Nicolas Perez | Universidad de la República (Uruguay) (original) (raw)
Papers by Nicolas Perez
2014 Ieee International Ultrasonics Symposium, Sep 1, 2014
Frequently in on line quality control, the surface roughness must be determined. The measure of t... more Frequently in on line quality control, the surface roughness must be determined. The measure of this parameter can be made in different ways, the machinist might use his fingernail, an automated system performs a local scan using a mechanical stylus, or non contact methods like ultrasound scan. In the ultrasound case we must use a model to evaluate the roughness, typically the root medium square value, translating the complex ultrasonic signal received in the transducer to a usefully value that can be understand by the operator. Mathematical models used for this propose are very complex for no specialists, ended in a closed formula.
Physics procedia
A new systematic and efficient algorithm to obtain the ten complex constants of piezoelectric mat... more A new systematic and efficient algorithm to obtain the ten complex constants of piezoelectric materials belonging to the 6mm symmetry class was developed. A finite element method routine was implemented in Matlab using eight-node axisymmetric elements. The algorithm raises the electrical conductance and resistance curves and calculates the quadratic difference between the experimental and numerical curves. Finally, to minimize the difference, an optimization algorithm based on the "Method of Moving Asymptotes" (MMA) is used. The algorithm is able to adjust the curves over a wide frequency range obtaining the real and imaginary parts of the material properties simultaneously.
Physics procedia
Ultrasonic through-transmission techniques have been widely used along decades for determining th... more Ultrasonic through-transmission techniques have been widely used along decades for determining the elastic constants of anisotropic composite materials. This work presents a new methodology that takes into account not only the transmitted waves but also the multiple reflections inside the sample. The superposition of different reflected waves are theoretically and experimentally identified and excluded, which avoids the distortion caused by pulse superposition. Additionally, the results of the Christoffel tensor optimization are evaluated in the reflected waves, improving the results validation. Experimental results using unidirectional carbon-matrix composite samples used in the aeronautical industry are presented.
Journal of Artificial Societies and Social Simulation, The
Cooperation among self-interested individuals pervades nature and seems essential to explain seve... more Cooperation among self-interested individuals pervades nature and seems essential to explain several landmarks in the evolution of live organisms, from prebiotic chemistry through to the origins of human societies. The iterated Prisoner's Dilemma (IPD) has been widely used in different contexts, ranging from social sciences to biology, to elucidate the evolution of cooperation. In this work we approach the problem from a different angle. We consider a system of adaptive agents, in a two dimensional grid, playing the IPD governed by Pavlovian strategies. We investigate the effect of different possible measures of success (MSs) used by the players to assess their performance in the game. These MSs involve quantities such as: the utilities of a player in each round U, his cumulative score (or 'capital' or 'wealth') W, his neighbourhood 'welfare' and combinations of them. The agents play sequentially with one of their neighbours and the two players update their 'behaviour' (C or D) using fuzzy logic which seems more appropriate to evaluate an imprecise concept like 'success' than binary logic. The steady states are characterised by different degrees of cooperation,'economic geographies' (population structure and maps of capital) and 'efficiencies' which depend dramatically on the MS. In particular, some MSs produce patterns of 'segregation' and 'exploitation'.
This work presents the development of an ultrasonic system for inspecting adhesive joints, using ... more This work presents the development of an ultrasonic system for inspecting adhesive joints, using the pulse-echo mode. In order to test the proposed system, a real pipe section made with fiberglass reinforced epoxy resin composite, purposely containing disbonds, was provided by PETROBRAS oil company. A mechanical structure embraces the tube, allowing for rotational and translational movements of the transducer along the outer surface of the joint. The ultrasound transducer was coupled to the joint by flowing tap water. Two step motors, one moving linearly and the other moving angularly, were controlled by a specifically developed hardware, which generates the control pulses and the trigger signal to synchronize the ultrasonic emission. The hardware was connected to a PC through an RS-232C interface, and a software was implemented to control the hardware through a based protocol. Ultrasonic pulses are emitted, received and amplified using a pulser/receiver. An A/D converter board was ...
