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Magnetic tracking systems have been widely investigated in biomedical engineering due to the transparency of the human body to static magnetic fields. We recently proposed a novel human-machine interface for prosthetic application, namely the myokinetic interface. This controls multi-articulated prostheses by tracking magnets implanted in the residual muscles of individuals with amputation. Previous studies in this area focused solely on the choice and tuning of the localization algorithm. Here, we addressed the role of the intrinsic properties of the sensors, by analysing their effects on the tracking accuracy and on the computation time of the localization algorithm, through experimentally-verified computer simulations. We observed that the tracking accuracy is primarily affected by the localization rate, which is directly related to the sampling frequency of the sensors, and less significantly affected by the sensor resolution. The computation time, instead, proved positively correlated to the number of MMs, and negatively correlated with the localization rate. Our results may contribute to the development of novel human-machine interfaces for prosthetic limbs and could be extended to a broad range of applications involving magnetic tracking.

Factory machine diagnosis is important for preventive maintenance. Diagnosis equipment needs to be reliable and easy to handle, and the diagnostic results should be easily recognizable. An equipment that meets the above conditions is developed; it comprises a laser beam source, leaf spring with a mirror and a magnet as a position-adjustable mass, a copper plate, and a remote switch, if necessary. The principle is based on optical lever and mechanical vibration resonance. The laser spot vibration trajectory is irradiated onto the wall, ceiling, floor of a factory, or the housing of a machine as a screen. An equipment (29 mm $\times35$ mm $\times22$ mm) placed on the vibrating machine irradiates a laser beam and the magnified vibration is displayed on the screen. In this paper, the theoretical model and the equipment are presented, and the measured vibrations for a test vibrator and an actual machine are shown. A peak-to-peak vibration of 0.006 mm measured by a vibrometer is magnified to the 115 mm laser beam spot trajectory. The magnification is 38,333 times (91.6 dB), which is even larger on screens placed farther away. The calculation results by the theoretical model are in good agreement with the measurements.

A new design of electromagnetic acoustic transducer (EMAT) is proposed for simultaneous measurement of in-plane and out of plane displacement components of Rayleigh wave. The EMAT consists of nine magnets and two meander-line-coils (MLCs). There almost only exists vertical or horizontal magnetic field at some specific positions in the magnetic field generated by the EMAT. By adjusting the interval between adjacent conductors and the position of conductors, the conductors in one coil are almost only in the vertical magnetic field and the conductors in the other coil are almost only in the horizontal magnetic field. Therefore, the two coils in this EMAT will almost only react with in-plane and out of plane displacements respectively. With this EMAT, repeated positioning or large area is not required during the measurement process. In addition, this EMAT can measure the two displacement components simultaneously without calculation. Meanwhile, this EMAT is much more sensitive to the ultrasonic waves for the magnetic field generated by the EMAT is enhanced. The measurement results of this EMAT are consistent with those of conventional EMATs, which indicates that the measurement results are accurate and reliable.

Magnetic resonance force microscopy is becoming increasingly important for three-dimensional image reconstruction inside a sample with non-invasive measurements. In this study, a magnetic resonance force sensor with a vacuum-packaged magnetic cantilever was developed for the detection of free radicals in an atmospheric environment. A 1.5- $\mu \text{m}$ -thick silicon-based cantilever, which was mounted with a 25- $\mu \text{m}$ -diameter Nd-Fe-B magnet at the end of the cantilever, was hermetically packaged in a vacuum cavity using an anodic-bonding technique. The evaluation of the pressure dependence on the quality factor of the mechanical magnet-based cantilever revealed that the packaged-cavity pressure was approximately in the range of $7.3\,\,\times10$ 2– $1.0\,\,\times10$ 3 Pa after vacuum packaging. The corresponding detection sensitivity of the magnet-based cantilever sensor was calculated to be $1.1\,\,\times10$ -13 N/ $\sqrt {Hz} $ . Based on the magnetic force interaction, the magnetic field gradients were detected by mapping the variations in the resonant frequency and resonant amplitude of the magnetic cantilever. Finally, the magnetic resonance force, caused by the electron spin resonance in a standard radical of 1, 1-Diphenyl-2-picrylhydrazyl, was detected with a spin density of $\sim 1.5\,\,\times10$ 15 spins/cm3 in an atmospheric environment. The proposed vacuum-packaged magnet-based cantilever confirmed the high feasibility of magnetic resonance force detection within a non-hermetic environment.

Passive magnetic localization is a wireless motion tracking method that can determine position and orientation of objects with embedded magnets. The magnetic field around the magnetic object can be detected using magnetometers. Afterward, using an optimization algorithm, the difference between the measured and calculated magnetic field (from the mathematical model of the magnetic field produced around the magnetic object) is minimized. However, using numerical optimization methods faces two main challenges: low computation speed to reach desirable accuracy and convergence to a local minimum. In this paper, we propose a method to analytically calculate the magnet’s orientation in terms of the magnet’s position. Therefore, the optimization problem is solved only to find the position unknowns. The experimental results demonstrate that the average position error is 2.0 mm and orientation error is 2.3° for a cube magnet with a 5 mm edge length. According to the experiments, by employing this method, computation speed becomes 2.1 times faster with respect to the conventional method. Furthermore, in contrast to the conventional method, the proposed technique is robust with respect to the initial conditions and the technique always converges towards the global minimum and gives the correct solution regardless of the initial guess.

