The goal of this research was to develop acoustic sensors and actuators for microfluidic applications. To this end, capacitive micromachined ultrasonic transducers (cMUTs) were developed which generate guided acoustic waves in fluid half-spaces and microchannels. An interdigital transducer structure and a phased excitation scheme were used to selectively excite guided acoustic modes which propagate in a single lateral direction. Analytical models were developed to predict the geometric dispersion of the acoustic modes and to determine the sensitivity of the modes to changes in material and geometric parameters. Coupled field finite element models were also developed to predict the effect of membrane spacing and phasing on mode generation and directionality. After designing the transducers, a surface micromachining process was developed which has a low processing temperature of 250C and has the potential for monolithically integrating cMUTs with CMOS electronics. The fabrication process makes extensive use of PECVD silicon nitride depositions for membrane formation and sealing. The fabricated interdigital cMUTs were placed in microfluidic channels and demonstrated to sense changes in fluid sound speed and flow rate using Scholte waves and other guided acoustic modes. The minimum detectable change in sound speed was 0.25m/s, and the minimum detectable change in flow rate was 1mL/min. The unique nature of the Scholte wave allowed for the measurement of fluid properties of a semi-infinite fluid using two transducers on a single substrate. Changes in water temperature, and thus sound speed, were measured and the minimum detectable change in temperature was found to be 0.1C. For fluid pumping, interdigital cMUTs were integrated into microchannels and excited with phase-shifted, continuous wave signals. Highly directional guided waves were generated which in turn generated acoustic streaming forces in the fluid. The acoustic streaming forces caused the fluid to be pumped in a single, electronically-controlled direction. For a power consumption of 43mW, a flow rate of 410nL/min was generated against a pressure of 3.4Pa; the thermodynamic efficiency was approximately 5x10-8%. Although the efficiency and pressure head are low, these transducers can be useful for precisely manipulating small amounts of fluid around microfluidic networks.

The analysis and development of robust sensing platforms based on solidly-mounted ZnO bulk acoustic wave devices was proposed. The exploitation of acoustic energy trapping was investigated and demonstrated as a method to define active sensing areas on a substrate. In addition, a new "hybrid" acoustic mode experiencing acoustic energy trapping was studied theoretically and experimentally. This mode was used as an explanation of historical inconsistencies in observed thickness-shear mode velocities. Initial theoretical and experimental results suggest that this mode is a coupling of thickness-shear and longitudinal particle displacements and, as such, may offer more mechanical and/or structural information about a sample under test. Device development was taken another step further and multi-mode ZnO resonators operating in the thickness-shear, hybrid, and longitudinal modes were introduced. These devices were characterized with respect to sample viscosity and conductivity and preliminary results show that, with further development, the multi-mode resonators provide significantly more information about a sample than their single-mode counterparts. An alternative to resonator-based platforms was also presented in the form of bulk acoustic delay lines. Initial conceptual and simulation results show that these devices provide a different perspective of typical sensing modalities by using properly designed input pulses, device tuning, and examining overall input and output signal spectra.