2000 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.00CH37121), 2000
At present, lot of piezoelectric broad band ultrasonic transducers use as active material piezoel... more At present, lot of piezoelectric broad band ultrasonic transducers use as active material piezoelectric ceramic composites. In a typical transducer based on piezocomposites the active material is mounted on a soft backing and one matching layer is placed on the front, radiating face, with the aim to match the acoustic impedance of the medium and to enlarge the bandwidth. In this paper an optimization work is shown to demonstrate that a composite configuration can be used in the matching layer in order to improve the efficiency and the band of the transducers. An approximated two-dimensional analytical model has been used to optimize the design of a composite-structured matching layer in the case of 2-2 composites, obtaining different results for the polymer and piezoceramic composite phases.
In applications like atomic spectroscopy, cooling atoms or telecommunications is necessary to hav... more In applications like atomic spectroscopy, cooling atoms or telecommunications is necessary to have laser light sources capable of tuning its central emitting frequency over a range of some GHz and a spectral bandwidth in the order of hundreds of kHz. This stabilization presents a demanding control problem, the relation between the instantaneous frequency of emission (1014 Hz) and bandwidth allowed (106 Hz) implies a relative error smaller to 0,01 ppm. The frequency is disturbed by mechanical vibration of the components, electrical noise and variations in the temperature among others. In this work we present the model, identification, design and later evaluation of a system of a close loop control to reject disturbances in the emitted radiation. Is detailed the description of the physical assembly used to stabilize the frequency, the control strategy, the technique to design the robust controllers using H∞ nor-malization and finally the obtained results are evaluated. The obtained re...
1998 IEEE Ultrasonics Symposium. Proceedings (Cat. No. 98CH36102), 1998
The dynamic behaviour of piezoelectric composites has attracted the attention of many researches ... more The dynamic behaviour of piezoelectric composites has attracted the attention of many researches after it has been successfully applied to medical ultrasound imaging. Many authors have studied 1-3 piezocomposites and have analyzed the influence of structural or material variations on their electromechanical behaviour. Different approaches are currently used for modeling the wave propagation and thickness mode in the periodic composite, the homogenization model "l, the finite element technique and the transfer (T) matrix unanswered questions regarding the wave technique 14'. However, there are still many propagation inside the composite structure, mode coupling and band structures due to the finite nature of the periodic composites system. 0-7803-4095-7/98/$10.00 0 1998 IEEE One of the main inconveniences showed by the 1-3 piezocomposites is the existence of lateral vibration modes due to its periodicity l ' . Different solutions have been proposed in order to attenuate these effects over the thickness mode. The first of them propose the use of a thin lateral scale enough to obtain the twice the thickness mode frequency. Another lowest electrically excited lateral resonance at near proposed solution is to use high shear stiffness polymers, which present a very high transverse phase velocity and then for a given pitch the lateral modes will stand at higher frequencies ' "l . An alternative to reduce the lateral wave resonance is to introduce randomness into the composite structures, since randomness can destroy many lateral resonances In this work we study experimentally the behaviour of that lateral modes in the case of non-periodic finite piezocomposite shuctures. In order to do it we made samples which present the first lateral frequency close to the thickness mode frequency, so this two modes and the second lateral mode couple presenting a significantly high level. Then we broke the array periodicity to study the lateral frequencies as a function of the dropped rods. Presently we don't know other works which simultaneously show the role of this periodicity breaking and the lateral diffracted field. Here we study the evolution of the modes attenuation over the piezocomposite periodicity breaking (number of rods radiated field as a function of the extent of the pseudorandomly outdropped). The goal is to obtain an homogeneous field produced essentially by the piston mode.
Ultrasonic techniques are widely used for non-destructive testing NDT. When dealing with standard... more Ultrasonic techniques are widely used for non-destructive testing NDT. When dealing with standard applications, a fluid is used to couple the transducer and the sample to be measured. The use of transducers coupled by air opens a wide range of possibilities for these tests, allowing the test of pieces that do not support a coupling liquid nor direct contact bonding, because the constituent materials or due to constraints related to on line operation or spatial geometries. The main difficulty to use transducers coupled by air is the huge mismatch of the acoustic impedance between a solid and the air. Due to the great difference of elastic properties and density in the interface transducer-air, the energy transferred from the transducer is very low. In this work we present a special application that consist of the surface roughness measurement in solid interfaces using air coupled transducers. Specially designed piezoelectric transducers were made for this application. These transducers are made of pzt-polymer piezocomposites, coupled to the air using two quarter length matching layers. The main objective of this work is the evaluation of these transducers to measure surface roughness. The set of samples selected are in the range of those found in industrial applications (irons submissive the corrosion and grinder stones of commercial use).
