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Introduction
Martín Germán González is a professor at the School of Engineering of the University of Buenos Aires (FIUBA), as well as a researcher at the National Scientific and Technical
Research Council (CONICET), Argentina and a member of the IEEE Photonics Society. Dr. González´s present research areas are design and characterization of ultrasonic sensors, optoacoustic imaging and artificial intelligence (machine and deep learning).
Current institution
Additional affiliations
January 2002 - June 2015
January 2002 - June 2015
January 2002 - June 2015
Education
April 2004 - March 2008
March 1997 - July 2003
Publications
Publications (86)
La quema de combustibles fósiles produce gases de efecto invernadero que afectan al cambio climático. La disposición incorrecta de residuos sólidos y efluentes, tanto industriales como sanitarios, producen una contaminación de los cuerpos de agua. Por ende, surge la necesidad del desarrollo de soluciones tecnológicas. Líneas de investigación del Gr...
Optoacoustic tomography image reconstruction has been a problem of interest in recent years. By exploiting the exceptional generative power of the recently proposed diffusion models we consider a scheme which is based on a conditional diffusion process. Using a simple initial image reconstruction method such as Delay and Sum, we consider a speciall...
Optoacoustic tomography image reconstruction has been a problem of interest in recent years. By exploiting the exceptional generative power of the recently proposed diffusion models we consider a scheme which is based on a conditional diffusion process. Using a simple initial image reconstruction method such as Delay and Sum, we consider a speciall...
PLA is a polymeric material widely used for 3D printing, with varied applications in medicine and engineering, among others. In many applications, it is important to determine mechanical properties, such as speed of sound (SoS), density and acoustic impedance, which are very susceptible to printing parameters such as nozzle diameter, temperature an...
La tomografía optoacústica (TOA) es una técnica de obtención de imágenes médicas que permite obtener resultados de alta resolución al combinar contraste óptico con detección ultrasónica. En los últimos años, muchos de los avances en TOA se deben al uso de algoritmos de aprendizaje profundo, es decir, aprendizaje orientado al reconocimiento de patro...
En este trabajo se aborda el estudio y desarrollo de un sistema que posibilita la obtención de imágenes de ultrasonido bidimensionales. El enfoque principal del desarrollo consistió en conseguir que el sistema sea apto para reutilizarlo en otras aplicaciones de índole semejante. Para este propósito, se empleó un transductor de inmersión comercial,...
![Figura 7: Esquema del sistema TOA usado en las simulaciones. [28].](publication/376578051/figure/fig4/AS:11431281212611254@1702737725319/Figura-7-Esquema-del-sistema-TOA-usado-en-las-simulaciones-28_Q320.jpg)
En este trabajo se propone el uso de una red generativa de confrontación (GAN) para efectuar un aumento de datos con el objetivo de mejorar la reconstrucción de imágenes en sistemas para tomografía optoacústica (TOA). Se utilizó el modelo denominado FastGAN que es una red compacta, capaz de generar imágenes de alta resolución a partir de un conjunt...
![Fig. 4: Estructura de la U-Net implementada por [16]. Cada rectángulo...](profile/M-Gonzalez-7/publication/371620562/figure/fig2/AS:11431281169309097@1687297929548/Estructura-de-la-U-Net-implementada-por-16-Cada-rectangulo-azul-corresponde-a-un-mapa_Q320.jpg)
El objetivo de este trabajo es el estudio de un método de pre-procesamiento de los datos medidos por un tomógrafo optoacústico bidimensional para reducir o eliminar los artefactos introducidos por la escasa cantidad de detectores en el sistema experimental y el acotado ancho de banda de estos. Para esta tarea, se utilizó una red neuronal profunda g...
Image reconstruction in optoacoustic tomography (OAT) is a trending learning task highly dependent on measured physical magnitudes present at sensing time. The large number of different settings, and also the presence of uncertainties or partial knowledge of parameters, can lead to reconstructions algorithms that are specifically tailored and desig...
