Real-time reaction monitoring with Nuclear Magnetic Resonance (NMR) spectroscopy is an emerging and increasingly important analytical technique. In this work, we develop and implement software to identify molecules and monitor a chemical reaction in real time using a low-field benchtop NMR operating at 24.35 MHz. The approach was validated using a simple acid-catalyzed elimination reaction, the dehydration of cyclohexanol to cyclohexene, and enabled both qualitative and semi-quantitative assessment of the reaction progress. Automated peak integration and yield calculation were performed at each time step, and the results were benchmarked against a high-field 400 MHz Bruker NMR instrument.

This paper describes a 3D electromagnetic tracking (EMT) system, based on quasi-static magnetic fields and a sub-millimeter 3D magnetometer, providing complete localization - both spatial and angular positions - during surgical procedures. By integrating miniaturized sensors into surgical tools, such as deep brain stimulation (DBS) electrodes, this tracking system offers complementary or alternative solutions for X-ray imaging. Each spatial position in the measurement volume (MV) is uniquely encoded by a vector of four magnetic field amplitudes using the multilateration principle. The orientation is derived from the three orthogonal components associated with this vector. The field generator (FG) was manufactured on printed circuit boards ensuring high reproducibility and accurate magnetic fields. Position localization was evaluated using a custom magnetic field camera placed at various positions in the MV while the orientation was evaluating using a stereotactic system used in DBS surgery. Finally, DBS implantations were simulated to conclude on the validity of the tracking system for DBS surgery. The system achieved spatial and angular errors of 1.72 mm and 0.89 degrees within a MV of 15 x 15 x 15 cm3 located at 18 cm from the FG and an update rate of the position of 0.4 Hz. Better performances - mean spatial and angular errors of 0.87 mm and 0.52 degrees - were achieved when simulating DBS implantations. With its large distance to the FG, this quasi-static EMT system is particularly well-suited for DBS surgery, offering regular feedback to neurosurgeons. The tracking system could also be adapted to other functional neurosurgeries.

This article presents the use of nanoscale perpendicular spin transfer torque magnetic tunnel junctions (STT-MTJs) as magnetic sensing units in which the conditioning electronics consists of simple circuits based on operational amplifier (OpAmp). This approach allows low-power ( mu W), nanoscale (50-100 nm), and high-frequency (100-1000 kHz) magnetic measurements, with, in addition, presenting CMOS compatibility for future mass production. Noise levels as low as 2 mu T/ Hz are achieved over a dynamic range of up to tens of milliteslas. The different circuits are demonstrated through theoretical modeling and confirmed with experimental measurements on fabricated devices, validating the working principle with sensing elements among the smallest ever reported to our knowledge. Further improvements are, however, required, in both the proposed electronics and stacks of the junctions, to lower the noise and reach the sub-microtesla noise level. Hence, this technology could open the way to new metrological possibilities, unaddressed with existing technologies, including photolithographic mask alignment or high-frequency current measurements, in the case of industrial applications, as well as measurements of magnetic beads and ferromagnetic particle detection in life sciences.

Magnetic localization does not require line of sight, this makes it suitable for various applications, including indoor navigation, surgical tracking, motion capture, and 3D body scanning. Magnetic localization is typically an inverse problem, in which the magnetic field generated by several sources is measured at a given point, and the goal is to determine the coordinates of that point from these measurements. Multiple approach exists to perform such calculation. In this paper, the focus is put on machine learning algorithms, namely Random Forest and KNearest Neighbors. The results have been shown using simulations for the training of the algorithm and verified on experimental data. A sub-millimeter mean absolute error has been demonstrated on simulated data. A performance gap remains between simulated data and experimental one, partially due intrinsic errors of the machine learning algorithm, but also due to discrepancy between simulation and experiment. This work highlights the potential of machine learning in enhancing the precision and reliability of magnetic localization systems.

PURPOSE:The aim of this paper is to introduce a new magnetic field exposimeter device that consists of goggles equipped with magnetic sensors for the assessment of the field exposure of MRI workers' heads. This is not possible with conventional pocket exposimeters. Hence, this device allows head-level field exposure to be measured, which can induce physiological effects on MRI workers, and which are required to be covered by managing the laboratory-related safety hazards directive 2013/35/EU. METHODS:Using on-chip monolithic three-axis Hall effect magnetometers, recently introduced on the market, we developed an exposimeter with unprecedented accuracy, which allows the measurement of the magnetic field closed to the organs which are the most impacted by strong magnetic fields: the brain, the eyes, and the tongue. RESULTS:The exposimeter prototypes were successfully tested around 3 T, 7 T, and 11.7 T MRI scanners on different workers and volunteers in real conditions. Comparisons with chest-level measurements lead typically to lower values than exposure recorded at the head-level, confirming the need for such head-level assessments. Exposure of the head above the limits established by the directive was also recorded (>2 T or >2.7 T/s). CONCLUSION:This new exposimeter allows for a more accurate assessment of field exposure of MRI workers. Further improvements in the miniaturization and the usability of the exposimeter will allow us to disseminate the device and open the way to a larger-scale study.

