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Papers by Artur Lopes Ribeiro

Research paper thumbnail of Virtual Instrument to Detect Defects in Conductive Materials

1-This paper describes a virtual instrument developed at the Instituto de Telecomunicações-Measur... more 1-This paper describes a virtual instrument developed at the Instituto de Telecomunicações-Measurement and Instrumentation Group, to detect defects in conductive plates using eddy current methods. The measuring system allows the use of different types of probes which enable the determination of different magnetic field components and reconstruction of distinct images of the scanned sample under test.

Research paper thumbnail of The Lift-Off Effect in Eddy Currents on Thickness Modeling and Measurement

IEEE Transactions on Instrumentation and Measurement, 2000

This paper uses a linear transformer model to investigate the effect of the lift-off on the resul... more This paper uses a linear transformer model to investigate the effect of the lift-off on the results of the thickness measurement of non-ferromagnetic metallic plates. The transformer model previews that the time derivative of the magnetization curves obtained for different gaps between the excitation coil and the plate should intercept in a single point when low magnetic coupling factors are considered. To assess the validity of the model, results are compared with experimental data obtained with a giant magnetoresistive (GMR) sensor probe. For comparison, the sensor output voltage time derivative must be performed as well. The similarity of the theoretical model results and those obtain experimentally with pulsed excitation, confirms the correctness of the transformer approach.

Research paper thumbnail of Detection and characterization of defects using GMR probes and artificial neural networks

Computer Standards & Interfaces, 2011

This work presents an eddy-current testing system based on a giant magnetoresistive (GMR) sensing... more This work presents an eddy-current testing system based on a giant magnetoresistive (GMR) sensing device. Non-destructive tests in aluminum plates are applied in order to extract information about possible defects: cracks, holes and other mechanical damages. Eddy-current testing (ECT) presents major benefits such as low cost, high checking speed, robustness and high sensitivity to large classes of defects. Coil based

Research paper thumbnail of Characterization of Defects in Aluminum Plates Using GMR Probes and Neural Network Signal Processing

Conductive specimens such as aluminum plates are tested in order to extract information about pos... more Conductive specimens such as aluminum plates are tested in order to extract information about possible cracks, flaws and other mechanical damages. Nowadays, eddy current testing (ECT) despite its major benefits (e.g. low cost, high checking speed, robustness and high sensitivity to large classes of defects) implies the utilization of fully coil based architecture probes or hybrid coil- magnetoresistive probes. This

Research paper thumbnail of Signal Processing in an Eddy Current Non-Destructive Testing System

Nowadays, eddy current non-destructive testing requires highly skilled operators that using hand-... more Nowadays, eddy current non-destructive testing requires highly skilled operators that using hand-operated eddy current testers are able to recognize defects in conductive materials. The objective of our work is to overcome this problem by implementing a microcomputer based system to detect and estimate the size of cracks and other defects in conductive non magnetic material, with minimum operator intervention. In

Research paper thumbnail of USING A MOUSE POINTER AS A POSITIONING DEVICE IN EDDY CURRENT TESTING

The use of Eddy currents is a well-known non-destructive technique used in the characterization o... more The use of Eddy currents is a well-known non-destructive technique used in the characterization of cracks in conductive non-magnetic materials. In this paper some experimental and finite element modelling tests with a new probe installed in a mouse pointer device connected to a PC are reported. This probe combines good sensitivity performances at low frequencies by using a giant magnetoresistor (GMR) magnetic sensor with an hand-held device capable of transferring easily its position to the PC.

Research paper thumbnail of Virtual Instrument to Detect Defects in Conductive Materials

1 -This paper describes a virtual instrument developed at the Instituto de Telecomunicações -Meas... more 1 -This paper describes a virtual instrument developed at the Instituto de Telecomunicações -Measurement and Instrumentation Group, to detect defects in conductive plates using eddy current methods. The measuring system allows the use of different types of probes which enable the determination of different magnetic field components and reconstruction of distinct images of the scanned sample under test.

Research paper thumbnail of Using the skin effect to estimate cracks depths in mettalic structures

This paper is concerned with the characterization of depth profiles defects in metallic structure... more This paper is concerned with the characterization of depth profiles defects in metallic structures. Experimental work using giant magnetoresistors (GMR) scanning automatically a metallic plate with eddy currents induced by an excitation coil has been carried out and is described. The results are analyzed in comparison with the simulation results obtained with a commercial finite element model for some test cases.