In this work we present the first application of software-defined optoelectronics (SDO) for bidimensional optoacoustic tomography (OAT). The SDO concept refers to optoelectronic systems where the functionality associated with the conditioning and processing of optical and electrical signals are digitally implemented and controlled by software. This...
Image reconstruction in optoacoustic tomography (OAT) is a trending learning task highly dependent on measured physical magnitudes present at sensing time. The large number of different settings, and also the presence of uncertainties or partial knowledge of parameters, can lead to reconstructions algorithms that are specifically tailored and desig...
In this paper we consider the problem of image reconstruction in optoacoustic tomography. In particular, we devise a deep neural architecture that can explicitly take into account the band-frequency information contained in the sinogram. This is accomplished by two means. First, we jointly use a linear filtered back-projection method and a fully de...
In this paper we consider the problem of image reconstruction in optoacoustic tomography. In particular, we devise a deep neural architecture that can explicitly take into account the band-frequency information contained in the sinogram. This is accomplished by two means. First, we jointly use a linear filtered back-projection method and a fully de...
A deep neural network architecture for improving the performance of a software-defined optoacoustic tomography device is presented. Our approach is a hybrid one, in the sense that a powerful data-driven architecture (a FD-UNet) is combined with a structure that exploits model-guided information, in the form of the forward and adjoint operators of t...
La tomografía optoacústica (TOA) es una modalidad de imagen no invasiva que combina los beneficios del contraste óptico con una resolución ultrasónica. La TOA se basa en la generación de ondas de ultrasonido mediante la iluminación de la muestra con pulsos láser de corta duración. La energía absorbida da como resultado un rápido aumento de la tempe...
Speeding up data acquisition and reducing the complexity of the detection system are among the central goals for advancing optoacoustic imaging. In this way, new reconstruction algorithms using the compressed sensing (CS) formalism have received considerable interest in recent years. This work presents a comparative study of reconstruction algorith...
We proposed a deep FD-UNet architecture that directly exploits the frequency content in the broadband sinogram of an optoacoustic measured signal for image reconstruction. The reconstructed images present a high degree of fidelity.
In this work, the source of the artifacts introduced in the images obtained with an optoacoustic tomography system based on the software-defined optoelectronics concept are analyzed and characterized. It is shown that the measured signals are affected both by the cylindrical geometry of the optical sensor and by electrical noise. The latter has wel...
For photoacoustic image reconstruction, certain parameters such as sensor positions and speed of sound have a major impact in the reconstruction process and must be carefully determined before data acquisition. Uncertainties in these parameters can lead to errors produced by a modeling mismatch, hindering the reconstruction process and severely aff...
For photoacoustic image reconstruction, certain parameters such as sensor positions and speed of sound have a major impact in the reconstruction process and must be carefully determined before data acquisition. Uncertainties in these parameters can lead to errors produced by a modeling mismatch, hindering the reconstruction process and severely aff...
A method for calibration of ultrasonic sensors for optoacoustics that provides both frequency response and sensitivity is presented. In order to obtain the bandwidth and the frequency response of an uncalibrated sensor, a point source with broadband spectra generated by a laser-induced bubble on a copper wire submerged in water is employed. On the...
En este trabajo se presenta el estudio, desarrollo y caracterización de un sensor ultrasónico cilíndricamente enfocado basado en un material polimérico piezoeléctrico. Para su diseño se realizaron simulaciones usando la herramienta comercial k-Wave y para su implementación se utilizó un método de construcción que tiene una gran repetibilidad y un b...
La obtención de imágenes optoacústicas es una técnica híbrida que se beneficia tanto del rico y versátil contraste óptico como de la alta resolución espacial asociada a la baja dispersión de propagación de las ondas ultrasónicas. Usualmente, se utilizan láseres de elevada energía (> 10 mJ) como fuente de luz los cuales son caros, no portátiles y ti...
