Design and Analysis of a Differential Waveguide Structure to Improve Magnetostrictive Linear Position Sensors

Magnetostrictive linear position sensors (MLPS) are high-precision sensors used in the industrial field for measuring the propagation time of ultrasonic signals in a waveguide. To date, MLPS have attracted widespread attention for their accuracy, reliability, and cost-efficiency in performing non-contact, multiple measurements. However, the sensor, with its traditional structure, is susceptible to electromagnetic interference, which affects accuracy. In the present study, we propose a novel structure of MLPS that relies on two differential waveguides to improve the signal-to-noise ratio, common-mode rejection ratio, and accuracy of MLPS. The proposed sensor model can depict sensor performance and the relationship of sensor parameters. Experimental results with the new sensor indicate that the new structure can improve accuracy to ±0.1 mm higher than ±0.2 mm with a traditional structure. In addition, the proposed sensor shows a considerable improvement in temperature characteristics

Multiphysics Finite Element Analysis of In-Pile Sensors for Advanced Nuclear Reactors

Nuclear reactors have large needs for in-pile sensors that are durable in high temperature, radioactive, and corrosive environments. With the use of multiphysics finite element analysis (FEA) researchers can speed up sensor prototyping. FEA also allows for a better fundamental understanding of sensors and enables sensor optimization. This research focuses on three types of in-pile sensors developed at Idaho National Laboratory: acoustic sensors, linear variable differential transformers (LVDT), and capacitance based strain gauges (CSG). Two acoustic sensors, magnetostrictive waveguides and piezoelectric surface acoustic wave (SAW) sensors were first modeled. These models showed the acoustic wave patterns and estimated the speed of sound. The modeling results were compared to results from laser Doppler vibrometer testing. The model was implemented to enhance the performance of the sensor designs. This research then modeled a LVDT sensor used to measure fuel rod deformation and structural health monitoring. A parametric FEA study was completed for the purpose of sensor miniaturization. The FEA model was also used to investigate the potential of adding a fiber optic cable through the LVDT core. This research eventually modeled CSGs used in nondestructive structural health monitoring. Multiphysics models were used to investigate the discrepancies in experiments and previous analytical models

Development of EMAT and piezoelectric transducers for high temperature ultrasonic thickness measurements

Improving reliability of components operating at high temperature, such as pipelines, boilers and reactors, within a range of industries is of importance in the asset management process. This thesis concerns the development and testing of ultrasound transducers for use at elevated temperatures, up to 500 _C, without the use of active cooling. Ultrasound thickness measurement applications employing these high temperature transducers includes both portable-type non-destructive testing (NDT) inspections and permanent condition monitoring, primarily towards detection of corrosion and erosion. The development and optimisation of an electromagnetic acoustic transducer (EMAT) design which generates and detects bulk radially polarised shear waves utilising a high temperature permanent magnet and a ceramic encapsulated spiral coil is discussed. This design was optimised for use on magnetite coated mild steel samples; it was shown that the magnetostriction mechanism tends to dominate, depending upon sample properties, producing large signals even at elevated temperatures. High temperature laboratory trials (up to 500 oC) demonstrated the non-linear change in signal amplitude with increasing temperature on magnetite coated mild steel samples, attributed to the complex non-linear relationship between magnetostrictive strains and applied external magnetic field. The EMAT provided good signal amplitude, even at relatively large sample-EMAT lift-off (up to 8.0 mm), demonstrating the applicability of this EMAT for high temperature scanning inspections. A longterm industrial field trial on a high temperature pipeline (≈ 350 oC) in a refinery exhibited the suitability of this design for high temperature continuous monitoring applications. A piezoelectric transducer with a novel compression-type design was optimised for application at high temperature, with the use of a waveguide, high temperature piezoelectric element and high temperature backing material; the optimisation of these components is discussed. This transducer design incorporates compression applied via a central bolt, to achieve acoustic coupling between the components, avoiding the use of adhesive layers, to generate bulk longitudinal waves. With the application of a bismuth titanate piezoelectric element, the transducer was able to generate signals on stainless steel whilst withstanding high temperatures (up to 500 oC) continuously without cooling

Detection of Magnetic Fields Using Fibre Optic Interferometric Sensors.