Research paper thumbnail of Liftoff Correction Based on the Spatial Spectral Behavior of Eddy-Current Images

IEEE Transactions on Instrumentation and Measurement, 2010

In this paper, a new processing scheme for compensating the liftoff effect is proposed to increas... more In this paper, a new processing scheme for compensating the liftoff effect is proposed to increase the signal-to-noise ratio of measurements carried out when a duralumin plate with artificially manufactured defects was scanned with eddy-current probes. The mathematical algorithm is based on the spatial frequency behavior of the output signals with the liftoff distance (the distance between the probe used for inspection and the sample) and its equivalent form (deconvolution) in the spatial domain. Results are presented for measurements performed at three different distances for the same defect of the duralumin plate.

Research paper thumbnail of Low-cost stand-alone system for eddy current testing of metallic non-ferromagnetic plates

This paper describes a nondestructive testing equipment designed with the purpose of being low-co... more This paper describes a nondestructive testing equipment designed with the purpose of being low-cost and able to work in a stand-alone way. The main feature is related to the integration of an eddy-current probe using a giant magnetoresistance (GMR) sensor with a computer mouse to be used as a positioning system. The system was constructed and tested. The results that were obtained allow the graphical representation of the acquired signals as a function of position, which is considered an improvement in relation to the systems that only represent the defect signatures.

Research paper thumbnail of Virtual Instrument to Detect Defects in Conductive Materials

1 -This paper describes a virtual instrument developed at the Instituto de Telecomunicações -Meas... more 1 -This paper describes a virtual instrument developed at the Instituto de Telecomunicações -Measurement and Instrumentation Group, to detect defects in conductive plates using eddy current methods. The measuring system allows the use of different types of probes which enable the determination of different magnetic field components and reconstruction of distinct images of the scanned sample under test.

Research paper thumbnail of Thickness measurement using transient eddy current techniques

This paper describes a pulsed eddy current (PEC) based non-destructive testing system used for ex... more This paper describes a pulsed eddy current (PEC) based non-destructive testing system used for experimental evaluation of material thickness and properties. Both classical and modern sensing methods of magnetic field have been carried out. An inductive as well as a giant magnetoresistive sensor based (GMR) probe have been used for sensing and the results obtained are presented and compared. The use of GMRs for this type of application is innovative and the post processing method too, since it evaluates the thicknesses of the conductive samples or of its non-conductive coatings, from the values obtained with the integration of measured signals.

Research paper thumbnail of Characterization of defects on rivets using a eddy current technique with GMRs

This paper presents the characterization of defects on rivets using an eddy current based measure... more This paper presents the characterization of defects on rivets using an eddy current based measurement system and signal processing algorithms to increase the signal to noise ratio. The instrument includes a planar eddy-current probe having a giant magnetoresistor (GMR) based sensor. The characterization of surface and sub-surface defects is depicted and the metrological performance analyzed.

Research paper thumbnail of A simple forward direct problem solver for eddy current non-destructive inspection of aluminum plates using uniform field probes

Measurement

In this paper we show that a simple algorithm used to model the eddy current inspection of an alu... more In this paper we show that a simple algorithm used to model the eddy current inspection of an aluminum plate can be used to preview the acquired voltage signals. Thus, the algorithm is suitable to work as a forward problem solver to determine the expected measurement signal obtained with a uniform excitation field probe including a giant magnetoresistor sensor. The algorithm is based on a conformal transformation and is able to preview the shape of the electrical current lines when a metallic plate with a superficial straight crack is subject to a sinusoidal excitation field with constant amplitude and orientation in a bounded zone around the sensor element. Simple and fast algorithms as the one presented in this paper are of paramount importance for testing inversion algorithms used to characterize defects in metallic plates.

Research paper thumbnail of Eddy current inspection of a duralumin plate

This article presents the results obtained when a duralumin plate with a slot was scanned with an... more This article presents the results obtained when a duralumin plate with a slot was scanned with an inductive probe in order to measure the eddy currents' magnetic field. A 3D finite element numeric model was used to preview the eddy current distribution. An analysis of the produced data and of the consequences of using image filters is included.

Research paper thumbnail of Characterization of Defects in Aluminum Plates Using GMR Probes and Neural Network Signal Processing

Conductive specimens such as aluminum plates are tested in order to extract information about pos... more Conductive specimens such as aluminum plates are tested in order to extract information about possible cracks, flaws and other mechanical damages. Nowadays, eddy current testing (ECT) despite its major benefits (e.g. low cost, high checking speed, robustness and high sensitivity to large classes of defects) implies the utilization of fully coil based architecture probes or hybrid coil- magnetoresistive probes. This

Research paper thumbnail of Signal Processing in an Eddy Current Non-Destructive Testing System

