Helena Ramos | Universidade de Lisboa (original) (raw)

Papers by Helena Ramos

2021 Telecoms Conference (ConfTELE), 2021

In this work we have proposed a model, based on the semi-analytical Boundary Element Method (BEM)... more In this work we have proposed a model, based on the semi-analytical Boundary Element Method (BEM), that predicts the perturbation magnetic flux density component arising due to a narrow opening embedded flaw present in an electrically conductive medium of finite thickness. We have derived the results based on the classical dipole model of flaws (scattering source) typically encountered in eddy current based nondestructive testing and evaluation. The problem that we have modeled is the field scattered by a rectangular flaw embedded in a conductive material, achieved by stacking two electrically conductive plates that are non-magnetic. A cylindrical coil scans the flaw. The excitation field varies time harmonically. The experimental verification was carried out by utilizing a highly sensitive giant magneto-resistive sensor. We have compared the model predicted results to the experimental study with a good agreement.

New challenges in water systems include different approaches from analysis of failures and risk a... more New challenges in water systems include different approaches from analysis of failures and risk assessment to system efficiency improvements and new innovative designs. In water distribution networks (WDNs), the risk function is a measure of its vulnerability level and security loss. Analyses of transient flows which are associated with the most dangerous operating conditions, are compulsory to grant the system liability both in water quantity, quality, and management. Specific equipment, such as air valves are used in pressurized water pipes to manage the air inside associated with the filling process, that can also act as a control mechanism, where the major limitation is its reliability. Advanced tools are developed specifically to smart water grids implementation and operation. The water system efficiency and water-energy nexus, through the implementation of suitable, pressure control and energy recovery devices, and pumped-storage hydropower solutions, provide guidelines for the determination of the most technical cost-effective result. Integrated analysis of water and energy allows more reliable, flexible, and sustainable eco-design projects, reaching better resilience systems through new concepts. The development of model simulations, based on hydraulic simulators and computational fluid dynamics (CFD), conjugating with field or experimental tests, supported by advanced smart equipment, allow the control, identification, and anticipation of complex events necessary to maintain the water system security and efficiency.

2015 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) Proceedings, 2015

Nondestructive testing in situations where there is a moving media has always been a challenging ... more Nondestructive testing in situations where there is a moving media has always been a challenging task. Motion induced eddy current testing is a good solution for testing metallic surfaces, as it does not require contact with the sample. This work presents a method to detect sub-surface defects in non-ferromagnetic material with motion induced eddy currents. A numerical model was used to verify the progression of eddy currents along the depth of a conductive plate and to obtain the magnetic field perturbation in the presence of sub-surface defects. A probe, including a permanent magnet to induce eddy currents and a magnetic sensor was moved in the vicinity of an aluminium plate with sub-surface defects to obtain experimental data and the results compared to those obtained with the numerical model. At higher speeds, the time of diffusion of deeper eddy currents takes, makes it possible to also estimate the depth of a sub-surface defect by measuring how far away the perturbation is from the moving magnet.

International Journal of Applied Electromagnetics and Mechanics, 2016

In this paper we present a method to determine the current density inside an aluminum plate using... more In this paper we present a method to determine the current density inside an aluminum plate using eddy current testing procedure to determine the existence of surface cracks. The general idea consists in generating eddy currents in the plate, which in the case of flawless material, must be of uniform density pointing along a pre-defined direction inside a given area on the plate surface. These currents are produced using a planar coil. The eddy current density is determined by inversion of the data obtained from the measurement of a single component of the resultant magnetic field. Tikhonov regularization is applied to the inverted data.

