordrag van die PIFA het met 16 dbm verbeter met die byvoeging van `n 10 mm lug gaping tussen die antenna en die agar model. Alhoewel die sein die vel van die renoster kan penetreer, is kommunikasie van `n in-vivo sender in die rug, bors of nek na `n ex-vivo ontvanger op die agterpoot, nie ideaal vir die gespesifiseerde antenna grootte en kragverbruik nie. Alle praktiese resultate was met hul ooreenstemmende simulasie modelle vergelyk en die ooreenkoms was bevredigend. Die vergelykbaarheid van die agar en simulasie renoster sy ("flank") modelle, was 67.38% met betrekking tot die doeltreffendheid van die kragoordrag tussen die sender en ontvanger antennas. Bespreking: Die simulasie en agar modelle bied voldoende benaderings van renoster weefsel, gebaseer op die evaluering van die doeltreffendheid van in-vivo en ex-vivo antennas se kragoordrag. Daarom word daar aanvaar dat beide modelle `n goeie basis vir die ontwerp van in-vivo en ex-vivo sensors vir renosters verteenwoordig. Die vergelykbaarheid van die simulasie en agar modelle kan egter verder verbeter word deur addisionele regte-wêreldse verswakkingsfaktore tot die rekenaar simulasies by te voeg. Verdere bevestiging kan toekomstig ondersoek word deur die analise van die diëlektriese eienskappe van werklike renoster weefsel.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/102982
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