Nowadays, eddy current non-destructive testing requires highly skilled operators that using hand-... more Nowadays, eddy current non-destructive testing requires highly skilled operators that using hand-operated eddy current testers are able to recognize defects in conductive materials. The objective of our work is to overcome this problem by implementing a microcomputer based system to detect and estimate the size of cracks and other defects in conductive non magnetic material, with minimum operator intervention. In order to reach the best solution different hardware implementations have to be investigated. This paper compares the results obtained with three techniques already tested: using a commercial lock-in amplifier, a dedicated electronic signal processing circuit and a data acquisition board (DAQ). The implementation using the DAQ requires more digital signal processing after the analog conversion than the other methods. In particular, cross correlation and sine-fitting of the sampled signals are used to estimate the phase difference between the excitation current and the sensing coils output signals. The results obtained are presented and compared within the paper.

Research paper thumbnail of Inductive Probe for Flaw Detection in non-Magnetic Metallic Plates Using Eddy Currents

This paper describes the design of an inductive sensor and its application to detect the presence... more This paper describes the design of an inductive sensor and its application to detect the presence of structural flaws inside electrically conducting nonmagnetic plates. The principle of operation is based on the measurement of the induced voltages in two sensing coils. These voltages are related to the eddy currents that are generated inside the plates with perturbations due to the electrical conductivity inhomogeneities. The modeling work aims at determining the optimum operating frequencies and the resulting signal magnitudes.

Research paper thumbnail of Eddy current image normalization in ndt of aluminum plates

This paper presents a normalization method that allows the comparison between data taken from dif... more This paper presents a normalization method that allows the comparison between data taken from different eddy current experiments. The experimental data were acquired by scanning an aluminum plate containing a machined long crack. Results show that with two data sets acquired for orthogonal directions of sensor orientation it is possible to preview the data for any other measurement direction.

Research paper thumbnail of USING A MOUSE POINTER AS A POSITIONING DEVICE IN EDDY CURRENT TESTING

The use of Eddy currents is a well-known non-destructive technique used in the characterization o... more The use of Eddy currents is a well-known non-destructive technique used in the characterization of cracks in conductive non-magnetic materials. In this paper some experimental and finite element modelling tests with a new probe installed in a mouse pointer device connected to a PC are reported. This probe combines good sensitivity performances at low frequencies by using a giant magnetoresistor (GMR) magnetic sensor with an hand-held device capable of transferring easily its position to the PC.

Research paper thumbnail of Virtual Instrument to Detect Defects in Conductive Materials

1-This paper describes a virtual instrument developed at the Instituto de Telecomunicações-Measur... more 1-This paper describes a virtual instrument developed at the Instituto de Telecomunicações-Measurement and Instrumentation Group, to detect defects in conductive plates using eddy current methods. The measuring system allows the use of different types of probes which enable the determination of different magnetic field components and reconstruction of distinct images of the scanned sample under test.

Research paper thumbnail of The Lift-Off Effect in Eddy Currents on Thickness Modeling and Measurement

IEEE Transactions on Instrumentation and Measurement, 2000

This paper uses a linear transformer model to investigate the effect of the lift-off on the resul... more This paper uses a linear transformer model to investigate the effect of the lift-off on the results of the thickness measurement of non-ferromagnetic metallic plates. The transformer model previews that the time derivative of the magnetization curves obtained for different gaps between the excitation coil and the plate should intercept in a single point when low magnetic coupling factors are considered. To assess the validity of the model, results are compared with experimental data obtained with a giant magnetoresistive (GMR) sensor probe. For comparison, the sensor output voltage time derivative must be performed as well. The similarity of the theoretical model results and those obtain experimentally with pulsed excitation, confirms the correctness of the transformer approach.

Research paper thumbnail of Detection and characterization of defects using GMR probes and artificial neural networks

Computer Standards & Interfaces, 2011

This work presents an eddy-current testing system based on a giant magnetoresistive (GMR) sensing... more This work presents an eddy-current testing system based on a giant magnetoresistive (GMR) sensing device. Non-destructive tests in aluminum plates are applied in order to extract information about possible defects: cracks, holes and other mechanical damages. Eddy-current testing (ECT) presents major benefits such as low cost, high checking speed, robustness and high sensitivity to large classes of defects. Coil based

Research paper thumbnail of Characterization of Defects in Aluminum Plates Using GMR Probes and Neural Network Signal Processing

Conductive specimens such as aluminum plates are tested in order to extract information about pos... more Conductive specimens such as aluminum plates are tested in order to extract information about possible cracks, flaws and other mechanical damages. Nowadays, eddy current testing (ECT) despite its major benefits (e.g. low cost, high checking speed, robustness and high sensitivity to large classes of defects) implies the utilization of fully coil based architecture probes or hybrid coil- magnetoresistive probes. This

