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Advances in Magnetic Sensors and Their Applications

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (20 March 2025) | Viewed by 19159

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Dr. Nicholas Sammut

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Department of Microelectronics and Nanoelectronics, Faculty of Information and Communications Technology, University of Malta, MSD 2080 Msida, Malta
Interests: microelectronics; micro-electromechanical systems; accelerator technology; sensors; systems and interfacing; precision measurement; magnetic measurement
Special Issues, Collections and Topics in MDPI journals

Dr. Marco Calvi

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Photon Science Division of the Paul Scherrer Institute, 5232 Villigen PSI, Switzerland
Interests: accelerator physics and technology; synchrotron light sources; free electron lasers; undulators and wigglers; permanent magnets; superconductivity; high-temperature superconductors (HTS); HTS REBCO bulks and tapes; magnetic measurement instrumentation; hall sensors; cryogenics

Special Issue Information

Dear Colleagues,

Advancements in the design and applications of magnetic sensors are at the forefront of many disciplines, ranging from physics to medicine. Magnetic sensors are also very prominent, being present in diverse technological fields, from atomic physics to space applications.

The aim of this Special Issue is to provide a forum for colleagues to publish their recent research, development, and innovation results related to advances in magnetic sensors and their applications. These include topics such as the following:

Fundamental concepts and techniques of magnetic sensing;
Magnetic sensors for big science subsystems including acceleration magnets, insertion devices, space applications, etc.;
Bio-electromagnetic sensing;
Characterisation of novel magnetic structures and their measurements;
Industrial magnetic sensing;
Sensing of magnetic material behaviours including harmonics, DC offsets, hysteresis, power losses, and coupled phenomena;
High-frequency and low-frequency magnetic sensors;
Sensing for the characterisation of permanent magnets, electromagnets, and superconducting magnets;
Electromagnetic device applications (including motors, transformers, etc.);
Magnetic sensor interfaces with instrumentation;
Sensing and magnetic standards;
Modelling, measurement, characterisation, and calibration of magnetic sensors;
Destructive and non-destructive magnetic sensing;
Magnetic sensors for micro and nanoscale applications;
Innovative applications of magnetic sensors;
Any other relevant topics.

Dr. Nicholas Sammut
Dr. Marco Calvi
Guest Editors

Manuscript Submission Information

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Keywords

magnetic sensors
magnetic sensing applications

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Published Papers (12 papers)

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Research

17 pages, 5664 KiB

Open AccessArticle

Phantom-Based Approach for Comparing Conventional and Optically Pumped Magnetometer Magnetoencephalography Systems

by Daisuke Oyama and Hadi Zaatiti

Sensors 2025, 25(7), 2063; https://doi.org/10.3390/s25072063 - 26 Mar 2025

Viewed by 373

Abstract

Magnetoencephalography (MEG) is a vital tool for understanding neural dynamics, offering a noninvasive technique for measuring subtle magnetic field variations around the scalp generated by synchronized neuronal activity. Two prominent sensor technologies exist: the well-established superconducting quantum interference device (SQUID) and the more recent optically pumped magnetometer (OPM). Although many studies have compared these technologies using human-subject data in neuroscience and clinical studies, a direct hardware-level comparison using dry phantoms remains unexplored. This study presents a framework for comparing SQUID- with OPM-MEG systems in a controlled environment using a dry phantom that emulates neuronal activity, allowing strict control over physiological artifacts. Data were obtained from SQUID and OPM systems within the same shielded room, ensuring consistent environmental noise control and shielding conditions. Positioning the OPM sensors closer to the signal source resulted in a signal amplitude approximately 3–4 times larger than that detected by the SQUID-MEG system. However, the source localization error of the OPM-MEG system was approximately three times larger than that obtained by the SQUID-MEG system. The cause of the large source localization error was discussed in terms of sensor-to-source distance, sensor count, signal–noise ratio, and the spatial coverage provided by the sensor array of the source signal. Full article

