Sensors

Research

14 pages, 5207 KiB

Open AccessArticle

Active Magnetic-Field Stabilization with Atomic Magnetometer

by Rui Zhang, Yudong Ding, Yucheng Yang, Zhaoyu Zheng, Jingbiao Chen, Xiang Peng, Teng Wu and Hong Guo

Sensors 2020, 20(15), 4241; https://doi.org/10.3390/s20154241 - 30 Jul 2020

Cited by 22 | Viewed by 5432

Abstract

A magnetically-quiet environment is important for detecting faint magnetic-field signals or nonmagnetic spin-dependent interactions. Passive magnetic shielding using layers of large magnetic-permeability materials is widely used to reduce the magnetic-field noise. The magnetic-field noise can also be actively monitored with magnetometers and then [...] Read more.

A magnetically-quiet environment is important for detecting faint magnetic-field signals or nonmagnetic spin-dependent interactions. Passive magnetic shielding using layers of large magnetic-permeability materials is widely used to reduce the magnetic-field noise. The magnetic-field noise can also be actively monitored with magnetometers and then compensated, acting as a complementary method to the passive shielding. We present here a general model to quantitatively depict and optimize the performance of active magnetic-field stabilization and experimentally verify our model using optically-pumped atomic magnetometers. We experimentally demonstrate a magnetic-field noise rejection ratio of larger than ∼800 at low frequencies and an environment with a magnetic-field noise floor of ∼40

{fT / Hz}^{1 / 2}

in unshielded Earth’s field. The proposed model provides a general guidance on analyzing and improving the performance of active magnetic-field stabilization with magnetometers. This work offers the possibility of sensitive detections of magnetic-field signals in a variety of unshielded natural environments. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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15 pages, 5826 KiB

Open AccessArticle

Analysis of Methods for Long Vehicles Speed Estimation Using Anisotropic Magneto-Resistive (AMR) Sensors and Reference Piezoelectric Sensor

by Vytautas Markevicius, Dangirutis Navikas, Donatas Miklusis, Darius Andriukaitis, Algimantas Valinevicius, Mindaugas Zilys and Mindaugas Cepenas

Sensors 2020, 20(12), 3541; https://doi.org/10.3390/s20123541 - 22 Jun 2020

Cited by 14 | Viewed by 2930

Abstract

With rapidly increasing traffic occupancy, intelligent transportation systems (ITSs) are a vital feature for urban areas. This paper analyses methods for estimating long (L > 10 m) vehicle speed and length using a self-developed system, equipped with two anisotropic magneto-resistive (AMR) sensors, and [...] Read more.

With rapidly increasing traffic occupancy, intelligent transportation systems (ITSs) are a vital feature for urban areas. This paper analyses methods for estimating long (L > 10 m) vehicle speed and length using a self-developed system, equipped with two anisotropic magneto-resistive (AMR) sensors, and introduces a method for verifying the results. A well-known cross-correlation method of magnetic signatures is not appropriate for calculating the vehicle speed of long vehicles owing to limited resources and a long calculation time. Therefore, the adaptive signature cropping algorithm was developed and used with a difference quotient of a magnetic signature. An additional piezoelectric polyvinylidene fluoride (PVDF) sensor and video camera provide ground truth to evaluate the performances. The prototype system was installed on the urban road and tested under various traffic and weather conditions. The accuracy of results was evaluated by calculating the mean absolute percentage error (MAPE) for different methods and vehicle speed groups. The experimental result with a self-obtained data set of 600 unique entities shows that the average speed MAPE error of our proposed method is lower than 3% for vehicle speed in a range between 40 and 100 km/h. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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13 pages, 5230 KiB

Open AccessArticle

Identification of Tiny Surface Cracks in a Rugged Weld by Signal Gradient Algorithm Using the ACFM Technique

by Xin’an Yuan, Wei Li, Xiaokang Yin, Guoming Chen, Jianming Zhao, Weiyu Jiang and Jiuhao Ge

Sensors 2020, 20(2), 380; https://doi.org/10.3390/s20020380 - 9 Jan 2020

Cited by 12 | Viewed by 3848

Abstract

It is still a big challenge to identify tiny surface cracks in a rugged weld due to the lift-off variations using the nondestructive testing (NDT) method. In this paper, the signal gradient algorithm is presented to identify the tiny surface crack in the [...] Read more.

