The aim of this thesis is to develop and investigate impact-based frequency up-conversion mechanisms to enhance the performance of the piezoelectric energy harvesters. Five different mechanisms are designed that use cantilever type piezoelectric transducers, and for each of them, mathematical models of the piezoelectric transducer are constructed by applying the discontinuous dynamics theory. The constructed mathematical models are analyzed to provide a deep understanding of the mechanical and electrical performance of the piezoelectric energy harvester, which enables us to optimize the system parameters to generate the maximum power. The numerical investigation illustrates that the impact-based frequency up-conversion mechanism can significantly improve the performance of the energy harvester.

High quality YbxY1-xAG (0≤x≤1) single crystals were grown by using the Czochralski method. The structural properties of YbxY1-xAG (0≤x≤1) single crystals were also investigated using the EXAFS method. Additionally, for the first time, EXAFS results were compared with XRD results. Moreover, without essential lattice structure transformation, YbxY1-xAG crystals can be found due to the varying of doping concentration in XRD measurements. However, EXAFS measurements indicated that the local fine structural variation around the Yb3+ ion depends on the Yb3+ concentration. This work also studies the two-photon luminescence spectra of a Yb3+ doped YAG crystals. To study the spectral performance of Yb:YAG crystal, intense green light (centered at about 544nm) was generated by the crystal upon excitation using a 973nm InGaAs LD pump source. The luminescence spectra were obtained for various Yb concentrations and the emission intensity were plotted versus Yb3+ concentration. The green emission light attributed to Yb3+ two-photon transition.

Up-conversion (UC) in rare-earth co-doped fluorides to convert diode laser light in the near infrared to red, green and blue visible light is applied to make possible high performance emissive displays. The infrared-to-visible UC in the materials we study is a sequential form of non-linear two photon absorption in which a strong absorbing constituent absorbs two low energy photons and transfers this energy to another constituent which emits visible light. Some of the UC emitters' most appealing characteristics for displays are: a wide color gamut with very saturated colors, very high brightness operation without damage to the emitters, long lifetimes and efficiencies comparable to those of existing technologies. Other advantages include simplicity of fabrication, versatility of operating modes, and the potential for greatly reduced display weight and depth. Thanks to recent advances in material science and diode laser technology at the excitation wavelength, UC selected materials can be very efficient visible emitters. However, optimal UC efficiencies strongly depend on chosing proper operating conditions. In this thesis, we studied the conditions required for optimization. We demonstrated that high efficiency UC depends on high pump irradiance, low temperature and low scattering. With this understanding we can predict how to optimally use UC emitters in a wide range of applications. In particular, we showed how our very efficient UC emitters can be applied to make full color displays and very efficient white light sources.

This thesis study presents the design, simulation, micro fabrication, and testing steps of microelectromechanical systems (MEMS) based electromagnetic micro power generators. These generators are capable of generating power using already available environmental vibrations, by implementing the electromagnetic induction technique. There are mainly two objectives of the study: (i) to increase the bandwidth of the traditional micro generators and (ii) to improve their efficiency at low frequency environmental vibrations of 1-100 Hz where most vibrations exist. Four main types of generators have been proposed within the scope of this thesis study. The first type of generator is mainly composed of 20 parylene cantilevers on which coils are fabricated, where the cantilevers are capable of resonating with external vibrations with respect to a stationary magnet. This generator has dimensions of 9.5&times / 8&times / 6 mm3, and it has been shown that 0.67 mV of voltage and 56 pW of power output can be obtained from a single cantilever of this design at a vibration frequency of 3.45 kHz. The second type generator aims to increase the bandwidth of the traditional designs by implementing cantilevers with varying length. This generator is sized 14&times / 12.5&times / 8 mm3, and the mechanical design and energy generation concept is similar to the first design. The test results show that by using 40 cantilevers with a length increment of 3 &amp / #956 / m, the overall bandwidth of the generator can be increased to 1000 Hz. It has also been shown that 9 mV of constant voltage and 1.7 nW of constant power output can be obtained from the overall device in a vibration frequency range of 3.5 to 4.5 kHz. The third type is a standard large mass coil type generator that has been widely used in the literature. In this case, the generator is composed of a stationary base with a coil and a magnet-diaphragm assembly capable of resonating with vibrations. The fabricated device has dimensions of 8.5&times / 7&times / 2.5 mm3, and it has been considered in this study for benchmarking purposes only. The test results show that 0.3 mV of voltage and 40 pW of power output can be obtained from the fabricated design at a vibration frequency of 113 Hz. The final design aims to mechanically up-convert low frequency environmental vibrations of 1-100 Hz to a much higher frequency range of 2-3 kHz. This type of generator has been implemented for the first time in the literature. The generator is composed of two parts / a diaphragm-magnet assembly on the top, and 20 cantilevers that have coils connected in series at the base. The diaphragm oscillates by low frequency environmental vibrations, and catches and releases the cantilevers from the tip points where magnetic nickel (Ni) areas are deposited. The released cantilevers then start decaying out oscillations that is at their damped natural frequency of 2-3 kHz. It has been shown with tests that frequency up-conversion is realized in micro scale. The fabricated device has dimensions of 8.5&times / 7&times / 2.5 mm3, and a maximum voltage and power output of 0.57 mV and 0.25 nW can be obtained, respectively, from a single cantilever of the fabricated prototype at a vibration frequency of 113 Hz.

