Papers by Ligia Ciocci Brazzano
arXiv (Cornell University), Mar 21, 2024
We present Montecarlo and Genetic Algorithm optimisations applied to the design of photodetectors... more We present Montecarlo and Genetic Algorithm optimisations applied to the design of photodetectors based on a transimpedance amplifier and a photodiode. The circuit performance is evaluated with a merit function and the systematic search method is used as a reference. The design parameters are the feedback network components and the photodiode bias voltage. To evaluate the optimisations, we define the relative difference between its merit and the optimum merit obtained by the systematic search. In both algorithms, the relative difference decreases with the number of evaluations, following a power law. The power-law exponent for the Genetic Algorithm is larger than that of Montecarlo (0.74 vs. 0.50). We conclude that both algorithms are advantageous compared to the systematic search method, and that the Genetic Algorithm shows a better performance than Montecarlo.
Revista elektrón, Nov 16, 2017
This paper presents the implementation and electric characterization of a broadband piezoelectric... more This paper presents the implementation and electric characterization of a broadband piezoelectric polymer sensor with linear geometry based on a thin film of polyvinylidene fluoride. The electrical impedance of the sensor was measured as a function of frequency, and it was found that the polymer was practically not altered by the sensor fabrication process. Also, the sensor frecuency response with a transimpedance amplifier was measured. Due to the high electrical capacitance of the device, a large reduction of the system broadband was found. Resumen-En este trabajo se presenta la implementación y caracterización eléctrica de un sensor polimérico piezoléctrico de banda ancha con geometría lineal, basado en una película delgada de fluoruro de polivinilideno. Se midió la impedancia eléctrica del sensor en función de la frecuencia, encontrándose que el polímero prácticamente no fue alterado por el proceso de fabricación del sensor. Además, se estudió la respuesta en frecuencia del sensor con un amplificador de transimpedancia, observándose una marcada reducción del ancho de banda del sistema debida a la elevada capacitancia del dispositivo.
Computer Physics Communications, 2016
The knowledge of electrical and mechanical properties of material, relies on a precise analysis o... more The knowledge of electrical and mechanical properties of material, relies on a precise analysis of the relaxation spectra. We explore the ability of a Bayesian method to achieve an accurate estimation of spectral parameters. We implemented a parallel-tempering Markov-chain Monte Carlo algorithm and used it to fit simulated and measured spectra. An exhaustive testing of the code shows that it presents an extremely good performance, accurately fitting complex spectra under strong noise and overlapping components. We conclude that this technique is quite suitable for relaxation spectra analysis, complementing classical methods.
Review of Scientific Instruments, Sep 1, 2017
In this work, we present a three-dimensional model for the design of wideband piezoelectric polym... more In this work, we present a three-dimensional model for the design of wideband piezoelectric polymer sensors which includes the geometry and the properties of the transducer materials. The model uses FFT and numerical integration techniques in an explicit, semi-analytical approach. To validate the model, we made electrical and mechanical measurements on homemade sensors for optoacoustic applications. Each device was implemented using a polyvinylidene fluoride thin film piezoelectric polymer with a thickness of 25 µm. The sensors had detection areas in the range between 0.5 mm 2 and 35 mm 2 and were excited by acoustic pressure pulses of 5 ns (FWHM) from a source with a diameter around 10 µm. The experimental data obtained from the measurements agree well with the model results. We discuss the relative importance of the sensor design parameters for optoacoustic applications and we provide guidelines for the optimization of devices.
In previous work we presented the implementation and electric characterization of a broadband pie... more In previous work we presented the implementation and electric characterization of a broadband piezoelectric polymer sensor with linear geometry, based on a thin film of polyvinylidene fluoride. In this paper we performed the electroacoustic characterization of the same sensor through the measurement of its response to short acoustic pulses (<50 ns), using a parametric model. We determined the polymer properties (relaxation time and acoustic attenuation), the reflexion coefficients of the water-polymer and polymer-substrate interfaces, the ultrasonic beam pattern and the sensitivity of the detector. The results of this work show that the implemented sensor is suitable for optoacoustic tomography detection systems.