Real-time guidance for the implantation of deep-brain-stimulation (DBS) electrodes in the context of stereotactic neurosurgery is essential but currently unavailable. Electromagnetic tracking (EMT) systems offer high-accuracy localization of tools in restricted volumes but face compatibility issues with stereotactic procedures due to electromagnetic distortions. This paper aims to evaluate and compare the localization performance (position and orientation) of a novel EMT system, the ManaDBS, specifically designed for stereotactic surgical environments, against the NDI Aurora, a commercially available EMT system. Two studies were conducted to assess the suitability of each EMT system for stereotactic DBS surgery. The first study evaluated performance accuracy within the measurement volume in the presence of two different stereotactic systems (Frame G and Vantage system, Elekta). The second study simulated a DBS surgical theater, performing implantation procedures with each EMT system and evaluating the position accuracy of the EMT sensor. The localization errors of Aurora (0.66 mm and 0.89°) were lower to those of ManaDBS (1.57 mm and 1.01°). However, in the presence of a stereotactic system, Aurora exhibited notable degradation (2.34 mm and 1.03°), whereas ManaDBS remained unaffected. This pattern persisted during simulated implantation in a DBS surgical environment, where nonlinear trajectories with significant error fluctuations along the implantation path were observed with Aurora system. The significant electromagnetic-field distortions render the Aurora system incompatible for stereotactic DBS surgery. However, the ManaDBS system exhibited no impact from these distortions, suggesting its potential suitability for DBS surgery and other potential applications in stereotactic neurosurgery.

Electromagnetic navigation systems (ENS) provide a promising solution for tracking electrode positioning during deep brain stimulation (DBS) surgery, enhancing precision and potentially improving clinical outcomes. Recent studies suggest that novel ENS based on quasi-static magnetic fields may be compatible with the DBS surgical environment, particularly with stereotactic systems — the gold standard for electrode implantation. However, a key challenge persists: ensuring seamless integration into the surgical workflow requires an efficient and reliable patient-to-image registration system. In this study, we present a novel registration system tailored for stereotactic procedures. The system employs flexible markers attached to the stereotactic frame, incorporating magnetic sensors and wireless communication to enable seamless interaction with the surgical environment. These markers are visible on preoperative computed tomography (CT) scans, eliminating the need for additional intraoperative imaging. The registration method demonstrated robust performance with automatic segmentation of the markers on CT images, achieving an average point matching error of 1.51 mm. During implantation tests, the system localized the ENS sensors with a target registration error of 2.54 ± 0.92 mm. This innovative navigation approach ensures precise localization, reducing reliance on repeated CT imaging for verification, thus streamlining the surgical workflow. Clinical Relevance— This proposes a registration-free approach for stereotactic neurosurgery, enabling the monitoring of electrode position and orientation during implantation.

Evaluating experimentally the human exposure to time varying magnetic fields is often complex due to the strongly non-homogeneous magnetic field observed near electromagnetic devices. This study investigates the use of an in-house ac magnetic field camera (MFC) to map the exposure coefficients defined by standards and guidelines (ICNIRP and ICES). As a case study this paper reports on the spatial distribution of the magnetic field exposure coefficients of a neurosurgical tracking system. Although initial field strengths were low, the frequency analysis revealed that exposure coefficients exceeded recommended limits in worst-case scenarios. To mitigate this, a bandwidth limitation of the magnetic field generated by the tracking system was implemented effectively reducing exposure levels. These results highlight the importance of optimized system design and signal processing to ensure compliance with safety standards in surgical applications.

This article presents a magnetic tracking system using on-chip anisotropic magnetoresistive (AMR) sensors. The system consists of four air-core coils sequentially generating four dc magnetic fields. The implemented localization algorithm is quadrilateration, and the accuracy of the system is dependent on the accuracy of the sensors and the simulated field maps. The performance of the system was evaluated using an in-house magnetic field camera (MFC), and the results showed that the system exhibits mean Euclidean errors below 1 mm where the source produces strong gradients. Given the dimensions of the sensors (0.82 × 0.82 mm2), this system is suitable for tracking minimally invasive surgical tools.

