Contactless measurement of electric current using magnetic sensors

We review recent advances in magnetic sensors for DC/AC current transducers, especially novel AMR sensors and integrated fluxgates, and we make critical comparison of their properties. Most contactless electric current transducers use magnetic cores to concentrate the flux generated by the measured current and to shield the sensor against external magnetic fields. In order to achieve this, the magnetic core should be massive. We present coreless current transducers which are lightweight, linear and free of hysteresis and remanence. We also show how to suppress their weak point: crosstalk from external currents and magnetic fields

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

Mathematical Model and Simulation of a Pneumatic Apparatus for In-Drilling Alignment of an Inertial Navigation Unit during Horizontal Well Drilling

Conventional methods in horizontal drilling processes incorporate magnetic surveying techniques for determining the position and orientation of the bottom-hole assembly (BHA). Such means result in an increased weight of the drilling assembly, higher cost due to the use of non-magnetic collars necessary for the shielding of the magnetometers, and significant errors in the position of the drilling bit. A fiber-optic gyroscope (FOG) based inertial navigation system (INS) has been proposed as an alternative to magnetometer -based downhole surveying. The utilizing of a tactical-grade FOG based surveying system in the harsh downhole environment has been shown to be theoretically feasible, yielding a significant BHA position error reduction (less than 100m over a 2-h experiment). To limit the growing errors of the INS, an in-drilling alignment (IDA) method for the INS has been proposed. This article aims at describing a simple, pneumatics-based design of the IDA apparatus and its implementation downhole. A mathematical model of the setup is developed and tested with Bloodshed Dev-C++. The simulations demonstrate a simple, low cost and feasible IDA apparatus

Wireless Sensor Node for Surface Seawater Density Measurements

An electronic meter to measure surface seawater density is presented. It is based on the measurement of the difference in displacements of a surface level probe and a weighted float, which according to Archimedes’ law depends on the density of the water. The displacements are simultaneously measured using a high-accuracy magnetostrictive sensor, to which a custom electronic board provides a wireless connection and power supply so that it can become part of a wireless sensor network. The electronics are designed so that different kinds of wireless networks can be used, by simply changing the wireless module and the relevant firmware of the microcontroller. Lastly, laboratory and at-sea tests are presented and discussed in order to highlight the functionality and the performance of a prototype of the wireless density meter node in a Bluetooth radio network. The experimental results show a good agreement of the values of the calculated density compared to reference hydrometer readings

Development and characterization of sensors fabricated from polymer based magnetoelectric nanocomposites