This work presents an alternative way to implement time reversal process. This process can be div... more This work presents an alternative way to implement time reversal process. This process can be divided into three main parts: system identification, signal processing and finally, the reemission of the timereversed signal. In the proposed variant, the traditional time domain system identification is replaced by the measure of the transfer function in frequency domain. The Inverse Fourier transform of the transfer function complex conjugate is used to obtain the temporal signal to be reemitted. We call this technique as Frequency Domain Time Reversal (FDTR).
Desde el 2000, Uruguay ha desarrollado un cambio de uso del suelo muy importante, pasando desde a... more Desde el 2000, Uruguay ha desarrollado un cambio de uso del suelo muy importante, pasando desde aproximadamente 200,000en el 2000 -a casi un millón de hectáreas bajo cultivos agrícolas. Un cambio de uso del suelo centrado principalmente en la región Litoral Oeste, región donde históricamente se había desarrollado la producción apícola nacional.
In oil industry, sand content in crude oils is commonly used as a parameter to determine the well... more In oil industry, sand content in crude oils is commonly used as a parameter to determine the well deterioration level and to assess horizontal wells collapse risk. The sand content measurement is usually performed by a sand content meter device, which is based on a sieves system. This device requires a human operator to collect and analyze the crude oil samples. In order to allow a real time sand content monitoring in crude oil, this work presents a new ultrasonic technique to determine solid particle concentration in liquids. This technique consists in emitting an ultrasonic wave by an ultrasonic transducer and measuring the backscattered ultrasonic signals produced by sand particles. Therefore, the objective of this work is to develop a measurement cell based on the ultrasonic waves scattering to estimate the sand particles concentration in crude oil. The experimental observations were made with a measuring cell built for laboratory batch testing and continuous solid particles flow. Ultrasound transducers with central frequencies ranging from 5 and 10 M Hz in pulse-echo mode were used. Laboratory batch tests using sand particles ranging in size from 100 to 500 µm in diameter shown that there is a linear relationship between the volumetric fraction of particle and ultrasonic backscattered energy. The backscattered energy is proportional to the squared voltage measured from the receiving transducer. The echo signal mean energy at a given time window corresponds to the instantaneous flowing sand content through the cell. A micro-controlled feeder device was developed to perform tests on continuous solid particles flow. An analytical balance was used to calibrate the feeder to operate in the range from 2 to 20 mg/s, producing a water mixture ranging from 200 to 2000 ppm. Tests with continuous flow are in agreement with the expected results from the adopted methodology. A backscattered energy computational model based on a transducer impulse response and a plane piston model was developed to understand the experimental results. This model predicts the linear relationship between the backscattered energy and the particle concentration observed experimentally. The results demonstrate the technical feasibility of continuous flow measurements of sand in oil.
Ultrasonic Langevin transducers are commonly used in power applications. Several nonlinear effect... more Ultrasonic Langevin transducers are commonly used in power applications. Several nonlinear effects influence their performance when the mechanical displacement is large. This work presents an iterative model that relates the transducer driving voltage to the mechanical displacement measured at the end face of its mechanical amplifier. This model uses a frequency domain method to compute the differential equation of motion, reproducing the systems frequency response around the main resonance of transducer. The main nonlinear effects reproduced by the model are a decrease of resonance frequency and the loss of symmetry in the frequency response around the resonance frequency.
All numerical techniques to simulate the behavior of piezoelectric transducers need the knowledge... more All numerical techniques to simulate the behavior of piezoelectric transducers need the knowledge of material parameters. In this work, a global sensitivity analysis (GSA) is proposed to determine a set of these elastic, piezoelectric and dielectric parameters. The GSA analysis is performed for piezoelectric ceramic disks by sweeping each parameter over a 40% range using the Finite Element Method (FEM). Plotting this results we can separate the properties that are very influential in the behavior, of those that are little relevant. From this we can determine a global derivate for each parameter.