Defect detection in conductive plates represents an important issue. This work presents designed ... more Defect detection in conductive plates represents an important issue. This work presents designed and implemented uniform eddy current probe architecture (UECP) that includes a planar excitation coil and a GMR magnetometer sensor array as part of a non-destructive testing (NDT) system developed using a virtual instrument system technology. The usage of GMR sensors provides frequency independent sensitivity to the UECP, assuring speed, depth, and higher resolution in eddy-current testing, while the usage of a set of GMR sensors allows rapid scanning of an area for defects in a single pass. A practical approach concerning the UECP design, implementation and experimental results obtained on cracks detection machined in aluminum plates for a single or multiple GMR sensor usage as main parts of UECP are presented. Experimental results regarding the usage of the novel eddy current probe to detect induced flaws in aluminum plates are included in the paper.

2007 IEEE Instrumentation & Measurement Technology Conference IMTC 2007, 2007

Page 1. Instrumentation and Measurement Technology Conference - IMTC 2007 Warsaw, Poland, May 1-3... more Page 1. Instrumentation and Measurement Technology Conference - IMTC 2007 Warsaw, Poland, May 1-3, 2007 Development of a IEEE 1451 Standard Compliant Smart Transducer Network with Time Synchronization Protocol ...

Abstract: The measurement of electrolytic conductivity is widely applied as a control parameter a... more Abstract: The measurement of electrolytic conductivity is widely applied as a control parameter and its relevance is continuously increasing, not only in industrial applications but also in the environmental monitoring domain. In this work the attention is focused on the electrical behavior of low cost in-situ four electrode conductivity cells for water quality monitoring in estuaries and oceans. The design of each cell, the choice of the cell constant suitable for the range of conductivities to be measured, the modeling of the current density distribution using a finite element method are described in detail. The experimental characterization of the cell versus frequency, temperature and salt concentration is also carried out. A frequency range where parasitic effects are minimized is identified.

This work presents two handheld instruments built at our laboratory able to detect sub-surface cr... more This work presents two handheld instruments built at our laboratory able to detect sub-surface cracks in a plate of conductive material. Both instruments contain a probe composed of an excitation coil and a giant magnetoresistance sensor (GMR) acting as the magnetic field sensor and includes a computer mouse pointer as positioning system. This configuration, despite its low cost, allows better performances in the detection of sub-surface defects than commercial equipments. Deeper defects in the material can be detected due not only to the high sensitivity of the GMR sensor, which is constant in a very large frequency range (10 Hz 1 MHz), but also because a precisely located graphical representation of the defect is delivered to the user due to the incorporated positioning system. The paper includes a description of the implementation of each device, the obtained results and a comparison of the performance.

This work presents two handheld instruments built at our laboratory able to detect sub-surface cr... more This work presents two handheld instruments built at our laboratory able to detect sub-surface cracks in a plate of conductive material. Both instruments contain a probe composed of an excitation coil and a giant magnetoresistance sensor (GMR) acting as the magnetic field sensor and includes a computer mouse pointer as positioning system. This configuration, despite its low cost, allows better performances in the detection of sub-surface defects than commercial equipments. Deeper defects in the material can be detected due not only to the high sensitivity of the GMR sensor, which is constant in a very large frequency range (10 Hz 1 MHz), but also because a precisely located graphical representation of the defect is delivered to the user due to the incorporated positioning system. The paper includes a description of the implementation of each device, the obtained results and a comparison of the performance.

Entropy, 2020

Photovoltaic (PV) system energy production is non-linear because it is influenced by the random n... more Photovoltaic (PV) system energy production is non-linear because it is influenced by the random nature of weather conditions. The use of machine learning techniques to model the PV system energy production is recommended since there is no known way to deal well with non-linear data. In order to detect PV system faults, the machine learning models should provide accurate outputs. The aim of this work is to accurately predict the DC energy of six PV strings of a utility-scale PV system and to accurately detect PV string faults by benchmarking the results of four machine learning methodologies known to improve the accuracy of the machine learning models, such as the data mining methodology, machine learning technique benchmarking methodology, hybrid methodology, and the ensemble methodology. A new hybrid methodology is proposed in this work which combines the use of a fuzzy system and the use of a machine learning system containing five different trained machine learning models, such a...