The existing yoke magnetizers can be used for large diameter bridge cable detection, but cannot provide the optimal bias magnetic field due to the repulsion of the polarities arranged in the circumferential direction, which reduces the energy conversion efficiency of the magnetostrictive longitudinal mode guided wave transducer. A magnetostrictive longitudinal mode guided wave transducer with the ring permanent biased magnet is provided to improve energy conversion efficiency for large diameter bridge cables. Firstly, a ring magnetizer for the axial magnetization is proposed, which inspired by the structure of the yoke magnetizer and the adjustable bias magnetic field generated by the solenoid coil. Then, the specific transducer with the ring magnetizers is designed for PES(C) 7–127 cable. Based on the magnetostrictive coupling coefficient curves and magnetization curve of the cable steel wire, the finite element models verify that the magnetization effect of the ring magnetizer is better than the yoke magnetizer for PES(C) 7–127 cables. Furthermore, the structural parameters of the ring magnetizers are optimized based on magnetization strength and magnetization uniformity. Finally, the improved efficiency of the transducer is verified by experiments. The energy conversion efficiency of the transducer is increased by 43.65% at the transmitting side, 4.76% at the receiving side, 48.41% at the both sides. Besides, the weight of the ring magnetizers is 19.85% lower than the yoke magnetizers.

Target positioning by the magnetic tracking system is extremely susceptible to the influence of the geomagnetic field. To accurately locate magnetic objects, we design a second-order magnetic gradient tensor (SMGT) system based on the plane-cross magnetic gradient tensor (MGT) system. With the constraint equation of MGT spatial invariants, the magnetic source position coordinates are solved by the SMGT and Euler deconvolution. The simulation shows when the Gaussian noise variance is less than 3 nT and a magnetic dipole with scalar 6000 Am2 moment within 10 m distance, the positioning accuracy of the method can be controlled within the range of about 3 m root-mean-square error (RMSE); in actual measurement, after system calibration, the method realized a small magnet (diameter 5 cm, thickness 0.5 cm) positioning where the RMSE is suppressed in 14 cm in a 2.1 m heading-line detection interval.

This work details the design and analysis of a permanent magnet flowmeter designed to be submerged in a pool type sodium fast reactor environment. Recently developed Samarium Cobalt rare earth magnets were utilized that have demonstrated resilience to temperature and neutron flux up to 550 °C and 1018 n/cm2, respectively. This paper will discuss the theory, design, calibration and uncertainty quantification of the flowmeter. The flowmeter was calibrated over a flowrate range of 11.4 - 90.9 LPM at temperatures of 220 and 400 °C, yielding an uncertainty in calibration of 2-3.6%. A finite element model was developed and validated experimentally, yielding

Non-destructive examination of steam generator (SG) tubes of Fast Breeder Reactors is of paramount importance. The inspection needs to be carried out from the inner side of an SG tube due to the constraint in accessibility. Recently, the magnetostrictive ultrasonic guided wave (MUGW) technique has been proposed as an alternative for the inspection of SG tubes. As a commercial MUGW probe for small-diameter ferromagnetic tubes is not available, it needs to be designed and developed with optimum parameters. This paper proposes a three-step optimization approach for the development of a MUGW probe, namely optimization of the diameter and length of a permanent magnet (for bias) finite element modeling based, optimization of the width of the transmitter and receiver coils of the probe by empirical modeling and the optimization of the number of turns of the transmitter and receiver coils by equivalent circuit models. A MUGW probe is fabricated and tested experimentally to validate the optimized parameters. Experiments show the validity of the approach in terms of generation, long-range propagation (47.6 m) of L(0,2) mode at 300 kHz, and the required sensitivity (multiple 10% wall thickness deep uniform wall loss circumferential grooves) in SG tubes.

Permanent magnet localization (PML) is designed for applications requiring non-line-of-sight motion tracking with millimetric accuracy. Current PML-based tongue tracking is not only impractical for daily use due to many sensors being placed around the mouth, but also requires a large training set of tracer motion. Our method was designed to overcome these shortcomings by generating a local magnetic field and removing the need for the localization to be trained with tracer rotations. An inertial measurement unit (IMU) is used as a tracer that moves in a local magnetic field generated by a magnet strip. The magnetic strength can be optimized to enable the strip to be placed further away from the tracer, thus hidden from view. The tracer is small ( $6\times 6\times 0.8$ mm 3) to reduce hindrance to natural tongue movements, and the strip is designed to be worn as a neckband. The IMU’s magnetometer measures the local magnetic field which is compensated for the tracer’s orientation by using the IMU’s accelerometer and gyroscope. The orientation-compensated magnetic measurements are then fed into a localization algorithm that estimates the tracer’s 3D position. The objective of this study is to evaluate the tracking accuracy of our method. In a $8\times 8\times 5$ cm 3 volume, positional errors of 1.6 mm (median) and 2.4 mm (third quartile, Q3) were achieved on a tracer being rotated ±50° along both pitch and roll. These results indicate this technology is promising for tongue tracking applications.

In this article, a low power and compact scanning micromirror for LiDAR (light detection and ranging) system is designed, fabricated, and characterized. A 5 mm-diameter scanning micromirror is electromagnetically actuated with multi-turn copper winding formed on the gimbal and magnet assembly formed under the silicon substrate. A unique magnetic circuit that generates an asymmetric radial magnetic field has been designed and analyzed. A series-connected double spring-mass system consisting of a gimbal and a mirror plate has been used to amplify the deflection angle. An analytic model of the system has been developed and verified with finite element analysis. Also, a reinforcement rim structure is utilized to reduce the dynamic deformation of the reflective surface down to 19.3 nmrms. An optical scan angle of 30° is obtained at 690 Hz, 17.4 mArms input, and corresponding power consumption is 7.8 mWrms. A prototype scanning system with $180^{\circ } \times 30^{\circ }$ field-of-view has been demonstrated with fabricated scanning micromirror as the vertical scanner. The proposed approach provides a simple and compact design for a large diameter scanning micromirror, which can potentially be utilized in various LiDAR applications.

