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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: without files , Transmit-receive circuit concepts for magneto-mechanical resonatorsPassive wireless sensors are crucial in modern medical and industrial settings to monitor procedures and conditions. We present two circuit concepts for the inductive excitation and signal reception of magneto-mechanical resonators, which are integrated into a transmit-receive signal chain. The focus is on comparing the concepts with respect to their ability to deliver power at different frequencies and to receive signals. Additional necessary components of the signal chain are illustrated for the full system context but not analyzed in detail. Instrumentation and design aim to be scalable for multi-channel arrays, using either off-the-shelf class-D audio amplifiers or a custom H-bridge.Publicationtype: Conference Paper39 - 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 Article23 19 - 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 , 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 , Model-based reconstruction in MPI accounting for field imperfections(Infinite Science Publishing, 2025-03-14); ; ; ; To date a system matrix has to be obtained through a tedious calibration measurement when employing a system matrix-based reconstruction in magnetic particle imaging. This problem can be effectively addressed by model-based reconstruction, which takes into account both particle and scanner parameters. In this study, we focus on the scanner parameters and in particular on the fact that the fields of experimental systems are imperfect. For experimental Lissajous-type data we show that the modeling error can be substantially reduced by about 18 % by incorporating field imperfections in both the transmit and receive coils.Publicationtype: Journal Article5 12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Empirical study of magnet distance on magneto-mechanical resonance frequency(De Gruyter, 2024-12-19); ; ; ; Determining the position and orientation of amedical instrument is essential for accurate procedures in en-doscopy, surgery, and vascular interventions. Recently, a novelsensor based on torsional pendulum-like magneto-mechanicalmotion has been proposed. This sensor is passive, wireless andinductively coupled to a transmit-receive coil array. This setupallows the determination of all 6 degrees of freedom usingthe characteristic resonance of the sensor. Additional physicalquantities such as temperature and pressure can be measuredbased on the frequency of the sensor, which mainly dependson the distance between the two involved permanent magnets.In this study, we analyze a sensor composed of two magneticcylinders with variable magnet-to-magnet distance and a basicphysical model based on a dipole assumption. Experimentalanalysis of the resonance frequency and comparison with themodel values show both qualitative and quantitative agreementwith an average relative error of only 0.8 %. This validates theimplemented model and shows the suitability of our magnetic-mechanical resonator made from cylindrical permanent mag-nets for sensing applications.Publicationtype: Journal Article24 69 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Design and Optimization of a Magnetic Field Generator for Magnetic Particle Imaging with Soft Magnetic MaterialsMagnetic field generators are a key component of Magnetic Particle Imaging (MPI) systems, and their power consumption is a major obstacle on the path to human-sized scanners. Despite their importance, a focused discussion of these generators is rare, and a comprehensive description of the design process is currently lacking. This work presents a methodology for the design and optimization of selection field generators operating with soft magnetic materials outside the linear regime in the context of MPI. Key elements are a mathematical model of magnetic field generators, a formalism for defining field sequences, and a relationship between power consumption and field sequence. These are used to define the design space of a field generator given its system requirements and constraints. The design process is then formulated as an optimization problem. Subsequently, this methodology is then utilized to design a new magnetic field generator specifically for cerebral imaging studies. The optimization result outperforms our existing MPI field generator in terms of power consumption and field of view size, providing a proof-of-concept for the entire methodology. As the approach is very general, it can be extended beyond the MPI context to other areas such as magnetic manipulation of medical devices and micro-robotics.Publicationtype: Journal Article17 10