2015 IEEE Metrology for Aerospace (MetroAeroSpace), 2015

This paper presents experimental and simulated results obtained using the eddy current nondestruc... more This paper presents experimental and simulated results obtained using the eddy current nondestructive method to conclude about the depth of linear cracks machined on an aluminum plate. Experimental tests were performed with a sinusoidal excitation field of fixed-amplitude and with a giant magnetoresistance-based sensor to measure the resultant magnetic field on the plate surface. To validate and better insight the experimental results, numerical simulations have been carried out with a commercial program for conditions similar to the experimental case studies. A scheme to infer about crack depth is proposed.

International Journal of Industrial Electronics and Drives, 2014

This paper presents a probe that permits the detection of longitudinal and circumferential defect... more This paper presents a probe that permits the detection of longitudinal and circumferential defects in stainless steel tubes. The defect detection is made by a measurement system based on eddy current (EC) and remote field testing (RFT). The probe includes an excitation coil and a giant magneto-resistance (GMR) magnetic sensor. This GMR sensor has high sensitivity in a large frequency range (0 Hz–1 MHz) which makes it a good candidate to analyse several defects in tubes using a remote field testing method. Experimental data were acquired by a measurement system to verify the sensitivity of the GMR in defect detection and to create a new probe. A simulation was made in order to verify the veracity of the obtained experimental results when the remote field testing method is applied. Finally, 2D maps representing the GMR output response at several angles of rotation around the defects were made and compared in this paper.

This paper is about different techniques for intelligent processing of data obtained with water q... more This paper is about different techniques for intelligent processing of data obtained with water quality monitoring distributed systems. The techniques include a set of fuzzy neural networks (FuNNs) for modelling measuring channels and Kohonen Self Organizing Maps (K-SOMs) for information classification. Elements of FuNN and K-SOM optimization in terms of architecture and training are presented and briefly discussed.

Wiley Encyclopedia of Electrical and Electronics Engineering, 1999

The sections in this article are 1 Distortionless System 2 Distortion Taxonomy and Terminology 3 ... more The sections in this article are 1 Distortionless System 2 Distortion Taxonomy and Terminology 3 Signal Distortion Measurement 4 Systems Distortion Measurement

Sensors (Basel, Switzerland), Jan 21, 2018

A velocity induced eddy current probe has been used to detect cracks in both non-ferromagnetic an... more A velocity induced eddy current probe has been used to detect cracks in both non-ferromagnetic and ferromagnetic metals. The simulation and experimental results show that this probe can successfully detect cracks in both cases, but further investigation shows that the underlying principles for inspecting non-ferromagnetic and ferromagnetic metals are actually different. For an aluminum plate, the induced eddy current density and the signal amplitude both increase with probe speed, which means the signal is caused by velocity induced eddy currents. For a steel plate, probe speed changes the baselines of the testing signals; however, it has little influence on signal amplitudes. Simulation results show that the signal for cracks in a steel plate is mainly caused by direct magnetic field perturbation rather than velocity induced eddy currents.

2015 IEEE Metrology for Aerospace (MetroAeroSpace), 2015

ABSTRACT

Sensors and Actuators A: Physical, 2015

This paper presents an enhancement in the probes to be used on a new nondestructive testing metho... more This paper presents an enhancement in the probes to be used on a new nondestructive testing method with eddy currents induced by velocity. In this method, a permanent magnet that is attached to a moving carriage creates eddy currents in the conductive material to be inspected. By measuring the opposing magnetic field generated by the eddy currents, it is possible to obtain information regarding the presence of defects. Different magnetic field sensors, such as, differential pickup coils, giant magneto resistors (GMR) and Hall sensors have been used and compared. A permanent magnet moving above a plate was studied using a numerical model to allow further improvements to be made in the probe. Depending on each sensor's geometry, sensing axis and range, its position and orientation must be strategically chosen in order to increase defect sensitivity. The best probe's position is the one that guarantees the highest sensibility to the defects' presence.