It is still a big challenge to identify tiny surface cracks in a rugged weld due to the lift-off variations using the nondestructive testing (NDT) method. In this paper, the signal gradient algorithm is presented to identify the tiny surface crack in the rugged weld using the alternating current field measurement (ACFM) technique. The ACFM simulation model and testing system was set up to obtain the insensitive signal to the lift-off variations. The signal gradient algorithm was presented to process the insensitive signal for the identification of the tiny surface crack in the rugged weld. The results show that the Bz signal is the insensitive signal to lift-off variations caused by the rugged weld. The signal to noise ratio (SNR) of the crack identification signal was greatly improved by the signal gradient algorithm, and a tiny surface crack can be identified effectively in the weld and the heat affected zone (HAZ). Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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11 pages, 2404 KiB

Open AccessArticle

Influence of Resonances on the Noise Performance of SQUID Susceptometers

by Samantha I. Davis, John R. Kirtley and Kathryn A. Moler

Sensors 2020, 20(1), 204; https://doi.org/10.3390/s20010204 - 30 Dec 2019

Cited by 6 | Viewed by 3631

Abstract

Scanning Superconducting Quantum Interference Device (SQUID) Susceptometry simultaneously images the local magnetic fields and susceptibilities above a sample with sub-micron spatial resolution. Further development of this technique requires a thorough understanding of the current, voltage, and flux (

I V Φ

) characteristics [...] Read more.

Scanning Superconducting Quantum Interference Device (SQUID) Susceptometry simultaneously images the local magnetic fields and susceptibilities above a sample with sub-micron spatial resolution. Further development of this technique requires a thorough understanding of the current, voltage, and flux (

I V Φ

) characteristics of scanning SQUID susceptometers. These sensors often have striking anomalies in their current–voltage characteristics, which we believe to be due to electromagnetic resonances. The effect of these resonances on the performance of these SQUIDs is unknown. To explore the origin and impact of the resonances, we develop a model that qualitatively reproduces the experimentally-determined

I V Φ

characteristics of our scanning SQUID susceptometers. We use this model to calculate the noise characteristics of SQUIDs of different designs. We find that the calculated ultimate flux noise is better in susceptometers with damping resistors that diminish the resonances than in susceptometers without damping resistors. Such calculations will enable the optimization of the signal-to-noise characteristics of scanning SQUID susceptometers. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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12 pages, 4207 KiB

Open AccessArticle

PT-Level High-Sensitivity Magnetic Sensor with Amorphous Wire

by Dongfeng He

Sensors 2020, 20(1), 161; https://doi.org/10.3390/s20010161 - 26 Dec 2019

Cited by 9 | Viewed by 4435

Abstract

A picotesla (PT) level high-sensitivity magnetic sensor with amorphous wire was developed. The magnetic sensor was composed of a (Fe_0.06Co_0.94)_72.5Si_2.5B₁₅ (FeCoSiB) amorphous wire with a coil wound around it. The amorphous wire had a [...] Read more.

A picotesla (PT) level high-sensitivity magnetic sensor with amorphous wire was developed. The magnetic sensor was composed of a (Fe_0.06Co_0.94)_72.5Si_2.5B₁₅ (FeCoSiB) amorphous wire with a coil wound around it. The amorphous wire had a diameter of 0.1 mm and a length of 5 mm. The coil was 30 turns. There was no electrical connection with the amorphous wire. The sensor was biased by an alternating current (AC) of about 1 MHz and a direct current (DC). To increase the sensitivity, a resonant circuit was used, and the signal amplitude of the magnetic sensor was increased 10 times from 10 mV/Gauss to about 100 mV/Gauss. The magnetic field resolution was improved 5 times from 30 pT/√Hz to 6 pT/√Hz. An eddy current testing system with a magnetic sensor was developed, and the artificial defects in an aluminum plate were evaluated. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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15 pages, 5070 KiB

Open AccessArticle

Inductive Position and Speed Sensors

by Pavel Ripka, Josef Blažek, Mehran Mirzaei, Pavol Lipovský, Miroslav Šmelko and Katarína Draganová

Sensors 2020, 20(1), 65; https://doi.org/10.3390/s20010065 - 21 Dec 2019

Cited by 28 | Viewed by 9667

Abstract

Magnetic position and speed sensors are rugged and durable. While DC magnetic sensors use permanent magnets as a field source and usually have only mm or cm range, inductive sensors use electromagnetic induction and they may work up to a distance of 20 [...] Read more.

