Design, modelling, characterization and implementation of acoustic lenses for modulation of ultrasound beams.

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/10251/159895TESISCompendi

Diseño y optimización de lentes acústicas de índice de refracción variable para la focalización de ultrasonidos en agua

En este trabajo se analizan las propiedades de propagación de las ondas sonoras en un sistema con simetría axial cuyos dispersores son toroides rígidos. El objetivo es el diseño, construcción y caracterización de un sistema para la focalización eficiente de las ondas mediante elementos pasivos (lente acústica). Mediante simulaciones numéricas en el dominio frecuencial, basadas en el método de los elementos finitos, se muestra la posibilidad de control espectral y espacial de las ondas acústicas propagándose a través de una estructura de compuesta de dispersores de tipo toroidal. El interés del uso de estructuras axisimétricas para la focalización radica en que ésta es la simetría presente en la mayoría de las fuentes acústicas tanto en el rango audible como en ultrasonidos. En el trabajo se discuten los resultados numéricos y los datos experimentales que se han obtenido para una lente axisimétrica que trabaja en el rango de grandes longitudes de onda (régimen de homogenización) y se comporta como un lente con un gradiente espacial de índice de refracción. Las propiedades de focalización y la caracterización del foco obtenido mediante esta lente son el eje principal de este trabajo. El sistema está diseñado bajo la suposición de que las ondas se propagan en el régimen de la acústica lineal, y por tanto podría ser totalmente re-escalado a otros rangos de frecuencia. Con vistas a futuras aplicaciones en un futuro se aplicación en ultrasonidos, donde la focalización cobra importancia en diversas aplicaciones.The properties of sound wave propagation in a sonic crystal with axial symmetry is analyzed. The scatters are rigid toroids. The aim is the design, construction and characterization of a system to get an high focalization of waves through passive elements (acoustic lens). The control of the frequency and spatial spectrum of the system is shown by means of numerical simulations in the frequency domain. Axi-symmetrical structures have been used for focalization purposes because it is the kind of symmetry found in most of the acoustic sources in the audible range as well as in ultrasound. The paper deals with the numerical results and the experimental data obtained for an axi-symmetrical lens working in the long wave length regime and behaves as a lens with a spatial gradient of refraction index. The system is designed under the supposition that the waves propagate according to lineal acoustic equations, and therefore it may be scaled to other frequency ranges.Tarrazó Serrano, D. (2013). Diseño y optimización de lentes acústicas de índice de refracción variable para la focalización de ultrasonidos en agua. Universitat Politècnica de València. http://hdl.handle.net/10251/35226Archivo delegad

Polyadic Cantor Fractals: Characterization, Generation, and Application as Ultrasonic Lenses

The term fractal was coined in 1975 by Benoit Mandelbrot. Since then, fractal structures have been widely used by the international scientific community. Its range of applications includes multiple areas, such as optics, physics, cryptography, medicine, economics, and so on. The application of fractal structures to modulate light beams in the field of optics has been extensively studied, and it has been shown that in some cases these new fractal lenses improve the response of traditional lenses. Fractal lenses are able to provide beamforming capabilities, and allow the optimization of the optical beam according to the specific requirements. In some applications, it may be necessary to improve the focus in a certain area, while in others it may be critical to obtain a sharp attenuation by means of destructive interference. It may even be required a beam profile with multiple focus and a certain control over them. This work investigates the application of fractal structures based on Polyadic Cantor sets as ultrasonic lenses, analyzing how the relation between the different design parameters and the performance of the lens. It is shown that the working frequency becomes a precise control mechanism that can modify dynamically the focus position of the lens

Enhancement of pupil-masked wavelength-scale gas-filled flat acoustic lens based on anomaly apodization effect

[EN] In this letter, the improvement in focus by the use of a pupil mask produced in an acoustic mesoscale cuboid particle ¿lled with CO2 is reported. Thereby, the result shows that the pupil mask increases the sound intensity and also increases the resolution (or a reduction of the full width at half maximum, FWHM) in focus compared to the non-masked one. These results are important because they con¿rm the effect of abnormal amplitude apodization for a one-wavelength dimension acoustic lens and demonstrate that it is possible to improve sound focusing of a cuboid gas-¿lled lens with one wavelength dimension. This is the smallest size of an acoustic lens ever considered in this type of literature, with side dimensions of the cube equal to one wavelength and a diameter to focus ratio of 2.5, the sound ampli¿cation in focus is 5.4 dB at 4125 Hz, with the resolution near to the diffraction limit.This work has been supported by TEC2015-70939-R (MINECO/FEDER). The research was partially supported by Tomsk Polytechnic University Competitiveness Enhancement Program.Rubio Michavila, C.; Tarrazó-Serrano, D.; Minin, OV.; Uris Martínez, A.; Minin, IV. (2019). Enhancement of pupil-masked wavelength-scale gas-filled flat acoustic lens based on anomaly apodization effect. Physics Letters A. 383:396-399. https://doi.org/10.1016/j.physleta.2018.11.014S39639938