2021 Telecoms Conference (ConfTELE), 2021

In this work we have proposed a model, based on the semi-analytical Boundary Element Method (BEM)... more In this work we have proposed a model, based on the semi-analytical Boundary Element Method (BEM), that predicts the perturbation magnetic flux density component arising due to a narrow opening embedded flaw present in an electrically conductive medium of finite thickness. We have derived the results based on the classical dipole model of flaws (scattering source) typically encountered in eddy current based nondestructive testing and evaluation. The problem that we have modeled is the field scattered by a rectangular flaw embedded in a conductive material, achieved by stacking two electrically conductive plates that are non-magnetic. A cylindrical coil scans the flaw. The excitation field varies time harmonically. The experimental verification was carried out by utilizing a highly sensitive giant magneto-resistive sensor. We have compared the model predicted results to the experimental study with a good agreement.

New challenges in water systems include different approaches from analysis of failures and risk a... more New challenges in water systems include different approaches from analysis of failures and risk assessment to system efficiency improvements and new innovative designs. In water distribution networks (WDNs), the risk function is a measure of its vulnerability level and security loss. Analyses of transient flows which are associated with the most dangerous operating conditions, are compulsory to grant the system liability both in water quantity, quality, and management. Specific equipment, such as air valves are used in pressurized water pipes to manage the air inside associated with the filling process, that can also act as a control mechanism, where the major limitation is its reliability. Advanced tools are developed specifically to smart water grids implementation and operation. The water system efficiency and water-energy nexus, through the implementation of suitable, pressure control and energy recovery devices, and pumped-storage hydropower solutions, provide guidelines for the determination of the most technical cost-effective result. Integrated analysis of water and energy allows more reliable, flexible, and sustainable eco-design projects, reaching better resilience systems through new concepts. The development of model simulations, based on hydraulic simulators and computational fluid dynamics (CFD), conjugating with field or experimental tests, supported by advanced smart equipment, allow the control, identification, and anticipation of complex events necessary to maintain the water system security and efficiency.

2015 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) Proceedings, 2015

Nondestructive testing in situations where there is a moving media has always been a challenging ... more Nondestructive testing in situations where there is a moving media has always been a challenging task. Motion induced eddy current testing is a good solution for testing metallic surfaces, as it does not require contact with the sample. This work presents a method to detect sub-surface defects in non-ferromagnetic material with motion induced eddy currents. A numerical model was used to verify the progression of eddy currents along the depth of a conductive plate and to obtain the magnetic field perturbation in the presence of sub-surface defects. A probe, including a permanent magnet to induce eddy currents and a magnetic sensor was moved in the vicinity of an aluminium plate with sub-surface defects to obtain experimental data and the results compared to those obtained with the numerical model. At higher speeds, the time of diffusion of deeper eddy currents takes, makes it possible to also estimate the depth of a sub-surface defect by measuring how far away the perturbation is from the moving magnet.

International Journal of Applied Electromagnetics and Mechanics, 2016

In this paper we present a method to determine the current density inside an aluminum plate using... more In this paper we present a method to determine the current density inside an aluminum plate using eddy current testing procedure to determine the existence of surface cracks. The general idea consists in generating eddy currents in the plate, which in the case of flawless material, must be of uniform density pointing along a pre-defined direction inside a given area on the plate surface. These currents are produced using a planar coil. The eddy current density is determined by inversion of the data obtained from the measurement of a single component of the resultant magnetic field. Tikhonov regularization is applied to the inverted data.

