This thesis discusses optoelectronic devices at mm-wave frequencies, focusing on optoelectronic beamforming and non-mechanical beam steering based on an optically excited Fresnel zone plate plasma. The optically controlled zone plate, termed the photo-injected Fresnel zone plate antenna (piFZPA) within this work, is introduced and a comprehensive theoretical framework developed. The design and optimisation of Fresnel zone plates are detailed, which determine the inherent performance of the piFZPA. A range of zone plates were designed, fabricated, and characterised at 94 GHz with up to 46 dBi gain, -26 dB sidelobe levels, and 67% aperture efficiency being measured for a quarter-wave design. The control of (sub) mm-wave beams by optical modulation of the complex permittivity of a semiconductor substrate is discussed. The significance of the free-carrier plasma dynamics, the effective lifetime, surface recombination, and the limits of the substrate which are imposed by the spatial resolution of the free-carrier plasma are highlighted, with the optimisation of these parameters discussed. The passivation quality of high-resistivity silicon wafers were characterised using a mm-wave photoconductance decay method, which yielded lifetime improvements from τ[subscript(eff)] = 60 us up to τ[subscript(eff)] ≈ 4,000 us, resulting in lowered recombination velocities (S = 15 cm/s). W-band characterisations of the passivated wafers illustrate the significance of surface recombination, with measured attenuations of up to 24 dB. Novel theoretical models are developed throughout this thesis, which yield insight into the requirements of optoelectronic devices, and are shown to agree well with measured data. The theoretical framework developed details the requirements, limitations, suitability, and design of piFZPAs at any frequency. A range of transmission-type piFZPAs are demonstrated and characterised at 94 GHz, both on-axis and off-axis, based on a novel architecture, with up to 8% aperture efficiency. Finally, the hybridisation of the piFZPA technique and well established visible display technologies, which has been developed throughout this thesis, enable low-cost, simple, and highly flexible optoelectronic devices, highlighting this method as an attractive solution to adaptive beamforming and non-mechanical steering at mm-wave and submm-wave frequencies.

Real-time optical scanning holography, which was first suggested by Poon and Korpel, was originally analyzed by Poon using an optical transfer function approach. The recording of holographic information using the optical heterodyne scanning technique has several advantages over conventional nonscanning optical holographic recording methods. We first review a new 3-D imaging technique called optical scanning holography (OSH) by acousto-optic two-pupil synthesis. We then derive 3-D holographic magnification, using three points configured as a 3-D object. We demonstrate three-dimensional imaging capability of OSH by holographically recording two planar objects at different depths and reconstructing the hologram digitally and optically using an electron-beam-addressed spatial light modulator (EBSLM). The second part of this dissertation investigates twin-image noise in optical scanning holography. In optical scanning holography, holographic information of an object is generated by 2-D active optical scanning. The optical scanning beam can be a time-dependent Gaussian apodized Fresnel zone pattern. We derive the resolution achievable with such a scanning beam. We then discuss the use of a larger and a smaller Fresnel zone pattern for holographic recording to investigate twin-image noise which results in the unwanted image in the reconstructed field. Finally, we discuss a novel multiplexing technique to solve the twin image problem in optical scanning holography without the use of a spatial carrier as commonly used in conventional off-axis holography. The technique involves simultaneously acquiring a sine and cosine Fresnel zone-lens pattern coded images by optical scanning. A complex addition of the two coded images then will be performed and decoded to give a twin-image rejection reconstruction. / Ph. D.