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

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24 pages, 8108 KiB

Open AccessArticle

Position Detection System for Moving-Magnet Linear Motors Based on a Magnetoresistive Sensor Array

by Jun Wang, Xiang Chen, Quyan Chen, Qing Xi and Haiyang Sun

Sensors 2025, 25(4), 1019; https://doi.org/10.3390/s25041019 - 8 Feb 2025

Viewed by 738

Abstract

The moving-magnet linear motor has received considerable attention in the development of logistic and factory automation in recent years. A reliable position detection system is the key to achieving the precise position and control of the motor. At present, the magnetic grid-scale and grating-scale are the most widely used traditional detection methods. However, these are not suitable for position detection with moving-magnet linear motors. They have the disadvantages of being easy to disturb, having a high cost, and exhibiting a limited measurement range. In this work, a moving-magnet linear motor position detection system based on an array of magnetoresistive sensors is used. The array is configured by arranging the magnetoresistive sensors at equal intervals along a line parallel to the trajectory of the armature. Then, the permanent magnet is fixed on the rotor and detected by sensors. When the rotor crosses the sensors in a parallel line, the changes in the magnetic field cause the magnetoresistive sensors to output two voltage signals directly proportional to the corresponding position changes. The signals are collected by the AD7606 and transmitted to the FPGA and STM32 controller for data processing, and the actual position of the rotor is calculated. This method has no length limitation and can be used for long-distance position detection. The experimental results show that the position detection system has a higher linear correlation coefficient compared with the magnetic grid ruler, in addition to a capability of ±9 μm accuracy, which verifies the validity of the position detection method for the moving-magnet linear motor. Full article

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

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12 pages, 2072 KiB

Open AccessArticle

Superconducting Quantum Magnetometer Based on Flux Focusing Effect for High-Sensitivity Applications

by Antonio Vettoliere and Carmine Granata

Sensors 2024, 24(12), 3998; https://doi.org/10.3390/s24123998 - 20 Jun 2024

Cited by 1 | Viewed by 1401

Abstract

A superconducting quantum magnetometer for high-sensitivity applications has been developed by exploiting the flux focusing of the superconducting loop. Unlike conventional dc SQUID magnetometers that use a superconducting flux transformer or a multiloop design, in this case, a very simple design has been employed. It consists of a bare dc SQUID with a large washer-shaped superconducting ring in order to guarantee a magnetic field sensitivity B_Φ less than one nT/Φ₀. The degradation of the characteristics of the device due to an inevitable high value of the inductance parameter β_L was successfully compensated by damping the inductance of the dc SQUID. The size of the magnetometer, coinciding with that of the washer, is 5 × 5 mm² and the spectral density of the magnetic field noise is 8 fT/√Hz with a low frequency noise knee of two Hz. The excellent performance of this simple magnetometer makes it usable for all high-sensitivity applications including magnetoencephalography. Full article

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

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17 pages, 884 KiB

Open AccessArticle

A Revisit of Electromagnetic Wave Scattering by a Metal Isotropic Body in a Lossless Environment with Magnetic Sensor Excitation

by Panayiotis Vafeas

Sensors 2024, 24(12), 3807; https://doi.org/10.3390/s24123807 - 12 Jun 2024

Viewed by 877

Abstract

This paper investigates the electromagnetic fields being scattered by a metal spherical object in a vacuum environment, providing a numerical implementation of the obtained analytical results. A time-harmonic magnetic dipole source, far enough, emits the incident field at low frequencies, oriented arbitrarily in the three-dimensional space. The aim is to find a detailed solution to the scattering problem at spherical coordinates, which is useful for data inversion. Based on the theory of low frequencies, the Maxwell-type problem is transformed into Laplace’s or Poisson’s interconnected equations, accompanied by the proper boundary conditions on the perfectly conducting sphere and the radiation conditions at infinity, which are solved gradually. Broadly, the static and the first three dynamic terms are sufficient, while the terms of a higher order are negligible, which is confirmed by the field graphical representation. Full article

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

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14 pages, 10332 KiB

Open AccessArticle

An Advanced Hall Element Array-Based Device for High-Resolution Magnetic Field Mapping