MRI Compatible Planar Material Acoustic Lenses

[EN] Zone plate lenses are used in many areas of physics where planar geometry is advantageous in comparison with conventional curved lenses. There are several types of zone plate lenses, such as the well-known Fresnel zone plates (FZPs) or the more recent fractal and Fibonacci zone plates. The selection of the lens material plays a very important role in beam modulation control. This work presents a comparison between FZPs made from different materials in the ultrasonic range in order to use them as magnetic resonance imaging (MRI) compatible materials. Three different MRI compatible polymers are considered: Acrylonitrile butadiene styrene (ABS), polymethyl methacrylate (PMMA) and polylactic acid (PLA). Numerical simulations based on finite elements method (FEM) and experimental results are shown. The focusing capabilities of brass lenses and polymer zone plate lenses are compared.This research was funded by spanish Ministerio de Economía y Competitividad (MINECO) TEC2015-70939-R.Tarrazó-Serrano, D.; Castiñeira Ibáñez, S.; Sánchez Aparisi, E.; Uris Martínez, A.; Rubio Michavila, C. (2018). MRI Compatible Planar Material Acoustic Lenses. Applied Sciences (Basel). 8(12):2634-1-2634-9. doi:10.3390/app8122634S2634-12634-981

Acoustical hooks: A new subwavelength self-bending beam

[EN] In this work, we report the first experimental observation of a new type of near-field curved acoustic beam confirmed by simulations. This new curved acoustical beam is generated by asymmetric distribution of the vortices in a polymer Janus particle (particle with broken symmetry) immersed in water. The origin of the vortices is in the conversion of an incident longitudinal wave mode to a shear wave in a solid and then back to a longitudinal wave in the water and has unique features, the radius of curvature of acoustical hook is less than the wavelength. Indeed, it is the smallest radius of curvature ever recorded for any acoustical beams. These results may be potentially useful when an object, located in the path of the beam, must be avoided. It could also have potential applications in particle manipulations.This work has been supported by Spanish Ministry of Science, Innovation and Universities (grant No. RTI2018-100792-B-I00). The research was partially supported by the Russian Foundation for Basic Research (Grant No. 20-57-S52001) and by Tomsk Polytechnic University Competitiveness Enhancement Program. D.T.-S. acknowledges financial support from MICINN BES-2016-07713 project.Rubio Michavila, C.; Tarrazó-Serrano, D.; Minin, OV.; Uris Martínez, A.; Minin, IV. (2020). Acoustical hooks: A new subwavelength self-bending beam. Results in Physics. 16:1-5. https://doi.org/10.1016/j.rinp.2019.102921S151