It is often claimed that the first Fresnel zone associated with the dominant frequency represents the spatial resolution limit of traveltime tomography. We show, however, that the relevant Fresnel limit for tomographic resolution is the maximum, not the dominant frequency in the data. For physically realizable causal wavelets, the maximum frequency is infinite. In practice, noise lowers the effective possible maximum frequency. To demonstrate these points, synthetic seismic data were generated for traveltime picking and inversion for a single, small velocity anomaly embedded in a homogeneous background velocity. A variety of traveltime picking techniques were tested and compared for their ability to detect the presence of objects smaller than that Fresnel zone associated with the dominant frequency. All methods produced accurate ray-theoretical (infinite-frequency) picks from noise-free seismic data for objects smaller than the dominant-frequency Fresnel zone. For the lowest dominant frequencies with Fresnel zones many times larger than the object, picking methods that focus on features along the onset of the first arrival were the most accurate, while cross-correlation with a known wavelet preformed less accurately. First-onset picking methods perform better because they take advantage of the highest frequencies in the data, whereas the correlation wavelet is typically in line with the dominant frequency. All methods successfully detected the presence of objects smaller than a wavelength. The inversion of the traveltime picks from the different picking methods always recovered the position and shape of the object. Random noise at a range of signal-to-noise ratios was then added to the seismic data and the data were repicked. Pick times with different noise realizations are statistically centered on the noise-free pick, not the time that would be recorded in the absence of the object. Trace stacking prior to picking or the averaging of many picks improves the signal-to-noise ratio and can extract signal that is not detected on an individual pick. An averaging of traveltime picks also occurs during tomographic inversion. This inherent signal-to-noise improvement allows tomography to image objects that are undetectable in individual trace picks. The resolution of tomography is limited not by the Fresnel zone associated with the dominant frequency, but by the accuracy of the traveltime picks. Resolution is further improved by dense ray coverage. / Master of Science

In this study nano-patterning was carried out using two different nano-optic devices namely- the NSOM and Fresnel zone plate. In the first study, NSOM was used to generate nano-patterns on selected semiconducting (Si and Ge) and metallic (Cr, Cu and Ag) targets under different laser pulse durations, laser energies and number of laser pulses. Based on the experimental results, femtosecond laser pulses, provided lower pattern generation thresholds on targets but higher damage thresholds to the NSOM probes at the wavelength (~400-410 nm) studied, compared with nanosecond laser pulses. Three different mechanisms were identified as the dominant processes for pattern generation under different conditions, namely nano-scale laser ablation, nano-scale thermal oxidation and nano-scale melting/recrystallization of the targets. Furthermore, the resulting nano-patterns also showed a significant dependence on the optical properties (i.e., absorption coefficient and surface reflectivity) of the target material. By comparing the obtained experimental results, it was concluded that the optical energy transport from the NSOM probe to the target dominates the pattern generation when femtosecond laser is applied to the NSOM system. When nanosecond laser is applied, both the thermal and optical energy transported from the NSOM probe to the targets attribute to the obtained morphology of nano-patterns on different targets under the experimental conditions studied. In the second study, a traditional Fresnel zone plate with a focus length of 3 micrometres was fabricated with a novel lift-off process in e-beam lithography. The fabrication process involved, using a HSQ/PMMA bi-layer in a negative tone lift-off process with a layer of conducting polyaniline for charge dissipation. HSQ was used as the high resolution negative resist for e-beam patterning and the PMMA under-layer was used to enable a HSQ lift-off process. The fabricated Fresnel zone plate was used to generate nano-patterns on a UV sensitive photoresist using nanosecond laser light with lamda~409nm. The smallest pattern sizes generated was close to the diffraction limit. Nano-pattern sizes generated on the photoresist were comparable with a numerically calculated intensity distribution at the focus spot of the designed Fresnel zone plate obtained from Scalar Diffraction Theory.

In this research, Fresnel zone plates were studied using an accurate, full-electromagnetic simulator based on the body-of-revolution finite-difference time-domain (BOR-FDTD) method. This tool was used to investigate zone plates for two different applications: zone plates used as antennas in communication systems and zone plates used as focusing elements in free-space, focused-beam measurement systems. Through detailed studies of zone plates for these applications, a number of general characteristics of the zone plate were given a more in-depth look than they have been given in the past. For the first application, parametric studies were performed for Soret, folded, and grooved-dielectric, phase-correcting zone plates for antenna applications. These studies were used to generate new design graphs, from which general observations are made about the effect of varying different parameters on the focusing ability of a zone plate. For the grooved-dielectric, phase-correcting zone plate, these studies show that a number of factors influence the focusing ability in ways that are unexpected, based on many of the simple techniques typically used to analyze zone plates. Each of these factors is evaluated individually. For the second application, a zone plate was designed to be used as a focusing element in a free-space, focused-beam measurement system. To determine the suitability of zone plates for this application, simulations and measurements of the electric field were used to compare this zone plate to a doubly-hyperbolic lens. A complete focused-beam system, using two zone plates as focusing elements, was used to measure the permittivity of different dielectric materials. These measurements are compared to results for a system that uses doubly-hyperbolic lenses and to published values. A technique for increasing the usable bandwidth of a zone plate in a focused-beam system was proposed and tested. Finally, as a topic for future research, the question is posed: Using the BOR-FDTD method, can a similar volume of material be shaped in a way that results in improved focusing performance compared to a traditional zone plate? Some insight into this open-ended question can be gained by examining preliminary results of the optimization of zone plates using of a genetic algorithm.

