Temperature considerations on Hall Effect sensors current-related sensitivity behaviour

The present paper focuses on evaluating the temperature effects on Hall Effect sensors sensitivity behavior. To this purpose, an analysis of the factors affecting the sensors current-related sensitivity is performed, consisting of several pertinent considerations. An analytical investigation of the carrier concentration temperature dependence including the freeze-out effect influence was performed. This information was subsequently included in accurate prediction of the current-related sensitivity temperature behavior. For a specific CMOS integration process of the Hall sensors, a parabolic curve is obtained for the relative variation of the current-related sensitivit

Temperature considerations on Hall Effect sensors current-related sensitivity behaviour

The present paper focuses on evaluating the temperature effects on Hall Effect sensors sensitivity behavior. To this purpose, an analysis of the factors affecting the sensors current-related sensitivity is performed, consisting of several pertinent considerations. An analytical investigation of the carrier concentration temperature dependence including the freeze-out effect influence was performed. This information was subsequently included in accurate prediction of the current-related sensitivity temperature behavior. For a specific CMOS integration process of the Hall sensors, a parabolic curve is obtained for the relative variation of the current-related sensitivity

Study of Hall Effect Sensor and Variety of Temperature Related Sensitivity

Hall effect sensors are used in many applications because they are based on an ideal magnetic field sensing technology. The most important factor that determines their sensitivity is the material of which the sensor is made. Properties of the material such as carrier concentration, carrier mobility and energy band gap all vary with temperature. Thus, sensitivity is also influenced by temperature. In this study, current-related sensitivity and voltage-related sensitivity were calculated in the intrinsic region of temperature for two commonly used materials, i.e. Si and GaAs. The results showed that at the same temperature, GaAs can achieve higher sensitivity than Si and it has a larger band gap as well. Therefore, GaAs is more suitable to be used in applications that are exposed to different temperatures

Regular Bulk CMOS Hall Effect Sensors Employment in Solid-State Power and Energy Meters

AbstractThis paper is intended to present an advanced technique to be used in solid-state power and energy meters, more specifically through the employment of the Hall effect sensors. From a qualitative point of view, an investigation into the sensing device is performed and geometrical consideration of the Hall cells onto the performance is analyzed. Different Hall cells (basic, L, XL, borderless and optimum) have been fabricated in a regular bulk CMOS technology and their main parameters were extracted. To this purpose, experimental results for the offset and sensitivity of different Hall cells are obtained. The dissipated power as well as the power-related sensitivity is calculated, for the five Hall cells in discussion

Giant Magnetoresistive Biosensors for Time-Domain Magnetorelaxometry: A Theoretical Investigation and Progress Toward an Immunoassay.

Magnetorelaxometry (MRX) is a promising new biosensing technique for point-of-care diagnostics. Historically, magnetic sensors have been primarily used to monitor the stray field of magnetic nanoparticles bound to analytes of interest for immunoassays and flow cytometers. In MRX, the magnetic nanoparticles (MNPs) are first magnetized and then the temporal response is monitored after removing the magnetic field. This new sensing modality is insensitive to the magnetic field homogeneity making it more amenable to low-power portable applications. In this work, we systematically investigated time-domain MRX by measuring the signal dependence on the applied field, magnetization time, and magnetic core size. The extracted characteristic times varied for different magnetic MNPs, exhibiting unique magnetic signatures. We also measured the signal contribution based on the MNP location and correlated the coverage with measured signal amplitude. Lastly, we demonstrated, for the first time, a GMR-based time-domain MRX bioassay. This approach validates the feasibility of immunoassays using GMR-based MRX and provides an alternative platform for point-of-care diagnostics

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

Real-time human ambulation, activity, and physiological monitoring:taxonomy of issues, techniques, applications, challenges and limitations

Automated methods of real-time, unobtrusive, human ambulation, activity, and wellness monitoring and data analysis using various algorithmic techniques have been subjects of intense research. The general aim is to devise effective means of addressing the demands of assisted living, rehabilitation, and clinical observation and assessment through sensor-based monitoring. The research studies have resulted in a large amount of literature. This paper presents a holistic articulation of the research studies and offers comprehensive insights along four main axes: distribution of existing studies; monitoring device framework and sensor types; data collection, processing and analysis; and applications, limitations and challenges. The aim is to present a systematic and most complete study of literature in the area in order to identify research gaps and prioritize future research directions