This work studies the adverse effects, as regards noise, of immersing in water an integrating line piezoelectric detector devoted to optoacoustic imaging. We found that the sensor, in conjunction with the acoustic coupling medium (water), behaves as a resonant dielectric antenna. This phenomenon limits the performance of the system because it effic...
La obtención de imágenes optoacústicas es una técnica híbrida que se beneficia tanto del rico y versátil contraste óptico como de la alta resolución espacial asociada a la baja dispersión de propagación de las ondas ultrasónicas. Usualmente, se utilizan láseres de elevada energía (> 10 mJ) como fuente de luz los cuales son caros, no portátiles y ti...
In this work we present what we believe is the first application of software-defined optoelectronics (SDO) for bidimensional optoacoustic tomography (OAT). The SDO concept refers to optoelectronic systems where the functionality associated with the conditioning and processing of optical and electrical signals are digitally implemented and controlle...
This work presents a detection system for optoacoustic tomography based on a polymer piezoelectric sensor and a transimpedance amplifier. The results of the electrical and acoustic characterization show that the system has a large bandwidth (63 MHz), high sensitivity (1630 {\mu}V/Pa) and low equivalent noise pressure (1 Pa). The described sensor de...
En este trabajo se presenta un interferómetro de dos haces homodino para la medición de ultrasonido pulsado. En este interferómetro, las ramas se separan inicialmente mediante un prisma de Rochon para luego ser recombinadas por un prisma no polarizado. Mediante una lámina retardadora de cuarto de onda y un polarizador se ajusta el interferómetro pa...
En este trabajo se presenta un método óptico para la determinación directa del coeficiente piezoeléctrico de películas delgadas de material polimérico. Esto se logra a través de la medición de desplazamientos mecánicos nanométricos generados en el film cuando es excitado con señales eléctricas armónicas de baja frecuencia (0.5 Hz). El sistema está...
We present a method to generate sub-microsecond quasi-unipolar pressure pulses. Our approach is based on the laser irradiation of a thin copper wire submerged in water. The acoustic waveforms were recorded using two different, well characterized, wideband detection techniques: piezoelectric and optical interferometry. The results show that the irra...
In this paper we present a method to determine the spatial resolution and sensitivity of systems for optoacoustic tomography (OAT). The method consists of obtaining the image of a sample based on a transparent film embedded in agarose. The film has a certain pattern made with a laser printer that allows to obtain the system spatial resolution. More...
We present a method to determine the thermal boundary conductance of gold nanoparticles in aqueous solution. The novel approach consists of two steps: first, measuring photoacoustic signals originated by laser-induced nanobubbles at different energies and, second, fitting the experimental data with a nanobubble generation model developed in a previ...
The flexibility offered by software-defined
hardware (SDH) platforms makes it possible to implement
optoelectronic systems which can be readily configured to
adapt to multiple high-speed optoelectronic engineering
applications. Two software-defined, optical heterodyne
interferometers (SDOI) were built using low-cost commercial
software-defined radi...
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 t...
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...
We present a new photoacoustic gas-trace measurement setup, based on a chirped optical chopper. This method combines features of the resonant and pulsed techniques. To show the advantages of this setup, we carried out a comparison with the resonant method in samples of NO2 contained in a one-dimensional acoustic resonator. The results show the chir...
En este trabajo se presenta un nuevo esquema de medición para espectroscopía fotoacústica de gases traza basado en un esquema de excitación up-chirp. Esta forma combina las ventajas de los esquemas resonante y pulsado. Para mostrar el potencial de esta técnica se la comparó con un esquema de excitación resonante sobre la medición de muestras de dió...
This paper shows that the use of filters based on the discrete wavelet transform (DWT) improves the sensitivity of photoacoustic systems for measurement of trace gases under conditions of unfavorable signal-to-noise ratio (SNR). To achieve this goal, a filter based on Meyer's DWT was designed and tested with simulated and measured signals. For the...