Multipath remains a dominant error source in Global Positioning System (GPS) applications that require high accuracy. With the use of differential techniques it is possible to remove many of the common-mode error sources, but the error effects of multipath have proven much more difficult to mitigate. The research aim of this work is to enhance the understanding of multipath propagation and its effects in GPS terrestrial applications, through the modelling of signal propagation behaviour and the resultant error effects. Multipath propagation occurs when environmental features cause combinations of reflected and/or diffracted replica signals to arrive at the receiving antenna. These signals, in combination with the original line-of-sight (LOS) signal, can cause distortion of the receiver correlation function and ultimately the discrimination function and hence errors in range estimation. To date, a completely satisfactory mitigation strategy has yet to be developed. In the search for such a mitigation strategy, it is imperative that a comprehensive understanding of the multipath propagation environment and the resultant error effects exists. The work presented here, provides a comprehensive understanding through the use of new modelling and simulation techniques specific to GPS multipath. This dissertation unites the existing theory of radio frequency propagation for the GPS L1 signal into a coherent treatment of GPS propagation in the terrestrial environment. To further enhance the understanding of the multipath propagation environment and the resultant error effects, this dissertation also describes the design and development of a new parabolic equation (PE) based propagation model for analysis of GPS multipath propagation behaviour. The propagation model improves on previous PE-based models by incorporating terrain features, including boundary impedance properties, backscatter and time-domain decomposition of the field into a multipath impulse response. The results provide visualisation as well as the defining parameters necessary to fully describe the multipath propagation behaviour. These resultant parameters provide the input for a correlation and discrimination model for visualisation and the generation of resultant receiver error measurements. Results for a variety of propagation environments are presented and the technique is shown to provide a deterministic methodology against real GPS data. The unique and novel combined modelling of multipath propagation and reception, presented in this dissertation, provides an effective set of tools that have enhanced the understanding of the behaviour and effect of multipath in GPS applications, and ultimately should aid in providing a solution to the GPS multipath mitigation problem.

The aim of this work was to prepare measuring workplace, perform the verication measurement, including the measurement phase, on the cylindrical surface. Measured data were compared with theoretical assumptions and were calculated directional patterns. Probes for measurement in the near sield were designed and realized.

Tesis por compendio / [ES] La capacidad de controlar y modificar los haces de energía ha sido motivo de investigación por parte de la comunidad científica desde largo tiempo atrás. En el campo de la acústica, este control energético de las ondas mecánicas tiene numerosas aplicaciones. Desde las aplicaciones industriales, alimentarias, farmacéuticas, etcétera hasta la biomedicina. Esta tesis se basa en la aplicación del control y modulación focal de los ultrasonidos para el uso en este último campo. Se puede modular y controlar los focos de ultrasonidos de diferentes formas. En este caso, se han desarrollado lentes planas que utilizan el principio de la difracción para lograr focalizar los haces. Las ventajas del uso de lentes planas de focalización permiten ser implementadas de forma sencilla en procesos de mecanización e incluso mediante impresión 3D. Se propone utilizar transductores planos que al emitir sobre una lente acústica, se produzca una conformación focal de características controladas. La lente conocida como lente de Fresnel (FZP) ha sido escogida como base de diseño en la implementación de las diferentes soluciones que logran cumplir con los objetivos marcados. Mediante la aplicación de modificaciones en una FZP se puede lograr pasar de una lente con capacidades extraordinarias de focalización a una lente capaz de controlar la resolución lateral y la profundidad de foco e incluso mejorar la ganancia. El objetivo final de aplicación es el uso en transductores de ultrasonidos de alta intensidad conocidos como HIFU. Mejorar la capacidad de resolución hace que se puedan desarrollar mejores terapias oncológicas que supongan un índice mayor de éxito en la lucha contra el cáncer. En la presente tesis se ha propuesto, además, una novedosa lente FZP basada en el cambio de fase que puede resultar un antes y un después en aplicaciones biomédicas. Se ha conseguido no solo mejorar la eficiencia de una FZP, sino que se ha conseguido