Research paper thumbnail of Signal Processing in an Eddy Current Non-Destructive Testing System

Nowadays, eddy current non-destructive testing requires highly skilled operators that using hand-... more Nowadays, eddy current non-destructive testing requires highly skilled operators that using hand-operated eddy current testers are able to recognize defects in conductive materials. The objective of our work is to overcome this problem by implementing a microcomputer based system to detect and estimate the size of cracks and other defects in conductive non magnetic material, with minimum operator intervention. In

Research paper thumbnail of USING A MOUSE POINTER AS A POSITIONING DEVICE IN EDDY CURRENT TESTING

The use of Eddy currents is a well-known non-destructive technique used in the characterization o... more The use of Eddy currents is a well-known non-destructive technique used in the characterization of cracks in conductive non-magnetic materials. In this paper some experimental and finite element modelling tests with a new probe installed in a mouse pointer device connected to a PC are reported. This probe combines good sensitivity performances at low frequencies by using a giant magnetoresistor (GMR) magnetic sensor with an hand-held device capable of transferring easily its position to the PC.

Research paper thumbnail of Virtual Instrument to Detect Defects in Conductive Materials

1 -This paper describes a virtual instrument developed at the Instituto de Telecomunicações -Meas... more 1 -This paper describes a virtual instrument developed at the Instituto de Telecomunicações -Measurement and Instrumentation Group, to detect defects in conductive plates using eddy current methods. The measuring system allows the use of different types of probes which enable the determination of different magnetic field components and reconstruction of distinct images of the scanned sample under test.

Research paper thumbnail of Using the skin effect to estimate cracks depths in mettalic structures

This paper is concerned with the characterization of depth profiles defects in metallic structure... more This paper is concerned with the characterization of depth profiles defects in metallic structures. Experimental work using giant magnetoresistors (GMR) scanning automatically a metallic plate with eddy currents induced by an excitation coil has been carried out and is described. The results are analyzed in comparison with the simulation results obtained with a commercial finite element model for some test cases.

Research paper thumbnail of Liftoff Correction Based on the Spatial Spectral Behavior of Eddy-Current Images

IEEE Transactions on Instrumentation and Measurement, 2010

In this paper, a new processing scheme for compensating the liftoff effect is proposed to increas... more In this paper, a new processing scheme for compensating the liftoff effect is proposed to increase the signal-to-noise ratio of measurements carried out when a duralumin plate with artificially manufactured defects was scanned with eddy-current probes. The mathematical algorithm is based on the spatial frequency behavior of the output signals with the liftoff distance (the distance between the probe used for inspection and the sample) and its equivalent form (deconvolution) in the spatial domain. Results are presented for measurements performed at three different distances for the same defect of the duralumin plate.

Research paper thumbnail of Low-cost stand-alone system for eddy current testing of metallic non-ferromagnetic plates

This paper describes a nondestructive testing equipment designed with the purpose of being low-co... more This paper describes a nondestructive testing equipment designed with the purpose of being low-cost and able to work in a stand-alone way. The main feature is related to the integration of an eddy-current probe using a giant magnetoresistance (GMR) sensor with a computer mouse to be used as a positioning system. The system was constructed and tested. The results that were obtained allow the graphical representation of the acquired signals as a function of position, which is considered an improvement in relation to the systems that only represent the defect signatures.

Research paper thumbnail of Virtual Instrument to Detect Defects in Conductive Materials

1 -This paper describes a virtual instrument developed at the Instituto de Telecomunicações -Meas... more 1 -This paper describes a virtual instrument developed at the Instituto de Telecomunicações -Measurement and Instrumentation Group, to detect defects in conductive plates using eddy current methods. The measuring system allows the use of different types of probes which enable the determination of different magnetic field components and reconstruction of distinct images of the scanned sample under test.

Research paper thumbnail of Thickness measurement using transient eddy current techniques

This paper describes a pulsed eddy current (PEC) based non-destructive testing system used for ex... more This paper describes a pulsed eddy current (PEC) based non-destructive testing system used for experimental evaluation of material thickness and properties. Both classical and modern sensing methods of magnetic field have been carried out. An inductive as well as a giant magnetoresistive sensor based (GMR) probe have been used for sensing and the results obtained are presented and compared. The use of GMRs for this type of application is innovative and the post processing method too, since it evaluates the thicknesses of the conductive samples or of its non-conductive coatings, from the values obtained with the integration of measured signals.

