No / Two Cylindrical Dielectric Resonators DR asymmetrically placed on a thin dielectric substrate and fed by a single rectangular slot for wideband wireless applications are presented. Optimized design procedures were applied within a well-known electromagnetic solver to achieve the improved elements dimensions of the antenna geometry. The simulated and measured results show that the proposed DRA can achieve 29% relative bandwidth at 10 dB return loss covering the spectrum range from 9.62 GHz to 12.9 GHz with a maximum gain of 8 dB.

No / A small dielectric resonator antenna has been designed for ultra wideband (UWB) communication system applications. The antenna element is a rectangular low permittivity ceramic block, with a dielectric constant of 9.4, and the modified T-shaped feed network includes a 50 ohm microstrip line to achieve strong coupling, and some bandwidth enhancement. The antenna performance is simulated and measured over a frequency band extending from 3100 MHz to 5500 MHz; the impedance bandwidth over this interval is 55.8% with VSWR <; 2, making the antenna suitable for UWB applications.

Yes / Potential demodulating ability in biological tissue exposed to Radio Frequency (RF) signals intrinsically requires an unsymmetrical diode-like nonlinear response in tissue samples. This may be investigated by observing possible generation of the second harmonic in a cavity resonator designed to have fundamental and second harmonic resonant frequencies with collocated antinodes. Such a response would be of interest as being a mechanism that could enable demodulation of information-carrying waveforms having modulating frequencies in ranges that could interfere with cellular processes. Previous work has developed an experimental system to test for such responses: the present work reports an electric circuit model devised to facilitate calibration of any putative nonlinear RF energy conversion occurring within a nonlinear test-piece inside the cavity. The method is validated computationally and experimentally using a well-characterised nonlinear device. The variations of the reflection coefficients of the fundamental and second harmonic responses of the cavity due to adding nonlinear and lossy material are also discussed. The proposed model demonstrates that the sensitivity of the measurement equipment plays a vital role in deciding the required input power to detect any second harmonic signal, which is expected to be very weak. The model developed here enables the establishment of a lookup table giving the level of the second harmonic signal in the detector as a function of the specific input power applied in a measurement. Experimental results are in good agreement with the simulated results. / Engineering and Physical Science Research Council through Grant EP/E022936A

Yes / A compact dielectric resonator antenna for ultra-wideband vehicular communication applications is proposed. Two cylindrical dielectric resonators are asymmetrically located with respect to the center of an offset rectangular coupling aperture, through which they are fed. Optimizing the design parameters results in an impedance bandwidth of 21%, covering the range from 5.9 to 7.32 GHz in the lower-band and a 53% relative bandwidth from 8.72 to 15 GHz in the upper-band. The maximum achieved gain is 12 dBi. Design details of the proposed antenna and the results of both simulations and experiment are presented and discussed.

No / A small dielectric resonator antenna has been designed for ultra wideband (UWB) communication system applications. The antenna element is a rectangular low permittivity ceramic block, with a dielectric constant of 9.4, and the modified T-shaped feed network includes a 50 ohm microstrip line to achieve strong coupling, and some bandwidth enhancement. The antenna performance is simulated and measured over a frequency band extending from 3100 MHz to 5500 MHz; the impedance bandwidth over this interval is 55.8% with VSWR <; 2, making the antenna suitable for UWB applications.

Цель работы заключается в теоретическом и экспериментальном исследовании новых типов электрических антенн. Проведено исследование в среде электромагнитного моделирования Ansoft HFSS, по результатам моделирования изготовлены прототипы и проведены измерения их характеристик. Новые типы антенны имеют большие перспективы дальнейшего развития, возможно изготовление активной антенны или использование ее в качестве элемента фазированной антенной решетки. / The purpose of work consists in theoretical and experimental research of new types of electric antennas. Study of electromagnetic environment simulation Ansoft HFSS, the simulation results of fabricated prototypes and measured their characteristics. New types of antennas have great potential for further development, it is possible to manufacture an active antenna or use it as element of a phased antenna array.