Magnetic position and speed sensors are rugged and durable. While DC magnetic sensors use permanent magnets as a field source and usually have only mm or cm range, inductive sensors use electromagnetic induction and they may work up to a distance of 20 m. Eddy current inductive sensors equipped with magnetoresistive sensors instead of inductive coils can operate at low frequencies, allowing detection through a conductive wall. In this paper, we make an overview of existing systems and we present new results in eddy current velocity and position measurements. We also present several types of inductive position sensors developed in our laboratories for industrial applications in pneumatic and hydraulic cylinders, underground drilling, large mining machines, and for detecting ferromagnetic objects on conveyors. While the most precise inductive position sensors have a resolution of 10 nm and linearity of 0.2%, precision requirements on the industrial sensors which we develop are less demanding, but they should have large working distance and large resistance to environmental conditions and interference. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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15 pages, 4824 KiB

Open AccessArticle

Influence of Moisture Content on Electromagnetic Response of Concrete Studied Using a Homemade Apparatus

by Zhe Li, Zuquan Jin, Shuangshuang Shao, Tiejun Zhao and Penggang Wang

Sensors 2019, 19(21), 4637; https://doi.org/10.3390/s19214637 - 25 Oct 2019

Cited by 8 | Viewed by 2977

Abstract

In this study, we examined the influence of moisture content on the electromagnetic response of concrete. A novel homemade electromagnetic monitoring apparatus was developed and used to evaluate the Hall effect voltage at both ends of concrete based on our previous study of [...] Read more.

In this study, we examined the influence of moisture content on the electromagnetic response of concrete. A novel homemade electromagnetic monitoring apparatus was developed and used to evaluate the Hall effect voltage at both ends of concrete based on our previous study of the Hall effect. We used four different concrete mix water/binder ratios: 0.30, 0.28, 0.26, and 0.24, and three conditions (relative humidity, carbonation, and water absorption) were examined in this experiment. The results show that the moisture content inside concrete influences the relative permeability of concrete. The variation in the Hall effect voltage is more influenced by carbonation than changes in relative humidity; water absorption increases the Hall effect voltage the least amongst the other examined factors. According to the experiment, a calibration system was established, and the relevant correction factors are provided. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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9 pages, 1901 KiB

Open AccessArticle

Double-Gap Magnetic Flux Concentrator Design for High-Sensitivity Magnetic Tunnel Junction Sensors

by Jiafei Hu, Minhui Ji, Weicheng Qiu, Long Pan, Peisen Li, Junping Peng, Yueguo Hu, Huiyan Liu and Mengchun Pan

Sensors 2019, 19(20), 4475; https://doi.org/10.3390/s19204475 - 15 Oct 2019

Cited by 17 | Viewed by 3717

Abstract

To improve the sensitivity of the magnetic tunnel junction(MTJ)sensor, a novel architecture for a double-gap magnetic flux concentrator (MFC) was studied theoretically and experimentally in this paper. The three-dimensional finite element model of magnetic flux was established to optimize the magnetic field amplification [...] Read more.

To improve the sensitivity of the magnetic tunnel junction(MTJ)sensor, a novel architecture for a double-gap magnetic flux concentrator (MFC) was studied theoretically and experimentally in this paper. The three-dimensional finite element model of magnetic flux was established to optimize the magnetic field amplification factor, with different gaps. The simulation results indicate that the sensitivity of an MTJ sensor with a double-gap MFC can be significantly better than that of a sensor with a traditional single-gap MFC, due to the fact that the magnetic magnification sharply increases with the decrease in effective gap width. Besides this, the half-bridge MTJ sensors with the double-gap MFC were fabricated using photolithography, ion milling, evaporation, and electroplating processes. Experimental results show that the sensitivity of the MTJ sensor increased by ten times compared to the sensor without the double-gap MFC, which underlines the theoretical predictions. Furthermore, there is no significant increase in the sensor noise. The work in this paper contributes to the development of high-performance MTJ sensors. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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10 pages, 4329 KiB

Open AccessArticle

Detection of Magnetomechanical Effect in Structural Steel Using GMR 2nd Order Gradiometer Based Sensors

by Carmela Bonavolontà, Massimo Valentino, Francesco Penta, Carmine Granata, Berardo Ruggiero, Paolo Silvestrini and Antonio Vettoliere

Sensors 2019, 19(19), 4147; https://doi.org/10.3390/s19194147 - 25 Sep 2019

Cited by 6 | Viewed by 2401

Abstract

The magneto-mechanical behaviour of structural steel specimens stressed up to the plastic deformation stage was investigated using a 2nd order gradiometer based on Giant Magneto Resistive (GMR) sensors. The correlation between the gradient of the magnetization and the dislocation density before the crack [...] Read more.