This work presents a new omnidirectional electromagnetic acoustic transducer (EMAT) employing a circumferential periodic permanent magnet array, which was proposed for generating and receiving shear-horizontal (SH) guided waves in an aluminum plate. The novel transducer consisted of 12 axially polarized sector magnets arranged in a circle, and the magnetic field directions of adjacent magnets were opposite. A spiral coil was arranged under the magnet array. A vertical magnetic field generated by the magnets and the circumferential eddy current generated by the spiral coil formed a Lorentz force in a plate acting in the radial direction of this new omnidirectional EMAT. By controlling the sizes of the sector magnets, the omnidirectional SH0 mode (fundamental SH guided wave mode) was generated. To maximize the output of the EMAT at the given excitation frequency, it was proposed to add acrylic spacers between the sector magnets and determine the size of the magnet based on the frequency bandwidth of the excitation signal while also optimizing the omnidirectional sound field. A three-dimensional (3D) finite element model of the EMAT was established using COMSOL Multiphysics to perform numerical simulations, and the effectiveness of the optimization method was verified. The effectiveness was verified by experiments. The simulations and experiments showed that the proposed EMAT could generate omnidirectional SH0 mode guided waves in an aluminum plate.

A novel magnetoplethysmogram (MPG) system is designed and developed for the real time, noninvasive monitoring of hemoglobin concentration in arterial blood. The basic principle of modulated magnetic signature of blood (MMSB), is validated with clinical trial. The MPG probe consists of a permanent magnet and a Giant Magneto Resistance (GMR) sensor. A strap and stand design enable reliable capture of continuous cycles of MPG with relative ease. Clinical validation with data from 64 patients carried out at the institute hospital of IIT Madras, using the proposed system gave a worst-case error of 6.5% in the measurement of hemoglobin concentration in arterial blood. Linear regression analysis using least square method, exhibited a standard deviation of 0.64 g/dL. Results from the clinical validation establish the practicability of the proffered MPG system.

This article presents a new magnetically coupled method to efficiently transfer vibrational energy from a source to a piezoelectric energy harvester. This method enables energy harvesting from vibration sources to which direct physical contact is not feasible or not preferred. The proposed harvester uses the piezoelectric cantilever in combination with two permanent magnets; one attached to the free end of the cantilever while the other magnet is firmly attached to the vibrational source facing the magnet on the cantilever. These magnets are kept in repulsive mode. As the source oscillates, the attached magnet follows the movement of the source. Due to this, the magnet on the cantilever gets perturbed and follows the movement of the source, bending the cantilever cyclically and generating a voltage output. This proposed arrangement not only (a) helps to scavenge energy without directly fitting the piezoelectric element and associated wiring on the vibrating source but also (b) provides more flexibility to adjust the resonant frequency, by varying the air gap between the magnets, (c) gives higher bandwidth compared to the conventional piezoelectric harvesters, ensuring less effect due to small mismatch between the frequency of the source and resonant frequency of the harvester. This is automatically achieved due to the nonlinearity of the system, introduced by the magnets. Prototypes of the proposed harvester and an equivalent conventional harvester are developed and tested. Results proved the functionality of the proposed harvester and showed superior performance in terms of gain, bandwidth, and charging time of a storage capacitor.

Magneto plethysmo gram (MPG), like the Photo plethysmo gram (PPG) is a signal that carries information on blood volume flow and is obtained noninvasively. Unlike PPG, MPG is obtained from a peripheral artery, such as radial, carotid or brachial. The magnetic flux required for obtaining an MPG is generated by a permanent magnet placed on the wrist surface such that the generated flux couples with the blood flow in the artery. In this work it is shown that maximum coupling of flux with the blood flow in radial artery occurs when the distance between the open end of the U shaped probe is 12 mm. In order to attain this result, first the probe is simulated using the finite element method. The distance between the pole faces is varied in steps of 1 mm. Simulation results clearly indicate that the optimal distance is 12mm. Next experiments were conducted with prototype probes of varying distances between the pole faces on 20 volunteers of different age and gender. The experimental results validate the result obtained by the simulation study.

Magnetic field sensors based on the strain-mediated magnetoelectric (ME) coupling are usually bulky and energy-consuming due to the requirement for DC magnetic bias field, and the use of piezoelectric ceramics or single crystals cannot bear overlarge strain due to their fragility. Here, we demonstrate a stress-mediated ME sensor operating in torque mode without magnetic bias field. Combined with elastic layers, the NdFeB permanent magnets induce compressive stress on the piezoelectric layer via torque effect under a weak magnetic field. The contribution from d33 piezoelectric coefficient is dominant to the ME effect, and a large ME voltage of 2480 mV is observed at 13.6 Oe. At the resonate frequency of 138.7 Hz, magnetoelectric coefficient is found to be as high as 6.08 V/cm Oe. Our results reveal that the proposed ME sensor mediated by stress is excellent in performance and reliable in durability, which is promising for magnetic sensor applications.

Positive displacement water meters are found throughout the world’s water distribution networks to totalize water consumption. Containing internal permanent magnets, the water meters are underutilized sensors. Flow data from these meter locations can be used to non-intrusively identify the operation of individual water loads from an aggregate data stream at the meter. This article models these meters as nonideal magnetic encoders and presents a methodology for inexpensively retrofitting these meters with digital flow rate measurement capabilities, effectively bringing them into the growing body of smart metering devices and non-intrusive load monitoring without any contact with the water passing through them. We present a model of the magnetic field produced by these meters, discuss associated magnetic sensing hardware, and describe compensation, flow rate estimation, and post-processing algorithms for flow rate extraction. Verification is provided with experimental results.