The principle aim of the work described in this thesis is to determine a suitable optical detection system for d.c. and low frequency magnetic fields which are likely to be encountered in practical magnetometer applications. To construct a sensitive magneotmeter one arm of an optical fibre Mach-Zehnder interferometer has been magnetically sensitised using a magnetostrictive material. Since the signal frequency range of interest was in the region of 0.01 to 10Hz, clearly the signal was in the same frequency band as the environmental noise associated with ambient temperature and pressure variations. Initially, a technique was developed to measure the magnetic field from the shift of the total fringe pattern generated by a modified Mach-Zehnder interferometer and a minimum detectable magnetic field of 10e-7 tesla.m. was obtained. This minimum detectable magnetic field has been improved by a number of modifications. A technique has been developed which utilises an a.c. bias field to put the magnetic signal on a carrier so that it can be measured at a frequency where the amplitude of the interferometer 1/f noise is much reduced. To maintain maximum interferometric sensitivity to this signal active homodyne demodulation techniques have been developed to maintain the interferometer at quadrature by compensating for the environmental noise. A minimum detectable magnetic field of 5x10e-10 tesla.m. has been achieved with this system. As an alternative to the Mach-Zehnder interferometer a Fabry-Perot interferometer, which utilises multiple-beam interference, has been considered. This type of interferometer consists of a single fibre with high reflectivity coatings on its ends. Such an interferometer has been used as a sensor and as an external cavity in laser frequency stabilisation scheme

Stress monitoring of cylindrical structures using guided waves

This thesis presents some approaches for guided wave based stress monitoring as a part of Structural Health Monitoring (SHM). SHM systems include different levels, from damage detection to prognosis, however, this work is focused on detection and on an estimation of the actual stress. The proposed stress monitoring strategies are based on different statistical and signal processing approaches such as Principal Component Analysis and Residuals. These techniques are applied on signals of elastic guided waves generated and sensed via Piezoelectrical (PZT) or Magnetostrictive transducers. Transducer devices are chosen in this work to generate longitudinal, flexural and torsional guided waves in cylindrical specimens, since their high performance, low energy consumption, weight and reasonable price. In order to guarantee the efficacy of the proposed techniques, they are tested in laboratory by emulating real installations and abnormal conditions. Experimental tests revealed that temperature and bonding layer between the PZT and the specimen influence on the performance of the monitoring scheme by changes in the guided wave propagation. Thus, the temperature effect on guided wave propagation was examined by checking the sensitivity of the PCA-based proposed approach. Then, a temperature compensation strategy is applied to improve stability and robustness of the scheme for structures subjected temperature changes. On the other hand, since the acoustoelasticity effect is predominant in the propagation of stressed guided waves, it was observed its incidence on the dispersion curves by using a SAFE method (Semi-Analytical Finite Element) to generate stressed dispersion curves via Effective Elastic Constants (EEC). Finally, as a consequence of some observations in the experimentation stage, it is proposed a scheme for monitoring the supports rigidity in pipelines based on a guided waves energy leakage perspective. The proposed approaches may promise the ability and capability of being implemented in different fields such as aerospace and gas/oil industry.En esta tesis se presentan algunos enfoques para el monitoreo de esfuerzos usando ondas guiadas como parte de un sistema de evaluación de integridad. Estos sistemas incluyen diferentes niveles de monitoreo que van desde la detección de daños hasta su predicción; sin embargo este trabajo se enfoca solo en la detección y estimación de un valor probable de esfuerzo. La estrategia de monitoreo propuesta se basa en diferentes enfoques estadísticos y de procesamiento de señales tales como Análisis de Componentes Principales y Residuos. Estas técnicas se aplican en señales que corresponden a ondas guiadas generadas por transductores piezoelectricos (PZT) o magnetostrictivos. Estos elementos tienen la capacidad de generar ondas guiadas longitudinales, de flexión y torsionales en especímenes cilíndricos, con alto desempeño, bajo consumo de energía, bajo peso y a un costo razonable. Para garantizar la efectividad de las técnicas propuestas, estas se prueban en laboratorio emulando una instalación real y bajo condiciones anormales de esfuerzo. Los resultados experimentales revelaron que la temperatura de los alrededores y la capa adhesiva entre el piezoelectrico y el espécimen influyen en el desempeño del esquema de monitoreo debido a los cambios que se producen en la propagación de onda . Por lo tanto, se estudia el efecto desde una perspectiva analítica el efecto de la temperatura en la propagación de la onda guiada y en consecuencia en el desempeño del enfoque de monitoreo propuesto. Basado en lo anterior, se aplica una estrategia de compensación del efecto de la temperatura para mejorar la estabilidad y la robustez del esquema propuesto ante escenarios de cambios de temperatura. Por otro lado, debido a que el efecto predominante en la propagación de ondas guiadas bajo esfuerzo es el efecto acoustoelastico, se estudia su influencia en las curvas de dispersión usando un método semi-analitico basado en elementos finitos (SAFE del inglés) en combinación con las Constantes Elásticas Efectivas (EEC del inglés) para estimar las curvas de dispersión de ondas guiadas bajo esfuerzo. Finalmente, como un resultados de la experimentación, se propone un esquema de monitoreo de rigidez de soportes de tubería cilíndrica basado en un perspectiva de energía de ultrasonido transferida al entorno vía contacto de superficies. El enfoque propuesto puede ser extendido al monitoreo de rigidez o contacto en otros sistemas en campos tales como el aeroespacial y en la industria del Gas/PetróleoPostprint (published version