by Tan Zhou, Jiangwei Cai and Xin Zhu

Sensors 2024, 24(12), 3773; https://doi.org/10.3390/s24123773 - 10 Jun 2024

Viewed by 2229

Abstract

The precise mapping of magnetic fields emitted by various objects holds critical importance in the fabrication of industrial products. To meet this requirement, this study introduces an advanced magnetic detection device boasting high spatial resolution. The device’s sensor, an array comprising 256 unpackaged gallium arsenide (GaAs) Hall elements arranged in a 16 × 16 matrix, spans an effective area of 19.2 mm × 19.2 mm. The design maintains a 1.2 mm separation between adjacent elements. For enhanced resolution, the probe scans the sample via a motorized rail system capable of executing specialized movement patterns. A support structure incorporated into the probe minimizes the measurement distance to below 0.5 mm, thereby amplifying the magnetic signal and mitigating errors from nonparallel probe–sample alignment. The accompanying interactive software utilizes cubic spline interpolation to transform magnetic readings into detailed two- and three-dimensional magnetic field distribution maps, signifying field strength and polarity through variations in color intensity and amplitude sign. The device’s efficacy in accurately mapping surface magnetic field distributions of magnetic and magnetized materials was corroborated through tests on three distinct samples: a neodymium–iron–boron magnet, the circular magnetic array from a smartphone, and a magnetized 430 steel plate. These tests, focused on imaging quality and magnetic field characterization, underscore the device’s proficiency in nondestructive magnetic field analysis. Full article

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

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17 pages, 2021 KiB

Open AccessArticle

Design and Characterisation of a Read-Out System for Wireless Monitoring of a Novel Implantable Sensor for Abdominal Aortic Aneurysm Monitoring

by Nuno P. Silva, Adnan Elahi, Eoghan Dunne, Martin O’Halloran and Bilal Amin

Sensors 2024, 24(10), 3195; https://doi.org/10.3390/s24103195 - 17 May 2024

Cited by 2 | Viewed by 1363

Abstract

Abdominal aortic aneurysm (AAA) is a dilation of the aorta artery larger than its normal diameter (>3 cm). Endovascular aneurysm repair (EVAR) is a minimally invasive treatment option that involves the placement of a graft in the aneurysmal portion of the aorta artery. This treatment requires multiple follow-ups with medical imaging, which is expensive, time-consuming, and resource-demanding for healthcare systems. An alternative solution is the use of wireless implantable sensors (WIMSs) to monitor the growth of the aneurysm. A WIMS capable of monitoring aneurysm size longitudinally could serve as an alternative monitoring approach for post-EVAR patients. This study has developed and characterised a three-coil inductive read-out system to detect variations in the resonance frequency of the novel Z-shaped WIMS implanted within the AAA sac. Specifically, the spacing between the transmitter and the repeater inductors was optimised to maximise the detection of the sensor by the transmitter inductor. Moreover, an experimental evaluation was also performed for different orientations of the transmitter coil with reference to the WIMS. Finally, the FDA-approved material nitinol was used to develop the WIMS, the transmitter, and repeater inductors as a proof of concept for further studies. The findings of the characterisation from the air medium suggest that the read-out system can detect the WIMS up to 5 cm, regardless of the orientation of the Z-shape WIMS, with the detection range increasing as the orientation approaches 0°. This study provides sufficient evidence that the proposed WIMS and the read-out system can be used for AAA expansion over time. Full article

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

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15 pages, 3167 KiB

Open AccessArticle

Online Measurement Method and System of Excitation Impedance of Current Transformers Based on Norton’s Theorem and Differential Method to Measure Difference of Two Currents

by Mengying Gan, Hongsen You and Jiansheng Yuan

Sensors 2024, 24(10), 3115; https://doi.org/10.3390/s24103115 - 14 May 2024

Cited by 1 | Viewed by 1115

Abstract

An online measurement method is proposed in this paper, and a system is established for detecting the excitation impedance of current transformers (CTs) based on Norton’s theorem. The theorem is carried out by connecting a resistance and an inductance at the secondary side port of the CT to get the equations for calculating the impedance. The iterative method is used to solve the equations, and the solution is revised to consider the nonlinearity of the core. The main variable in the equations is the variation of the secondary current with the resistance or inductance. To obtain the secondary current variation accurately, which is less than 1‰ of the current, a differential method is proposed, which is based on charging two capacitors and measuring the difference of their voltages instead of measuring each current separately first and then obtaining the current variation by subtraction. This is equivalent to saving two currents first and then measuring the current difference. The differential method avoids the problem of error amplification in the process of measuring two currents separately first and then subtracting them to obtain the current variation and solves the problem that two currents do not appear simultaneously. The results verify the correctness and accuracy of the proposed method and system. The acquisition of the excitation impedance is the basis for obtaining the working characteristics of CT cores, including magnetic and loss characteristics, as well as the error of CTs. Full article