This paper presents the design, fabrication and testing of a prototype resonant magnetic field sensor utilizing piezoelectric excitation and detection with ferromagnetic film at the free end of micro-cantilever for magnetic field detection. The change in the resonant frequency of the beam due to the presence of an external magnetic field is measured using a sensing piezo at the fixed end of the beam. Customized process steps are followed with six masks to fabricate the micro resonant magnetic field sensor with Aluminum nitride as piezoelectric material and soft ferromagnetic material for magnetic field detection. The mechanical, electrical and magnetic characterizations are carried out to evaluate the performance of the sensor. Results from analytical and experimentation are in close agreement and are in the same dimensional range. Dispenser printed permanent magnets are also integrated and this is the first of its kind to enhance the magnetic property in micro resonant magnetic field sensors.

We present a new Hall sensor design for the accurate and robust measurement of linear displacement. Implemented in CMOS, the sensor is based on a novel gradient measurement concept combining Hall elements with integrated magnetic concentrators. In typical applications with practical Ferrite magnets, the peak output voltage of the Hall transducers is only around 1.7 mV at the maximum operating temperature of 160°C, and thus requires high-performance low-offset readout electronics. Over its 15-mm linear displacement range, the sensor’s total error is 1% including manufacturing tolerances, trimming accuracy, temperature, aging effects, and practical magnet constraints. In addition, the sensor is immune to magnetic stray fields up to 5 mT, complying with the most stringent automotive norm.

In this paper, we develop computational model to analyze the magnetic concentrating effect of integrated magnetic concentrator (IMC) on surrounding external magnetic field. We present an IMC-based three-axis Hall sensor model that enables to measure both inclination angles and absolute strength of a random external magnetic field. An IMC changes surrounding parallel magnetic components into perpendicular components, and therefore allows the horizontal Hall plates to measure both the strength and inclination angles of parallel external magnetic fields. We develop a finite element method (FEM) based model in COMSOL Multiphysics for the three-axis Hall sensor. Key factors influencing IMC’s magnetic concentrating effect, including material property and sensor structure, are investigated and discussed using the developed model. Comparing to traditional IMC-based three-axis angular sensors, a reference permanent magnet is no longer needed in the sensor. A measurement accuracy of 0.8 and 1.2 degrees are achieved respectively for the angles of $\alpha $ and $\theta $ of external magnetic field.

Guided wave is advantageous to inspect pipe-like structures because of its long-distance propagation. Due to the curved structure of pipeline, guided wave can spread spirally with a helix angle. However, the current transducers focus more on the narrow or omni-directional beam than the helical form. This work presents the designed transducer to generate helical Lamb wave with concentrated beam. The transducer is developed using permanent magnets and arc-coil based on the principle of electromagnetic-acoustic conversion. The numerical analysis applying finite element method is conducted to verify the theoretical model of the transducer. The angular profiles are obtained to study the propagation of helical Lamb wave. Further, experiments are designed to demonstrate the performance of proposed transducer. The results from the experiments show good agreement with the numerical simulations. Besides, the parameter of central width is investigated and the half-angle of divergence is calculated. The results are compared with that from traditional transducers. The comparison indicates the superiority of the proposed transducer in generating helical Lamb wave. Therefore, the designed transducer could be a potential alternation for pipeline inspection based on guided wave.

This work explores the design of a magnetic levitation configuration enhanced by a dual-Halbach array that enables density-based measurement and manipulation in a flexible, open-plan space. The two-parallel arranged Halbach arrays with concentrated magnetic flux allow the use of magnetic gradients parallel to the faces of the magnets to levitate samples in paramagnetic solutions. Compared to the commonly used MagLev device in which a sample container remains obscured by the magnets, the dual-Halbach array places no physical barriers to physical sampling while levitating in the magnetic field, gaining easy access to specific populations of samples in paramagnetic solutions. The strength of the linear gradient in density can be tuned by setting the gap between the two arrays, enabling accurate and convenient density measurement with tunable sensitivity. The access to manipulate specific populations of samples and ability to tune measurement sensitivity provide an operationally simple method for iterative separation and purification procedures. The design of the magnetic levitation configuration enhanced by the dual-Halbach array provides an accurate, inexpensive and easy-to-operate method that would be useful for analysis, quality control, purification in the fields of agriculture science, pharmaceutical industry and materials science.

Resolvers as position sensors need a high frequency AC excitation voltage, and the induced voltage in their 2-phase perpendicular windings are amplitude modulated (AM) signals. For calculating the position, it is required to demodulated the output signals and calculate their envelopes. Then, inverse tangent can be used for calculating the position. Despite the advantages of resolvers, there are some drawbacks in their application. Calculating the envelopes is always one of the deep concerns in using resolvers. Furthermore, due to low-amplitude of the excitation flux, the performance of the resolvers is strongly affected by electromagnetic interference by the stray fields of motor and brake. Complicated winding process is the next challenge of resolvers. The last concern is referred to the high speed applications where to maintain the accuracy of the sensor it is required to increase the excitation frequency. While, the maximum frequency of excitation is limited by the frequency response of the employed ferromagnetic core and the employed resolver to digital converter (RDC). To overcome all the mentioned worries, a new permanent magnet (PM) resolver is proposed in this paper. The presented resolver has no copper winding and no need to the high frequency excitation. It is equipped by low-price Hall Effect sensors to measure the magnetic flux density and has a robust performance in high electromagnetic disturbance environments. All the analysis is done using time stepping finite element method (TSFEM) and verified by experimental measurements on a built prototype.