Transient Analysis of Fresnel Zone Plates for Ultrasound Focusing Applications

[EN] Fresnel Zone Plates are planar lenses that can be used to focus ultrasound beams. This kind of acoustic lenses can play a key role in the resolution of ultrasonic NDT systems. In this type of pulse-echo applications, the pulse duration is an important parameter that specifies the axial resolution, and thus, shorter ultrasound pulses provide higher resolutions. However, acoustic lenses exhibit a transient response that should be considered when setting the pulse duration, as pulses shorter than the transient state duration result in degradation in the response of acoustic lenses in terms of focal intensity, focal displacement, and lateral and axial resolutions. In this work, a thorough analysis of the transient response of Fresnel Zone Plates is discussed, demonstrating that the transient state should be considered in order to achieve optimal focusing performance. Theoretical and numerical results are presented, showing very good agreement.This work has been supported by Spanish MICINN RTI2018-100792-B-I00 project, Generalitat Valenciana AICO/2020/139 and the Russian Governmental program "Science" project FSWW-2020-0014. The research is carried out within the framework of Tomsk Polytechnic University Competitiveness Enhancement Program grant VIU-MNOL NK 187/2020. S.P.-L. acknowledges financial support from Universitat Politècnica de València grant program PAID-01-18. D.T.-S. acknowledges financial support from MICINN BES-2016-07713 project.Pérez-López, S.; Tarrazó-Serrano, D.; Dolmatov, DO.; Rubio Michavila, C.; Candelas Valiente, P. (2020). Transient Analysis of Fresnel Zone Plates for Ultrasound Focusing Applications. Sensors. 20(23):1-9. https://doi.org/10.3390/s20236824S192023Albu, S., Joyce, E., Paniwnyk, L., Lorimer, J. P., & Mason, T. J. (2004). Potential for the use of ultrasound in the extraction of antioxidants from Rosmarinus officinalis for the food and pharmaceutical industry. Ultrasonics Sonochemistry, 11(3-4), 261-265. doi:10.1016/j.ultsonch.2004.01.015Li, J.-T., Han, J.-F., Yang, J.-H., & Li, T.-S. (2003). An efficient synthesis of 3,4-dihydropyrimidin-2-ones catalyzed by NH2SO3H under ultrasound irradiation. Ultrasonics Sonochemistry, 10(3), 119-122. doi:10.1016/s1350-4177(03)00092-0McCann, D. ., & Forde, M. . (2001). Review of NDT methods in the assessment of concrete and masonry structures. NDT & E International, 34(2), 71-84. doi:10.1016/s0963-8695(00)00032-3Chen, J., Xiao, J., Lisevych, D., Shakouri, A., & Fan, Z. (2018). Deep-subwavelength control of acoustic waves in an ultra-compact metasurface lens. Nature Communications, 9(1). doi:10.1038/s41467-018-07315-6Thomas, J.-L., & Fink, M. A. (1996). Ultrasonic beam focusing through tissue inhomogeneities with a time reversal mirror: application to transskull therapy. IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, 43(6), 1122-1129. doi:10.1109/58.542055Melde, K., Mark, A. G., Qiu, T., & Fischer, P. (2016). Holograms for acoustics. Nature, 537(7621), 518-522. doi:10.1038/nature19755Castiñeira-Ibáñez, S., Tarrazó-Serrano, D., Fuster, J., Candelas, P., & Rubio, C. (2018). Polyadic Cantor Fractal Ultrasonic Lenses: Design and Characterization. Applied Sciences, 8(8), 1389. doi:10.3390/app8081389Rubio, C., Fuster, J., Castiñeira-Ibáñez, S., Uris, A., Belmar, F., & Candelas, P. (2017). Pinhole Zone Plate Lens for Ultrasound Focusing. Sensors, 17(7), 1690. doi:10.3390/s17071690Zhou, Q., Xu, Z., & Liu, X. (2019). High efficiency acoustic Fresnel lens. Journal of Physics D: Applied Physics, 53(6), 065302. doi:10.1088/1361-6463/ab5878Schindel, D. W., Bashford, A. G., & Hutchins, D. A. (1997). Focussing of ultrasonic waves in air using a micromachined Fresnel zone-plate. Ultrasonics, 35(4), 275-285. doi:10.1016/s0041-624x(97)00011-5Calvo, D. C., Thangawng, A. L., Nicholas, M., & Layman, C. N. (2015). Thin Fresnel zone plate lenses for focusing underwater sound. Applied Physics Letters, 107(1), 014103. doi:10.1063/1.4926607Tarrazó-Serrano, D., Pérez-López, S., Candelas, P., Uris, A., & Rubio, C. (2019). Acoustic Focusing Enhancement In Fresnel Zone Plate Lenses. Scientific Reports, 9(1). doi:10.1038/s41598-019-43495-xSalazar, J., Turó, A., Chávez, J. A., Ortega, J. A., & García, M. J. (2000). Transducer resolution enhancement by combining different excitation pulses. Ultrasonics, 38(1-8), 145-150. doi:10.1016/s0041-624x(99)00177-8Salazar, J., Turo, A., Chavez, J. A., Ortega, J. A., & Garcia, M. J. (2003). High-power high-resolution pulser for air-coupled ultrasonic nde applications. 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Sound focusing of a wavelength-scale gas-filled flat lens

[EN] The capability of focusing of a novel acoustic lens based on a mesoscale acoustic cuboid particle filled with CO2 gas is analysed. This flat lens is able to focus sound in the same way that conventional curved acoustic lenses do. It is shown that the sound speed inside the cuboid is the responsible for this effect. By changing the percentage of CO2, the sound speed inside the cube changes and, therefore, the focusing properties change as well. The focusing effect is numerically investigated and experimentally validated. The results obtained allow the design of new flat low cost acoustic lenses with wavelength-scale dimensions for different applications.This work has been supported by TEC2015-70939-R (MINECO/FEDER). The research was partially supported by Tomsk Polytechnic University Competitiveness Enhancement Program. IVM and OVM would like to thank Dr RUBEN PICO VILA for useful discussions.Rubio Michavila, C.; Tarrazó-Serrano, D.; Minin, OV.; Uris Martínez, A.; Minin, IV. (2018). Sound focusing of a wavelength-scale gas-filled flat lens. EPL (Europhysics Letters). 123(6):64002-1-64002-4. https://doi.org/10.1209/0295-5075/123/64002S64002-164002-4123

Numerical simulation and laboratory measurements on the influence of fractal dimension on the acoustic beam modulation of a Polyadic Cantor Fractal lenses

[EN] The possibility of modulating the ultrasound beam produced by a transducer through lenses has become an important task. The fact that these lenses are flat, facilitates their design, construction and applications. If, in addition, the design itself incorporates geometries that affect differently the foci profile on the axial axis of the lens, improvements become more significant. In this work the design of a flat lens based on a Polyadic Cantor fractal geometries is presented. The influence of the so-called fractal dimension on the modulation of the ultrasonic beam to obtain the foci is analysed. In this paper, experimental results under controlled conditions are presented. The numerical solutions obtained have been validated.Investigation supported by the Ministry of Economy, Industry and Competitiveness, and the European Regional Development Fund TEC2015-70939-R (MINECO/FEDER).Tarrazó-Serrano, D.; Castiñeira Ibáñez, S.; Candelas Valiente, P.; Fuster Escuder, JM.; Rubio Michavila, C. (2019). Numerical simulation and laboratory measurements on the influence of fractal dimension on the acoustic beam modulation of a Polyadic Cantor Fractal lenses. Applied Acoustics. 148:119-122. https://doi.org/10.1016/j.apacoust.2018.12.012S11912214