The magneto-mechanical behaviour of structural steel specimens stressed up to the plastic deformation stage was investigated using a 2nd order gradiometer based on Giant Magneto Resistive (GMR) sensors. The correlation between the gradient of the magnetization and the dislocation density before the crack initiation inside the test material was reported. The capability of the GMR scanning sensor to detect the residual magnetization due to the tensile stress with a non-invasive technique was demonstrated. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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8 pages, 2035 KiB

Open AccessArticle

Fine-Tuning and Optimization of Superconducting Quantum Magnetic Sensors by Thermal Annealing

by Antonio Vettoliere, Berardo Ruggiero, Massimo Valentino, Paolo Silvestrini and Carmine Granata

Sensors 2019, 19(17), 3635; https://doi.org/10.3390/s19173635 - 21 Aug 2019

Cited by 4 | Viewed by 3308

Abstract

In the present article, we present the experimental results concerning the fine-tuning and optimization of superconducting quantum interference device (SQUID) parameters by thermal annealing. This treatment allows for the modification of the parameters in order to meet a specific application or to adjust [...] Read more.

In the present article, we present the experimental results concerning the fine-tuning and optimization of superconducting quantum interference device (SQUID) parameters by thermal annealing. This treatment allows for the modification of the parameters in order to meet a specific application or to adjust the device parameters to prevent the increase of magnetic field noise and work instability conditions due to a different critical current with respect to the design value. In particular, we report the sensor critical current, the voltage–flux (V–Φ) characteristics and the spectral density of the magnetic field of SQUID magnetometers for different annealing temperatures. The measurements demonstrate that it is possible to achieve a fine control of the most important device parameters. In particular, we show that thermal annealing allows for the reduction of SQUID noise by more than a factor of 5 and makes the device working operations very stable. These results are very useful in view of quantum technology applications related to superconducting quantum computing where the correct functioning of the quantum bit depends on the fine control of the superconducting quantum device parameters and selectable annealing is possible by using a suitable laser as a thermal source. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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17 pages, 3992 KiB

Open AccessArticle

Calibration of Off-the-Shelf Anisotropic Magnetoresistance Magnetometers

by Leonard Schulz, Philip Heinisch and Ingo Richter

Sensors 2019, 19(8), 1850; https://doi.org/10.3390/s19081850 - 18 Apr 2019

Cited by 19 | Viewed by 5045

Abstract

Magnetometers based on the anisotropic magnetoresistive effect are used in many applications for orientation determination, by measuring the magnetic field of the Earth. As sensors of this type are commercial, off-the-shelf components, manufacturers provide limited information on their measurement performance. Therefore, we present [...] Read more.

Magnetometers based on the anisotropic magnetoresistive effect are used in many applications for orientation determination, by measuring the magnetic field of the Earth. As sensors of this type are commercial, off-the-shelf components, manufacturers provide limited information on their measurement performance. Therefore, we present a (to date) unprecedented comprehensive calibration study on three state-of-the-art digital anisotropic magnetoresistance magnetometers, to precisely determine various performance parameters and stability across different sensors of the same model. With the evaluation of sensitivity, noise, offset, and orientation determination, as well as considering dependencies on temperature and frequency, the performance of each sensor can be improved significantly, enabling their implementation in demanding fields of application (such as in satellites). Different measurement and calibration techniques, specifically aimed at the characteristics of the examined magnetometers, were utilized, using a sophisticated magnetic laboratory that has served as a calibration facility for several interplanetary space missions. Our study allows operators to decide whether to consider anisotropic magnetoresitance magnetometers for their application and, more importantly, to be able to (at least partially) skip a time-intensive and complicated calibration by using the sensor parameters given in this paper. To that end, the most promising sensor is recommended. The sensor examination suggests a good comparability of different sensors of the same model, and shows the importance of noise regarding the sensor performance with a noise floor up to 124 nT/