En este trabajo se muestra que la utilización de filtros basados en la transformada wavelet discreta (DWT) mejora la sensibilidad de sistemas fotoacústicos para medición de gases traza bajo condiciones de relación señal a ruido (SNR) desfavorables. Para lograr este objetivo se diseñó un filtro basado en la DWT de Meyer y se lo probó con senales sim...
This paper describes the design and performance of a phase demodulation scheme based on software-defined radio (SDR), applied in heterodyne interferometry. The phase retrieval is performed in real time by means of a low-cost SDR with a wideband optoelectronic front-end. Compared to other demodulation schemes, the system is quite simpler, versatile,...
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....
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...
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 measurement...
In this paper we present the study of three sensors, based on piezoelectric polymer thin films, for photoacoustic systems used in the characterization of liquids. Its performance was compared by carrying out measurements on well-known liquids. From the measured data, the sensitivity, noise level and quantification limit of each of the sensors were...
The generation of nanobubbles by laser irradiation of nanoparticles is of great interest in various applications in biophotonics. In a previous work we presented a model that adequately describes the phenomenon at low concentration of nanoparticles (<0.1 nM) and low repetition rate laser pulses (<0.5 Hz). The model is based on the classical nucleat...
La generación de nanoburbujas por irradiación laser de nanopartículas presenta gran interés para diversas
aplicaciones en biofotónica. En un trabajo previo presentamos un modelo que describe adecuadamente el
fenómeno para bajas concentraciones de nanopartículas (< 0.1 nM) y bajas tasas de repetición de pulsos láser (< 0.5 Hz). El mismo está basado...
One of the major difficulties that students find in the basic subjects of Electricity and Magnetism is the understanding of the magnetic properties of matter. In particular, the determination of the directions of magnetic vectors in simple devices constructed with ferromagnetic materials such as magnets, transformers and electromagnets. The confusi...
This work presents the theoretical analysis of the effects of dielectric relaxation on the response of polymer piezoelectric sensors. In systems that obtain spatial information from temporal signals, such as optoacoustic tomography, the accurate characterization of transducers is very important. There are many works in the literature about reconstr...
Piezoelectric polymers are of great interest due to their physical properties that allow their use in many applications. Their are particularly important for biomedical applications. Moreover, broadband sensor development requires a reliable system to measure the piezoelectric coefficient of these materials. In this work, we propose an interferomet...
Los polímeros piezoeléctricos presentan gran interés debido a sus propiedades físicas que permiten su utilización en gran cantidad de aplicacionesentre ellas se destacan las biomédicas. Para su utilización en el desarrollo de sensores de banda ancha, es de particular interés contar con un sistema confiable para medir el coeficiente piezoeléctrico d...
We present a novel design for large area, wideband, polymer piezoelectric sensor with low capacitance. The large area allows better spatial resolution in applications such as photoacoustic tomography and the reduced capacitance eases the design of fast transimpedance amplifiers. The metalized piezoelectric polymer thin film is segmented into N sect...
The modeling of bubbles initiated by laser-irradiated nanoparticles is of interest for many applications. There is at present no comprehensive physical picture for all the stages of the process. We present an alternative approach with a key assumption: the vapor bubble evolves adjacent to the nanoparticle. To take into account the irreversible evol...
The magnification and the Fresnel number determine the mode profile and losses in a bare unstable resonator. Upon inclusion of gain, both the beam pattern and the reflectivity are changed, more than in a stable cavity, because the counter-propagation intensities differ spatially and saturate the amplifier in a way that alters the mode profile, the...
This paper presents a model suitable to design and characterize broadband thin film
sensors based on piezoelectric
polymers. The aim is to describe adequately the sensor behavior, with a reasonable number of parameters and based on well-known physical equations. The mechanical variables are described by an acoustic transmission line. The electrical...
In this work a procedure for characterization of polymeric piezoelectric sensors is proposed. Results are presented for two sensors based on polyvinylidene fluoride (PVDF). The electrical impedances of the sensors in the range between 100 Hz and 30 MHz were measured. Then, the spatial and temporal responses of near-field were determined using thin...