Control and Measurement System for a Compressing Unit

Pulp for making paper is produced in grinding machines whose operation principle is based on the compression of logs against a grinding stone. The aim of this Master Thesis is to develop and implement a control and measurement system for a laboratory compressing unit which carries out this first step in paper making process. For this purpose, a hand drive and a computer interface are designed and configured. The thesis is divided in three sections. In the literature study the theories involved in the research work are analyzed. Control and measurement methods are detailed as well as the hydraulic system needed to operate the compressing unit. In the second section the development of a control and measurement method suitable for the unit is carried out. It is based on the study of the most important variables involved in the process. Last section focuses on the implementation of the control and measurement system. A hand drive and a computer interface are considered. The latter is developed using LabView software. In this section, the hand drive design is analyzed and the LabView code is explained. In addition, a measurement approximation method is implemented in order to display the correct variable values. Finally a verification of the whole system is carried out. The results of this study suggest that the control and measurement system satisfies the requisites needed to develop future researches related to this compressing unit. The values displayed by the hand drive and computer interfaces are similar to the theoretical ones and the control system avoids dangerous situations. This Master Thesis suggests future research work in order to improve the accuracy of the control and measurement system. /Kir1

Stress monitoring of cylindrical structures using guided waves

This thesis presents some approaches for guided wave based stress monitoring as a part of Structural Health Monitoring (SHM). SHM systems include different levels, from damage detection to prognosis, however, this work is focused on detection and on an estimation of the actual stress. The proposed stress monitoring strategies are based on different statistical and signal processing approaches such as Principal Component Analysis and Residuals. These techniques are applied on signals of elastic guided waves generated and sensed via Piezoelectrical (PZT) or Magnetostrictive transducers. Transducer devices are chosen in this work to generate longitudinal, flexural and torsional guided waves in cylindrical specimens, since their high performance, low energy consumption, weight and reasonable price. In order to guarantee the efficacy of the proposed techniques, they are tested in laboratory by emulating real installations and abnormal conditions. Experimental tests revealed that temperature and bonding layer between the PZT and the specimen influence on the performance of the monitoring scheme by changes in the guided wave propagation. Thus, the temperature effect on guided wave propagation was examined by checking the sensitivity of the PCA-based proposed approach. Then, a temperature compensation strategy is applied to improve stability and robustness of the scheme for structures subjected temperature changes. On the other hand, since the acoustoelasticity effect is predominant in the propagation of stressed guided waves, it was observed its incidence on the dispersion curves by using a SAFE method (Semi-Analytical Finite Element) to generate stressed dispersion curves via Effective Elastic Constants (EEC). Finally, as a consequence of some observations in the experimentation stage, it is proposed a scheme for monitoring the supports rigidity in pipelines based on a guided waves energy leakage perspective. The proposed approaches may promise the ability and capability of being implemented in different fields such as aerospace and gas/oil industry.En esta tesis se presentan algunos enfoques para el monitoreo de esfuerzos usando ondas guiadas como parte de un sistema de evaluación de integridad. Estos sistemas incluyen diferentes