Research paper thumbnail of Characterization of defects on rivets using a eddy current technique with GMRs

This paper presents the characterization of defects on rivets using an eddy current based measure... more This paper presents the characterization of defects on rivets using an eddy current based measurement system and signal processing algorithms to increase the signal to noise ratio. The instrument includes a planar eddy-current probe having a giant magnetoresistor (GMR) based sensor. The characterization of surface and sub-surface defects is depicted and the metrological performance analyzed.

Research paper thumbnail of A simple forward direct problem solver for eddy current non-destructive inspection of aluminum plates using uniform field probes

Measurement

In this paper we show that a simple algorithm used to model the eddy current inspection of an alu... more In this paper we show that a simple algorithm used to model the eddy current inspection of an aluminum plate can be used to preview the acquired voltage signals. Thus, the algorithm is suitable to work as a forward problem solver to determine the expected measurement signal obtained with a uniform excitation field probe including a giant magnetoresistor sensor. The algorithm is based on a conformal transformation and is able to preview the shape of the electrical current lines when a metallic plate with a superficial straight crack is subject to a sinusoidal excitation field with constant amplitude and orientation in a bounded zone around the sensor element. Simple and fast algorithms as the one presented in this paper are of paramount importance for testing inversion algorithms used to characterize defects in metallic plates.

Research paper thumbnail of Eddy current inspection of a duralumin plate

This article presents the results obtained when a duralumin plate with a slot was scanned with an... more This article presents the results obtained when a duralumin plate with a slot was scanned with an inductive probe in order to measure the eddy currents' magnetic field. A 3D finite element numeric model was used to preview the eddy current distribution. An analysis of the produced data and of the consequences of using image filters is included.

Research paper thumbnail of Characterization of Defects in Aluminum Plates Using GMR Probes and Neural Network Signal Processing

Conductive specimens such as aluminum plates are tested in order to extract information about pos... more Conductive specimens such as aluminum plates are tested in order to extract information about possible cracks, flaws and other mechanical damages. Nowadays, eddy current testing (ECT) despite its major benefits (e.g. low cost, high checking speed, robustness and high sensitivity to large classes of defects) implies the utilization of fully coil based architecture probes or hybrid coil- magnetoresistive probes. This

Research paper thumbnail of Signal Processing in an Eddy Current Non-Destructive Testing System

Nowadays, eddy current non-destructive testing requires highly skilled operators that using hand-... more Nowadays, eddy current non-destructive testing requires highly skilled operators that using hand-operated eddy current testers are able to recognize defects in conductive materials. The objective of our work is to overcome this problem by implementing a microcomputer based system to detect and estimate the size of cracks and other defects in conductive non magnetic material, with minimum operator intervention. In order to reach the best solution different hardware implementations have to be investigated. This paper compares the results obtained with three techniques already tested: using a commercial lock-in amplifier, a dedicated electronic signal processing circuit and a data acquisition board (DAQ). The implementation using the DAQ requires more digital signal processing after the analog conversion than the other methods. In particular, cross correlation and sine-fitting of the sampled signals are used to estimate the phase difference between the excitation current and the sensing coils output signals. The results obtained are presented and compared within the paper.

Research paper thumbnail of Inductive Probe for Flaw Detection in non-Magnetic Metallic Plates Using Eddy Currents

This paper describes the design of an inductive sensor and its application to detect the presence... more This paper describes the design of an inductive sensor and its application to detect the presence of structural flaws inside electrically conducting nonmagnetic plates. The principle of operation is based on the measurement of the induced voltages in two sensing coils. These voltages are related to the eddy currents that are generated inside the plates with perturbations due to the electrical conductivity inhomogeneities. The modeling work aims at determining the optimum operating frequencies and the resulting signal magnitudes.

Research paper thumbnail of Eddy current image normalization in ndt of aluminum plates

This paper presents a normalization method that allows the comparison between data taken from dif... more This paper presents a normalization method that allows the comparison between data taken from different eddy current experiments. The experimental data were acquired by scanning an aluminum plate containing a machined long crack. Results show that with two data sets acquired for orthogonal directions of sensor orientation it is possible to preview the data for any other measurement direction.

Research paper thumbnail of USING A MOUSE POINTER AS A POSITIONING DEVICE IN EDDY CURRENT TESTING

The use of Eddy currents is a well-known non-destructive technique used in the characterization o... more The use of Eddy currents is a well-known non-destructive technique used in the characterization of cracks in conductive non-magnetic materials. In this paper some experimental and finite element modelling tests with a new probe installed in a mouse pointer device connected to a PC are reported. This probe combines good sensitivity performances at low frequencies by using a giant magnetoresistor (GMR) magnetic sensor with an hand-held device capable of transferring easily its position to the PC.