© 2001-2012 IEEE. Magnetic target tracking is a low-cost, portable, and passive method for tracking materials wherein magnets are physically attached or embedded without the need for line of sight. Traditional magnet tracking techniques use optimization algorithms to determine the positions and orientations of permanent magnets from magnetic field measurements. However, such techniques are constrained by high latencies, primarily due to the numerical calculation of the gradient. In this study, we derive the analytic gradient for multiple-magnet tracking and show a dramatic reduction in tracking latency. We design a physical system comprising an array of magnetometers and one or more spherical magnets. To validate the performance of our tracking algorithm, we compare the magnet tracking estimates with state-of-the-art motion capture measurements for each of four distinct magnet sizes. We find comparable position and orientation errors to state-of-the-art magnet tracking, but demonstrate increased maximum bandwidths of 336%, 525%, 635%, and 773% for the simultaneous tracking of 1, 2, 3, and 4 magnets, respectively. We further show that it is possible to extend the analytic gradient to account for disturbance fields, and we demonstrate the simultaneous tracking of 1 to 4 magnets with disturbance compensation. These findings extend the use of magnetic target tracking to high-speed, real-time applications requiring the tracking of one or more targets without the constraint of a fixed magnetometer array. This advancement enables applications such as low-latency augmented and virtual reality interaction, volitional or reflexive control of prostheses and exoskeletons, and simplified multi-degree-of-freedom magnetic levitation.

Accurate rotor position is essential for a permanent magnet synchronous motor (PMSM) to execute vector control. Due to the big volume, the resolver and the encoder as standard position sensors cannot be used in the space-limited application. The sensor-less methods whose characteristic are sensitive to the parameter of the motor cannot be used in mass-produce. Therefore, this paper presents tunnel magnetoresistance (TMR) sensors as a sensing element embedded into the PMSM to detect the magnetic field applied by the built-in magnets and high-frequency time pulses served as a measurement standard to measure the position. TMR sensors excited by the altering voltage are integrated with the PMSM without taking up extra space. Besides, the rotation position is measured by counting the time pulses corresponding to the phase shift of the TMR sensor’s output signal, which is a simple and effective method to detect the position. Related design aspects include the corresponding signal circuit, and the sensing element is introduced in detail in this paper. Experimental results prove the validity of the proposed method, and multi-group TMR sensors are used to get higher detection accuracy. Although developed for the PMSM, the presented embedded position detecting approach can be used for where the space is limited or the other types of actuators to make it integration.

Fast online detection of inter-turn short-circuit faults for permanent magnet synchronous machines (PMSMs) is a challenging task. Previous attempts based on phase currents or back EMF monitoring lack the capability to accurately locate the inter-turn short-circuit faults in stator windings. This paper proposed a new approach to online inter-turn short-circuit fault detection for PMSMs by means of sensing the external stray magnetic field outside the motor stator yoke. The stray magnetic field provides the information about the phase currents as well as the status of stator windings and thus, the location of inter-turn short-circuit fault can be detected accordingly. In this paper, the inter-turn short-circuit model and the stray magnetic flux model for PMSMs were theoretically analyzed. Both FEM simulations and experiments have been presented to validate the effectiveness of the proposed approach. A sensor array composed of 24 sensitive tunneling magnetoresistive (TMR) sensor units was employed to measure the stray magnetic field distribution outside the PMSM stator yoke. The experimental results show that both the location and severity of the inter-turn short-circuit fault in PMSMs were effectively detected using the proposed approach.

Due to the interference of the onboard magnetic material, the magnetometer intrinsic parameters differ from factory specification, and the cross-sensor misalignment between magnetometers and other sensors is distorted as well. This paper proposes an efficient full magnetometer calibration algorithm at the aid of gyroscopes by solving a homogeneous least-squared problem. The algorithm is able to accomplish both the intrinsic and cross-sensor calibration in a single step. It can serve as a coarse calibration method alone or be used as a good initial value for other fine algorithms for more accurate result.

This paper describes the design of a simple non-contact-type pressure transducer using a Bourdon tube and a Hall sensor where the effect of atmospheric temperature is compensated. In this design, a pressure sensing Hall IC is fixed with the nonmagnetic aluminum casing of a Bourdon gauge in front of a tiny disc-type permanent magnet rigidly attached with the free tip of the Bourdon tube. With the increase of pressure of the fluid inside the Bourdon tube, the free end along with the magnet moves toward the Hall sensor, and the magnetic field intensity due to the magnet on the Hall sensor increases with an increase of pressure. Due to this magnetic field, the outputs of the Hall sensor and the transducer circuit consisting of a differential amplifier and an instrumentation amplifier increase with the increase of pressure of the fluid inside the Bourdon tube. The transducer circuit consists of a unity gain differential amplifier circuit where the output of a second identical temperature sensing Hall IC is subtracted from the pressure sensing Hall IC output in order to compensate the effect of ambient temperature in the proposed transducer. The theoretical equations describing the operation of the transducer are derived in this paper. The static characteristic curves of a prototype design of the transducer are determined experimentally. The experimental results are reported in this paper. The characteristics curves are found to follow the theoretical equations with good repeatability and are free from ambient temperature effect.

This paper proposes the design of a linear magnetic position sensor (LMPS) to detect the mover position of the permanent magnet linear synchronous machines (PMLSMs). The working principle of the LMPS is based on the well-known Hall-Effect. The Hall-Effect-based design of LMPS is considered because it provides a low cost and relatively harsh environment susceptible alternative for the position detection for long track PMLSM system. The initial design was performed using 3D-finite element analysis and genetic algorithm-based deterministic optimization. Based on the initial model, four LMPS were manufactured and tested under the output constraint of peak flux density > 0.1T and total harmonic distortion < 3%. From the test results, it is concluded that the manufactured LMPS suffered significant deviation in output compared to the simulation model. These anomalies arise because of the manufacturing tolerances. To further improve the design and manufacturing process of the LMPS considering the effect of tolerance, a reliability-based robust design optimization (RBRDO) of the LMPS is proposed. The results of RBRDO confirms its usefulness for the design process of the LMPS in terms of undesired design non-compliance cost and great robustness without sacrificing the accuracy of the output signal.