Tese de Doutoramento em Engenharia Electrónica e de ComputadoresSensors are increasingly used in many applications areas, integrated in structures, industrial machinery, or in the environment, contributing to improve the society level of well-being. It is expected that sensorization will play on of the most relevant roles in the fourth industrial revolution, and allow, together with mechanization and informatization, a full automation. Particularly, magnetic sensors allow measurements, without physical contact, of parameters such as direction, presence, rotation, angle, or current, in addition to magnetic field. In this way, for most applications, such sensors offer a safe, noninvasive and non-destructive measurement, as well as provide a reliable and almost maintenance-free technology. Industry demands for smaller, cheaper and low-powered magnetic sensors, motivating the exploration of new materials and different technologies, such as polymerbased magnetoelectric (ME) composites. These composites are flexible, versatile, lightweight, low cost, easy to model in complicated shapes, and typically involve a lowtemperature fabrication process, being in this way, a solution for innovative magnetic sensor device applications. Therefore, the main objective of this thesis is the development of polymer-based ME sensors to be incorporated into technological devices. Thus, the ME effect is increasingly being considered an attractive alternative for magnetic field and current sensing, being able to sense static and dynamic magnetic fields. In order to obtain a wide-range ME response, a nanocomposite of Tb0.3Dy0.7Fe1.92 (Terfenol-D)/CoFe2O4/poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) was produced and their morphological, piezoelectric, magnetic and magnetoelectric properties investigated. The obtained composites reveals a high piezoelectric response (≈-18 pC∙N- 1) that is independent of the weight ratio between the fillers. In turn, the magnetic properties of the composites are influenced by the composite composition. It was found that the magnetization saturation values decrease with increasing CoFe2O4 content (from 18.5 to 13.3 emu∙g-1) while the magnetization and coercive field values increase (from 3.7 to 5.5 emu∙g-1 and from 355.7 to 1225.2 Oe, respectively) with increasing CoFe2O4 content. Additionally, the films show a wide-range dual-peak ME response at room temperature with the ME coefficient increasing with increasing weight content of Terfenol-D, from 18.6 mV∙cm-1∙Oe-1 to 42.3 mV∙cm-1∙Oe-1. The anisotropic ME effect on a Fe61.6Co16.4Si10.8B11.2 (FCSB)/poly(vinylidene fluoride) (PVDF)/FCSB laminate composite has been used for the development of a magnetic field sensor able to detect both magnitude and direction of ac and dc magnetic fields. The accuracy (99% for both ac and dc sensors), linearity (92% for the dc sensor and 99% for the ac sensor), sensitivity (15 and 1400 mV∙Oe-1 for the dc and ac fields, respectively), and reproducibility (99% for both sensors) indicate the suitability of the sensor for applications. A dc magnetic field sensor based on a PVDF/Metglas composite and the corresponding readout electronic circuits for processing the output ME voltage were developed. The ME sensing composite presents an electromechanical resonance frequency close to 25.4 kHz, a linear response (r2=0.997) in the 0–2 Oe dc magnetic field range, and a maximum output voltage of 112 mV (ME voltage coefficient α33 of ≈30 V∙cm-1∙Oe-1). By incorporating a charge amplifier, an ac–rms converter and a microcontroller with an on chip analog-to-digital converter (ADC), the ME voltage response is not distorted, the linearity is maintained, and the ME output voltage increases to 3.3 V (α33effective=1000 V∙cm-1∙Oe-1). The sensing device, including the readout electronics, has a maximum drift of 0.12 Oe with an average total drift of 0.04 Oe, a sensitivity of 1.5 V∙Oe-1 (15 kV∙T-1), and a 70 nT resolution. Such properties allied to the accurate measurement of the dc magnetic field in the 0–2 Oe range makes this polymerbased device very attractive for applications, such as Earth magnetic field sensing, digital compasses, navigation, and magnetic field anomaly detectors. A dc current sensor device based on a ME PVDF/Metglas composite, a solenoid, and the corresponding electronic instrumentation were developed. The ME sample exhibits a maximum α33 of 34.48V∙cm-1∙Oe-1, a linear response (r2=0.998) and a sensitivity of 6.7 mV∙A-1. With the incorporation of a charge amplifier, a precision ac/dc converter and a microcontroller, the linearity is maintained (r2=0.997), the ME output voltage increases to a maximum of 2320 mV and the sensitivity is increased to 476.5 mV∙A-1. Such features indicate that the fabricated ME sensing device is suitable to be used in non-contact electric current measurement, motor operational status checking, and condition monitoring of rechargeable batteries, among others. In this way, polymer-based ME composites proved to be suitable