Polymer Testing, Aug 1, 2014
Piezoelectric materials are usually characterized using resonant methods. However, piezoelectric ... more Piezoelectric materials are usually characterized using resonant methods. However, piezoelectric polymers are used in broadband devices, thus requiring characterization over a wide range of frequencies. In this work, we present a non-resonant method for the broadband electromechanical characterization of piezoelectric polymer thin films. The procedure is based on measuring the complex capacitance of a sample of known geometry under three conditions: free, blocked and immersed in a fluid of known acoustic properties. The behaviour of the sample under study is modelled as a one-dimensional transducer and treated as a two-port network that relates the measurable electrical and mechanical variables. Also, the sample is considered as a free-space radiator when immersed in a fluid. The method determines the intensive and the equivalent circuit parameters of piezoelectric polymer films, allowing the characterization of elastic and electrical properties in a broad frequency range. In order to test the method, we performed isothermal capacitance measurements on a sample of poly(vinylidene fluoride) at a temperature of 298 K. The sample was measured along the direction of the poling field and in the frequency range from 10 Hz to 10 MHz. The results given by the method agree with those reported by other authors.
The detection system for optoacoustic tomography (OAT) usually employs broadband piezoelectric se... more The detection system for optoacoustic tomography (OAT) usually employs broadband piezoelectric sensors based on polymeric materials. Polyvinylidene fluoride (PVDF) and its copolymers are amongst the most popular ones. Within our knowledge, the existing reconstruction algorithms for OAT neglect the electrical and mechanical relaxation processes of the polymeric material. In a previous work, it was found that the ultimate limits of the polymeric sensor performance are given by the material properties. In this work a deconvolution filter, that minimizes the distortions introduced by the sensor, was developed based on a parametric model. This filter was used in a reconstruction algorithm based on the backprojection method with simulated signals from an 2-D OAT. The results show that it is possible to obtain a remarkable improvement in the resolution of the image.Resumen— El sistema de detección para tomografía optoacústica (TOA) generalmente emplea sensores piezoeléctricos de banda ancha basados en materiales poliméricos. El fluoruro de polivinilideno (PVDF) y sus copolímeros se encuentran entre los más populares. Según nuestro conocimiento, los algoritmos de reconstrucción existentes para TOA no tienen en cuenta los procesos de relajación eléctrica y mecánica del material polimérico. En un trabajo previo, se encontró que los límites últimos del rendimiento del sensor están dados por las propiedades del material polimérico. En este trabajo se desarrolló un filtro de desconvolución, basado en un modelo paramétrico, que minimiza las distorsiones introducidas por el sensor. Este filtro se usó en un algoritmo de reconstrucción basado en el método de retroproyección con señales simuladas de un TOA 2-D. Los resultados muestran que es posible obtener una mejora notable en la resolución de la imagen.
2021 IEEE UFFC Latin America Ultrasonics Symposium (LAUS)
In this work we carry out a detailed analysis of the design and performance of an optical quasi-p... more In this work we carry out a detailed analysis of the design and performance of an optical quasi-point ultrasound detector for optoacoustic tomography. The detector is a two-dielectric system based on a glass prism (for light coupling) and water. The behaviour of the system is analyzed for six different modes of operation that arise from monitoring the amplitude and phase of the electric field of the reflected optical beam. For both amplitude and phase monitoring, we consider modes of operation centered on parallel and perpendicular components of the electric field individually and a differential mode (parallel-perpendicular). For each operation mode, we estimate the best set of parameters (refractive indices and angle of incidence). We verify that the optimum performance, in terms of sensitivity, is obtained when the angle of incidence of the interrogation beam is close to the critical angle. The best performance for operation modes based on monitoring an individual parameter is obtained by means of glass prisms with low refractive index, whereas for differential modes of operation higher refractive indices are preferred. We verify the linearity of each configuration by means of the numerical calculation of the total harmonic distortion
Revista Elektrón, 2017
Optoacoustic imaging is a hybrid technique with a rapid evolution within the area of biomedical i... more Optoacoustic imaging is a hybrid technique with a rapid evolution within the area of biomedical imaging. It combines the rich and versatile optical contrast with the high spatial resolution associated with the low-dispersion ultrasonic wave propagation nature. Its application raises a series of difficult problems that require further developments. One of them, the objective of this work, is to analyze how the optoacoustic image reconstruction algorithms are affected by the use of non-ideal (real) broadband sensors. In particular, as an original contribution, we study the case of integrating ultrasonic sensors based on piezoelectric polymer thin films. In order to achieve this, a temporary back-projection algorithm was implemented for line detectors. Then, using a parametric model for this type of sensors, we studied the influence of the use of a real device on the efficiency of the implemented algorithm.