Iron detection plays a crucial role across various scientific and industrial fields due to its significant impact on health, safety, or product quality. Despite its importance, iron detection raises several challenges, including the need for highly sensitive and accurate measurement techniques. In this paper, we propose a novel iron detection method based on a custom magnetic field camera (MFC) specifically designed for high-resolution and synchronous measurements. The MFC includes an array of 8 x 8 monolithic integrated magnetic sensors with a resolution of 42 nT, enabling the detection of iron, for instance, in food samples or iron particles, in both static and dynamic conditions. Operating at a sampling rate of 110 Hz, this MFC paves the way for new metrological opportunities.

Tactile sensing in the human body is achieved via the skin. This has inspired the fabrication of synthetic skins with pressure sensors for potential applications in robotics, bio‐medicine, and human–machine interfaces. Tactile sensors based on magnetic elements are promising as they provide high sensitivity and a wide dynamic range. However, current magnetic tactile sensors mostly detect pressures of solid objects and operate at relatively high forces about 100 mN. Herein, these limitations are addressed by manufacturing soft, stretchable, and hair‐like structures that are permanently magnetized to achieve high‐resolution, cost‐effective, and high‐resolution pressure sensing. Combining these hair‐like structures with advances in 3D magnetic‐field measurements allows us to monitor directional tactile pressures without solid contact. To prove the concept of this technology, a bio‐inspired soft device is built with a hairy structure that senses and reports environmental mechanical stresses, similar to that of human skin. Simple self‐assembly of the soft magnetic hair structure makes our approach easy to scale for large‐area applications.

Abstract The aim of this study was to compare the use of static magnetic field (SMF) body-worn exposure monitors equipped with single or spatially distributed probes. The SMF exposure monitor allow to study the time-pattern of head movement-related exposure to SMF (B, mT; dB/dt, mT/s) while active near 1.5 T and 7 T magnetic resonance imaging (MRI) magnets. When analysing the distribution of B-field samples recorded during a simple walk around MRI magnets, using relevant statistical tests it was found that the results recorded by various probes are statistically significantly different. The observed scale of differences between the results from various probes revealed the possible misclassification of localised exposure of particular head sections when only a single probe is used to evaluate exposure (especially with respect to dB/dt values). Larger differences between probes were found in recordings near MRI magnets of smaller dimensions (1.5 T).

Optically pumped magnetometers represent a breakthrough in magnetic measurements, enabling new applications across various fields including medicine. In this paper, we propose a novel electromagnetic tracking approach using optically pumped magnetometers to detect ac magnetic fields generated by small, thin, and flexible coils with sub-nanotesla noise levels. This approach could facilitate tasks such as catheter localization, monitoring of endoscopic capsules, and capturing object shapes without a line of sight. This first proof-of-concept demonstrates a position error of less than 3 mm in two dimensions. In addition, we investigated the impact of coil bending on tracking error, which is crucial for applications where the coil deforms during tracking. While similar tracking performance was observed up to 60 degrees of bending, larger curvatures resulted in a significant rise in the tracking error.

This letter demonstrates the use of an field-programmable gate array and commercially available Hall effect magnetic field sensors to create a magnetic field camera offering high-speed capability for ac measurements. The achieved performance of the presented camera reaches 7 kHz of sampling rate over an array of 7 x 7 sensors, covering an area of 56 mm x 56 mm (31.36 cm(2)), synchronously sampled with a recording capability of up to 10 hours on X-, Y-, and Z-axes. The sensors exhibit a dynamic range of +/- 266 mT, and a typical rms noise of 140 mu T (peak-to-peak noise of 1 mT). Through its synchronous sampling capability and 7 kHz sampling rate, this camera fills a gap observed in the field of magnetic field cameras, in which mainly dc applications were addressed up to now. This opens the way to new metrological possibilities in several domains, ranging from industrial and physics applications to biomedical engineering.

Nuclear magnetic resonance spectroscopy is a technique for the identification and the quantification of chemical molecules in a sample that has been perfectly established for decades. The transition from laboratory NMR to portable NMR for in-field measurements present a quite high number of technological challenges. One of them is the synchronization between signals emitted and received by the device during NMR measurement. With the use of on-the-shelf hardware, such as software defined radio which drastically reduces development costs, distortion might be introduced due to latencies between several Free Induction Decay (FID) recordings, preventing direct FID accumulation for NMR spectrums improvement. The aim of this paper is to study a software method that compensates the latencies, thus enabling NMR signal accumulation. This technique has been tested in simulation and has proved effective even when signal-to-noise ratios are below 0 dB.