Defect detection in conductive plates represents an important issue. This work presents designed ... more Defect detection in conductive plates represents an important issue. This work presents designed and implemented uniform eddy current probe architecture (UECP) that includes a planar excitation coil and a GMR magnetometer sensor array as part of a non-destructive testing (NDT) system developed using a virtual instrument system technology. The usage of GMR sensors provides frequency independent sensitivity to the UECP, assuring speed, depth, and higher resolution in eddy-current testing, while the usage of a set of GMR sensors allows rapid scanning of an area for defects in a single pass. A practical approach concerning the UECP design, implementation and experimental results obtained on cracks detection machined in aluminum plates for a single or multiple GMR sensor usage as main parts of UECP are presented. Experimental results regarding the usage of the novel eddy current probe to detect induced flaws in aluminum plates are included in the paper.

2007 IEEE Instrumentation & Measurement Technology Conference IMTC 2007, 2007

Page 1. Instrumentation and Measurement Technology Conference - IMTC 2007 Warsaw, Poland, May 1-3... more Page 1. Instrumentation and Measurement Technology Conference - IMTC 2007 Warsaw, Poland, May 1-3, 2007 Development of a IEEE 1451 Standard Compliant Smart Transducer Network with Time Synchronization Protocol ...

Abstract: The measurement of electrolytic conductivity is widely applied as a control parameter a... more Abstract: The measurement of electrolytic conductivity is widely applied as a control parameter and its relevance is continuously increasing, not only in industrial applications but also in the environmental monitoring domain. In this work the attention is focused on the electrical behavior of low cost in-situ four electrode conductivity cells for water quality monitoring in estuaries and oceans. The design of each cell, the choice of the cell constant suitable for the range of conductivities to be measured, the modeling of the current density distribution using a finite element method are described in detail. The experimental characterization of the cell versus frequency, temperature and salt concentration is also carried out. A frequency range where parasitic effects are minimized is identified.

This work presents two handheld instruments built at our laboratory able to detect sub-surface cr... more This work presents two handheld instruments built at our laboratory able to detect sub-surface cracks in a plate of conductive material. Both instruments contain a probe composed of an excitation coil and a giant magnetoresistance sensor (GMR) acting as the magnetic field sensor and includes a computer mouse pointer as positioning system. This configuration, despite its low cost, allows better performances in the detection of sub-surface defects than commercial equipments. Deeper defects in the material can be detected due not only to the high sensitivity of the GMR sensor, which is constant in a very large frequency range (10 Hz 1 MHz), but also because a precisely located graphical representation of the defect is delivered to the user due to the incorporated positioning system. The paper includes a description of the implementation of each device, the obtained results and a comparison of the performance.

This work presents two handheld instruments built at our laboratory able to detect sub-surface cr... more This work presents two handheld instruments built at our laboratory able to detect sub-surface cracks in a plate of conductive material. Both instruments contain a probe composed of an excitation coil and a giant magnetoresistance sensor (GMR) acting as the magnetic field sensor and includes a computer mouse pointer as positioning system. This configuration, despite its low cost, allows better performances in the detection of sub-surface defects than commercial equipments. Deeper defects in the material can be detected due not only to the high sensitivity of the GMR sensor, which is constant in a very large frequency range (10 Hz 1 MHz), but also because a precisely located graphical representation of the defect is delivered to the user due to the incorporated positioning system. The paper includes a description of the implementation of each device, the obtained results and a comparison of the performance.

Entropy, 2020

Photovoltaic (PV) system energy production is non-linear because it is influenced by the random n... more Photovoltaic (PV) system energy production is non-linear because it is influenced by the random nature of weather conditions. The use of machine learning techniques to model the PV system energy production is recommended since there is no known way to deal well with non-linear data. In order to detect PV system faults, the machine learning models should provide accurate outputs. The aim of this work is to accurately predict the DC energy of six PV strings of a utility-scale PV system and to accurately detect PV string faults by benchmarking the results of four machine learning methodologies known to improve the accuracy of the machine learning models, such as the data mining methodology, machine learning technique benchmarking methodology, hybrid methodology, and the ensemble methodology. A new hybrid methodology is proposed in this work which combines the use of a fuzzy system and the use of a machine learning system containing five different trained machine learning models, such a...

