Investigating the effect organic tissue has on the electromagnetic waves when targeting the visual cortex
| dc.contributor.advisor | Van der Merwe, J. | en_ZA |
| dc.contributor.advisor | Van den Heever, Dawie | en_ZA |
| dc.contributor.author | Dreyer, Rita Liezl | en_ZA |
| dc.contributor.other | Stellenbosch University. Faculty of Engineering. Institute of Biomedical Engineering. | en_ZA |
| dc.date.accessioned | 2023-03-02T08:22:04Z | |
| dc.date.accessioned | 2023-05-18T07:05:37Z | |
| dc.date.available | 2023-03-02T08:22:04Z | |
| dc.date.available | 2023-05-18T07:05:37Z | |
| dc.date.issued | 2023-03 | |
| dc.description | Thesis (MEngSc)--Stellenbosch University, 2023. | en_ZA |
| dc.description.abstract | ENGLISH SUMMARY: The concept of using electromagnets to stimulate the visual cortex to elicit a phosphene response in the visual field is not novel. Instead, it is the basis of one of the prefered non-invasive neurostimulation methods to address vision loss. The problem, however, lies in the lack of effectiveness and specificity of electromagnetic-based prostheses. The current trend is to improve the design of micro-scale magnetic coils. The effect of the organic tissue, explicitly human organic layers over the visual cortex, on electromagnetic waves has not been explored yet. This study aimed to investigate how organic tissues (skin, facia, skull and meninges) affect electromagnetic waves targeting the visual cortex. This effect should be considered when calibrating electromagnetic-based neurostimulation devices. This study focused explicitly on the maximum field strength, RMS (root-mean-square) value of an alternating current (AC) waveform and the difference between the input and output frequencies. The study tested individual layers of organic tissue and the amalgamation of the layers, including a section of the visual cortex, at 5, 10, 15, 20, and 25 Hz. A bloodless pig's head proved to be a reliable test material since it is physiologically and anatomically similar to human tissue. A fluxgate was used as a sensor to detect changes in all three axes, as the visual cortex is a three-dimensional area. To minimise external interference, the experiment was conducted in a wooden box on the premises of the South African National Space Agency (SANSA), as it has buildings that have minimal electromagnetic interference. The frequency and sinusoidal wave format were controlled by a signal generator, while a DC power supply controlled the current and power. A single pig's head was dissected, with each layer placed in a plastic ziplock bag. The individual layers were tested by placing them between the electromagnet and the fluxgate on a wooden frame held up by a wooden jig. Each test was conducted three times while keeping the distance constant. Temperature control was considered; however, due to electromagnetic interference, the set-up was removed. The experiment was conducted instead at a room temperature of 30 °C. The results showed, unexpectedly, that organic tissue generally increased rather than decreased the magnetic field (maximum field strength, RMS). This trend was observed in the z-, y- and x-axes, where the z-axis had the highest magnetic strength, and the x-axis had the lowest. The effect of the organic tissue was dependent on the input frequency and the type of organic tissue used. The results observed in each axis were independent of the other axes. Only organic tissues of the skin, skull, and brain had an impact on the frequency. One could hypothesize that variations in the output frequencies for these particular organic tissues were caused by the resonance frequencies of these tissues. The findings of this thesis can help to calibrate electromagnetic-based visual prostheses in order to increase the effectiveness and specificity of the devices. However, further studies on a human model should be conducted for more precise calibration. | en_ZA |