implementar en materiales compatibles con resonancia magnética. Se han desarrollado modelos numéricos basados en el método de los elementos finitos que emulan la física involucrada. Las medidas han sido realizadas en condiciones controladas por un sistema robotizado de alta precisión. Todos los resultados obtenidos y publicados han sido desarrollados de forma numérica y experimental, validándose el método de trabajo y dando consistencia a las soluciones propuestas. / [CA] La capacitat de controlar i modificar els feixos d'energia ha sigut motiu d'investigació per part de la comunitat científica des de llarg temps arrere. En el camp de l'acústica, este control energètic de les ones mecàniques té nombroses aplicacions. Des de les aplicacions industrials, alimentàries, farmacèutiques, etcètera fins la biomedicina. Esta tesi es basa en l'aplicació del control i modulació focal dels ultrasons per a l'ús en este últim camp. Es pot modular i controlar els focus d'ultrasons de diferents formes. En este cas, s'han desenvolupat lents planes que utilitzen el principi de la difracció per a aconseguir focalitzar els feixos. Els avantatges de l'ús de lents planes de focalització permeten ser implementades de forma senzilla en processos de mecanització i inclús per mitjà d'impressió 3D. Es proposa utilitzar transductores plans que a l'emetre sobre una lent acústica, es produïsca una conformació focal de característiques controlades. La lent coneguda com a lent de Fresnel (FZP) ha sigut triada com a base de disseny en la implementació de les diferents solucions que aconseguixen complir amb els objectius marcats. Per mitjà de l'aplicació de modificacions en una FZP es pot aconseguir passar d'una lent amb capacitats extraordinàries de focalització a una lent capaç de controlar la resolució lateral i la profunditat de focus i inclús millorar el guany. L'objectiu final d'aplicació és l'ús en transductores d'ultrasons d'alta intensitat coneguts com HIFU. Millorar la capacitat de resolució fa que es puguen desenvolupar millors teràpies oncològiques que suposen un índex major d'èxit en la lluita contra el càncer. En la present tesi s'ha proposat, a més, una nova lent FZP basada en el canvi de fase que pot resultar un abans i un després en aplicacions biomèdiques. S'ha aconseguit no sols millorar l'eficiència d'una FZP, sinó que s'ha aconseguit implementar en materials compatibles amb ressonància magnètica. S'han desenvolupat models numèrics basats en el mètode dels elements finits que emulen la física involucrada. Les mesures han sigut realitzades en condicions controlades per un sistema robotitzat d'alta precisió. Tots els resultats obtinguts i publicats han sigut desenvolupats de forma numèrica i experimental, validant-se el mètode de treball i donant consistència a les solucions proposades. / [EN] The ability to control and modify energy beams has been the subject of research by the scientific community for a long time. In the acoustic field, this energetic control of mechanical waves has numerous applications. From industrial, food, pharmaceutical applications, et cetera, to biomedicine. This thesis is based on the ultrasound control and focal modulation applications. It is possible to modulate and control the ultrasound focii in different ways. In this case, flat lenses were developed based on the principle of diffraction to focus the beams. The advantages of using flat focusing lenses allow them to be easily implemented in machining and drilling processes and even through 3D printing. It was proposed to use planar transducers that when emitting on an acoustic lens, controlled characteristics of focal conformation were produced. The lens known as Fresnel Zone Plane (FZP) was chosen as the implementation design basis for the different solutions that manage to fulfill the objectives set. By applying modifications to an FZP it was possible to go from a lens with extraordinary focusing capabilities to a lens that was capable to control lateral resolution, depth of focus and even improving the gain. The final objective application was the use in high intensity ultrasound transducers known as HIFU. Improving the ability to resolve makes it possible to develop better cancer therapies that represent a higher rate of success in the fight against cancer. In the present thesis, a novel FZP lens based on phase change has also been proposed that can be a before and after in biomedical applications. It has not only been possible to improve the efficiency of an FZP, but it has also been possible to implement it in materials compatible with magnetic resonance imaging. Numerical models based on the finite element method were developed for emulating the involved physics. Measurements were carried out under controlled conditions by a high precision robotic system. All the results obtained and published were developed numerically and experimentally, validating the working method and giving consistency to the proposed solutions. / I want to acknowledge the following public funding sources that have made possible this research: Grant BES-2016-077133 (Ministerio de Ciencia, Innovación y Universidades de España) Project TEC2015-70939-R (MINECO/FEDER). Tomsk Polytechnic University within the framework of Tomsk Polytechnic University Competitiveness Enhancement Program. / Tarrazó Serrano, D. (2020). Design, modelling, characterization and implementation of acoustic lenses for modulation of ultrasound beams [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/159895 / TESIS / Compendio