This thesis study presents the design, simulation, and fabrication of a low frequency electromagnetic micro power generator. This power generator can effectively harvest energy from low frequency external vibrations (1-100 Hz). The main objective of the study is to increase the efficiency of the previously proposed structure in METU-MEMS Center, which uses the frequency up-conversion technique to harvest energy from low frequency vibration. The proposed structure has been demonstrated by constructing several macro scale prototypes. In one of the constucted prototypes, the diaphragms are connected to a fixed frame via metal springs. The upper diaphragm having lower resonance frequency carries a magnet, and the lower diaphragm carries a hand wound coil and a magnetic piece for converting 6 Hz external vibrations up to 85 Hz, resulting a maximum voltage and power levels of 11.1 mV and 5.1 &micro / W, respectively. In an improved prototype, the metal springs are replaced with rubber ones, providing higher energy conversion efficiency and flexibility to tune the resonance frequency of both diaphragms to desired values. This prototype provides 104 &micro / W maximum power and 37.7 mV maximum voltage in response to vibration levels of 30 Hz. The proposed structure is also suitable to be realized by using microfabrication techniques. Hence, the structure to be microfabricated is studied and optimized for this purpose. When scaled to microelectromechanical dimensions, the expected maximum power and voltage from the 10 x 8.5 x 2.5 mm3 generator is 119 nW and 15.2 mV, respectively. A microfabrication process has also been designed for the proposed generator structure. According to this process, the structure consists of a stack of two pieces, each carrying different diaphragms. The diaphragms are made of parylene, and the coil and the magnetic piece are electroplated copper and nickel, respectively. As a result of this study, a new topology is proposed for harvesting energy at low frequency vibrations by the frequency up-conversion technique, and an efficiency improvement is expected with more than three orders of magnitude (119 nanoWatts output for the same size) compared to the study realized in our laboratory in converting low frequency (70-150 Hz) environmental vibrations to electrical energy.

No description available.

Cette thèse s’intéresse à une approche dite hybride de l’information quantique. Deux approches traditionnellement séparées, variables discrètes et variables continues, sont combinées dans une même expérience nécessitant à la fois comptage de photons (nombre de photons) et détection homodyne (quadratures). Cette architecture hybride a d’abord été utilisée pour générer des états non-gaussiens de la lumière de grande fidélité, par exemple état de Fock et chat de Schrödinger optique,qui correspondent à deux types d’encodages utilisés en information quantique. L’utilisation de détecteurs supraconducteurs à forte efficacité a permis d’obtenir un taux de préparation sans précédent, ce qui facilite l’utilisation ultérieure de ces états. Ces deux types d’état sont ensuite été combinés pour réaliser pour la première fois une intrication hybride entre qubits optiques de nature différente. Son extension à des qutrits a également été obtenue.Ces nouvelles ressources ouvrent la voie à la mise en oeuvre de réseau quantique hétérogène où les opérations et les techniques propres aux variables discrètes et continues peuvent être efficacement combinées.Ce travail de thèse a également été consacré à la mise en oeuvre d’un système de conversion de fréquence à haute efficacité et faible bruit, basé sur deux lasers à fibres synchronisés.Ce convertisseur de fréquence quantique permet non seulement d’étendre les états quantiques à des longueurs d’onde difficilement accessibles avec la technologie actuelle, mais constitue également un détecteur de photons à haute performance, surtout dans le régime infrarouge.Basé sur ce système, plusieurs applications ont ensuite été démontrées, comme la détection infrarouge résolue en nombre de photons et l’imagerie infrarouge ultra-sensible. / The thesis focuses on the experimental investigation of the optical hybrid approach forquantum information processing. Specifically, two traditionally separated approaches, i.e.the discrete and the continuous-variable ones, are combined in the same experiment with twodistinct quantum measurements based on photon counting (photon number) and homodynedetection (quadrature components).The optical hybrid approach is first applied to generate high-fidelity non-Gaussian states,e.g. Fock states and Schrödinger cat states, which correspond to two types of qubit encodingsused in optical quantum information. The use of high-efficiency superconducting nanowiresingle-photon detectors leads to an unprecedented preparation rate, which facilitates thesubsequent use of these states. For instance, the two types of states are combined to generatefor the first time a hybrid entanglement between particle-like and wave-like optical qubits, aswell as the extension to hybrid qutrit entanglement. These novel resources may pave the wayto implement heterogeneous networks where discrete and continuous-variable operations andtechniques can be efficiently combined. Additionally, we also experimentally demonstratefor the first time the so-called squeezing-induced micro-macro entangled states.During this PhD, efforts have also been dedicated to implement a high-efficiency andlow-noise frequency up-conversion system based on two synchronized fiber lasers. Suchquantum frequency converter not only permits to extend the spectra of quantum statesto difficultly accessible wavelengths with current technology, but also constitutes a highperformancephoton detector especially in the infrared regime. Based on the conversionsystem, several applications are demonstrated, such as infrared photon-number-resolvingdetection, and few-photon-level infrared imaging.