2014 Ieee International Ultrasonics Symposium, Sep 1, 2014
Frequently in on line quality control, the surface roughness must be determined. The measure of t... more Frequently in on line quality control, the surface roughness must be determined. The measure of this parameter can be made in different ways, the machinist might use his fingernail, an automated system performs a local scan using a mechanical stylus, or non contact methods like ultrasound scan. In the ultrasound case we must use a model to evaluate the roughness, typically the root medium square value, translating the complex ultrasonic signal received in the transducer to a usefully value that can be understand by the operator. Mathematical models used for this propose are very complex for no specialists, ended in a closed formula.
Physics procedia
A new systematic and efficient algorithm to obtain the ten complex constants of piezoelectric mat... more A new systematic and efficient algorithm to obtain the ten complex constants of piezoelectric materials belonging to the 6mm symmetry class was developed. A finite element method routine was implemented in Matlab using eight-node axisymmetric elements. The algorithm raises the electrical conductance and resistance curves and calculates the quadratic difference between the experimental and numerical curves. Finally, to minimize the difference, an optimization algorithm based on the "Method of Moving Asymptotes" (MMA) is used. The algorithm is able to adjust the curves over a wide frequency range obtaining the real and imaginary parts of the material properties simultaneously.
Physics procedia
Ultrasonic through-transmission techniques have been widely used along decades for determining th... more Ultrasonic through-transmission techniques have been widely used along decades for determining the elastic constants of anisotropic composite materials. This work presents a new methodology that takes into account not only the transmitted waves but also the multiple reflections inside the sample. The superposition of different reflected waves are theoretically and experimentally identified and excluded, which avoids the distortion caused by pulse superposition. Additionally, the results of the Christoffel tensor optimization are evaluated in the reflected waves, improving the results validation. Experimental results using unidirectional carbon-matrix composite samples used in the aeronautical industry are presented.
Journal of Artificial Societies and Social Simulation, The
Cooperation among self-interested individuals pervades nature and seems essential to explain seve... more Cooperation among self-interested individuals pervades nature and seems essential to explain several landmarks in the evolution of live organisms, from prebiotic chemistry through to the origins of human societies. The iterated Prisoner's Dilemma (IPD) has been widely used in different contexts, ranging from social sciences to biology, to elucidate the evolution of cooperation. In this work we approach the problem from a different angle. We consider a system of adaptive agents, in a two dimensional grid, playing the IPD governed by Pavlovian strategies. We investigate the effect of different possible measures of success (MSs) used by the players to assess their performance in the game. These MSs involve quantities such as: the utilities of a player in each round U, his cumulative score (or 'capital' or 'wealth') W, his neighbourhood 'welfare' and combinations of them. The agents play sequentially with one of their neighbours and the two players update their 'behaviour' (C or D) using fuzzy logic which seems more appropriate to evaluate an imprecise concept like 'success' than binary logic. The steady states are characterised by different degrees of cooperation,'economic geographies' (population structure and maps of capital) and 'efficiencies' which depend dramatically on the MS. In particular, some MSs produce patterns of 'segregation' and 'exploitation'.
This work presents the development of an ultrasonic system for inspecting adhesive joints, using ... more This work presents the development of an ultrasonic system for inspecting adhesive joints, using the pulse-echo mode. In order to test the proposed system, a real pipe section made with fiberglass reinforced epoxy resin composite, purposely containing disbonds, was provided by PETROBRAS oil company. A mechanical structure embraces the tube, allowing for rotational and translational movements of the transducer along the outer surface of the joint. The ultrasound transducer was coupled to the joint by flowing tap water. Two step motors, one moving linearly and the other moving angularly, were controlled by a specifically developed hardware, which generates the control pulses and the trigger signal to synchronize the ultrasonic emission. The hardware was connected to a PC through an RS-232C interface, and a software was implemented to control the hardware through a based protocol. Ultrasonic pulses are emitted, received and amplified using a pulser/receiver. An A/D converter board was ...