\sqrt{Hz}

at 1 Hz. Additionally, depending on the sensor model, the sensitivity is 14 nT at best, and the attitude determination error can be reduced to about 0.3° with the given calibration. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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Review

Jump to: Research, Other

20 pages, 506 KiB

Open AccessReview

Magnetic Tunnel Junction Applications

by Nilson Maciel, Elaine Marques, Lírida Naviner, Yongliang Zhou and Hao Cai

Sensors 2020, 20(1), 121; https://doi.org/10.3390/s20010121 - 24 Dec 2019

Cited by 50 | Viewed by 7219

Abstract

Spin-based devices can reduce energy leakage and thus increase energy efficiency. They have been seen as an approach to overcoming the constraints of CMOS downscaling, specifically, the Magnetic Tunnel Junction (MTJ) which has been the focus of much research in recent years. Its [...] Read more.

Spin-based devices can reduce energy leakage and thus increase energy efficiency. They have been seen as an approach to overcoming the constraints of CMOS downscaling, specifically, the Magnetic Tunnel Junction (MTJ) which has been the focus of much research in recent years. Its nonvolatility, scalability and low power consumption are highly attractive when applied in several components. This paper aims at providing a survey of a selection of MTJ applications such as memory and analog to digital converter, among others. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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Other

Jump to: Research, Review

14 pages, 3970 KiB

Open AccessLetter

Compensation System for Biomagnetic Measurements with Optically Pumped Magnetometers inside a Magnetically Shielded Room

by Anna Jodko-Władzińska, Krzysztof Wildner, Tadeusz Pałko and Michał Władziński

Sensors 2020, 20(16), 4563; https://doi.org/10.3390/s20164563 - 14 Aug 2020

Cited by 31 | Viewed by 4238

Abstract

Magnetography with superconducting quantum interference device (SQUID) sensor arrays is a well-established technique for measuring subtle magnetic fields generated by physiological phenomena in the human body. Unfortunately, the SQUID-based systems have some limitations related to the need to cool them down with liquid [...] Read more.

Magnetography with superconducting quantum interference device (SQUID) sensor arrays is a well-established technique for measuring subtle magnetic fields generated by physiological phenomena in the human body. Unfortunately, the SQUID-based systems have some limitations related to the need to cool them down with liquid helium. The room-temperature alternatives for SQUIDs are optically pumped magnetometers (OPM) operating in spin exchange relaxation-free (SERF) regime, which require a very low ambient magnetic field. The most common two-layer magnetically shielded rooms (MSR) with residual magnetic field of 50 nT may not be sufficiently magnetically attenuated and additional compensation of external magnetic field is required. A cost-efficient compensation system based on square Helmholtz coils was designed and successfully used for preliminary measurements with commercially available zero-field OPM. The presented setup can reduce the static ambient magnetic field inside a magnetically shielded room, which improves the usability of OPMs by providing a proper environment for them to operate, independent of initial conditions in MSR. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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10 pages, 3010 KiB

Open AccessLetter

Defect Classification Using Postpeak Value for Pulsed Eddy-Current Technique

by Jiuhao Ge, Chenkai Yang, Ping Wang and Yongsheng Shi

Sensors 2020, 20(12), 3390; https://doi.org/10.3390/s20123390 - 16 Jun 2020

Cited by 8 | Viewed by 2672

Abstract

In this paper, a feature termed as the postpeak value is proposed for the pulsed eddy current technique (PECT). Moreover, a method using the postpeak value is proposed to classify surface and reverse defects. A PECT system is built for verification purposes. Experiment [...] Read more.

In this paper, a feature termed as the postpeak value is proposed for the pulsed eddy current technique (PECT). Moreover, a method using the postpeak value is proposed to classify surface and reverse defects. A PECT system is built for verification purposes. Experiment results prove that the postpeak feature value has better performance than that of the traditional peak value in the case of reverse defect detection. In contrast, the peak value is better than the postpeak value in the case of surface defect detection. Experiment results also validate that the proposed classification algorithm has advantages: classification can be achieved in real time, the calculation process and results are easy to understand, and supervised training is unnecessary. Full article

(This article belongs to the Special Issue Advanced Magnetic Sensors and Their Applications)

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