Detection of winding faults in permanent magnet synchronous machines (PMSMs) with stranded winding designs remains a challenging task for conventional diagnostic techniques. This paper proposes a new sensing approach to this problem by investigating the application of dedicated electrically non-conductive and electromagnetic interference immune fiber Bragg grating (FBG) temperature sensors embedded in PMSM windings to enable winding open-circuit fault diagnosis based on observing the fault thermal signature. The final element analysis thermal and electromagnetic models of the examined practical PMSM design are first developed and used to enable the understanding of open-circuit winding fault-induced signature that can be used for effective diagnostic purposes, indicating in situ thermal excitation as an optimal diagnostic measurand. A purpose build test rig with an inverter-driven commercial PMSM instrumented with in situ FBG sensors monitoring phase winding hot spots is then used to evaluate the efficacy of the proposed diagnostic scheme. It is shown that unambiguous diagnosis and severity trending of winding open-circuit faults is enabled by the use of in situ FBG sensors. A comparison with conventional fault diagnostic technique utilizing current signal sensing and analysis is also reported, indicating the considerable advantages of the proposed monitoring scheme employing FBG sensors.

Magnetic localization provides a feasible way to estimate the position and orientation of the wireless capsule endoscopy embedded with a permanent magnet. However, the magnetic localization suffers from the drifting effect from magnetic noises and the uncertain initial guess during the optimization. In this paper, a localization system with noise cancellation is proposed to reduce the drifting effect of the geomagnetic noise and obtain the initial guess in a simple and effective way. Compared to the prior arts, the proposed system is able to achieve a lower positioning and orientation error under the same system configuration and makes it possible for the patient to move around while wearing the localization system. Besides, the proposed algorithm improves the consistency of positioning error within the localization region. Within a volume of 380 mm by 270 mm by 240 mm covered by 16 digital magnetic sensors, the average positioning error obtained from the proposed algorithm is around 10 mm and the average orientation error is around 12°.

Miniaturization of nuclear magnetic resonance (NMR) systems has seen a tremendous development during the last two decades. However, it has not gained popularity particularly, for biological investigations due to high manufacturing cost, sophisticated tools requirement, and mismatching problems arising due to connecting wire between radio frequency (RF) coil and transmission line. The aim of the research work presented in this paper is to develop cost effective, portable, and benchtop NMR system for biological investigation related to healthcare. In this paper, RF planar spiral coil is developed on double sided printed circuit board (PCB) using conventional PCB technology having high-quality factor of 29.265 at 21.287 MHz. Then, the same coil is used to develop on-chip NMR probe by extending the transmission line. This developed probe is a novel design, which improves the coupling between RF coil and transmission line; and hence, improves the sensitivity of NMR. A pair of permanent magnets having 0.5 T magnetic field strength with rectangular iron yoke has been used in the NMR system. Finally, the efficiency of this portable NMR was tested by recording the NMR spectrum of human blood cells. The spectrum obtained was compared to the commercial NMR (Bruker, ULTRASHIELD −500 PLUS) and found to be similar with remarkably small sample volume requirement. Moreover, in this research, we report a very low-cost coil and probe with novel probe design using CST tool, for the first time to the best of our knowledge.

Magnetic sensors are widely used in automotive and industrial applications to measure linear or angular movements. Although the measurement of the magnetic field vector offers the opportunity to estimate all mechanical degrees of freedom, previous approaches could not be applied in these environments. This paper presents an improved method for sensing a magnetic source’s position and orientation with six degrees of freedom. To solve the underlying inverse magnetostatic problem, an Unscented Kalman Filter in combination with an analytical model of the magnetic source’s field is used. The performance of the method is demonstrated on the basis of a novel multi-axis input device. It comprises a cuboid magnet and a CMOS (Complementary metal-oxide-semiconductor) Hall-Sensor array with up to 36 elements. The localization algorithm and the measurement model are implemented in an efficient way to achieve real-time capability and sampling rates up to 80Hz on embedded hardware. This outperforms known methods significantly and allows for a wide application of multi-degree of freedom sensors. Moreover, an absolute position and orientation accuracy of 71 $\mu \text{m}$ and 1.4° are achieved. The work describes the basis for advanced input devices but can also be transferred to other kinds of magnetic localization problems.

This paper proposes a bistable cantilever-based current sensing scheme for measuring dc current flow in a two-wire appliance cord constantly without using a cord separator to realize wide measurement range and high sensitivity without extra component from the typical cantilever-based oscillating type dc sensing system. Bistability has been introduced into dc current sensing system for the first time simply by changing the positions of magnet pole and current core. Through theoretical analysis and analytical studies, we find that as the applied dc current increases, the bistable sensing system also exhibits interwell oscillations and intrawell oscillations as the bistable energy harvester. It is proved that the output displacement amplitude is approximately proportional to the applied dc current in the interwell oscillations area where the vibrational trajectory is symmetric and the output displacement amplitude is dramatically improved. Therefore, on the same conditions the measurement range of the proposed work is 11 times wider than the oscillating type and the sensitivity is over 2 times higher than the oscillating one. In addition, we find that as interval decreases or magnet’s volume increases, the sensitivity increases accordingly while the maximum range determined by interwell oscillations area decreases. The differential equation of the proposed system is further analyzed to predict the relative output displacement. The method proposed here could shed light on bistable current sensing scheme and might be applied to self-powered current sensing system in vibrational environment.