| dc.description.abstract | AFRIKAANSE OPSOMMING: Elektromagnetiese stimulasie van die visuele korteks, wat 'n fosfeenreaksie in die visuele veld te ontlok, is een van die voorkeur nie-indringende neurostimulasies om sigverlies aan te spreek. Elektromagneties-gebaseerde prosteses het egter ‘n gebrek aan effektiwiteit en spesifisiteit. Die huidige tendens is om die ontwerp van magnetiese spoele op mikroskaal te verbeter. Die effek van die organiese weefsel, eksplisiet menslike organiese lae oor die visuele korteks, op elektromagnetiese golwe. Hierdie studie se doel was om ondersoek in te stel oor hoe organiese weefsel elektromagnetiese golwe beinvloed, wanneer die visuele korteks geteiken word. Die resultate van hierdie studie kan vir die kalibrering van elektromagneties-gebaseerde neurostimuleringstoestelle gebruik word. Hierdie studie fokus spesifiek op die maksimum veldsterkte, die WGK (wortel-gemiddelde-kwadraat) waarde van 'n WS-golfvorm asook die verskil tussen die inset- en uitsetfrekwensie. Die studie het getoets by verskillende frekwensies (5, 10, 15, 20 en 25 Hz), op individuele lae van die organiese weefsel en die amalgamasie van die lae, insluitend 'n gedeelte van die visuele korteks. 'n Bloedlose varkkop is 'n betroubare proef onderwerp aangesien dit fisiologies en anatomies soortgelyk is aan mense. Aangesien die visuele korteks 'n driedimensionele area is, was ‘n Vloedpoort sensor gebruik om veranderinge in al drie asse te meet. Die eksperiment is in 'n houtkis op die terrein van die Suid-Afrikaanse Nasionale Ruimte-agentskap (SANSA) uitgevoer, om die effek van elektromagnetiese steurings van geboue te minimeer. Die frekwensie en sinusvormige golfvorm is deur 'n seingenerator beheer, terwyl 'n GS-kragbron die stroom en drywing beheer het. Die vark se kop is gedissekteer en elke laag is in 'n plastiek rits sak geplaas. Die individuele lae is getoets deur elke laag tussen die elektromagneet en vloedpoort op 'n houtraam te plaas, wat deur 'n houtmal vasgehou word. Elke toets is drie keer uitgevoer terwyl die afstand konstant gehou is. Temperatuurbeheer is oorweeg, maar is egter verwyder weens moontlike elektromagneet-interferensie. Die eksperiment is by 30 grade celsius uitgevoer. In teenstelling met die verlies aan sterkte wat verwag is, het die resultate gewys dat organiese weefsel oor die algemeen die magnetiese veld (maksimum veldsterkte, RMS) verhoog het. Hierdie neiging is waargeneem in die Z-, Y- en X-asse, waar die Z-as die hoogste magnetiese sterkte gehad het, en die x-as die laagste. Die verandering in veldsterkte wat die organiese weefsel veroorsaak het, was afhanklik van die insetfrekwensie en die tipe organiese weefsel. Die resultate wat in elke as waargeneem is, was onafhanklik van die ander as. Slegs die organiese weefsel van die vel, skedel en brein het 'n impak op frekwensie gehad. Variasies in die uitsetfrekwensies vir hierdie spesifieke organiese weefsels kan moontlik verduidelik word deur die resonansiefrekwensies van hierdie organiese weefsels. Die resultate van hierdie tesis kan gebruik word om elektromagneties-gebaseerde visuele prosteses te kalibreer om die doeltreffendheid en spesifisiteit van die toestelle te verhoog. Verdere ondersoek op 'n menslike model word aanbeveel vir meer akkurate kalibrasie. | af-ZA |
| dc.description.version | Masters | |
| dc.format.extent | xvi, 91 pages : illustrations, includes annexures | |
| dc.identifier.uri | http://hdl.handle.net/10019.1/127127 | |
| dc.language.iso | en_ZA | en_ZA |
| dc.publisher | Stellenbosch : Stellenbosch University | |
| dc.rights.holder | Stellenbosch University | |
| dc.subject.lcsh | Visual Cortex | en_ZA |
| dc.subject.lcsh | Electromagnetic waves | en_ZA |
| dc.subject.lcsh | Magnetic brain stimulation | en_ZA |
| dc.subject.name | UCTD | |
| dc.title | Investigating the effect organic tissue has on the electromagnetic waves when targeting the visual cortex | en_ZA |
| dc.type | Thesis | en_ZA |
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