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Item type:Publication, Access status: with files , Parameter estimation for model-based sensing of magneto-mechanical resonatorsMagneto-mechanical resonators (MMRs) represent a recently proposed type of passive sensor that enables the estimation of its pose as well as sensing other parameters in its environment. The working principle of MMRs entails an excitation of the sensors by oscillating magnetic fields, followed by a readout process facilitated by inductive receiver coils. The sensing technology relies on real-time parameter estimation. This encompasses the solution of a nonlinear inverse problem, with the induced signals and a suitable forward model as inputs. The aim of this paper is twofold: first, to introduce a reference model and simplified models for the MMR dynamics and inductive readout, and second, to provide robust and real-time capable methods to estimate themodel parameters. The effectiveness of the presented methods is evaluated in terms of their real-time potential, precision, and accuracy. All presented methods demonstrate the capacity to estimate the measured signal, with the simplified methods reducing the corresponding parameter estimation time by up to two orders of magnitude at the expense of less than 4% deviation for large maximum deflection angles.Publicationtype: Journal Article21 10 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Randomized greedy Kaczmarz for multi-contrast magnetic particle imaging(Infinite Science Publishing, 2026-03-18); ; ; ; Multi-contrast magnetic particle imaging allows for separating signals from different tracer materials or microenvi-ronments from one joint measurement, yielding multi-channel images that distinguish tracers or encode properties such as temperature or viscosity. However, leakage artifacts enforce a noticeably longer application of iterative standard methods like the Kaczmarz algorithm to reach satisfactory reconstruction results. A greedy randomized version of the Kaczmarz method is adapted, showing the potential for faster recovery.Publicationtype: Journal Article16 9 - 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 16 - 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 Paper95 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 Article24 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: 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 , Wireless and passive pressure detection using magneto-mechanical resonances in process engineering(IOP Publishing, 2025-08-31); ; ; ; A custom-developed magneto-mechanical resonator (MMR) for wireless pressure measurement is investigated for potential applications in process engineering. The MMR sensor utilises changes in the resonance frequency caused by pressure on a flexible 3D printed membrane. The thickness of the printed membrane plays a crucial role in determining the performance and sensitivity of MMRs and can be tailored to meet the requirements of specific applications. The study includes static and dynamic measurements to determine the pressure sensitivity and temporal resolution of the sensor. The results show a minimum sensitivity of 0.06 Hz mbar − 1 and are in agreement with theoretical calculations and measurements. The maximum sensor readout frequency is 2 Hz in this study. Additionally, the temperature dependence of the sensor is investigated, revealing a significant dependence of the resonance frequency on temperature. The developed MMR offers a promising and versatile method for precise pressure measurements in process engineering environments.Publicationtype: Journal Article72 69 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Efficient iterative reconstruction for an MPI equilibrium model with anisotropy(Infinite Science Publishing, 2025-03-14); ; ; Image reconstruction in Magnetic Particle Imaging (MPI) typically requires a system matrix, obtained through a time-consuming calibration process. To bypass this, various model-based approaches have been explored. Recent work demonstrated successful reconstruction by adapting a Chebyshev approach with Tikhonov-regularized least squares (LS) under an equilibrium model with anisotropy. In this study, we introduce an efficient evaluation of the forward and adjoint operators for the anisotropy model, enabling the use of iterative solvers and alternative regularization methods for image reconstruction.Publicationtype: Journal Article15 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