This paper presents a new and efficient sensor for monitoring the presence of wear debris received by the storage tank in hydraulic systems. The proposed sensor plug employs a magnetic approach to attract the ferrous debris in the storage tank. A capacitive sensing scheme is employed in the same sensor plug to sense the presence of the debris accumulated on the plug. This combination of the magnetic and capacitive features in a single sensor for debris monitoring is new and it helps to realize a very sensitive sensor. The proposed sensor is designed in an ingenious way that the permanent magnet that is used to form the magnetic field in the vicinity of the sensor, to attract the debris towards the sensor, itself serves as one of the electrodes of the capacitive sensor. This approach improves the sensitivity and keeps the number of components in the sensor minimum. A prototype of the proposed sensor has been developed and tested. In the prototype, the change in capacitance of the sensor is measured using a high-resolution capacitance-to-digital converter. The sensor was tested after integrating it in a hydraulic test bed which has a controlled debris injection facility to the hydraulic circuit. The output of the sensor was found to be very sensitive to the typical ferrous debris that was introduced in the system. The proposed low-cost sensor will find applications in debris monitoring of underwater and land-based hydraulic systems.

Epoxies and resins can require careful temperature sensing and control in order to monitor and prevent degradation. To sense the temperature inside a mold, it is desirable to utilize a small, wireless sensing element. In this paper, we describe a new architecture for wireless temperature sensing and closed-loop temperature control of exothermic polymers. This architecture is the first to utilize magnetic field estimates of the temperature of permanent magnets within a temperature feedback control loop. We further improve performance and applicability by demonstrating sensing performance at relevant temperatures, incorporating a cure estimator, and implementing a nonlinear temperature controller. This novel architecture enables unique experimental results featuring closed-loop control of an exothermic resin without any physical connection to the inside of the mold. In this paper, we describe each of the unique features of this approach, including magnetic field-based temperature sensing, extended Kalman filtering for cure state estimation, and nonlinear feedback control over time-varying temperature trajectories. We use experimental results to demonstrate how low-cost permanent magnets can provide wireless temperature sensing up to $\sim 90^{\circ }C$ . In addition, we use a polymer cure-control testbed to illustrate how internal temperature sensing can provide improved temperature control over both short and long time-scales. This wireless temperature sensing and control architecture holds value for a range of manufacturing applications.

The self-sensing magnetic bearing technology offers significant cost savings and the potential for dynamics advantages due to its fundamental sensor-actuator collocation. This paper proposes a rotor displacement self-sensing scheme for the permanent magnet bias magnetic bearings (PMB) using double-channel PWM demodulation with a 90-degree phase shift. Based on the proposed structure of PMB, the self-sensing principle is presented by the magnetic circuit analysis. Then, the linear relationships between the rotor displacement and neutral voltage of the coil coupled in the x- and y-axis are derived. The two triangle carrier waves with a 90-degree phase shift are used to obtain two uncorrelated linear equations. For the hardware implementations, the rotor displacements in the x- and y-axis can be solved within a PWM cycle by the logic gate demodulation circuit. To validate the proposed self-sensing method, experiments are carried on a 10 kW magnetic levitated motor; the experiment results show that the self-sensing magnetic bearing has a characteristic of high sensitivity, large linear range, and wide dynamic range.

We present a measurement system for the viscosity and density of a fluid featuring a permanent magnet as measurement body, which is levitated in an actively controlled magnetic field. The behavior of the system is illustrated using different measurement body shapes. The basic concepts and the modeling of the electromechanical system are discussed. Utilizing special measurement modes, the sensor system allows for measuring viscosity and density independently. When put into operation, the magnet is controlled to stay at a constant levitation position. Due to a special actuation scheme, the magnet also rotates around its vertical axis. Using this setup and immersing the magnet in a fluid, it is possible to analyze viscosity and density of all kinds of fluids, except ferrofluids (which would distort the magnetic fields). The magnetic levitation system avoids any electrical or mechanical connections penetrating the walls of the measurement chamber; only the levitated permanent magnetic measurement body is in contact with the sample fluid.

Magnetic position and orientation detection systems have been penetrating the market in the last years due to their excellent properties. Specifically, the development of the cost effective 3-D Hall sensor brings new possibilities for consumer applications. In this paper, we propose a new magnetic design of a four-axis multimedia control element, which requires only a single magnet and a single 3-D Hall sensor. The development is based on an analytical model, which enables an efficient multivariate geometric optimization procedure. Optimal parameters are evaluated and discussed with respect to magnetic state separation up to several millitesla using a reasonable set of discrete rotational and tilt states. Experiments to prove the concept are presented.

This paper presents a gas flowmeter by using the rotation of a diamagnetically levitated magnet rotor to measure the gas flowrate. Two highly oriented pyrolytic graphite (HOPG) sheets are introduced to build a diamagnetic levitation structure. By adjusting the distance between the two HOPG sheets, the diamagnetic levitation structure can be tuned to obtain a single potential well, which ensures the stable levitation and rotation of the magnet rotor and improves the stability of the sensor. The maximum distance for achieving a single potential well is measured to be 3.1 mm. The feasibility of the proposed flowmeter was verified by experiment. The performance of the sensor was tested, and the maximum relative error is 5.56%.

With the advantage of low cost and small size, a hall sensor has been exploited to detect motor position, and this strategy has attracted much attention. A challenge is that measurement model parameters vary with position and vary from motor to motor because of the machining errors of permanent magnets. While, most existing methods use other auxiliary displacement sensors to calibrate model parameters off-line, which require a lot of preliminary work and lose adaptation when they are applied in industry. In this paper, an on-line simultaneous computation of model parameters and position method is proposed to measure position for a permanent magnet synchronous linear motor. The measurement model with Fourier series is employed to approximate the mapping relationship between magnetic field strength and mover position. Based on the continuous variation characteristics of model parameters and position, a simultaneous computational algorithm is proposed to real-timely compute model parameters and position without other sensors. In the experiments of one-way and reciprocating motion, magnetic field information is detected by a self-designed hall sensor array. Experimental results indicate that the standard deviation of measurement error is less than $10~\mu \text{m}$ with the comparison of a reference optical encoder.

