Les développements récents en physique, et technologiques, ont permis l’élaboration de nouveaux matériaux magnéto-électro-élastique, comme les composites multicouches piézoélectriques / piézomagnétiques. Leur coefficient magnétoélectrique, très grand en comparaison de celui des matériaux constitués d’une seule phase, a suscité récemment un grand nombre de travaux, menant au développement de capteurs, d’actionneurs, de systèmes de conversion d’énergie magnétique-électrique, et dans les mémoires à état solide.Cette thèse porte sur l’étude théorique et expérimentale des ondes acoustiques de surface dans des structures multicouches piézomagnétiques. Une description théorique des matériaux magnéto-élastiques, reposant sur la dérivation d’un modèle de matériau piézomagnétique équivalent, est utilisée conjointement à une technique numérique afin de calculer les courbes de dispersion et les formes des modes des ondes acoustiques se propageant dans des composites piézo-électro-magnétiques déposés sur un substrat. Ce modèle, très général, peut être utilisé pour différents types de structures et pour une intensité et une direction quelconques du champ magnétique externe appliqué. Les structures réalisées en salle blanche sont constituées d’un film mince de 20 couches de TbCo2 (5nm)/FeCo(5nm) déposé sur un substrat de LiNbO3 entre deux peignes interdigités. Une comparaison, entre les variations de la vitesse de phase d’ondes acoustiques de surface induites par l’application d’un champ magnétique externe modélisées et mesurées, est réalisée. Un bon accord quantitatif entre les mesures et les calculs théoriques, et cela pour toutes les orientations du champ magnétique (suivant l’axe facile ou l’axe difficile) et pour différents modes acoustiques, est obtenu. Le mode transverse horizontal présente les plus grandes variations de vitesse, proche de 20% pour un film dont l’épaisseur serait celle de la longueur d’onde acoustique / Recent developments in physics and technology allow the elaboration of new magneto-electro- elastic materials such as multilayered piezoelectric-piezomagnetic composites. Their large magne- toelectric coefficient, compared to the one of single phase materials, recently attracted a large number of studies, and they are now widely used in the development of sensors, actuators, magnetic- electric energy converting devices, and solid state memories.This PhD thesis addresses the experimental and theoretical investigations of guided elastic waves propagation in piezomagnetic multi-layered structure. A theoretical description of magneto- elastic materials, based on the derivation of an equivalent piezomagnetic material of a magnetostric- tive thin film, is used in conjunction with a numerical method to compute propagation constants, i.e. dispersion curves, and mode shapes of elastic waves in layered piezoelectric-piezomagnetic com- posites deposited on a substrate. This model can be used for different structures, and for an applied external magnetic field of any intensity and direction.The realized structures are composed of a 20xTbCo2(5nm)/FeCo(5nm) nanostructured multi- layer deposited between two Aluminum Inter-Digitals Transducers forming a surface acoustic wave delay line, on a LiNbO3 substrate. A comparison between the calculated and measured phase velocity variation under the action of the external magnetic field orientation and magnitude is made. A quantitative agreement between the measured and modeled phase velocity shift for all external magnetic field configurations (hard axis and easy axis) and for different shape modes of elastic waves at their first and third harmonic operation frequencies is obtained. The shear horizontal mode exhibits a maximum phase velocity shift close to 20% for a ratio close to 1 between magneto-elastic film thickness and wavelength