2018 IEEE Biennial Congress of Argentina (ARGENCON), 2018
The detection system for optoacoustic tomography (OAT) usually employs broadband piezoelectric se... more The detection system for optoacoustic tomography (OAT) usually employs broadband piezoelectric sensors based on polymeric materials. Polyvinylidene fluoride (PVDF) and its copolymers are amongst the most popular ones. Within our knowledge, the existing reconstruction algorithms for OAT neglect the electrical and mechanical relaxation processes of the polymeric material. In a previous work, it was found that the ultimate limits of the polymeric sensor performance are given by the material properties. In this work a deconvolution filter, that minimizes the distortions introduced by the sensor, was developed based on a parametric model. This filter was used in a reconstruction algorithm based on the backprojection method with simulated signals from an 2-D OAT. The results show that it is possible to obtain a remarkable improvement in the resolution of the image.Resumen— El sistema de detección para tomografía optoacústica (TOA) generalmente emplea sensores piezoeléctricos de banda ancha basados en materiales poliméricos. El fluoruro de polivinilideno (PVDF) y sus copolímeros se encuentran entre los más populares. Según nuestro conocimiento, los algoritmos de reconstrucción existentes para TOA no tienen en cuenta los procesos de relajación eléctrica y mecánica del material polimérico. En un trabajo previo, se encontró que los límites últimos del rendimiento del sensor están dados por las propiedades del material polimérico. En este trabajo se desarrolló un filtro de desconvolución, basado en un modelo paramétrico, que minimiza las distorsiones introducidas por el sensor. Este filtro se usó en un algoritmo de reconstrucción basado en el método de retroproyección con señales simuladas de un TOA 2-D. Los resultados muestran que es posible obtener una mejora notable en la resolución de la imagen.
In this work we present the study, development and characterization of a cylindrical focused ultr... more In this work we present the study, development and characterization of a cylindrical focused ultrasonic sensor based on a piezoelectric polymeric material. For the design and implementation of the transducer, we carried out simulations using the commercial tool k-Wave and we used a construction method with great repeatability and low cost. For the characterization of the detection system (sensor + amplifier), we made electrical and acoustic measurements that allowed to determine its sensitivity and equivalent pressure noise. The results of this work show that the implemented sensor is suitable for optoacoustic tomography.
2018 IEEE Biennial Congress of Argentina (ARGENCON), 2018
In previous work we presented the implementation and electric characterization of a broadband pie... more In previous work we presented the implementation and electric characterization of a broadband piezoelectric polymer sensor with linear geometry, based on a thin film of polyvinylidene fluoride. In this paper we performed the electroacoustic characterization of the same sensor through the measurement of its response to short acoustic pulses (<50 ns), using a parametric model. We determined the polymer properties (relaxation time and acoustic attenuation), the reflexion coefficients of the water-polymer and polymer-substrate interfaces, the ultrasonic beam pattern and the sensitivity of the detector. The results of this work show that the implemented sensor is suitable for optoacoustic tomography detection systems.
Review of Scientific Instruments, 2021
Designing detection systems based on transimpedance amplifiers is a complex task because noise, f... more Designing detection systems based on transimpedance amplifiers is a complex task because noise, frequency response, and stability are coupled constraints. This work presents a straightforward design method of detection systems based on transimpedance amplifiers. We take into account the objectives, scope of the design, and requirements and specifications, including the input signal levels. According to the small-signal model, the noise and stability are analyzed in detail. We present a systematic procedure to search for the acceptable values of the feedback network components based on these analyses. Then, we define a merit function to compare the performance of the acceptable combinations of feedback network components. For every acceptable combination, the function gives a quantitative measure of the degree of compliance for each design parameter: signal-to-noise ratio, highest operating frequency, and phase margin. As an example, we apply the method to optimize the design of an o...
