La spectrométrie photoacoustique QEPAS constitue l’une des méthodes les plussensibles pour la détection de gaz à l’état de traces. Ses performances sont étroitement liées àcelles de sa source de lumière infrarouge cohérente et de son résonateur mécanique qui détecteles ondes acoustiques. La thèse a pour objectif de développer ces deux briques élémentaires.Dans un premier temps, les performances des résonateurs mécaniques sont modélisées, permettantde mieux comprendre leur comportement. Une formule analytique originale de leurfacteur de qualité y est incorporée, permettant de prédire avec précision les pertes qu’ils subissentlorsqu’ils résonnent dans un gaz. Grâce à ces modèles, de nouveaux résonateurs optimiséssont conçus et réalisés, aboutissant à des performances améliorées. Dans un secondtemps, les sources cohérentes infrarouges QCL et OPO sont améliorées pour la photoacoustique.L’impulsion de pompe optimale pour un OPO est présentée pour distribuer au mieuxl’énergie de pompe disponible dans le temps, et ainsi maximiser le rendement de rayonnementinfrarouge disponible. Un logiciel de simulation numérique original des OPOs est égalementcréé, et permet de simuler rapidement le spectre d’émission d’un OPO quelconque. / Infrared photoacoustic spectrometry QEPAS is one of the most sensitive techniquefor trace gas sensing. The goal of the thesis is to improve the two key elements of the instrument: the mechanical resonator and the coherent infrared light source.First, the use of resonators as an acoustic waves sensor is investigated, allowing to better understandtheir behavior. Our modeling include a new analytical formula of their quality factor,predicting the amount of losses they experience when immersed within a gaz. The models areused to design and fabricate new custom resonators, leading to enhanced performances. Second,two infrared sources named QCL and OPO are optimized for the photoacoustic application.The optimal pump pulse for an OPO is derived to efficiently distribute the available pumpenergy in time, hence maximizing the yield of infrared light. A simulation software has alsobeen created for OPOs, able to quickly predict the spectrum of any type of OPO.

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The first objective of this Dissertation is to present a methodology to calculate analytically the mode shapes and corresponding natural frequencies and determine critical buckling loads of mechanically coupled microbeam resonators with a focus on micromechanical filters. The second objective is to adopt a nonlinear approach to build a reduced-order model and obtain closed-form expressions for the response of the filter to a primary resonance. The third objective is to investigate the feasibility of employing subharmonic excitation to build bandpass filters consisting of either two sets of two beams coupled mechanically or two sets of clamped-clamped beams. Throughout this Dissertation, we treat filters as distributed-parameter systems. In the first part of the Dissertation, we demonstrate the methodology by considering a mechanical filter composed of two beams coupled by a weak beam. We solve a boundary-value problem (BVP) composed of five equations and twenty boundary conditions for the natural frequencies and mode shapes. We reduce the problem to a set of three linear homogeneous algebraic equations for three constants and the frequencies in order to obtain a deeper insight into the relation between the design parameters and the performance metrics. In an approach similar to the vibration problem, we solve the buckling problem to study the effect of the residual stress on the static stability of the structure. To achieve the second objective, we develop a reduced-order model for the filter by writing the Lagrangian and applying the Galerkin procedure using its analytically calculated linear global mode shapes as basis functions. The resulting model accounts for the geometric and electric nonlinearities and the coupling between them. Using the method of multiple scales, we obtain closed-form expressions for the deflection and the electric current in the case of one-to-one internal and primary resonances. The closed-form solution shows that there are three possible operating ranges, depending on the DC voltage. For low DC voltages, the effective nonlinearity is positive and the filter behavior is hardening, whereas for large DC voltages, the effective nonlinearity is negative and the filter behavior is softening. We found that, when mismatched DC voltages are applied to the primary resonators, the first mode is localized in the softer resonator and the second mode is localized in the stiffer resonator. We note that the excitation amplitude can be increased without worrying about the appearance of multivaluedness when operating the filter in the near-linear range. The upper bound in this case is the occurrence of the dynamic pull-in instability. In the softening and hardening operating ranges, the adverse effects of the multi-valued response, such as hysteresis and jumps, limit the range of the input signal. To achieve the third objective, we propose a filtration technique based on subharmonic resonance excitation to attain bandpass filters with ideal stopband rejection and sharp rolloff. The filtration mechanism depends on tuning two oscillators such that one operates in the softening range and the other operates in the hardening range. Hardware and logic schemes are necessary to realize the proposed filter. We derive a reduced-order model using a methodology similar to that used in the primary excitation case, but with all necessary changes to account for the subharmonic resonance of order one-half. We observe that some manipulations are essential for a structure of two beams coupled by a weak spring to be suitable for filtration. To avoid these complications, we use a pair of single clamped-clamped beams to achieve our goal. Using a model derived by attacking directly the distributed-parameters problem, we suggest design guidelines to select beams that are potential candidates for building a bandpass filter. We demonstrate the proposed mechanism using an example. / Ph. D.