Tesis por compendio / [ES] La focalización de ultrasonidos tiene muchas aplicaciones en una gran variedad de áreas tanto científicas como industriales. Los ultrasonidos focalizados son una de las herramientas principales usada por médicos en todo el mundo para obtener imágenes biomédicas de diferentes tipos de tejidos y órganos de manera no invasiva. En las últimas décadas, el uso de ultrasonidos focalizados de alta intensidad (HIFU, por sus siglas en inglés) ha surgido como una de las técnicas principales para el tratamiento de cáncer mediante la ablación térmica de tumores de manera no invasiva. Además, los ultrasonidos focalizados están emergiendo en los últimos años como uno de los métodos más prometedores para el tratamiento de las enfermedades cerebrales, con la aparición de nuevas técnicas disruptivas como la apertura reversible de la barrera hematoencefálica o la neuromodulación. En entornos industriales, los ultrasonidos son ampliamente utilizados como uno de los métodos principales para la evaluación no destructiva de materiales y estructuras, debido a que las ondas acústicas pueden penetrar en los objetos a distancias donde la luz no puede debido a la elevada absorción y dispersión. En este sentido, diseñar estructuras capaces de focalizar ultrasonidos es de una gran relevancia tanto para la comunidad científica como para los sectores médicos e industriales. Esta tesis presenta nuevos diseños de lentes acústicas capaces de controlar los parámetros principales del haz de ultrasonidos focalizados, proporcionando diferentes tipos de perfiles de focalización adecuados para una gran variedad de aplicaciones y escenarios. En particular, se han diseñado y adaptado al campo de los ultrasonidos las lentes de Fresnel (Fresnel Zone Plates, FZPs), ampliamente utilizadas en el campo de la óptica. Se ha presentado una nueva técnica de modulación espacio-temporal capaz de controlar la posición del foco de ultrasonidos tanto en espacio como en tiempo, aumentando así la versatilidad de este tipo de dispositivos. También se ha demostrado el funcionamiento en el campo de la acústica de nuevos diseños basados en aplicar secuencias binarias a una lente de Fresnel convencional, como las secuencias fractales de Cantor o las secuencias de M-bonacci generalizadas, capaces de modificar las propiedades de focalización de las lentes, incluyendo el número, posición y forma de los focos acústicos. Además, se introduce un nuevo diseño de lentes esféricas rellenas de líquido capaces de generar jets ultrasónicos, con mucho potencial en aplicaciones de imagen de alta resolución en campo cercano. Se ha demostrado que, cambiando el líquido interno de la lente o ajustando el ratio de mezcla entre dos líquidos, se pueden controlar los parámetros principales del jet. Los diseños propuestos en la tesis han sido validados tanto empleando simulaciones numéricas como realizando medidas experimentales, allanando el camino para el uso de este tipo de estructuras en aplicaciones de focalización de ultrasonidos. / [CA] La focalització d'ultrasons té moltes aplicacions en moltes àrees científiques i industrials. Els ultrasons focalitzats són una de les eines principals utilitzada per metges a tot el món per obtenir imatges biomèdiques de diferents tipus de teixits i òrgans de manera no invasiva. En les últimes dècades, els ultrasons focalitzats d'alta intensitat (HIFU, per les seues sigles en anglès) han aparegut com una de les tècniques principals per al tractament de càncer mitjançant l'ablació de tumors de manera no invasiva. A més, els ultrasons focalitzats estan emergint en els últims anys com un dels mètodes més prometedors per al tractament de les malalties cerebrals, amb l'aparició de noves tècniques disruptives com l'obertura reversible de la barrera hematoencefàlica o la neuromodulació. En entorns industrials, els ultrasons són àmpliament utilitzats com un dels mètodes principals per a l'avaluació no destructiva de materials i estructures, pel fet que les ones acústiques poden penetrar en els objectes a distàncies on la llum no pot a causa de l'elevada absorció i dispersió. En aquest sentit, dissenyar estructures capaces de focalitzar ultrasons és d'una gran rellevància tant per a la comunitat científica com per als sectors mèdics i industrials. Aquesta tesi presenta nous dissenys de lents acústiques capaços de controlar els paràmetres principals del feix d'ultrasons focalitzats, proporcionant diferents tipus de perfils de focalització adequats per a una gran varietat d'aplicacions i escenaris. En particular, s'han dissenyat