2000 IEEE Ultrasonics Symposium. Proceedings. An International Symposium (Cat. No.00CH37121), 2000
At present, lot of piezoelectric broad band ultrasonic transducers use as active material piezoel... more At present, lot of piezoelectric broad band ultrasonic transducers use as active material piezoelectric ceramic composites. In a typical transducer based on piezocomposites the active material is mounted on a soft backing and one matching layer is placed on the front, radiating face, with the aim to match the acoustic impedance of the medium and to enlarge the bandwidth. In this paper an optimization work is shown to demonstrate that a composite configuration can be used in the matching layer in order to improve the efficiency and the band of the transducers. An approximated two-dimensional analytical model has been used to optimize the design of a composite-structured matching layer in the case of 2-2 composites, obtaining different results for the polymer and piezoceramic composite phases.
In applications like atomic spectroscopy, cooling atoms or telecommunications is necessary to hav... more In applications like atomic spectroscopy, cooling atoms or telecommunications is necessary to have laser light sources capable of tuning its central emitting frequency over a range of some GHz and a spectral bandwidth in the order of hundreds of kHz. This stabilization presents a demanding control problem, the relation between the instantaneous frequency of emission (1014 Hz) and bandwidth allowed (106 Hz) implies a relative error smaller to 0,01 ppm. The frequency is disturbed by mechanical vibration of the components, electrical noise and variations in the temperature among others. In this work we present the model, identification, design and later evaluation of a system of a close loop control to reject disturbances in the emitted radiation. Is detailed the description of the physical assembly used to stabilize the frequency, the control strategy, the technique to design the robust controllers using H∞ nor-malization and finally the obtained results are evaluated. The obtained re...
1998 IEEE Ultrasonics Symposium. Proceedings (Cat. No. 98CH36102), 1998
The dynamic behaviour of piezoelectric composites has attracted the attention of many researches ... more The dynamic behaviour of piezoelectric composites has attracted the attention of many researches after it has been successfully applied to medical ultrasound imaging. Many authors have studied 1-3 piezocomposites and have analyzed the influence of structural or material variations on their electromechanical behaviour. Different approaches are currently used for modeling the wave propagation and thickness mode in the periodic composite, the homogenization model "l, the finite element technique and the transfer (T) matrix unanswered questions regarding the wave technique 14'. However, there are still many propagation inside the composite structure, mode coupling and band structures due to the finite nature of the periodic composites system. 0-7803-4095-7/98/$10.00 0 1998 IEEE One of the main inconveniences showed by the 1-3 piezocomposites is the existence of lateral vibration modes due to its periodicity l ' . Different solutions have been proposed in order to attenuate these effects over the thickness mode. The first of them propose the use of a thin lateral scale enough to obtain the twice the thickness mode frequency. Another lowest electrically excited lateral resonance at near proposed solution is to use high shear stiffness polymers, which present a very high transverse phase velocity and then for a given pitch the lateral modes will stand at higher frequencies ' "l . An alternative to reduce the lateral wave resonance is to introduce randomness into the composite structures, since randomness can destroy many lateral resonances In this work we study experimentally the behaviour of that lateral modes in the case of non-periodic finite piezocomposite shuctures. In order to do it we made samples which present the first lateral frequency close to the thickness mode frequency, so this two modes and the second lateral mode couple presenting a significantly high level. Then we broke the array periodicity to study the lateral frequencies as a function of the dropped rods. Presently we don't know other works which simultaneously show the role of this periodicity breaking and the lateral diffracted field. Here we study the evolution of the modes attenuation over the piezocomposite periodicity breaking (number of rods radiated field as a function of the extent of the pseudorandomly outdropped). The goal is to obtain an homogeneous field produced essentially by the piston mode.
Ultrasonic techniques are widely used for non-destructive testing NDT. When dealing with standard... more Ultrasonic techniques are widely used for non-destructive testing NDT. When dealing with standard applications, a fluid is used to couple the transducer and the sample to be measured. The use of transducers coupled by air opens a wide range of possibilities for these tests, allowing the test of pieces that do not support a coupling liquid nor direct contact bonding, because the constituent materials or due to constraints related to on line operation or spatial geometries. The main difficulty to use transducers coupled by air is the huge mismatch of the acoustic impedance between a solid and the air. Due to the great difference of elastic properties and density in the interface transducer-air, the energy transferred from the transducer is very low. In this work we present a special application that consist of the surface roughness measurement in solid interfaces using air coupled transducers. Specially designed piezoelectric transducers were made for this application. These transducers are made of pzt-polymer piezocomposites, coupled to the air using two quarter length matching layers. The main objective of this work is the evaluation of these transducers to measure surface roughness. The set of samples selected are in the range of those found in industrial applications (irons submissive the corrosion and grinder stones of commercial use).