We present the development of a transversally excited CO2 laser that operates at pressures up to 200 kPa and 50 Hz repetition rate. The laser has been designed to trigger photo-chemical reactions. We perform a detailed study of the well-known system of capacitive transfer to exploit its virtues and avoid the use of complex system of greater cost an...
This work describes the dielectric properties of piezoelectric poly(vinylidene fluoride) (PVDF) thin films in the frequency and temperature ranges relevant for usual applications. We measured the isothermal dielectric relaxation spectra of commercial piezoelectric PVDF thin films between 10 Hz to 10 MHz, at several temperatures from 278 K to 308 K....
To establish the methodical basis for the development and certification of fluorescence quantum yield standards, we determined the fluorescence quantum yield Φ(f) of rhodamine 6G (R6G) with two absolute methods with complementary measurement principles, here optical spectroscopy using an integrating sphere setup and pulsed laser photoacoustic spect...
Based on measuring the change of the photoacoustic (PA) signal generated by laser-induced nanobubbles, a new way to detect gold nanoparticles (GNPs) aggregation is demonstrated and applied to selective protein detection.
A pulsed photoacoustic system is used to determine the fluorescence quantum yield of diluted dye solutions in highly scattering media. In order to show its accuracy, the quantum yield of Rhodamine 6G in water and ethanol was calculated. The chemical Fuchsin was utilized as a dye reference because the entire excitation energy is converted into nonra...
In this paper, we present a pulsed photoacoustic configuration for the detection of lead ion in aqueous solution based on the dissolution of gold nanoparticle. The photoacoustic signal is generated by laser-induced nanobubble. This technique allows for a sensitive measurement of size changes of the gold nanoparticles in the presence of lead ions ev...
We introduce the application of a differential microphone in an LED-excited photoacoustic system devoted to NO2 measurement. The microphone ports pick up out-of-phase signals generated in two resonators, thus achieving a larger electrical signal and good common mode noise rejection. The reduced noise floor and LEDs with higher optical power, made i...
In this paper we propose a mathematical model and an approximate equation to explain the behavior found on the photoacoustic effect generated by laser-induced nanobubbles in colloidal gold solutions. To obtain the equation, we developed a simulation program based on the widely known Rayleigh–Plesset model. A set of measurements was carried out to a...
We present a simple resonant photoacoustic (PA) setup based on a modulated CW CO2 laser and a synchronic detection system that acquires the signal and the reference through the sound card of a PC. The precise phase reading of this system allows detecting the delay of the signal coming from the excited CO2 molecules immersed in air and, with an adeq...
We introduce a beam profiler of pulsed lasers based on the photoacoustic technique. The method assumes that the initial pressure distribution inside the acoustic cell follows the laser intensity pattern if absorbed energy relaxes rapidly. This initial pressure condition can be described as a superposition of acoustic modes of different amplitudes a...
The photoacoustic technique, based on an Nd:YAG pulsed laser at 532 nm, was used to investigate a binary gas mixture of NO2 and air contained in a cylindrical glass cell. In order to improve the method, some characteristic parameters, cell quality factor and resonance frequency were analyzed. As the buffer gas pressure increases, the former rises a...
The analysis of the NO2 content in the exhaust gases of diesel engines is performed by a new simple resonant photoacoustic system. It consists of a special design of transversal illumination from LEDs attached to a cylindrical glass cell. LEDs emitting at 464 and 400 nm allow carrying out differential measurements, to take into account possible int...
We report a new way of reducing the background originated by window absorption in resonant photoacoustics. The technique employs a secondary light source that is absorbed by the window but not by the gas sample. This auxiliary source is modulated 180 degrees apart from the one used to probe the gas. This way the window is heated almost uniformly du...
We report on the application of neural-network processing to pulsed photoacoustics for improving the detection limit by subtracting the window-heating-associated background. This technique was applied to the measurement of ethylene traces excited by a TEA (transverse electrical discharge in gas at atmospheric pressure) CO 2 laser. The signal contai...