This thesis endeavors towards developing various concepts employed in analysis and design of acoustic filters for varied applications ranging from combination mufflers for automobiles to complex networks of gas carrying ducts to multiply connected complex automotive silencing devices to the noise control coatings for underwater applications. A two-dimensional wave modeling approach has been proposed to evaluate sound attenuation characteristics of dissipative mufflers of finite length with/without extended inlet and outlet tubes including very large mufflers. The correctness of the method has been validated through comparison with experimental results from literature. Two other frequently used approximate schemes have been discussed briefly with reference to the available literature. These three approaches have then been weighed against each other to show the effectiveness and limitations of each one. A thorough comparison study has been performed to investigate each one’s extent of applicability. A parametric study with different parameters suggests some useful design guidelines that can be put to use while designing such mufflers. Benefits and drawbacks of reactive and dissipative mufflers have been discussed with an intention of striking a compromise between them to achieve a better transmission quality over a broad frequency range. This has been accomplished by combining these two types of mufflers/filters explicitly. These combination mufflers are analyzed using a transfer matrix based approach by extending the aforesaid concept of two-dimensional wave modeling for finite dissipative ducts. The present approach has been used to analyze axi-symmetric circular lined plenum chambers also. The effectiveness of the bulk reaction assumption to model absorptive lining is illustrated. A parametric study has been carried out to investigate the effects of different thicknesses and placements of the absorptive lining. The contributions of reflective and absorptive portion of the combination mufflerto overall attenuation performance have been investigated from the designer’s point of view A generalized algorithm has been developed for studying the plane sound wave propa- gation in a system of interconnected rigid-walled acoustic filter elements. Interconnection between various elements is represented by a connectivity matrix. Equations of volume velocity continuity and pressure equilibrium at the interconnections are generated using this connectivity matrix and are solved using the Gauss-Jordan elimination scheme to get the overall transfer matrix of the system. The algorithm used for generalized labeling of the network and computation of Transmission Loss has also been discussed. The algorithm has been applied to investigate a multiply connected automobile mufflers as a network of acoustic elements which guides the way to a specialized application discussed next. Results for some configurations have been compared with those from the FEM analysis and experiments. A parametric study with respect to some geometric variables is carried out. The acoustical similarity between apparently different networks is discussed. The approach is flexible to incorporate any other acoustic elements, provided the acoustic variables at the junctions of the element can be related by a transfer matrix a priori. Commercial automotive mufflers are often too complex to be broken into a cascade of one dimensional elements with predetermined transfer matrices. The one dimensional (1-D) scheme presented here is based on an algorithm that uses user friendly visual volume elements to generate the system equations which are then solved using a Gauss-Jordan elimination scheme to derive the overall transfer matrix of the muffler. This work attempts and succeeds to a great extent in exploiting the speed of the one dimensional analysis with the flexibility, generality and user friendliness of three dimensional analysis using geometric modeling. A code based on the developed algorithm has been employed to demonstrate the generality of the proposed method in analyzing commercial muffers by considering three very diverse classes of mufflers with different kinds of combinations of reactive, perforated and absorptive elements. Though the examples presented in the thesis are not very complex for they are meant to be just representative cases of certain classes of mufflers, yet the algorithm can handle a large domain of commercial mufflers of high degree of complexity. Results from the present algorithm have been validated through comparisons with both the analytical and the more general, three-dimensional FEM based results. The forte of the proposed method is its power to construct the system matrix consistent with the boundary conditions from the geometrical model to evaluate the four pole parameters of the entire muffer and thence its transmission loss,etc. Thus, the algorithm can be used in conjunction with the transfer matrix based muffler programs to analyze the entire exhaust system of an automobile. A different kind of acoustic filter than the above mentioned cases is then taken up for investigation. These refer to the specialized underwater acoustic filters laid as linings on submerged bodies. These kind of underwater noise control linings have three different types of objectives, namely, Echo Reduction, Transmission Reduction (TL maximization) and a combination thereof. These coatings have been shown to be behaving very differently with different shape, size and number of air channels present in the layer. In this regard, a finite element model based methodology has been followed. An hybrid type finite element based on the Pian and Tong formulation has been modified and used so as to make the computational efforts less demanding as compared to the original one. The developed finite element has been shown to be immune to the difficulties that arise due to the near incompressible characteristics of the viscoelastic materials used and the high distortion of the elements of the FE mesh. The adequacy of this formulation has been shown by comparing its results with the analytical, FE based, and experimental results. Then, this methodology has been used to analyze and generate design curves to control various geometrical parameters for proper designing of these linings. Different unit cell representations for different types of distributions of air cavities on the linings have been discussed. Four different types of layers have been introduced and analyzed to address different objectives mentioned above. They have been termed as the Anechoic layer, Insulation layer and Combination Layer of coupled and decoupled type in this thesis. The first two layers have been designed to achieve very dissimilar characteristics and the next two layers have been designed to balance their disparities. A thorough parametric study has been carried out on the geometrical parameters of all the layers to come up with the design guidelines. For anechoic and the insulation layers, different distributions have been analyzed with different unit cell geometries and their usability in specific situations has been outlined. Effect of static pressure has also been studied by using an approximate finite element method. This method can be used to simulate deep-sea testing environment.