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

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17 pages, 4645 KiB

Open AccessArticle

Key Contributors to Signal Generation in Frequency Mixing Magnetic Detection (FMMD): An In Silico Study

by Ulrich M. Engelmann, Beril Simsek, Ahmed Shalaby and Hans-Joachim Krause

Sensors 2024, 24(6), 1945; https://doi.org/10.3390/s24061945 - 18 Mar 2024

Cited by 3 | Viewed by 1681

Abstract

Frequency mixing magnetic detection (FMMD) is a sensitive and selective technique to detect magnetic nanoparticles (MNPs) serving as probes for binding biological targets. Its principle relies on the nonlinear magnetic relaxation dynamics of a particle ensemble interacting with a dual frequency external magnetic field. In order to increase its sensitivity, lower its limit of detection and overall improve its applicability in biosensing, matching combinations of external field parameters and internal particle properties are being sought to advance FMMD. In this study, we systematically probe the aforementioned interaction with coupled Néel–Brownian dynamic relaxation simulations to examine how key MNP properties as well as applied field parameters affect the frequency mixing signal generation. It is found that the core size of MNPs dominates their nonlinear magnetic response, with the strongest contributions from the largest particles. The drive field amplitude dominates the shape of the field-dependent response, whereas effective anisotropy and hydrodynamic size of the particles only weakly influence the signal generation in FMMD. For tailoring the MNP properties and parameters of the setup towards optimal FMMD signal generation, our findings suggest choosing large particles of core sizes

d_{C} > 25

nm with narrow size distributions (

σ < 0.1)

to minimize the required drive field amplitude. This allows potential improvements of FMMD as a stand-alone application, as well as advances in magnetic particle imaging, hyperthermia and magnetic immunoassays. Full article

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

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11 pages, 6653 KiB

Open AccessCommunication

Performance of Fluxgate Magnetometer with Cu-Doped CoFeSiB Amorphous Microwire Core

by Bin Wang, Weizhi Xu, Xiaoping Zheng, Sida Jiang, Zhong Yi, Peng Wang and Xiaojin Tang

Sensors 2024, 24(1), 309; https://doi.org/10.3390/s24010309 - 4 Jan 2024

Cited by 1 | Viewed by 2837

Abstract

In this study, we investigated the effects of Cu doping on the performance of CoFeSiB amorphous microwires as the core of a fluxgate magnetometer. The noise performance of fluxgate sensors primarily depends on the crystal structure of constituent materials. CoFeSiB amorphous microwires with varying Cu doping ratios were prepared using melt-extraction technology. The microstructure of microwire configurations was observed using transmission electron microscopy, and the growth of nanocrystalline was examined. Additionally, the magnetic performance of the microwire and the noise of the magnetic fluxgate sensors were tested to establish the relationship between Cu-doped CoFeSiB amorphous wires and sensor noise performance. The results indicated that Cu doping triggers a positive mixing enthalpy and the reduced difference in the atomic radius that enhances the degree of nanocrystalline formation within the system; differential scanning calorimetry analysis indicates that this is due to Cu doping reducing the glass formation capacity of the system. In addition, Cu doping affects the soft magnetic properties of amorphous microwires, with 1% low-doping samples exhibiting better soft magnetic properties. This phenomenon is likely the result of the interaction between nanocrystalline organization and magnetic domains. Furthermore, a Cu doping ratio of 1% yields the best noise performance, aligning with the trend observed in the material’s magnetic properties. Therefore, to reduce the noise of the CoFeSiB amorphous wire sensor, the primary goal should be to reduce microscopic defects in amorphous alloys and enhance soft magnetic properties. Cu doping is a superior preparation method which facilitates control over preparation conditions, ensuring the formation of stable amorphous wires with consistent performance. Full article