niveles de monitoreo que van desde la detección de daños hasta su predicción; sin embargo este trabajo se enfoca solo en la detección y estimación de un valor probable de esfuerzo. La estrategia de monitoreo propuesta se basa en diferentes enfoques estadísticos y de procesamiento de señales tales como Análisis de Componentes Principales y Residuos. Estas técnicas se aplican en señales que corresponden a ondas guiadas generadas por transductores piezoelectricos (PZT) o magnetostrictivos. Estos elementos tienen la capacidad de generar ondas guiadas longitudinales, de flexión y torsionales en especímenes cilíndricos, con alto desempeño, bajo consumo de energía, bajo peso y a un costo razonable. Para garantizar la efectividad de las técnicas propuestas, estas se prueban en laboratorio emulando una instalación real y bajo condiciones anormales de esfuerzo. Los resultados experimentales revelaron que la temperatura de los alrededores y la capa adhesiva entre el piezoelectrico y el espécimen influyen en el desempeño del esquema de monitoreo debido a los cambios que se producen en la propagación de onda . Por lo tanto, se estudia el efecto desde una perspectiva analítica el efecto de la temperatura en la propagación de la onda guiada y en consecuencia en el desempeño del enfoque de monitoreo propuesto. Basado en lo anterior, se aplica una estrategia de compensación del efecto de la temperatura para mejorar la estabilidad y la robustez del esquema propuesto ante escenarios de cambios de temperatura. Por otro lado, debido a que el efecto predominante en la propagación de ondas guiadas bajo esfuerzo es el efecto acoustoelastico, se estudia su influencia en las curvas de dispersión usando un método semi-analitico basado en elementos finitos (SAFE del inglés) en combinación con las Constantes Elásticas Efectivas (EEC del inglés) para estimar las curvas de dispersión de ondas guiadas bajo esfuerzo. Finalmente, como un resultados de la experimentación, se propone un esquema de monitoreo de rigidez de soportes de tubería cilíndrica basado en un perspectiva de energía de ultrasonido transferida al entorno vía contacto de superficies. El enfoque propuesto puede ser extendido al monitoreo de rigidez o contacto en otros sistemas en campos tales como el aeroespacial y en la industria del Gas/Petróle

Control and Measurement System for a Compressing Unit

Pulp for making paper is produced in grinding machines whose operation principle is based on the compression of logs against a grinding stone. The aim of this Master Thesis is to develop and implement a control and measurement system for a laboratory compressing unit which carries out this first step in paper making process. For this purpose, a hand drive and a computer interface are designed and configured. The thesis is divided in three sections. In the literature study the theories involved in the research work are analyzed. Control and measurement methods are detailed as well as the hydraulic system needed to operate the compressing unit. In the second section the development of a control and measurement method suitable for the unit is carried out. It is based on the study of the most important variables involved in the process. Last section focuses on the implementation of the control and measurement system. A hand drive and a computer interface are considered. The latter is developed using LabView software. In this section, the hand drive design is analyzed and the LabView code is explained. In addition, a measurement approximation method is implemented in order to display the correct variable values. Finally a verification of the whole system is carried out. The results of this study suggest that the control and measurement system satisfies the requisites needed to develop future researches related to this compressing unit. The values displayed by the hand drive and computer interfaces are similar to the theoretical ones and the control system avoids dangerous situations. This Master Thesis suggests future research work in order to improve the accuracy of the control and measurement system. /Kir1