This work presents an alternative way to implement time reversal process. This process can be div... more This work presents an alternative way to implement time reversal process. This process can be divided into three main parts: system identification, signal processing and finally, the reemission of the timereversed signal. In the proposed variant, the traditional time domain system identification is replaced by the measure of the transfer function in frequency domain. The Inverse Fourier transform of the transfer function complex conjugate is used to obtain the temporal signal to be reemitted. We call this technique as Frequency Domain Time Reversal (FDTR).
Desde el 2000, Uruguay ha desarrollado un cambio de uso del suelo muy importante, pasando desde a... more Desde el 2000, Uruguay ha desarrollado un cambio de uso del suelo muy importante, pasando desde aproximadamente 200,000en el 2000 -a casi un millón de hectáreas bajo cultivos agrícolas. Un cambio de uso del suelo centrado principalmente en la región Litoral Oeste, región donde históricamente se había desarrollado la producción apícola nacional.
In oil industry, sand content in crude oils is commonly used as a parameter to determine the well... more In oil industry, sand content in crude oils is commonly used as a parameter to determine the well deterioration level and to assess horizontal wells collapse risk. The sand content measurement is usually performed by a sand content meter device, which is based on a sieves system. This device requires a human operator to collect and analyze the crude oil samples. In order to allow a real time sand content monitoring in crude oil, this work presents a new ultrasonic technique to determine solid particle concentration in liquids. This technique consists in emitting an ultrasonic wave by an ultrasonic transducer and measuring the backscattered ultrasonic signals produced by sand particles. Therefore, the objective of this work is to develop a measurement cell based on the ultrasonic waves scattering to estimate the sand particles concentration in crude oil. The experimental observations were made with a measuring cell built for laboratory batch testing and continuous solid particles flow. Ultrasound transducers with central frequencies ranging from 5 and 10 M Hz in pulse-echo mode were used. Laboratory batch tests using sand particles ranging in size from 100 to 500 µm in diameter shown that there is a linear relationship between the volumetric fraction of particle and ultrasonic backscattered energy. The backscattered energy is proportional to the squared voltage measured from the receiving transducer. The echo signal mean energy at a given time window corresponds to the instantaneous flowing sand content through the cell. A micro-controlled feeder device was developed to perform tests on continuous solid particles flow. An analytical balance was used to calibrate the feeder to operate in the range from 2 to 20 mg/s, producing a water mixture ranging from 200 to 2000 ppm. Tests with continuous flow are in agreement with the expected results from the adopted methodology. A backscattered energy computational model based on a transducer impulse response and a plane piston model was developed to understand the experimental results. This model predicts the linear relationship between the backscattered energy and the particle concentration observed experimentally. The results demonstrate the technical feasibility of continuous flow measurements of sand in oil.
Ultrasonic Langevin transducers are commonly used in power applications. Several nonlinear effect... more Ultrasonic Langevin transducers are commonly used in power applications. Several nonlinear effects influence their performance when the mechanical displacement is large. This work presents an iterative model that relates the transducer driving voltage to the mechanical displacement measured at the end face of its mechanical amplifier. This model uses a frequency domain method to compute the differential equation of motion, reproducing the systems frequency response around the main resonance of transducer. The main nonlinear effects reproduced by the model are a decrease of resonance frequency and the loss of symmetry in the frequency response around the resonance frequency.
All numerical techniques to simulate the behavior of piezoelectric transducers need the knowledge... more All numerical techniques to simulate the behavior of piezoelectric transducers need the knowledge of material parameters. In this work, a global sensitivity analysis (GSA) is proposed to determine a set of these elastic, piezoelectric and dielectric parameters. The GSA analysis is performed for piezoelectric ceramic disks by sweeping each parameter over a 40% range using the Finite Element Method (FEM). Plotting this results we can separate the properties that are very influential in the behavior, of those that are little relevant. From this we can determine a global derivate for each parameter.