i adaptat al camp dels ultrasons les lents de Fresnel (Fresnel Zone Plates, FZPs), àmpliament utilitzades en el camp de l'òptica. S'ha presentat una nova tècnica de modulació espai-temporal capaç de controlar la posició del focus d'ultrasons tant en espai com en temps, augmentant així la versatilitat d'aquest tipus de dispositius. També s'ha demostrat el funcionament en el camp de l'acústica de nous dissenys basats en aplicar seqüències binàries a una lent de Fresnel convencional, com les seqüències fractals de Cantor o les seqüències de M-bonacci generalitzades, capaces de modificar les propietats de focalització de les lents, incloent el nombre, posició i forma dels focus acústics. A més, s'introdueix un nou disseny de lents esfèriques plenes de líquid capaces de generar jets ultrasònics, amb molt potencial en aplicacions d'imatge d'alta resolució en camp proper. S'ha demostrat que, canviant el líquid intern de la lent o ajustant la ràtio de barreja entre dos líquids, es poden controlar els paràmetres principals del jet. Els dissenys proposats en la tesi han estat validats tant emprant simulacions numèriques com realitzant mesures experimentals, aplanant el camí per a l'ús d'aquest tipus d'estructures en aplicacions de focalització d'ultrasons. / [EN] Ultrasound focusing has many applications in a wide range of fields. Focused ultrasound is one of the main tools used by doctors all over the world to obtain biomedical images of different kind of tissues non-invasively. In the past decades, high intensity focused ultrasound (HIFU) appeared as one of the fundamental techniques for cancer treatment through non-invasive thermal tumor ablation. In addition, focused ultrasonic waves are recently emerging as one of the main tools to treat brain diseases, with novel disruptive techniques such as blood-brain barrier opening or neuromodulation. In industrial environments, ultrasonic waves are widely employed as one of the primary methods for the non-destructive evaluation (NDE) of materials and structures, as acoustic waves are able to penetrate deep into objects otherwise opaque using optical techniques. In this sense, designing structures capable of focusing ultrasonic waves is of great interest and relevance for the scientific, the industrial, and the biomedical sectors. This thesis devises new designs of acoustic lenses capable of controlling the main parameters of the focused ultrasound beam, achieving different kinds of focusing profiles suitable for a wide variety of scenarios. In particular, Fresnel Zone Plates (FZPs), commonly used in optics, are designed and adapted to the ultrasound domain. A novel spatio-temporal modulation technique capable of controlling the ultrasound focus location in both time and space is presented, increasing the versatility of this kind of devices. New design techniques based on applying a binary sequence to FZPs are also demonstrated, such as Cantor fractal sequences or generalized M-bonacci sequences, which modify the focusing properties of the lens, including the number, location, and shape of the different acoustic foci. In addition, acoustic jets generated by liquid-filled spherical lenses are devised for near-field high resolution imaging, demonstrating their applicability in the ultrasound domain. It is demonstrated that, by changing the inner liquid of the spherical lens or by tuning the mixing ratio between two liquids, the main focal parameters of the ultrasonic jet can be accurately controlled. The proposed designs are validated using both numerical simulations and experimental measurements, paving the way for the use of these kind of structures in focused ultrasound applications. / This work would not have been possible without the following funding sources: PAID-01-18 personal FPI grant from Universitat Politècnica de València; Spanish government MINECO TEC2015-70939-R project; Spanish government MICINN RTI2018-100792-B-I00 project; Generalitat Valenciana AICO/2020/139 project. / Pérez López, S. (2021). Design of Acoustic Lenses for Ultrasound Focusing Applications [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/179907 / TESIS / Compendio

[EN] Nature is nonlinear. The linear description of physical phenomena is useful for explain observations with the simplest mathematical models, but they are only accurate for a limited range of input values. In the case of intense acoustics waves, linear models obviate a wide range of physical phenomena that are necessary for accurately describe such high-amplitude waves, indispensable for explain other exotic acoustic waves and mandatory for developing new applied techniques based on nonlinear processes. In this Thesis we study the interactions between nonlinearity and other basic wave phenomena such as non-classical attenuation, anisotropic dispersion and periodicity, and diffraction in specific configurations. First, we present intense strain waves in a chain of cations coupled by realistic interatomic potentials. Here, the nonlinear ionic interactions and lattice dispersion lead to