Higher frequencies in the MHz and GHz range and the increasing miniaturization lead to a higher load of the SAW (surface acoustic wave) metallizations. This higher SAW load and the intrinsic stresses result in a stress induced material transport, called acoustomigration. These microstructural changes can destroy the characteristic of the SAW device. Different Al based material combinations were investigated by different authors to improve the reliability of the metallizations and to delay the cost-intensive change to Cu based metallizations. The Cu based metallizations with TaSiN diffusion barriers were also investigated in this work. The barrier layers are necessary to impede the oxygen diffusion into the Cu layer and the Cu diffusion into the piezoelectric substrate. Also in this work the analytical TEM were used as a tool to investigate these microstructural changes in the SAW electrodes. Chemical changes in the metallizations were analysed by EDXS and EELS. The locally high resolved stress measurement in metallizations is a challenge for the future. The CBED (convergent beam electron diffraction) technique has shown the best resolution, however, it can only be applied to TEM lamellas. The aim of this work was to measure the stress within the SAW metallizations by using the CBED method. With it, we could correlate the microstructural changes with the causing stresses within the metallizations. To qualify the CBED method the thermal expansion of Al and Cu single crystals was measured by using a new model for thin TEM lamallas.

Diese Dissertation beschäftigt sich mit der Entwicklung eines neuartigen Konzepts für Herstellung und Handhabung von Mikrofluidiksystemen auf der Basis akustischer Oberflächenwellen (SAW) sowie der Nutzung dieses Konzepts zur Fertigung anwendungsrelevanter Teststrukturen. Schwerpunkte sind dabei unter anderem eine hohe Leistungsbeständigkeit und Lebensdauer der Chipbauelemente und eine hohe technologische Flexibilität bezüglich Herstellung und Einsatz. Ausgehend von einer modularen Betrachtungsweise der Bauelemente wurden vielseitig einsetzbare, elektrisch-optimierte Interdigitalwandler entworfen, verschiedene Herstellungsvarianten für vergrabene Interdigitalwandler hoher Leistungsbeständigkeit auf piezoelektrischen Lithiumniobat-Substraten entwickelt und experimentell verifiziert, ein Sputterverfahren für amorphe SiO2-Dünnschichten hoher Qualität optimiert und eine Federstiftkontakt-Halterung entworfen. Durch Kombination dieser Technologien wurden SAW-Bauelemente für die mikrofluidische Aktorik mit hoher Performance und Reproduzierbarkeit entworfen, charakterisiert und beispielhaft für das elektroakustische Zerstäuben von Fluiden und das Mischen in Mikrokanälen eingesetzt.