This paper presents an optimization study for a miniature electromagnetic energy harvester, by incorporating a non-magnetic inertial mass (tungsten) along with the axially oriented moving magnets. The aim is to decrease the operation frequency and increase the output power of the harvester with the usage of higher density material and larger magnetic flux density. Dimensions of the magnets are optimized according to the harvester dimensions and magnetic flux gradients. Additionally, coil length, width, resistance, and position have been optimized through finite element analysis and experimentally validated. Simulation results show that using a single-magnet structure is not efficient for increasing the output power of the system. Test results also reveal that multi-magnet structures with inertial mass yield to higher output voltages and smaller resonance frequencies. Effects of the improvements on the moving structure are analyzed in detail and experimentally validated. The operation frequency of the harvester decreases with the addition of inertial mass and axially oriented moving magnets, while the output power increases due to greater magnetic flux contributions provided by repulsive forces. Compared with the single-magnet structure, a modified design with a similar size yields to a decrease in the resonance frequency (from 10 to 7 Hz) and an increase in the output power. The optimized harvester has a volume of 7 cm3 and generates 0.5 $\text{V}_{\mathrm {RMS}}$ , 240 $\mu \text{W}_{\mathrm {RMS}}$ output power (@7 Hz and 0.5 g peak acceleration).

We report a fiber-optic sensor based on Fresnel reflection for real-time monitoring of cryogenic temperatures. Coating highly thermo-sensitive polymers on the facet of optical fiber, we obtain average measurement sensitivity 0.04 dB/K in temperature range of 90–298 K. We show theoretical background of polymer’s thermo-optic response and the experimental results performed with two kinds of coating polymers, epoxy resin, and polymethyl methacrylate. The experimental results confirm the suitability for cryogenic temperature sensing applications, such as superconducting lines and magnets with simple and cost-effective sensor structure and signal processing.

Recent advances in robotics promise a future where robots co-exist and collaborate with humans in unstructured environments, which will require frequent physical interactions where accurate tactile information will be crucial for performance and safety. This article describes the design, fabrication, modeling, and experimental validation of a soft-bodied tactile sensor that accurately measures the complete 3-D force vector for both normal and shear loading conditions. Our research considers the detection of changes in the magnetic field vector due to the motion of a miniature magnet in a soft substrate to measure normal and shear forces with high accuracy and bandwidth. The proposed sensor is a pyramid-shaped tactile unit with a tri-axis Hall element and a magnet embedded in a silicone rubber substrate. The non-linear mapping between the 3-D force vector and the Hall effect voltages is characterized by training a neural network. We validate the proposed soft force sensor over static and dynamic loading experiments and obtain a mean absolute error below 11.7 mN or 2.2% of the force range. These results were obtained for a soft force sensor prototype and loading conditions not included in the training process, indicating strong generalization of the model. To demonstrate its utility, the proposed sensor is used in a force-controlled pick-and-place experiment as a proof-of-concept case study.

This paper concerns the nature of the peculiar second-order buoyancy experienced by a magnet in magnetic fluid acceleration sensor. The equilibrium differential equation of magnetic fluid under the action of magnetic field and gravity field is established and the expression for calculating the second-order buoyancy is derived. Three practical and effective methods to calculate the second-order buoyancy called surface integral method, magnetic force method, and equivalent magnetic force method are proposed. Besides, the second-order buoyancy is calculated by the three methods mentioned above and measured experimentally. The calculation results are in very good agreement with the experimental results, for all the three methods, the calculation error is less than 7% compared with the numerical range of second-order buoyancy. Both calculation and experimental results show that the second-order buoyancy increases rapidly with the decrease of the axial distance between the bottom of the magnet and the container, and the trend can be fitted well by an exponential function.

Though medical implantable devices are highly suitable for continuous and real-time patient monitoring, their battery replacement is a costly and complicated procedure. To extend the functional life of medical implants, energy harvesting methods have been investigated that convert the motions of the cardiovascular system to electrical energy. In this paper, we present the potential of such an energy harvester to operate as a sensor for cardiovascular parameters estimation, thus enabling the realization of a novel self-powered implantable cardiovascular monitor. This energy harvester is based on electromagnetic induction and exploits a conductive coil that moves along with an artery inside a magnetic field, applied by two permanent ring magnets. A similar device was fabricated and in order to test it, an experimental setup was developed that simulates arterial wall motion. Our in vitro experiments demonstrated that the voltage induced in the coil is linearly related with arterial wall velocity and heart rate (coefficient of determination $R^{2}>0.99$ ). Moreover, the induced voltage was associated with blood pressure and the deforming artery’s radius through a second-order polynomial fit ( $R^{2}>0.99$ ).

High pole number permanent magnet (PM) motors, due to their high torque density, have been receiving considerable attentions in recent years. To achieve an accurate position control in PM machines, resolvers are suggested for industrial applications. Mechanical and electromagnetic considerations in the case of high pole number resolvers lead the machine designers to choose small cores with low slot numbers. This paper proposes two different on-tooth winding configurations to achieve high pole number without increasing the slot numbers, while the accuracy of the detected position is intended to be the maximum value. Variable turn on tooth winding (VTTW) is compared with fractional slot concentrated winding (FSCW) for two-phase machines. By the aid of winding function’s harmonic contents and winding factors, the accuracy of different configurations is analyzed and confirmed by the 3-D time stepping finite-element method. Results show that the wound field resolver equipped with FSCW has higher accuracy than the VTTW. Moreover, it is shown that concentrated winding suffers from sub-harmonics. In this regard, a modification on the rotor winding is performed to decrease the total harmonic distortion of output signals and decrease the estimated position error. In addition, the role of winding layers and displacement angle between them is further investigated in this paper. Finally, a prototype with 20-pole 6-layer FSCW resolver has been constructed. Practical results are in good agreement with the analytical predictions.