2015 IEEE Metrology for Aerospace (MetroAeroSpace), 2015

This paper presents experimental and simulated results obtained using the eddy current nondestruc... more This paper presents experimental and simulated results obtained using the eddy current nondestructive method to conclude about the depth of linear cracks machined on an aluminum plate. Experimental tests were performed with a sinusoidal excitation field of fixed-amplitude and with a giant magnetoresistance-based sensor to measure the resultant magnetic field on the plate surface. To validate and better insight the experimental results, numerical simulations have been carried out with a commercial program for conditions similar to the experimental case studies. A scheme to infer about crack depth is proposed.

International Journal of Industrial Electronics and Drives, 2014

This paper presents a probe that permits the detection of longitudinal and circumferential defect... more This paper presents a probe that permits the detection of longitudinal and circumferential defects in stainless steel tubes. The defect detection is made by a measurement system based on eddy current (EC) and remote field testing (RFT). The probe includes an excitation coil and a giant magneto-resistance (GMR) magnetic sensor. This GMR sensor has high sensitivity in a large frequency range (0 Hz–1 MHz) which makes it a good candidate to analyse several defects in tubes using a remote field testing method. Experimental data were acquired by a measurement system to verify the sensitivity of the GMR in defect detection and to create a new probe. A simulation was made in order to verify the veracity of the obtained experimental results when the remote field testing method is applied. Finally, 2D maps representing the GMR output response at several angles of rotation around the defects were made and compared in this paper.

This paper is about different techniques for intelligent processing of data obtained with water q... more This paper is about different techniques for intelligent processing of data obtained with water quality monitoring distributed systems. The techniques include a set of fuzzy neural networks (FuNNs) for modelling measuring channels and Kohonen Self Organizing Maps (K-SOMs) for information classification. Elements of FuNN and K-SOM optimization in terms of architecture and training are presented and briefly discussed.

Wiley Encyclopedia of Electrical and Electronics Engineering, 1999

The sections in this article are 1 Distortionless System 2 Distortion Taxonomy and Terminology 3 ... more The sections in this article are 1 Distortionless System 2 Distortion Taxonomy and Terminology 3 Signal Distortion Measurement 4 Systems Distortion Measurement

Sensors (Basel, Switzerland), Jan 21, 2018

A velocity induced eddy current probe has been used to detect cracks in both non-ferromagnetic an... more A velocity induced eddy current probe has been used to detect cracks in both non-ferromagnetic and ferromagnetic metals. The simulation and experimental results show that this probe can successfully detect cracks in both cases, but further investigation shows that the underlying principles for inspecting non-ferromagnetic and ferromagnetic metals are actually different. For an aluminum plate, the induced eddy current density and the signal amplitude both increase with probe speed, which means the signal is caused by velocity induced eddy currents. For a steel plate, probe speed changes the baselines of the testing signals; however, it has little influence on signal amplitudes. Simulation results show that the signal for cracks in a steel plate is mainly caused by direct magnetic field perturbation rather than velocity induced eddy currents.

2015 IEEE Metrology for Aerospace (MetroAeroSpace), 2015

ABSTRACT

Sensors and Actuators A: Physical, 2015

This paper presents an enhancement in the probes to be used on a new nondestructive testing metho... more This paper presents an enhancement in the probes to be used on a new nondestructive testing method with eddy currents induced by velocity. In this method, a permanent magnet that is attached to a moving carriage creates eddy currents in the conductive material to be inspected. By measuring the opposing magnetic field generated by the eddy currents, it is possible to obtain information regarding the presence of defects. Different magnetic field sensors, such as, differential pickup coils, giant magneto resistors (GMR) and Hall sensors have been used and compared. A permanent magnet moving above a plate was studied using a numerical model to allow further improvements to be made in the probe. Depending on each sensor's geometry, sensing axis and range, its position and orientation must be strategically chosen in order to increase defect sensitivity. The best probe's position is the one that guarantees the highest sensibility to the defects' presence.