Microelectromechanical resonators have found widespread applications in timing, sensing and spectral processing. One of the important performance metrics of MEMS resonators is the temperature sensitivity of their frequency. The main objective of this dissertation is the compensation and control of the temperature sensitivity of silicon resonators through engineering of device geometry and structural composition. This has been accomplished through formation of composite platforms or novel geometries based on dispersion characteristics of guided acoustic waves in single crystalline silicon (SCS) microstructures. Furthermore, another objective of this dissertation is to develop efficient longitudinal piezoelectric transduction for in-plane resonance modes of SCS resonators that have lithographically-defined frequencies, to reduce their motional resistance (Rm). A uniformly distributed matrix of silicon dioxide pillars is embedded inside the silicon substrate to form a homogenous composite silicon-oxide platform (SilOx) with nearly perfect temperature-compensated stiffness moduli. Temperature-stable micro-resonators implemented in SilOx platform operating in any desired in- and out-of-plane resonance modes show full compensation of linear temperature coefficient of frequency (TCF). Overall frequency drifts as small as 80 ppm has been achieved over the industrial temperature range (-40°C to 80°C) showing a 40x improvement compared to uncompensated native silicon resonators. A 27 MHz temperature-compensated MEMS oscillator implemented using SilOx resonator demonstrated sub-ppm instability over the industrial temperature range. Besides this, a new formulation of different resonance modes of SCS resonators based on their constituent acoustic waves is presented in this dissertation. This enables engineering of the acoustic resonator to provide several resonance modes with mechanical energy trapped in central part of the resonator, thus obviating narrow tethers traditionally used for anchoring the cavity to the substrate. This facilitates simultaneous piezoelectric-transduction of multiple modes with different TCFs through independent electrical ports, which can realize highly accurate self-temperature sensing of the device using a beat frequency (fb) generated from linear combination of different modes. Piezoelectrically-transduced multi-port silicon resonators implemented using this technique provide highly temperature-sensitive fb with a large TCF of ~8500 ppm/°C showing 100x improvement compared to other Quartz/MEMS counterparts, suggesting these devices as highly sensitive temperature sensors for environmental sensing and temperature-compensated/oven-controlled crystal oscillator (TCXO/OCXO) applications. Another part of this dissertation introduces a novel longitudinal piezoelectric transduction technique developed for implementation of low Rm silicon resonators operating in lithographically defined in-plane modes. Aluminum nitride films deposited on the sidewalls of thick silicon microstructures provides efficient electromechanical transduction required to achieve low Rm. 100 MHz SCS bulk acoustic resonators implemented using this transduction technique demonstrates Rm of 33Ω showing a 100x improvement compared to electrostatically transduced counterparts. Low-loss narrow-band filters with tunable bandwidth and frequency have been implemented by electrical coupling of these devices, showing their potential for realization of truly reconfigurable and programmable filter arrays required for software-defined radios.

Advancing the field of nanotechnology to incorporate the unique properties observed at the nanoscale into functional devices has become a major scientific thrust of the 21st century. New fabrication tools and assembly techniques are required to design and manufacture devices based on one-dimensional nanostructures. Three techniques for manipulating nanomaterials post-synthesis have been developed. Two of them involve direct contact manipulation through the utilization of a physical probe. The third uses optically generated surface acoustic waves to reproducibly control and assemble one-dimensional nanostructures into desired locations. The nature of the third technique is non-contact and limits contamination and defects from being introduced into a device by manipulation. While the effective manipulation of individual nanostructures into device components is important for building functional nanosystems, commercialization is limited by this one-device-at-a-time process. A new approach to nanostructure synthesis was also developed to site-specifically nucleate and grow nanowires between two electrodes. Integrating synthesis directly with prefabricated device architectures leads to the possible mass production of NEMS, MEMS and CMOS systems based upon one-dimensional nanomaterials. The above processes have been pursued to utilize piezoelectric ZnO nanobelts for applications in high frequency electronic filtering as well as biological and chemical sensing. The high quality, single crystal, faceted nature of these materials make them ideal candidates for studying their properties through the designs of a bulk acoustic resonator. The first ever piezoelectric bulk acoustic resonator based on bottom-up synthesized belts will be demonstrated. Initial results are promising and new designs are implemented to scale the device to sub-micron dimensions. Multiple models will be developed to assist with design and testing. Some of models presented will help verify experimental results while others will demonstrate some of the problems plaguing further investigations.