Significant progress has been made in the development of magnetic micromanipulation for minimally invasive surgery. The development of systems to localize millimeter-sized robots during magnetic manipulation without line-of-sight detection remains, however, a challenging task. In this study, we focused on the development of a tracking system aiming to fill this gap. A robot which consists of a cylindrical magnet of 1 mm diameter is localized using a 2D array of 3D magnetoresistive sensors. The system, also called magnetic field camera, provides tracking of the robot with a refresh rate of 2 Hz. The developed tracking algorithm reaches a mean absolute error for the position and the orientation of, respectively 0.56 mm and 5.13° in 2D. This system can be added to existing magnetic manipulation systems allowing closed loop control of the navigation. The performances of the magnetic field camera are not affected by an exposure to strong magnetic fields. Exposures up to 3 T have been validated. Increasing the integrability of the magnetic field camera into magnetic manipulation systems. The presented tracking system makes it possible to target applications such as minimally invasive eye surgery or drug delivery. The high spatial and magnetic resolutions allow the tracking of magnetic particles, down to 200 μm diameter, when placed close to the surface. The system could also be suitable for the localization of small objects for 2D biomanipulation.

This article demonstrates a new type of magnetic sensor using a perpendicular spin transfer torque magnetic tunnel junction (MTJ). The sensing element has a cylindrical shape of 50 nm in diameter and is to our knowledge among the smallest magnetic sensor ever reported. This article describes the principle of operation of the sensing element and the associated signal processing electronics, which delivers a signal proportional to the external magnetic field. Experimental results are detailed and compared to the state-of-the-art commercially available integrated magnetic sensors as well as published magnetoresistive sensors based on MTJs with comparable size. The measured sensitivity of the developed sensor is 1.28 V/T, and its dynamic range reaches 80 mT. The measured noise level is $21.8\,\mu \text{T}/\surd $ Hz. Two different operating principles of the proposed sensor are described and compared, one based on a time-to-digital converter and one based on a pulsewidth-modulated (PWM) signal. Both methods require only standard microelectronics components, which are suitable for monolithic integration of the sensing element with its conditioning electronics. Subsequent improvements of the sensing element as well as conditioning electronics are required to further lower the noise level. The sensing element and its conditioning electronics are compatible with fabrication processes already used in magnetic random access memory fabrication. This opens the way to mass production and addresses various markets, such as consumer electronics, automotive, industrial sensing, physics experiments, or medical devices.

Remote magnetic navigation (RMN) offers various possibilities for medical interventions. Magnetic catheters can be wirelessly steered with high precision and accuracy through complex structures, as they are generally more dexterous and flexible than their manually steered counterparts. Position feedback is essential for many tasks. However, most of the commercially available systems do not integrate well with the magnetic navigation systems (MNSs). As a result, fluoroscopy is still widely used in many interventions despite the known associated health risks. In this study, we propose a localization method that uses multiple Hall sensors to measure the magnetic fields produced by the MNS and estimate the full sensor pose without the need for a separate dedicated mapping system. This makes the MNS a two-in-one system that can be used for simultaneous navigation and localization of a medical tool. We perform an optimization of the sensors' array design in simulation and investigate the influence of the magnetic fields and gradients on the localization accuracy to provide information on the minimal requirements for an MNS for this task.

This paper presents the use of the spin transfer torque effect in perpendicular magnetic tunnel junctions to operate the devices as magnetic sensors. The junctions, specifically designed for sensing applications exhibit close to low-coercivity, allowing the sensitivity to be as high as 25 mV/mT for a large dynamic range of 20 mT. In addition, the junctions have diameters ranging from 20 to 100 nanometers, making them among the smallest magnetic sensing elements ever reported to our knowledge. A single operational amplifier operates the junction and outputs a voltage proportional to the external magnetic field. This paper opens the way to a monolithic integration of both the conditioning electronics and the perpendicular magnetic tunnel junction.

This article describes an alternative to high-field electromagnetic tracking system, by using low consumption generator and high-performance magnetic sensors. Monotonically varying magnetic fields over three positions are created to produce magnetic field gradients, which encode each spatial point uniquely. Millimetric size sensors capable of measuring their local magnetic field with high resolution are used to sense the gradient field. Such sensors can be embedded in surgical tools, such as catheters or brain electrodes. With a low power consumption and low-field generator, the integrability of the electromagnetic system in a surgical theater is greatly enhanced. This system leads to unambiguous and orientation-independent spatial encoding with a mean absolute error of 3 mm at 42 cm from the field generator using the last generation 3-D axis magnetoresistive sensors. A calibration of the sensors was performed and leads to significant improvement in the localization over the $Z$ -axis.