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Item type:Publication, Access status: with files , Topology considerations for an iron-core coil module field generator(Infinite Science Publishing, 2026-03-18); ; ; ; The selection-field generator of a Magnetic Particle Imaging (MPI) scanner is typically the system’s largest power consumer. For potential use in intensive care units, it would be highly desirable to operate MPI scanners from a standard wall outlet without dedicated high-power infrastructure. Several concepts for more efficient selection-field generation have been proposed in recent years. In this work, we propose a novel generator design based on an array of soft-iron core coils arranged at an angle around the scanner bore. This geometry reduces overall electrical power demand while enabling gradient strengths of up to 0.5 T m¹. The design was simulated and optimized using magnetostatic simulations in COMSOL Multiphysics. To ensure reliable modeling of the soft-iron cores, prototype coils were built and their magnetic fields were measured, providing experimental validation of the simulation models.Publicationtype: Journal Article7 7 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Coordinate transformations for magnetic fields’ solid spherical harmonic coefficientsMagnetic particle imaging fundamentally relies on magnetic fields, so accurate characterization of the fields is crucial for various applications, such as sequence planning or model-based reconstructions. Magnetic fields can be compactly represented by solid harmonic expansions, whose coefficients efficiently describe the field distribution. However, in practice, the coordinate systems of measurement devices are not always perfectly aligned with the scanner’s coordinate system, complicating direct comparison and integration of measured data from different setups. In this work, we present methods for transforming solid harmonic coefficients under translations, rotations, and point reflections. These transformations enable consistent mapping of field representations into a common coordinate system, allowing direct comparison of magnetic fields obtained in different coordinate frames.Publicationtype: Conference Paper10 15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Simulating Gadolinium-induced magnetic field variations for temperature sensing with magneto-mechanical resonatorsSmall-size magneto-mechanical resonators (MMR) represent an emerging class of passive, wireless sensors that combine a sensing functionality with a tracking option. The operation principle is based on a resonating rotor oscillation whose frequency is defined by the magnetic flux density of a stator magnet. One general sensing mechanism is the coupling of an external parameter to this resonator frequency. In this study, we investigate an approach for encoding a temperature information as a shift in the natural oscillation frequency utilizing the temperature-dependent magnetic properties of gadolinium (Gd). We perform an isolated simulation study on the temperature scaling of the magnetic field generation for stators coated with Gd of varying thickness. Our results show that the magnetic phase transition of Gd at its Curie temperature leads to a pronounced change in the magnetic permeability enabling a significant magnetic shielding behavior only for lower temperatures. In the transition regime, we find a peak sensitivity reaching 45.8 Hz/K exceeding existing values from the literature by up to a factor of 20. The findings of this work are an important step toward quantitative high-sensitivity temperature extraction with MMRs.Publicationtype: Conference Paper94 45 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , 3D magnetic field camera with sub-second temporal resolution(IEEE, 2026-01-01); ; ; ; Accurate and efficient volumetric magnetic field measurements are essential for a wide range of applications. Conventional methods are often limited in terms of measurement speed and applicability, or suffer from scaling problems at larger volumes. This work presents a proof-of-concept field camera designed to measure magnetic fields within a spherical volume at a frame rate of 10 Hz. The camera features an array of 3D Hall magnetometers positioned according to a spherical t-design, allowing simultaneous magnetic field data acquisition from the surface of the sphere. The approach enables the efficient representation of all three components of the magnetic field inside the sphere using a sixth-degree polynomial, significantly reducing measurement time compared to sequential methods. This work details the design, calibration, and measurement methods of the field camera. To evaluate its performance, we compare it to a sequential single-sensor measurement by examining a magnetic gradient field. The obtained measurement uncertainties of approx. 1% demonstrate the feasibility of the approach and its potential applicability to a variety of future applications.Publicationtype: Journal Article23 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Efficient measurement and representation of magnetic fields in tomographic imaging using ellipsoidal harmonics(2025-12-01); ; ; ; Given the pivotal role of magnetic fields in modern medicine, there is an increasing necessity for a precise characterization of their strength and orientation at high spatial and temporal resolution. As source-free magnetic fields present in tomographic imaging can be described by harmonic polynomials, they can be efficiently represented using spherical harmonic expansions, which allows for measurement at a small set of points on a sphere surrounding the field of view. However, the majority of closed-bore systems possess a cylindrical field of view, making a sphere an inadequate choice for coverage. Ellipsoids represent a superior geometrical choice, and the theory of ellipsoidal harmonic expansions can be applied to magnetic fields in an