for magnetic field and current sensor applications.Os sensores estão a ser cada vez mais utilizados em diversas áreas, integrados em estruturas, máquinas industriais ou projetos ambientais, contribuindo para melhorar o nível de bem-estar e eficiência da nossa sociedade. Espera-se que a “sensorização” contribua decisivamente para a quarta revolução industrial, e que permita, em conjunto com a mecanização e a informatização, uma completa automação. Em particular, os sensores magnéticos permitem medir parâmetros como a direção, presença, rotação, ângulo ou corrente, para além do campo magnético, tudo isto sem qualquer contacto físico. Assim, para a maioria das aplicações, estes sensores oferecem uma medição segura, não invasiva e não destrutiva, para além de garantirem uma tecnologia confiável e de escassa manutenção. A indústria procura e exige sensores magnéticos mais pequenos, mais baratos e de baixo consumo, daí a motivação para explorar novos materiais e diferentes tecnologias, tais como os compósitos magnetoelétricos (ME) baseados em polímeros. Estes compósitos são flexíveis, versáteis, leves, de baixo custo, fáceis de se modelar em formas complexas e tipicamente envolvem um processo de fabricação a baixa temperatura, constituindo uma solução fiável e de qualidade para os sensores magnéticos. É da constatação deste potencial que surge este estudo e o objetivo desta tese: o desenvolvimento de sensores ME de base polimérica. O efeito ME é cada vez mais considerado como uma alternativa credível para a medição de campo magnético e da intensidade da corrente elétrica, podendo detetar campos magnéticos estáticos e dinâmicos. De modo a obter uma gama mais alargada de resposta ME, produziram-se nanocompósitos de Tb0.3Dy0.7Fe1.92 (Terfenol-D)/CoFe2O4/poli(fluoreto de vinilideno trifluor-etileno) (P(VDF-TrFE) e as suas propriedades morfológicas, piezoelétricas, magnéticas e magnetoelétricas foram investigadas. Os compósitos obtidos revelam uma elevada resposta piezoelétrica (≈-18 pC∙N-1) que é independente da percentagem de cada material magnetoestrictivo. Por sua vez, as propriedades magnéticas são influenciadas pela composição dos compósitos. Verificou-se que a magnetização de saturação diminuí com o aumento da percentagem de CoFe2O4 (de 18.5 para 13.3 emu∙g-1) enquanto que a magnetização e o campo coercivo aumentam (de 3.7 para 5.5 emu∙g-1 e de 355.7 para 1225.2 Oe, respetivamente) com o aumento da percentagem em massa de CoFe2O4. O efeito ME anisotrópico num compósito Fe61.6Co16.4Si10.8B11.2 (FCSB)/ poli(fluoreto de vinilideno) (PVDF)/FCSB laminado foi utilizado para desenvolver um sensor de campo magnético capaz de detetar tanto a magnitude como a direção de campos magnéticos ac e dc. A exatidão (99% para ambos os sensores ac e dc), linearidade (92% para o sensor dc e 99% para o ac), sensibilidade (15 e 1400 mV∙Oe-1 para o sensor dc e ac, respetivamente) e reprodutibilidade (99% para ambos os sensores) indicam a aptidão destes sensores para aplicações avançadas. Desenvolveu-se ainda um sensor de campo magnético dc baseado num compósito ME de PVDF/Metglas, bem como a correspondente eletrónica de leitura para processar a tensão de saída ME. O compósito ME apresenta uma ressonância eletromecânica de aproximadamente 25.4 kHz, uma resposta linear (r2=0.997) para uma gama de campos magnéticos dc entre 0–2 Oe e uma tensão de saída máxima de 112 mV (coeficiente ME α33≈30 V∙cm-1∙Oe-1). Ao incorporar um amplificador de carga, um conversor ac–rms e um microcontrolador com um conversor analógico-digital (ADC), a tensão ME não é distorcida, a linearidade manteve-se e a tensão ME aumentou para 3.3 V (α33efectivo=1000 V∙cm-1∙Oe-1). O sensor, incluindo a eletrónica de leitura, obteve um desvio máximo de 0.12 Oe com um desvio total médio de 0.04 Oe, uma sensibilidade de 1.5 V∙Oe-1 (15 kV∙T-1) e 70 nT de resolução. Tais propriedades aliadas à medida exata do campo magnético dc entre 0–2 Oe tornam este dispositivo indicado para aplicações como sensores de campo magnético terrestre, compassos digitais, navegação e detetores de anomalia no campo magnético. Foi ainda possível desenvolver e otimizar um sensor de corrente baseado num compósito ME de PVDF/Metglas, num solenoide e na correspondente eletrónica de instrumentação. A amostra ME exibe um α33 máximo de 34.48V∙cm-1∙Oe-1, uma resposta linear (r2=0.998) e uma sensibilidade de 6.7 mV∙A-1. Com a incorporação de um amplificador de carga, um conversor ac/dc de precisão e um microcontrolador, a linearidade manteve-se, a tensão ME aumentou para um máximo de 2320 mV e a sensibilidade subiu para 476.5 mV∙A-1. Estas propriedades tornam este sensor ME apropriado para a medição de corrente elétrica sem contato, para a verificação do estado de funcionamento de motores e para monitorização da condição de baterias recarregáveis, entre outros. Concluindo-se deste modo que os compósitos de ME com base em polímeros provaram ser adequados para aplicações na medição de campos magnéticos e intensidade de corrente elétrica