La génération d’impulsions courtes d’ondes acoustiques de surface est étudiée, en s’inspirant du principe de l’amplification des impulsions chirpées qui est utilisée pour la génération d’impulsions laser ultrabrèves. La compression temporelle des impulsions est généralement réalisée à l’aide d’éléments dispersifs. Dans ce travail, un transducteur à ondes acoustiques de surface pouvant émettre des impulsions brèves est utilisé comme élément dispersif. Une étude comparative des transducteurs à peignes interdigités chirpés est menée avec un modèle du premier ordre et un modèle dit de matrice mixte. Des dispositifs à ondes acoustiques de surface sont conçus et réalisés à partir des résultats de simulation numérique. La façon de distribuer la période dans le transducteur est étudiée. L’apparition de bandes interdites dues aux réflexions internes dans le transducteur chirpé et son effet sur l’émission directionnelle des ondes surface sont en particulier observées et étudiées.Un interféromètre optique différentiel dans le domaine temporel et stabilisé est ensuite proposé afin de caractériser les impulsions brèves. Le transducteur à ondes acoustiques de surface est placé à l’extérieur de l’interféromètre. Des expériences sont conduites avec un transducteur à peignes interdigités chirpé ayant une bande opérationnelle couvrant la gamme de fréquences 200 MHz – 400 MHz et produisant des impulsions de 10 ns avec un déplacement hors-plan maximal de 36 nm. La réponse interférométrique est comparée à une mesure électrique directe obtenue à l’aide d’un transducteur de réception large bande ; une bonne correspondance des deux mesures est observée. Les influences de la différence de chemin optique dans l’interféromètre et du choix du point d’observation sur la surface sont discutées. La compression de l’impulsion le long du transducteur chirpé est observée expérimentalement.Finalement, une étude comparative de différents filtres de compression temporelle est présentée, dans l’objectif d’obtenir des impulsions optimales à la fois courtes temporellement et de forte intensité, pour un élément dispersif donné. Le filtre inverse est identifié comme le plus efficace et nous permet de produire les impulsions de plus grande amplitude. Afin d’optimiser la compression de l’impulsion pour les dispositifs fabriqués, des expériences sont conduites pour trouver les courbes de compromis optimal dans chaque cas de modulation de la période du transducteur. / Generation of short pulses with surface acoustic waves (SAW) is studied, in analogy with the principle of chirped pulse amplification (CPA) used to produce ultrashort laser pulses. Temporal compression of pulses is generally achieved with dispersive elements. A SAW transducer emitting short SAW pulses is used as a dispersive element in this work. A comparative study of chirped inter digital transducers (CIDTs) using the first order model and the p-matrix model is presented. SAW devices are designed and fabricated using the simulation results and the effect of the varying pitch of the CIDts on the response is studied. Appearance of band gaps due to internal reflections within the CIDts and its effect on the directionality of the CIDTs are in particular found and studied.A stabilized time-domain differential optical interferometer is then proposed in order to characterize short pulses, with the surface acoustic wave (SAW) sample placed outside the interferometer. Experiments are conducted with surface acoustic waves excited by a chirped inter-digital transducer on a piezoelectric lithium niobate substrate having an operational bandwidth covering the 200 MHz – 400 MHz frequency range and producing 10 ns pulses with 36 nm maximum out-of-plane displacement. The interferometric response is compared with a direct electrical measurement obtained with a receiving wide bandwidth inter-digital transducer and good correspondence is observed. The effects of varying the path difference of the interferometer and the measurement position on the surface are discussed. Pulse compression along the chirped inter-digital transducer is observed experimentally.Finally, a comparative study of different filter designs for generating short pulses is presented with an objective to find a design to produce the optimal pulse which is short in width and high in amplitude, for a given dispersive element. The inverse filter is found to be the most efficient as it produces a short pulse with the highest amplitude. To optimize the pulse compression for the fabricated devices, experiments are conducted to find the optimal trade-off curve for each chirp case.

The objective of this dissertation is to improve the performance of surface acoustic wave (SAW) biosensors for use in point-of-care-testing (POCT) applications. SAW biosensors have the ability to perform fast, accurate detection of an analyte in real time without the use of labels. However, the technology suffers from the inability to differentiate between specific and non-specific binding. Due to this limitation, direct testing of bodily fluids using SAW sensors to accurately determine an analyte's concentration is difficult. In addition, these sensors are challenged by the need to detect small concentrations of a biomarker that are typically required to give a clinical diagnosis. Sensitivity, selectivity and reliability are three critical aspects for any sensing platform. To improve sensitivity the delay path of a SAW sensor has been modified with microcavities filled with various materials. These filled cavities increased sensitivity by confining wave energy to the surface by way of constructive interference and waveguiding. Thus, the improved sensitivity will result in a lower limit of detection. In addition, insertion loss is decreased as a consequence of increased wave confinement to the surface. Sensor selectivity and reliability are adversely affected by non-specific binding of unwanted species present in a sample. To address this issue a multifunctional SAW sensor is presented. The sensor consists of two SAW delay lines oriented orthogonal to each on ST-quartz in order to generate two distinct wave modes. One wave mode is used for sensing while the other is used to remove loosely bound material. By using the same transduction mechanism for both removal and sensing, the sensor chip is simplified and complex electronics are avoided. The findings of this research involve the technological advances for SAW biosensors that make their use in POCT possible.