<p dir="ltr">Gyroscopes have become an integral part of many application spaces ranging from consumer electronics to navigation. As navigation and movement tracking becomes necessary through inertial measurement units (that comprises gyroscopes and accelerometers) in myriad of scenarios especially when global navigation and satellite system (GNSS) is not available, stability of gyroscopes plays a detrimental role in the accuracy of navigation. Recent developments in micro-electromechanical systems (MEMS) based gyroscopes enabled them to penetrate into navigation grade application spaces. MEMS based miniaturization approach also revived the interest in nuclear magnetic resonance gyroscopes (NMRGs). In parallel, emerging atomic gyroscope technologies are getting attention such as using quantum defects in single crystal diamond. </p><p><br></p><p dir="ltr">Considering innovative ways MEMS can improve gyroscopes, we investigate solid state gyroscope technologies in piezoelectric MEMS and nuclear spin based platforms for next generation rotation sensing that is shock and vibration insensitive. For the first part of this study, we explore a piezoelectric resonator that can excite wine-glass mode (WGM) and tangential mode. WGM is used for rotation sensing applications in various excitation mechanisms in literature. However, we demonstrate the capability of exciting WGM without the need for segmented electrodes in piezoelectric domain that allows self-alignment of the excitation electrodes using a unique property of Lead Magnesium Niobate-Lead Titanate (PMN-PT). In the second part of the study, we explore Nitrogen-Vacancy (NV) centers in diamond to be used as gyroscopes exploiting the rotation sensitivity of nuclear spins. NV center-based gyroscopes provide solid-state solution with comparable or superior performance without any moving parts. We propose mechanical coupling to NV centers in diamond using piezoelectrically excited bulk acoustic waves (BAW) to extend the coherence time of nuclear spins by dynamical decoupling. We explore piezoelectric coupling design space of AlN thin film BAW resonators (FBARs) to enable efficient mechanical drive to improve Rabi oscillations in diamond to overcome one of the most important bottlenecks of realizing a gyroscope, which is the mitigation and control of nuclear spin and electron spin interaction in diamond NV center system.</p>

Silicon Nanowire-based biosensors owe their sensitivity to the large surface area to volume ratio of the nanowires. However, presently they have only been shown to detect specific bio-markers in low-salt buffer environments. The first part of this thesis presents a pertinent next step in the evolution of these sensors by presenting the specific detection of a target analyte (NT-ProBNP) in a physiologically relevant solution such as serum. By fabrication of the nanowires down to widths of 60 nm, choosing appropriate design parameters, optimization of the silicon surface functionalization recipe and using a reduced gate oxide thickness of 5 nm; these sensors are shown to detect the NT-ProBNP bio-marker down to 2ng/ml in serum. The observed high background noise in the measured response of the sensor is discussed and removed experimentally by the addition of an extra microfabrication step to employ a differential measurement scheme. It is also shown how the modulation of the local charge density via external static electric fields (applied by on-chip patterned electrodes) pushes the sensitivity threshold by more than an order of magnitude. These demonstrations bring the silicon nanowire-based biosensor platform one step closer to being realized for point-of-care (POC) applications. In the second half of the thesis, it is demonstrated how silicon micromechanical piezoelectric resonators could be tasked to provide wireless power to such POC bio-systems. At present most sensing and actuation platforms, especially in the implantable format, are powered either via onboard battery packs which are large and need periodic replacement or are powered wirelessly through magnetic induction, which requires a proximately located external charging coil. Using energy harnessed from electric fields at distances over a meter; comprehensive distance, orientation, and power dependence for these first-generation devices is presented. The distance response is non-monotonic and anomalous due to multi-path interferences, reflections and low directivity of the power receiver. This issue is studied and evaluated using COMSOL Multiphysics simulations. It is shown that the efficiency of these devices initially evaluated at 3% may be enhanced up to 15% by accessing higher frequency modes.

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Small scale renewable energy harvesting is an attractive solution to the growing need for power in remote technological applications. For this purpose, localized thermal gradients on-chip—created via radiative cooling—could be exploited to produce microscale renewable heat engines running on environmental heat. This could allow self-powering in small scale portable applications, thus reducing the need for non-renewable sources of electricity and hazardous batteries. In this work, we demonstrate the creation of a local thermal gradient on-chip by radiative cooling of a 90 nm thick freestanding silicon nitride nanomechanical resonator integrated on a silicon substrate at ambient temperature. The reduction in temperature of the thin film is inferred by tracking its mechanical resonance frequency, under high vacuum, using an optical fiber interferometer. Experiments were conducted on 15 different days during fall and summer months, resulting in successful radiative cooling in each case. Maximum temperature drops of 9.3 K and 7.1 K are demonstrated during the day and night, respectively, in close correspondence with our heat transfer model. Future improvements to the experimental setup could enhance the temperature reduction to 48 K for the same membrane, while emissivity engineering potentially yields a maximum theoretical cooling of 67 K with an ideal emitter. This thesis first elaborates a literature review on the field of radiative cooling, along with a theoretical review of relevant thermal radiation concepts. Then, a heat transfer model of the radiative cooling experiment is detailed, followed by the experimental method, apparatus, and procedures. Finally, the experimental and theoretical results are presented, along with future work and concluding remarks.