Effect of Inductive Coil Shape on Sensing Performance of Linear Displacement Sensor Using Thin Inductive Coil and Pattern Guide

This paper discusses the effect of inductive coil shape on the sensing performance of a linear displacement sensor. The linear displacement sensor consists of a thin type inductive coil with a thin pattern guide, thus being suitable for tiny space applications. The position can be detected by measuring the inductance of the inductive coil. At each position due to the change in inductive coil area facing the pattern guide the value of inductance is different. Therefore, the objective of this research is to study various inductive coil pattern shapes and to propose the pattern that can achieve good sensing performance. Various shapes of meander, triangular type meander, square and circle shape with different turn number of inductive coils are examined in this study. The inductance is measured with the sensor sensitivity and linearity as a performance evaluation parameter of the sensor. In conclusion, each inductive coil shape has its own advantages and disadvantages. For instance, the circle shape inductive coil produces high sensitivity with a low linearity response. Meanwhile, the square shape inductive coil has a medium sensitivity with higher linearity

Development of magnetostrictive active members for control of space structures

The goal of this Phase 2 Small Business Innovative Research (SBIR) project was to determine the technical feasibility of developing magnetostrictive active members for use as truss elements in space structures. Active members control elastic vibrations of truss-based space structures and integrate the functions of truss structure element, actively controlled actuator, and sensor. The active members must control structural motion to the sub-micron level and, for many proposed space applications, work at cryogenic temperatures. Under this program both room temperature and cryogenic temperature magnetostrictive active members were designed, fabricated, and tested. The results of these performance tests indicated that room temperature magnetostrictive actuators feature higher strain, stiffness, and force capability with lower amplifier requirements than similarly sized piezoelectric or electrostrictive active members, at the cost of higher mass. Two different cryogenic temperature magnetostrictive materials were tested at liquid nitrogen temperatures, both with larger strain capability than the room temperature magnetostrictive materials. The cryogenic active member development included the design and fabrication of a cryostat that allows operation of the cryogenic active member in a space structure testbed

Design and application of magnetostrictive materials

Magnetostriction is the change in shape of materials under the influence of an external magnetic field. The cause of magnetostriction change in length is the result of the rotation of small magnetic domains. This rotation and re-orientation causes internal strains in the material structure. The strains in the structure lead to the stretching (in the case of positive magnetostriction) of the material in the direction of the magnetic field. During this stretching process the cross-section is reduced in a way that the volume is kept nearly constant. The size of the volume change is so small that it can be neglected under normal operating conditions. Applying a stronger field leads to stronger and more definite re-orientation of more and more domains in the direction of magnetic field. When all the magnetic domains have become aligned with the magnetic field the saturation point has been achieved. This paper presents the state of the art of the magnetostrictive materials and their applications such as: Reaction Mass Actuator, A standard Terfenol-D Actuator, Linear Motor Based on Terfenol-D (Worm Motor), Terfenol-D in Sonar Transducers, Terfenol-D Wireless Rotational Motor, Terfenol-D Electro-Hydraulic Actuator, Wireless Linear Micro-Motor, Magnetostrictive Film Applications, Magnetostrictive Contactless Torque Sensors and many other applications. The study shows that excellent features can be obtained by Magnetostrictive materials for many advanced applications