This thesis takes a fresh approach to cochlear mechanics. Over the last quarter of a century, we have learnt that the cochlea is active and highly tuned, observations suggesting that something may be resonating. Rather than accepting the standard traveling wave interpretation, here I investigate whether a resonance theory of some kind can be applied to this remarkable behaviour.¶ A historical survey of resonance theories is first conducted, and advantages and drawbacks examined. A corresponding look at the traveling wave theory includes a listing of its short-comings.¶ A new model of the cochlea is put forward that exhibits inherently high tuning. The surface acoustic wave (SAW) model suggests that the three rows of outer hair cells (OHCs) interact in a similar way to the interdigital transducers of an electronic SAW device. Analytic equations are developed to describe the conjectured interactions between rows of active OHCs in which each cell is treated as a point source of expanding wavefronts. Motion of a cell launches a wave that is sensed by the stereocilia of neighbouring cells, producing positive feedback. Numerical calculations confirm that this arrangement provides sharp tuning when the feedback gain is set just below oscillation threshold.¶ A major requirement of the SAW model is that the waves carrying the feedback have slow speed (5-200 mm/s) and high dispersion. A wave type with the required properties is identified - a symmetric Lloyd-Redwood wave (or squirting wave) - and the physical properties of the organ of Corti are shown to well match those required by theory.¶ The squirting wave mechanism may provide a second filter for a primary traveling wave stimulus, or stand-alone tuning in a pure resonance model. In both, cyclic activity of squirting waves leads to standing waves, and this provides a physical rendering of the cochlear amplifier. In keeping with pure resonance, this thesis proposes that OHCs react to the fast pressure wave rather than to bending of stereocilia induced by a traveling wave. Investigation of literature on OHC ultrastructure reveals anatomical features consistent with them being pressure detectors: they possess a cuticular pore (a small compliant spot in an otherwise rigid cell body) and a spherical body within (Hensens body) that could be compressible. I conclude that OHCs are dual detectors, sensing displacement at high intensities and pressure at low. Thus, the conventional traveling wave could operate at high levels and resonance at levels dominated by the cochlear amplifier. ¶ The latter picture accords with the description due to Gold (1987) that the cochlea is an ‘underwater piano’ - a bank of strings that are highly tuned despite immersion in liquid.¶ An autocorrelation analysis of the distinctive outer hair cell geometry shows trends that support the SAW model. In particular, it explains why maximum distortion occurs at a ratio of the two primaries of about 1.2. This ratio also produces near-integer ratios in certain hair-cell alignments, suggesting that music may have a cochlear basis.¶ The thesis concludes with an evaluation and proposals to experimentally test its validity.

It is demonstrated that by using a miniature chemical reaction vessel under adaptive mechatronic control, it is possible to design and construct a low-cost carbon dioxide measurement system. With further development such a system would be potentially suitable for low-cost commercial application, in particular as sacrificial, single-mission instrumentation packages in horticultural cargo monitoring. Current instrumentation systems for carbon dioxide (CO2) gas measurement are reviewed and their limitations with respect to low cost commercial applications determined. These utilise technology intended for laboratory measurements. In particular the optical energy absorbance of CO2 in the infra-red electromagnetic spectrum. These systems require large optical paths (typically 10cm) in order to measure small CO2 concentrations. This in turn has a large impact on the physical size of the sensing system. Of the many applications requiring online CO2 sensing packages (such as medical, petroleum, environmental and water treatment)the horticultural industry is the primary focus for this research. CO2 sensing systems are primarily used in horticulture to monitor the produce environment and help extend storage time. For these applications CO2 concentrations are typically low (in the range 0 to 1%) and the paramount need is for low-cost (and possibly disposable) sensing packages. The basis of the measurement technique is the use of bulk (but small volume) aqueous chemical reaction under mechatronic control. Unlike thin film technologies where very thin membranes are passively exposed to the gaseous sample, here a small volume (approximately 2mL) of simple and very cheap liquid chemical indicator (calcium hydroxide solution) is used to produce an opaque precipitate. CO2 concentration is then assessed by low-cost optical attenuation measurements of the developing opacity of the solution. The instrumentation package comprises pumps, flowmeter, reaction cell and infra-red optics for the turbidity measurement, plus reagent and waste vessels, pipelines and electronics. During each measurement cycle, the reaction cell is flushed, with fresh chemical indicator and a sample of gas admitted. The indicator and the sample gas are then vigorously mixed and the change in the indicators optical properties measured at regular intervals. An embedded 8-bit microcontroller performs the necessary analysis to deduce the CO2 concentration (as percentage by volume) for the sample gas by reference to one or more of five ``Time-To-Threshold'' calibration models. These models evaluate the trend in turbidity development as precipitate is formed. First and second prototypes of the measurement system have been constructed and their (low-cost) components and overall performance evaluated, the first a `proof-of-concept' and the second to investigate methodology shortcomings. As a result the design of a third prototype is outlined. The measurement systems have been shown to work adequately well within expected limitations, resulting in a usable low-cost measurement technique. The current prototypes have a useful range of at least 5% to 100% CO2 with a discrimination of typically +-6%. Deficiencies, particularly performance at low concentrations, are identified and potential enhancements for future prototypes proposed.

