"Transmission loss needs to be considered in the design of telecommunication systems. If telecommunication systems have high transmission loss, the signals lose too much of their strength, which results in poor reception in television networks and lost calls in cellular networks. Total transmission loss, in the MHz-GHz range, has several different loss components, some of which are poorly characterized. Conductor loss is the largest loss component and the most difficult to predict. It is known that the conductor geometry or features influences the conductor loss. However, current numerical, analytical and empirical tools do not accurately predict this loss component, and there is little experimental data available to explain and show the impact of these conductor geometries. The conductor shape is heavily influenced by the ceramic substrate surface roughness, and this is especially true for printed circuit boards fabricated with thick-film technology. The two conductor features of interest are the conductor-edge angle and conductor-ceramic interface. For thick-film circuits, the edge of the conductor does not have a square cross section but has a tapered shape or angle. The conductor-ceramic interface is also rough at the micron scale. Since the current density is concentrated at the extremities of the conductor then these features, conductor-ceramic interface and conductor edges, can potentially have a large impact on conductor loss. For this study, the surfaces of ceramic substrates were subjected to different surface finishes that resulted in distinctly different surface characteristics. This in turn resulted in a range of conductor-ceramic interfaces and conductor-edge angle geometries. The impact of the conductor-edge angle and conductor-ceramic interface features on conductor loss was measured over a range of frequencies and conductor conductivities to ascertain the level of their contribution. It was shown quantitatively that the conductor-edge angle was significantly altered by the surface roughness and heavily influenced the conductor loss result. The consensus for decades has been that greater surface roughness causes the ceramic-conductor interface geometry to have a greater impact on conductor loss, increasing the conductor loss. However, this study has shown that greater surface roughness also causes the conductor-edge angle feature to have a smaller or reduced impact on conductor loss, improving the conductor loss result - this has not been considered previously. Focusing on only one of these features can give an anomalous loss prediction; both features need to be considered for the calculation of conductor loss for thick-film applications. The low frequency loss results are as expected but the high frequency (greater than 5GHz) results depend on edge angle and therefore thick-film paste viscosity, and substrate surface roughness. "

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Antenna implants are used to establish a telemetry link to enable wireless data transfer, suitable for telemedicine and other medical applications. Inbody environments with water-based tissues lead to severe power absorption, making signal strength and radiation efficiency challenging yet central performance aspects of antenna implants. Fundamental performance limits exist regarding radiation efficiency; however, these limits consider theoretically ideal Hertzian dipoles. A semi-analytical model is used to evaluate the feasibility of previously determined fundamental bounds and the optimal dipole solution, both with respect to physical necessities of finite material conductivity and antenna size. This study uses a spherical model to represent a simplified in-body environment with various phantom compositions. Furthermore, the study focuses on implants operating within the Medical Implant Communication System (MICS) frequency band, but models and methods are not restricted to the considered frequency. The work contributes to the field of implantable antennas in several aspects; evaluating the feasibility of fundamental bounds, establishing more realistic performance limits, and determining the optimal dipole solution with respect to radiation efficiency. Other findings are presented in related areas, particularly concerning conductor loss and evaluation of the impedance for antennas inside a high-loss phantom. Moreover, the work presents a suggested method to measure electrically small magnetic dipole antennas. Methods and models are documented in a substantial theoretical derivation, and findings are verified using independent methods. Neglecting necessary antenna aspects like finite size and conductivity can lead to faulty conclusions on implant performance. Providing a more realistic performance target helps predict the performance of realistic antenna designs. Ultimately, increased knowledge of implanted antennas simplifies the design process to achieve high-performance implants. / Antennimplant används för att etablera en telemetrilänk som möjliggör trådlös dataöverföring, exempelvis användbart inom telemedicin och andra medicinska tillämpningar. Vattenbaserade kroppsmiljöer resulterar i kraftig absorption, vilket implicerar att signalstyrka samt strålningseffektivit blir utmanande men även centrala prestanda egenskaper för antennimplnatat. Det existerar fundamentala prestandabegränsningar för strålningseffektivitet, men dessa gränser är etablerade med hänsyn till teoretiskt ideala elementära dipoler. En semi-analytisk modell används för att utvärdera rimligheten av tidigare begränsningar samt den optimala dipolen, bägge med hänsyn till nödvändiga aspekter som ändlig konduktivitet och antennstorlek. Denna studie använder en sfärisk modell för att representera en simplifierad kroppslig miljö med olika vävnadskompositioner. Studien fokuserar på antennimplantat inom frekvensbandet dedikerat för Medical Implant Communication System (MICS) enheter, men modeller och metoder är typiskt inte begränsade inom omnämnt band. Arbetet bidrar till området för implanterbara antenner i flera aspekter; att utvärdera rimligheten av fundamentala gränser, fastställa mer realistiska prestandagränser samt bestämma den optimala dipolen med avseende på strålningseffektivitet. Andra resultat presenteras inom relaterade aspekter som metallförlust och utvärdering av en antenns last eller ingångs impedans inuti sfäriska och kroppsliga miljöer. Dessutom presenteras en metod för att mäta elektriskt små magnetiska dipoler. Metoder och modeller är dokumenterade eller demonstrerade via härledning, och centrala resultat har verifieras med oberoende metoder. Att förbise nödvändiga aspekter som ändlig storlek och konduktivitet kan leda till felaktiga slutsatser gällande prestanda. Däremot, att fastställa en mer realistisk gräns bidrar till att förutsäga prestandan i realistiska tillämpningar. I slutändan så resulterar ökad kunskap i en simplifierad designprocess som underlättar i strävan till att uppnå högpresterande antennimplantat.