Boundary shape optimization is a technique to search for an optimal shape by modifying the boundary of a device with a pre-specified topology. We consider boundary shape optimization of acoustic horns in loudspeakers and brass wind instruments. A horn is an interfacial device, situated between a source, such as a waveguide or a transducer, and surrounding space. Horns are used to control both the transmission properties from the source and the spatial power distribution in the far-field (directivity patterns). Transmission and directivity properties of a horn are sensitive to the shape of the horn flare. By changing the horn flare we design transmission efficient horns. However, it is difficult to achieve both controllability of directivity patterns and high transmission efficiency by using only changes in the horn flare. Therefore we use simultaneous shape and so-called topology optimization to design a horn/acoustic-lens combination to achieve high transmission efficiency and even directivity. We also design transmission efficient interfacial devices without imposing an upper constraint on the mouth diameter. The results demonstrate that there appears to be a natural limit on the optimal mouth diameter. We optimize brasswind instruments with respect to its intonation properties. The instrument is modeled using a hybrid method between a one-dimensional transmission line analogy for the slowly flaring part of the instrument, and a finite element model for the rapidly flaring part. An experimental study is carried out to verify the transmission properties of optimized horn. We produce a prototype of an optimized horn and then measure the input impedance of the horn. The measured values agree reasonably well with the predicted optimal values. The finite element method and the boundary element method are used as discretization methods in the thesis. Gradient-based optimization methods are used for optimization, in which the gradients are supplied by the adjoint methods.

Dans cette thèse, nous étudions et développons différentes familles de schémas d’intégration en temps pour les EDO linéaires. Dans la première partie, après avoir introduit les définitions et propriétés utilisées pour construire les schémas en temps, nous présentons deux méthodes de discrétisation en espace et une revue des schémas de Runge-Kutta (RK) qui sont couramment utilisés dans la littérature. Dans la seconde partie on présente une méthodologie pour construire deux familles de schémas A-stable pour un ordre quelcomque. Puis on fournit des schémas explicites, construits en maximisant leur nombre CFL pour un profil de spectre donné. Ces schémas explicites sont ensuite combinés aux schémas implicites A-stable, pour construire des schémas localement implicites que nous décrivons. En plus des tests de validations des schémas pour des problèmes en dimension un et deux de l’espace, nous présentons des résultats numériques obtenus en résolvant des problèmes de propagation d’ondes acoustiques et électromagnétiques en dimensions trois dans la troisième partie. / In this thesis, we study and develop different families of time integration schemes for linear ODEs. After presenting the space discretisation methods and a review of classical Runge-Kutta schemes in the first part, we construct high-order A-stable time integration schemes for an arbitrary order with low-dissipation and low-dispersion effects in the second part. Then we develop explicit schemes with an optimal CFL number for a typical profile of spectrum. The obtained CFL number and the efficiency on the typical profile for each explicit scheme are given. Pursuing our aim, we propose a methodology to construct locally implicit methods of arbitrary order. We present the locally implicit methods obtained from the combination of the A-stable implicit schemes we have developed and explicit schemes with optimal CFL number. We use them to solve the acoustic wave equation and provide convergence curves demonstrating the performance of the obtained schemes. In addition of the different 1D and 2D validation tests performed while solving the acoustic wave equation, we present numerical simulation results for 3D acoustic wave and the Maxwell’s equations in the last part.

Récemment, les systèmes multicapteurs ont trouvé de nombreuses applications dans des domaines tels que l’industrie agroalimentaire, l’environnement, la médecine et la défense. Parmi les technologies existantes, les capteurs à ondes acoustiques de surface sont l’une des plusprometteuses et fait l’objet de nombreuses recherches. Les travaux décrits dans ce manuscrit concernent le développement d’algorithmes permettant la reconnaissance de composés chimiques et l’estimation de leur concentration. Cette étude décrit une méthode permettant d’estimer les paramètres des phénomènes de transduction. L’intérêt de ces derniers est mis en évidence expérimentalement dans des applications consistant à identifier des toxiques chimiques, des capsules de café contrefaites et à détecter la présence de DMMP et de 4-NT en présence d’interférents. / Recently, gas sensor arrays have found numerous applications in areas such as the food, the environment, the medicine and the defenseindustries. Among the existing technologies, the surface acoustic wave technology is one of the most promising and has been the subject of abundant research. The work described in this manuscript concerns the development of algorithms allowing the recognition of chemical compounds and the estimation of their concentration. This study describes a method for estimating the parameters of transduction phenomena. Their interest is demonstrated experimentally in applications consisting in identifying toxic chemical compounds, counterfeit coffee capsules and in detecting the presence of DMMP and 4-NT in the presence of interfering compounds.