In this thesis, the study focuses on the tunable frequency ratio of Sierpinski Gasket fractal antennas and we use the SAW substrate of piezoelectric material. By using the fractal structure and the substrate of piezoelectric material, the goal of the miniaturized antenna is achieved. The proposed antenna can be widely used in wireless communication products. Firstly, we design the Sierpinski Gasket fractal antenna on the FR4 substrate. The asymmetric geometry of Sierpinski Gasket fractal structure is proposed and we choose the proper discontinuity locations to design the three-band and tunable antenna for IEEE 802.11b/g/a wireless communication systems. The preliminary design of the Sierpinski Gasket fractal structure on the piezoelectric substrate allows us to compare simulated and measured results to improve the non-ideal processing factors. Finally, comparing with the existing products, we reduce the size of the miniaturized fractal antenna to 5x5mm^2 on the SAW substrate by coplanar waveguide, coupled-fed, shorting with conductive adhesive and high iteration stage of half-Sierpinski Gasket fractal structure for GPS band and IEEE 802.11b/g applications.

The temperature coefficient of frequency (TCF), electromechanical coupling coefficient (K2) and surface acoustic wave (SAW) velocity are the major factors when choosing the substrates for surface acoustic wave devices. There exist a wide range for the designer to controll the above factors. This thesis adopted several methods to change the properties of SAW devices. First, the SAW velocity is increased using aluminum nitride (AlN) thin films deposited on z-cut LiNbO3 substrates. Besides, the ST-quartz is adopted as substrate for comparison to clarify the temperature characteristic of AlN itself. The well-known positive TCF material, silicon dioxide (SiO2), is also deposited on z-cut LiNbO3 substrates for the purpose of improving the TCF of SAW devices. Finally, the optimal piezoelectric bilayer structures will be conducted for the improvement of the properties of SAW devices on LiNbO3 substrate. AlN and SiO2 thin films are selected to be deposited on z-cut LiNbO3 and ST-cut quartz substrates using the reactive RF magnetron sputtering. The characteristics of AlN thin films are evaluated using the analyses of XRD, SEM and AFM. The optimized growth parameters of highly c-axis oriented AlN films deposited on LiNbO3 substrate are sputtering pressure of 3.5 mTorr, nitrogen concentration (N2/N2+Ar) of 60%, RF power density of 8.1 W/cm2 and substrate temperature of 400¢J. On the other hand, the optimal parameters for highly c-axis oriented AlN films deposited on quartz substrate are sputtering pressure of 15 mTorr, nitrogen concentration of 30%, RF power density of 8.1 W/cm2 and substrate temperature of 400¢J. In addition, the interdigital transducers (IDTs) are fabricated on LiNbO3, AlN/LiNbO3, SiO2/LiNbO3, quartz and AlN/quartz substrates, respectively. The characteristic parameters of SAW devices are measured by Hewlett-Packard (HP) 8720 network analyzer. For SiO2/LiNbO3 SAW devices, the SiO2 thin films reveal the compensation of TCF, but the surface wave velocity remain almost unchanged. For AlN/quartz SAW devices, the positive temperature coefficient of AlN is clarfied by taking ST-quartz substrates as comparison. For AlN/LiNbO3 SAW devices, the characteristic improvements of frequency increase and TCF compensation of LiNbO3 SAW devices are achieved at the same time.