the formation of supersonic kinks. These intrinsically-nonlinear localized dislocations travel long distances without changing its properties and explain the formation of dark traces in mica crystals. Then, we analyze nonlinear wave processes in a system composed of multilayered acoustic media. The rich nonlinear dynamics of this system is characterized by its strong dispersion. Here, harmonic generation processes and the relation with its band structure are presented, showing that the nonlinear processes can be enhanced, strongly minimized or simply modified by tuning the layer parameters. In this way, we show how the dynamics of intense monochromatic waves and acoustic solitons can be controlled by artificial layered materials. In a second part, we include diffraction and analyze four types of singular beams. First, we study nonlinear beams in two dimensional sonic crystals. In this system, the inclusion of anisotropic dispersion is tuned for obtain simultaneous self-collimation for fundamental and second harmonic beams. The conditions for optimal second harmonic generation are presented. Secondly, we present limited diffraction beam generation using equispaced axisymmetric diffraction gratings. The obtained beams are truncated version of zero-th order Bessel beams. Third, the grating spacing can be modified to achieve focusing, where the generated nonlinear beams presents high gain, around 30 dB, with a focal width which is between the diffraction limit and the sub-wavelength regime, but with its characteristic high amplitude side lobes strongly reduced. Finally, we observe that waves diffracted by spiral-shaped gratings generate high-order Bessel beams, conforming nonlinear acoustic vortex. The conditions to obtain arbitrary-order Bessel beams by these passive elements are presented. Finally, the interplay of nonlinearity and attenuation in biological media is studied in the context of medical ultrasound. First, a numerical method is developed. The method solves the constitutive relations for nonlinear acoustics and the frequency power law attenuation of biological media is modeled as a sum of relaxation processes. A new technique for reducing numerical dispersion based on artificial relaxation is included. Second, this method is used to study the harmonic balance as a function of the power law, showing the role of weak dispersion and its impact on the efficiency of the harmonic generation in soft-tissues. Finally, the study concerns the nonlinear behavior of acoustic radiation forces in frequency power law attenuation media. We present how the interplay between nonlinearity and the specific frequency power law of biological media can modify the value for acoustic radiation forces. The relation of the nonlinear acoustic radiation force with thermal effects are also discussed. The broad range of nonlinear processes analyzed in this Thesis contributes to understanding the behavior of intense acoustic waves traveling trough complex media, while its implications for enhancing existent applied acoustics techniques are presented. / [ES] La Naturaleza es no lineal. La descripción lineal de los fenómenos físicos es de gran utilidad para explicar nuestras observaciones con modelos matemáticos simples, pero éstos sólo son precisos en un limitado rango de validez. En el caso de onda acústica de alta intensidad, los modelos lineales obvian un amplio rango de fenómenos físicos que son necesarios para describir con precisión las ondas de gran amplitud, pero además son necesarios para explicar otros procesos más exóticos e indispensables para desarrollar nuevas aplicaciones basadas en propagación no lineal. En esta Tesis, estudiamos las interacciones entre no linealidad y otros procesos complejos como atenuación no-clásica, dispersión anisotrópica y periodicidad, y difracción en configuraciones específicas. En primer lugar, presentamos ondas de deformación en una cadena de cationes acoplados por potenciales realísticas. Aquí, las interacciones no lineales entre iones, producen la conformación de kinks supersónicos. Estas dislocaciones localizadas intrínsecamente no lineales viajan por la red largas distancias sin variar sus propiedades, y pueden explicar la formación de trazas en minerales como la mica. Aumentando la escala del problema, estudiamos los procesos acústicos no lineales en medios multicapa. La rica dinámica de estos medios está caracterizada por la fuerte dispersión debido a la periodicidad del sistema. Aquí, estudiamos los procesos de generación de harmónicos, mostrando como modificando la estructura podemos potenciar, minimizar, o simplemente modificar artificialmente la transferencia de energía entre las componentes espectrales, y de esta manera controlar la dinámica de las ondas y solitones en el interior de la estructura. En la segunda parte, incluimos difracción y analizamos cuatro tipos de haces singulares. En primer lugar, analizamos haces ultrasónicos no lineales en cristales de sonido bidimensionales. En este sistema, las propiedades de anisotropía del medio son