We present a simple personal computer based, synchronic detection system that emulates a lock-in amplifier at audio frequencies. The inputs of the sound card are used to acquire two sets of samples: the one to be measured, previously preamplified, and the reference. From the last one, two "quasiorthogonal" signals are derived to perform dual-phase...
We present a new, very compact resonant photoacoustic system based on a simple closed pipe, transversally illuminated by an array of blue light-emitting diodes uniformly distributed along the tube to produce an acoustic signal from N O <sub>2</sub>– N <sub>2</sub> samples. The illumination is modulated in a particular way as to produce amplificatio...
Usually, the design of the electrodes of fast-transverse-flow CO2 lasers relies more on experimental data than on theoretical analysis. Traditional systems sustain a stable, high-power discharge but the current distribution generates a peaked, non-uniform small-signal-gain pattern. We present a theoretical model suitable for the design of electrode...
We present a numerical and experimental study of two adapted filters devised to the quantitative analysis of weak photoacoustic signals. The first one is a simple convolution-type one and the other is based on neural networks of the multilayer perceptron type. The theoretical signal used as one of the inputs in both filters is derived from the solu...
Time-consuming, trial and error methods have usually been key tools in the design and search of optimum performance of the electrodes in fast-transverse-flow CO2 lasers. These tests sought a large, uniformly pumped volume and high small-signal gain. The later is determined by a complex interaction between the electron density, the flow speed and th...
Presentamos el uso de un filtro basado en redes neuronales destinado a la extensión del rango dinámico de detectores piroeléctricos en la región de bajas energías. Para ello se entrenó un perceptron multicapa, a través del método de aprendizaje backpropagation, tomando como señal teórica la obtenida del modelo eléctrico equivalente. Como experiment...
Some authors have used several microphones in order to improve the detection limit of photoacoustic signals. This solution shows a rather slow improvement of the S/N ratio, which grows as the square root of the microphones number. In this work we show an alternative based on a differential microphone, coupled to two acoustic cavities, which receive...
Se desarrolló una celda simple de vidrio cerrada de forma cilíndrica, para aplicación en detección optoacústica, que es iluminada transversalmente con 32 LEDs azules distribuidos uniformemente a lo largo del tubo. Se forzó la excitación del segundo modo longitudinal iluminando en un semiciclo la zona central, comprendida entre los nodos de la onda...
Se aplicó la técnica optoacústica pulsada a la detección de trazas de etileno en nitrógeno, excitando con un láser TEA de CO2. Se utilizó una celda unidimensional con filtros de cuarto de onda en los extremos a fin de reducir la intensidad de la señal generada por la absorción de las ventanas de KCl que cierran la celda. Sin embargo, a pesar de est...
La técnica fotoacústica es un método muy sensible para la detección de trazas gaseosas en el estudio de la contaminación ambiental y otras aplicaciones. Uno de los principales problemas que presenta es el proceso de adsorción-desorción, presente en el caso de moléculas polares como el agua, el amoníaco o el dióxido de nitrógeno, que produce importa...
A resonant photoacoustic system for measurement of gas traces in mixtures has been improved. It is based on an automatically tunable CO2 laser. The mechanically modulated beam crosses through a cylindrical cell ended with quarter wavelength filters. The acoustic signal is detected by a microphone placed in the centre of the resonator which contains...
La magnificación y el número de Fresnel determinan los modos y pérdidas de un resonador inestable vacío. Aquellos se ven alterados por la inclusión de un medio con ganancia más marcadamente que en una cavidad estable porque en una de este tipo el perfil espacial de las intensidades contrapropagantes dentro de ella son marcadamente diferentes lo que...
Se desarrolló una celda simple de vidrio cerrada de forma cilíndrica, para aplicación en detección optoacústica, que es iluminada transversalmente con 32 LEDs azules distribuidos uniformemente a lo largo del tubo. Se forzó la excitación del segundo modo longitudinal iluminando en un semiciclo la zona central, comprendida entre los nodos de la onda...