The composition-dependent Curie temperature and bias-dependant dielectric permittivity of Barium Strontium Titanate (BST) makes it very attractive for tunable application in the RF/Microwave regime. In this research work, the performance of BST varactors fabricated on the conventional Pt/Ti/SiO2/Si bottom electrode stack were compared with those fabricated using chemical vapor deposited Nanocrystalline Diamond (NCD) as the diffusion barrier layer instead of SiO2. The varactors fabricated on NCD films displayed much better symmetry in capacitance-voltage behavior and better overall quality factors than varactors fabricated on SiO2. The improvement in performance can be attributed to existence of stable interfaces in the devices fabricated on NCD which reduced the bottom electrode losses at high frequencies. The SiO2 based BST varactors on the other hand displayed better reliability and breakdown fields. The main purpose of this research work is to develop a robust Metal Insulator Metal (MIM) structure to achieve better all round performance of BST varactors. In the second part of this research work, the prospect of developing diamond based layered Surface Acoustic Wave (SAW) devices using Ba0.8Sr0.2TiO3 as the piezoelectric layer is investigated. Structural characterization of BST thin films deposited on Si/NCD/Pt and Si/SiO2/Ti/Pt stack were performed using X-Ray Diffraction (XRD) and Atomic Force Microscopy (AFM). Cross-sectional studies on the two stacks were performed using Scanning Electron Microscopy (SEM). X-Ray Mapping (XRM) was then done to ascertain the quality of the interfaces and to check for interdiffusion between layers. MIM structures in the Coplanar Waveguide (CPW) configuration were fabricated using conventional lithography and etching techniques for high frequency measurements. The performance of the fabricated varactors was characterized from 100 MHz to 1 GHz. For the SAW application, structural characterization of Ba0.8Sr0.2TiO3 on Chemical Vapor Deposited (CVD) diamond was done and the deposition procedure was optimized to obtain thick BST films. SAW bandpass filters and resonators were designed wherein the device geometry was varied over a wide range in order to characterize the variation in device performance with geometry. Finally interdigital capacitor structures were fabricated and used for conducting Curie temperature measurements on the deposited BST films in order to determine the operation range of the deposited BST films.

Surface acoustic wave (SAW) sensors detect chemical and biological species by monitoring the shifts in frequency of surface acoustic waves generated on piezoelectric substrates. Incorporation of nanomaterials having increased surface area as sensing layer have been effective in improving the sensitivity as well as miniaturization of SAW sensors. Selectivity, sensitivity and speed of response are the three primary aspects for any type of sensor. This dissertation focuses on design and development of SAW devices with novel transducer configurations employing nanomaterial sensing layers for enhanced sensing, improved selectivity, and speed of response. The sensing mechanism in these SAW sensors is a complex phenomenon involving interactions across several different length and time scales. Surface acoustic wave propagation at the macro-scale is influenced by several kinetic phenomena occurring at the molecular scale such as adsorption, diffusion, reaction, and desorption which in turn depend on the properties of nanomaterials. This suggests the requirement of a multi-scale model to effectively understand and manipulate the interactions occurring at different length scales, thereby improving sensor design. Sensor response modeling at multiple time and length scales forms part of this research, which includes perturbation theories, and simulation techniques from finite element methods to molecular-level simulations for interpreting the response of these surface acoustic wave chemical and biosensors utilizing alloy nanostructures as sensing layers. Molecular modeling of sensing layers such as transition metal alloy nanoclusters and nanowires is carried out to gain insights into their thermodynamic, structural, mechanical and dynamic properties. Finite element technique is used to understand the acoustic wave propagation at the macroscale for sensing devices operating at MHz frequencies and with novel transducer designs. The findings of this research provide insights into the design of efficient surface acoustic wave sensors. It is expected that this work will lead to a better understanding of surface acoustic wave devices with novel transducer configurations and employing nanomaterial sensing layers.

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