The first objective of this dissertation is to present hybrid numerical-analytical approaches and reduced-order models to simulate microelectromechanical systems (MEMS) in multi-physics fields. These include electric actuation (AC and DC), squeeze-film damping, thermoelastic damping, and structural forces. The second objective is to investigate MEMS phenomena, such as squeeze-film damping and dynamic pull-in, and use the latter to design a novel RF-MEMS switch. In the first part of the dissertation, we introduce a new approach to the modeling and simulation of flexible microstructures under the coupled effects of squeeze-film damping, electrostatic actuation, and mechanical forces. The new approach utilizes the compressible Reynolds equation coupled with the equation governing the plate deflection. The model accounts for the slip condition of the flow at very low pressures. Perturbation methods are used to derive an analytical expression for the pressure distribution in terms of the structural mode shapes. This expression is substituted into the plate equation, which is solved in turn using a finite-element method for the structural mode shapes, the pressure distributions, the natural frequencies, and the quality factors. We apply the new approach to a variety of rectangular and circular plates and present the final expressions for the pressure distributions and quality factors. We extend the approach to microplates actuated by large electrostatic forces. For this case, we present a low-order model, which reduces significantly the cost of simulation. The model utilizes the nonlinear Euler-Bernoulli beam equation, the von K´arm´an plate equations, and the compressible Reynolds equation. The second topic of the dissertation is thermoelastic damping. We present a model and analytical expressions for thermoelastic damping in microplates. We solve the heat equation for the thermal flux across the microplate, in terms of the structural mode shapes, and hence decouple the thermal equation from the plate equation. We utilize a perturbation method to derive an analytical expression for the quality factor of a microplate with general boundary conditions under electrostatic loading and residual stresses in terms of its structural mode shapes. We present results for microplates with various boundary conditions. In the final part of the dissertation, we present a dynamic analysis and simulation of MEMS resonators and novel RF MEMS switches employing resonant microbeams. We first study microbeams excited near their fundamental natural frequencies (primary-resonance excitation). We investigate the dynamic pull-in instability and formulate safety criteria for the design of MEMS sensors and RF filters. We also utilize this phenomenon to design a low-voltage RF MEMS switch actuated with a combined DC and AC loading. Then, we simulate the dynamics of microbeams excited near half their fundamental natural frequencies (superharmonic excitation) and twice their fundamental natural frequencies (subharmonic excitation). For the superharmonic case, we present results showing the effect of varying the DC bias, the damping, and the AC excitation amplitude on the frequency-response curves. For the subharmonic case, we show that if the magnitude of the AC forcing exceeds the threshold activating the subharmonic resonance, all frequency-response curves will reach pull-in. / Ph. D.

No / This paper presents a circuit model which is used to calibrate the performance of nonlinear RF energy conversion inside a high quality factor resonant cavity with a known nonlinear loading device. The nonlinear radiofrequency energy conversion can be detected by exciting the fundamental operating frequency and observing the second harmonic resonant frequency within a doubly resonant cavity. By implementing the proposed mathematical model, the required input power can be estimated to maximise the chance of detecting the weak second harmonic signal prior to carry out the measurement.