analogous manner. Despite the mathematical principles underpinning ellipsoidal harmonics being well-established, their utilization in practical applications remains relatively limited. In this study, we present an effective and flexible approach to measuring and representing magnetic fields present in tomographic imaging, which draws upon the theory of ellipsoidal harmonic expansions.Publicationtype: Journal Article27 18 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Uncertainties of a spherical magnetic field cameraSpherical harmonic expansions are well-established tools for estimating magnetic fields from surface measurements and are widely used in applications such as tomographic imaging, geomagnetism, and biomagnetism. Although the mathematical foundations of these expansions are well understood, the impact of real-world imperfections, on the uncertainty of the field model has received little attention. In this work, we present a systematic uncertainty propagation analysis for a magnetic field camera that estimates the field from surface measurements using a spherical array of Hall magnetometers arranged in a spherical t-design. A Monte Carlo-based approach is employed to quantify how sensor-related uncertainties, such as calibration errors and positioning inaccuracies, affect the spatial distribution of the estimated field's uncertainty. The results offer insights into the robustness of spherical harmonic methods and help identify the dominant sources of uncertainty in practical implementations.Publicationtype: Conference Paper29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Natural frequency dependency of magneto-mechanical resonators on magnet distanceThe precise derivation of physical quantities like temperature or pressure at arbitrary locations is useful in numerous contexts, e.g. medical procedures or industrial process engineering. The novel sensor technology of magneto-mechanical resonators (MMR), based on the interaction of a rotor and stator permanent magnet, allows for the combined tracking of the sensor position and orientation while simultaneously sensing an external measurand. Thereby, the quantity is coupled to the torsional oscillation frequency, e.g. by varying the magnet distance. In this paper, we analyze the (deflection angle-independent) natural frequency dependency of MMR sensors on the rotor-stator distance, and evaluate the performance of theoretical models. The three presented sensors incorporate magnets of spherical and/or cylindrical geometry and can be operated at adjustable frequencies within the range of 61.9-307.3 Hz. Our proposed method to obtain the natural frequency demonstrates notable robustness to variations in the initial deflection amplitudes and quality factors resulting in statistical errors on the mean smaller than 0.05%. We find that the distance-frequency relationship is well described by an adapted dipole model accounting for material and manufacturing uncertainties. Their combined effect can be compensated by an adjustment of a single parameter which drives the median model deviation generally below 0.2%. Our depicted methods and results are important for the design and calibration process of new sensor types utilizing the MMR technique.Publicationtype: Journal Article61 53 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Current-to-field prediction for non-linear magnetic systems via neural networks(Infinite Science Publishing, 2025-03-14); ; ; ; Accurate magnetic field knowledge is crucial for magnetic particle imaging, affecting performance estimation, sequence generation, and reconstruction. Especially for non-linear field generators, such as those with built-in soft iron, conventional field simulations, such as the finite element method, are computationally demanding. We propose the use of neural networks to predict the coefficients of the spherical harmonic expansions of the fields from the input currents, drastically speeding up current-to-field prediction.Publicationtype: Journal Article8 15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Power-efficient control of non-linear magnetic field generators for MPI(Infinite Science Publishing, 2025-03-14); ; ; The scaling of electrical power constitutes a significant challenge when adapting Magnetic Particle Imaging (MPI) to a human scale. The use of coils incorporating soft-iron cores serves to reduce power usage, but also introduces spatial imperfections and non-linearities in the current-to-field relationship. This study proposes methodologies for the control of the magnetic field output of a system comprising 18 coils, subject to the influence of saturated iron. In particular, we integrate current sequence optimization with neural network-based predictions for field and gradient values, thereby enabling the precise and power-optimal generation of magnetic fields. The proposed framework for controlling non-linear magnetic field generators represents a significant advancement in MPI technology, paving the way for the development of human-scale, power-efficient medical imaging solutions.Publicationtype: Journal Article7 9 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Experimental study on efficient field measurement using ellipsoidal harmonicsThis work demonstrates the application of ellipsoidal harmonic expansions for magnetic field representation in Magnetic Particle Imaging (MPI) using measured data. While previous studies focused on simulated fields, we validate the method with field data acquired from a selection field generator of an MPI head imaging system using an ellipsoidal t-design. The approach is validated by comparing the harmonic expansion results to dense principal axis measurements, confirming accurate field characterization. This study highlights the potential of ellipsoidal harmonics to improve the speed and accuracy of magnetic field measurements and representation in MPI.Publicationtype: Journal Article4 8