Journal of Modern Optics, 2021
Sensors based on surface plasmon resonance present attractive features for the detection of narro... more Sensors based on surface plasmon resonance present attractive features for the detection of narrow acoustic pulses since they can behave as quasi-point detectors. In order to detect fast ultrasound pressure waves, the system senses the intensity of the reflected beam for a fixed angle of incidence and for a fixed wavelength. Therefore, optimal conditions for Kretschmann's glass-metal-water configuration are presented. Optimization is performed by means of numerical simulations of the reflectivity curves for different low-cost metallic films with different thicknesses and angles of incidence. Zn, Ti, Cr, Al, and Cu are evaluated and compared with Au. In addition, the wavelength selection is discussed, and the oxidation effects are also briefly analysed.
Optics Communications, 2020
In this work, the first and second order effects for reflected and transmitted pulses with a Gaus... more In this work, the first and second order effects for reflected and transmitted pulses with a Gaussian distribution of frequencies are analytically developed and interpreted. They show some peculiar characteristics that bear certain parallelism with those of monochromatic beams with a Gaussian distribution of amplitudes. However, when the former are considered, the results of the first and second order effects obtained analytically are more difficult to interpret and are clearly limited by the principle of causality. We show that pulses show some peculiar characteristics when they reflect and transmit through linear media: time delay, shifting of the mean frequency and modification of the pulse width. In addition to these effects we show and analyze the unexpected presence of chirping when a simple structure of non-dispersive materials is considered.
Elektron, 2020
Este trabajo presenta criterios de selección de materiales y parámetros de celdas en cuña para re... more Este trabajo presenta criterios de selección de materiales y parámetros de celdas en cuña para refractometría en el rango visible. Estas celdas consisten en dos prismas de ángulo recto enfrentados, que definen una cavidad con forma de cuña entre ellas, en la que se coloca la muestra cuyo índice de refracción se desea medir. Éste se determina a partir de la desviación de un haz luminoso que atraviesa la celda. Este modelo para fines de ingeniería tiene en cuenta la geometría de la celda y los índices de refracción del material de la celda y de la muestra. A partir de allí realizamos el cálculo numérico y trazado de rayos correspondiente al sistema óptico. También proponemos ajustes polinómicos para simplificar el tratamiento numérico, como complemento de las ecuaciones completas. Estos polinomios dan el índice de refracción de la muestra como una función explícita del ángulo de deflexión. Se incluye además el análisis de los errores de la aproximación.
Elektron, 2017
La obtención de imágenes optoacústicas es una técnica híbrida con una rápida evolución dentro del... more La obtención de imágenes optoacústicas es una técnica híbrida con una rápida evolución dentro del área de imágenes biomédicas. Ésta se beneficia tanto del rico y versátil contraste óptico como de la alta resolución espacial asociada con la naturaleza de baja dispersión de propagación de las ondas ultrasónicas. Su aplicación plantea una serie de difíciles problemas que exigen ulteriores desarrollos. Uno de ellos, el objetivo de este trabajo, es analizar cómo afecta a los algoritmos de reconstrucción de imágenes optoacústicas el uso de sensores no ideales (reales) de banda ancha. En particular, como aporte original, se estudia el caso de los sensores ultrasónicos extensos basados en películas delgadas de polímeros piezoeléctricos. Para lograr esto, se implementó un algoritmo de retroproyección temporal para detectores lineales. Luego, usando un modelo paramétrico para este tipo de sensores, se estudió la influencia del uso de un dispositivo real sobre la eficiencia del susodicho algor...
Elektron, 2017
En este trabajo se presenta la implementación y caracterización eléctrica de un sensor polimérico... more En este trabajo se presenta la implementación y caracterización eléctrica de un sensor polimérico piezoléctrico de banda ancha con geometría lineal, basado en una película delgada de fluoruro de polivinilideno. Se midió la impedancia eléctrica del sensor en función de la frecuencia, encontrándose que el polímero prácticamente no fue alterado por el proceso de fabricación del sensor. Además, se estudió la respuesta en frecuencia del sensor con un amplificador de transimpedancia, observándose una marcada reducción del ancho de banda del sistema debida a la elevada capacitancia del dispositivo.
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Papers by Ligia Ciocci Brazzano