The rise of connected devices and the internet of things has increased the need for systems capable of transmitting high frequency signals wirelessly. An important part of these systems are the filters. Filters remove signals within unwanted frequency ranges. These filters can be implemented using e.g. periodic structures. In this article, we present a design for such a filter that aims to have a stopband between 3-6 [GHz] using square complementary split ring resonators (CSRR) on a substrate integrated waveguide (SIW). The design is based on a dimensional parametric study. An alternative design based on circular CSRR's is also presented and discussed. The design is validated using a commercially available software and a novel method simulating higher order of modes (HOM). The novel simulation method is shown to be advantageous due to its ability to evaluate the attenuation coefficient of a periodic filter. Additionally, a quadratic CSRR structure was shown to have a larger stopband and a similar attenuation coefficient when compared to circular CSRR structure when applied on a SIW. Furthermore, an impedance matching structure for the both CSRR filters were designed and both filters were simulated. / Förekomsten av uppkopplade enheter och användandet av sakernas internet har ökat behovet av system som kan sända högfrekventa signaler trådlöst. En viktig del av dessa system är filter, som eliminerar signaler inom oönskade frekvensband. Dessa filter kan implementeras med periodiska strukturer. I denna rapport presenterar vi en design för ett sådant filter med ett stoppband mellan 3-6 [GHz] som använder sig av kvadratiska "complementary split ring resonators" (CSRR) på en "substrate integrated waveguide" (SIW). Designen är baserad på en geometrisk parametrisk studie. En alternativ design som använder sig av cirkulära CSSRs presenteras och diskuteras. Den föreslagna designen valideras med en kommersiellt tillgänglig och en egenframställd metod vid namn "higher order of modes" (HOM) metoden. Den egenframställda simulationsmetoden visas vara fördelaktig då den är kapabel att evaluera filtrets attenuationskoefficient. Utöver detta visas att en design baserad på kvadratiska CSRRs vara fördelaktig då den genererar ett större stoppband och liknande attenuationskoefficient jämfört med den cirkulära CSSR designen vid tillämpning på en SIW. Fortsättningsvis presenteras en matchande struktur för båda filter varpå båda kompletta filter simuleras. / Kandidatexjobb i elektroteknik 2022, KTH, Stockholm

<p>With the advent of increasingly complex radio systems at higher frequencies and the slowing of traditional CMOS process scaling with power concerns, there has been an increased focus on integration, architectural, and material innovations as a continued path forward in MEMS and logic. This work presents the first comprehensive experimental study of resonant body transistors in a commercial 14nm FinFET process, demonstrating differential radio frequency transduction as a function of transistor biasing through electrostatic, piezoresistive, and threshold voltage modulation. The impact of device design changes on unreleased resonator performance are further explored, highlighting the importance of phononic confinement in achieving an f*Q product of 8.2*10¹¹ at 11.73 GHz. Also shown are initial efforts towards the understanding of coupled oscillator architectures and a perovskite nickelate material system. Finally, development of resonators based on two-dimensional materials, whose scale is particularly attractive for high-frequency nano-mechanical resonators and acoustic devices, is discussed. Experiments towards dry transfer of tellurene flakes using geometries printed via two photon polymerization are presented along with optimization of a fabrication process for gated RF devices, presenting new opportunities for high-frequency electro-mechanical interactions in this topological material. </p>

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No / To mitigate potential interferences with coexisting wireless systems operating over 3.3-3.6 GHz, 5.15-5.35 GHz, or 5.725-5.825 GHz bands, four novel band-notched antennas suitable for ultra-wideband (UWB) applications are proposed. These include UWB antennas with a single wide notched band, a single narrow notched band, dual notched bands, and triple notched bands. Each antenna comprises a half-circle shaped patch with an open rectangular slot and a half-circle shaped ground plane. Good band-notched performance is achieved by using high permittivity and low dielectric loss substrate, and inserting quarter-wavelength horizontal/vertical stubs or alternatively embedding quarter-wavelength open-ended slots within the feed line. The results of both simulation and measurement confirm that the gain suppression of the single and multiple band-notched antennas in each desired notched band are over 15 dB and 10 dB, respectively. The radiation pattern of the proposed triple band-notched design is relatively stable across the operating frequency band.