ajustadas para obtener la auto-colimación simultánea del primer y segundo harmónico. Así, se obtiene la propagación no difractiva para las dos componentes. En segundo lugar, presentamos haces de difracción limitada empleando rejillas de difracción axisimétricas. Por último, demostramos la generación de haces de Bessel de orden superior mediante estructuras en espiral. En la última parte, estudiamos la competición entre no linealidad y la atenuación y dispersión observable en medios biológicos en el contexto de las aplicaciones de biomédicas de los ultrasonidos. En primer lugar desarrollamos un nuevo método computacional para la dependencia frecuencial en forma de ley de potencia de la absorción característica de los tejidos. Este método en dominio temporal es usado posteriormente para revisar los procesos básicos no lineales prestando especial interés en el paper de la dispersión del tejido. Por último, la resolución de las ecuaciones constitutivas nos permite abordar la descripción no lineal de la fuerza de radiación acústica producida en tejidos biológicos, y las implicaciones existentes con la deposición de energía y transferencia de momento para ondas ultrasónicas de alta intensidad. El amplio abanico de procesos no lineales analizados en esta tesis contribuye a una mejor comprensión de la dinámica de las ondas acústicas de alta intensidad en medios complejos, donde las implicaciones existentes en cuanto a la mejora de sus aplicaciones prácticas son puestas de manifiesto. / [CA] La Naturalesa és no lineal. La descripció lineal dels fenòmens físics és de gran utilitat per a explicar les nostres observacions amb models matemàtics simples, però aquests sol són precisos en un limitat rang de validesa. En el cas d'ona acústica d'alta intensitat, els models lineals obvien un ampli rang de fenòmens físics que són necessaris per a descriure amb precisió les ones de gran amplitud, però a més són necessaris per a explicar altres processos més exòtics i indispensables per a desenvolupar noves aplicacions basades en propagació no lineal. En aquesta Tesi, estudiem les interaccions entre no-linealitat i altres processos complexos com atenuació no-clàssica, dispersió anisotròpica i periodicitat, i difracció en configuracions específiques. En primer lloc, presentem ones de deformació en una cadena de cations acoblats per potencials realistes. Ací, les interaccions no lineals entre ions, produeixen la conformació de kinks supersònics. Aquestes dislocacions localitzades intrínsecament no lineals viatgen per la xarxa llargues distàncies sense variar les seues propietats, i poden explicar la formació de traces en minerals com la mica. Augmentant l'escala del problema, estudiem els processos acústics no lineals en mitjans multicapa. La rica dinàmica d'aquests mitjans es caracteritza per la forta dispersió a causa de la periodicitat del sistema. Ací, estudiem els processos de generació d'harmònics, mostrant com modificant l'estructura podem potenciar, minimitzar, o simplement modificar artificialment la transferència d'energia entre les components espectrals, i d'aquesta manera controlar la dinàmica de les ones i solitons a l'interior de l'estructura. En la segona part, incloem difracció i analitzem quatre tipus de feixos singulars. En primer lloc, analitzem feixos ultrasònics no lineals en cristalls de so bidimensionals. En aquest sistema, les propietats d'anisotropia del medi són ajustades per a obtenir l'acte-col·limació simultània del primer i segon harmònic. Així, s'obté la propagació no difractiva per a les dues components. En segon lloc, presentem feixos de difracció limitada emprant reixetes de difracció axisimètriques. Per últim, vam demostrar la generació de feixos de Bessel d'ordre superior mitjançant estructures en espiral. En l'última part, estudiem la competició entre no linealitat i l'atenuació i dispersió observable en medis biològics en el context de les aplicacions biomèdiques dels ultrasons. En primer lloc desenvolupem un nou mètode computacional per a la dependència freqüencial en forma de llei de potència de l'absorció característica dels teixits biològics. Aquest mètode en domini temporal és usat posteriorment per a revisar els processos bàsics no lineals prestant especial interés en el paper de la dispersió del teixit. Per últim, la resolució de les equacions constitutives ens permet abordar la descripció no lineal de la força de radiació acústica produïda en teixits biològics, i les implicacions existents amb la deposició d'energia i transferència de moment per a ones ultrasòniques d'alta intensitat. L'ampli ventall de processos no lineals analitzats en aquesta tesi contribueix a una millor comprensió de la dinàmica de les ones acústiques d'alta intensitat en medis complexos, on les implicacions existents quant a la millora de les seues aplicacions practiques són posades de manifest. / Jiménez González, N. (2015). Nonlinear Acoustic Waves in Complex Media [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/53237 / TESIS / Premios Extraordinarios de tesis doctorales