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

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16 pages, 6143 KiB

Open AccessArticle

Magnetostatic Simulation and Design of Novel Radiofrequency Coils Based on Transverse Field Current Elements for Magnetic Resonance Applications

by Giulio Giovannetti, Marcello Alecci and Angelo Galante

Sensors 2024, 24(1), 237; https://doi.org/10.3390/s24010237 - 31 Dec 2023

Cited by 2 | Viewed by 1417

Abstract

Radiofrequency (RF) coils are key components in Magnetic Resonance (MR) systems and can be categorized into volume and surface coils according to their shapes. Volume RF coils can generate a uniform field in a large central sample’s region, while surface RF coils, usually smaller than volume coils, typically have a higher Signal-to-Noise Ratio (SNR) in a reduced Region Of Interest (ROI) close to the coil plane but a relatively poorer field homogeneity. Circular and square loops are the simplest and most used design for developing axial field surface RF coils. However, for specific MR applications, the use of dedicated transverse field RF coils can be necessary or advantageous. Building on a previously developed and validated RF coil simulator, based on the magnetostatic approach, here we explore the potential applications of novel multiple axial field and transverse field surface RF coils in non-standard configurations. We demonstrate via numerical simulations that simple volume RF coils, matching a Helmholtz-like design, can be built with two identical transverse field RF coils separated by a given distance. Following well-known principles, the SNR of such novel configurations can be improved by a factor of up to √2 by combining two 90^° rotated coils, producing, inside a central ROI, a circularly polarized B₁ field. Full article

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

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20 pages, 31075 KiB

Open AccessArticle

Research on a Wire Rope Breakage Detection Device for High-Speed Operation Based on the Multistage Excitation Principle

by Zhou Zhou, Xiuheng Zhang, Ran Deng, Lu Han, Meng Zhou, Zhuangzhuang Ma, Xiangdong Chang and Yuxing Peng

Sensors 2023, 23(23), 9298; https://doi.org/10.3390/s23239298 - 21 Nov 2023

Cited by 2 | Viewed by 1992

Abstract

Wire rope breakage, as damage easily produced during the service period of wire rope, is an important factor affecting the safe operation of elevators. Especially in the high-speed elevator operation process, the problem of magnetization unsaturation caused by speed effects can easily lead to deformation of the magnetic flux leakage detection signal, thereby affecting the accuracy and reliability of wire breakage quantitative detection. Therefore, this article focuses on the problem that existing wire rope detection methods cannot perform non-destructive testing on high-speed elevator wire ropes and conducts design and experimental research on a high-speed running wire rope breakage detection device based on the principle of multi-stage excitation. The main research content includes simulation research on the multistage excitation, structural design, and simulation optimization of open–close copper sheet magnetizers and the building of a detection device for wire rope breakage detection experimental research. The simulation and experimental results show that the multistage magnetization method can effectively solve the problem of magnetization unsaturation caused by the velocity effect. The multistage excitation device has a good wire breakage recognition effect for speeds less than or equal to 3 m/s. It can detect magnetic leakage signals with a minimum of four broken wires and has good detection accuracy. It is a new and effective wire breakage detection device for high-speed elevator wire rope, providing important technical support for the safe and reliable operation of high-speed elevators. Full article

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

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17 pages, 12842 KiB

Open AccessArticle

A Novel Tactile Sensing System Utilizing Magnetorheological Structures for Dynamic Contraction and Relaxation Motions

by Yu-Jin Park, Bo-Gyu Kim, Eun-Sang Lee and Seung-Bok Choi

Sensors 2023, 23(22), 9035; https://doi.org/10.3390/s23229035 - 8 Nov 2023

Cited by 1 | Viewed by 1881

Abstract

It is well known that the rheological properties of magnetorheological (MR) material change under a magnetic field. So far, most works on MR materials have been oriented toward actuating characteristics instead of sensing functions. In this work, to realize dynamic tactile motion, a spherical MR structure was designed as a sensor, incorporating a magnetic circuit core to provide maximum dynamic motion. After manufacturing a prototype (sample), a sinusoidal magnetic field of varying exciting frequency and magnitude was applied to the sample, and the dynamic contraction and relaxation motion depending on the exciting magnetic field was observed. Among the test results, when 10% deformation occurred, the instantaneous force generated was from 2.8 N to 8.8 N, and the force when relaxed was from 1.2 N to 3.5 N. It is also shown that the repulsive force within this range can be implemented using an acceptable input current. The special tactile sensing structure proposed in this work can be used as a sensor to measure the field-dependent viscoelastic properties of human tissues such as stomach, liver, and overall body. In addition, it could be usefully applied to robot surgery, because it can mimic the dynamic motions of various human organs under various surgical conditions. Full article

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

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