Frank Ludwig

Technische Universität Braunschweig

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Co-Authors

Meinhard Schilling

Technische Universität Braunschweig

108

H. Schlarb

Deutsches Elektronen-Synchrotron DESY

Krzysztof Czuba

Warsaw University of Technology

Thilo Viereck

Technische Universität Braunschweig

John Clarke

University of California, Berkeley

Matthias Hoffmann

Deutsches Elektronen-Synchrotron DESY

Uroš Mavrič

Deutsches Elektronen-Synchrotron DESY

Thilo Wawrzik

Technische Universität Braunschweig

E. Dantsker

Torrance Memorial Medical Center

M. Felber

Stanford University

Cooperative Institutions

Deutsches Elektronen-Synchrotron DESY

401

Universität Hamburg

142

Kaiser (Czechia)

125

Technische Universität Braunschweig

European X-Ray Free-Electron Laser

Physikalisch-Technische Bundesanstalt

Technical University of Munich

Centre National de la Recherche Scientifique

Humboldt-Universität zu Berlin

European Organization for Nuclear Research

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Determination of the effective anisotropy constant of magnetic nanoparticles – Comparison between two approaches

Journal of Magnetism and Magnetic Materials (2020)

Tamara Kahmann Enja Laureen Rösch Keiji Enpuku Takashi Yoshida Frank Ludwig

Single domain

10.1016/j.jmmm.2020.167402

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Citations (26)

Investigation of superparamagnetic Fe3O4 nanoparticles by fluxgate magnetorelaxometry for use in magnetic relaxation immunoassays

Journal of Applied Physics (2006)

Frank Ludwig E. Heim Dirk Menzel Martin Schilling

We have investigated the magnetorelaxation (MRX) of various magnetite (Fe3O4) nanoparticle samples with organic shells with regard to their suitability for the realization of a magnetic relaxation immunoassay. The MRX of magnetic nanoparticles (MNP), immobilized by freeze-drying, was measured for magnetization fields between 0.2 and 2.0mT and for magnetization times between 0.2 and 20s using a differential fluxgate setup. The experimental data were analyzed on the basis of the magnetic-moment superposition model, providing information on magnetic properties, such as anisotropy constant and saturation magnetization, on the dynamics of the magnetization and relaxation process, as well as on the size distribution of MNP cores.

Superparamagnetism

Stoner–Wohlfarth model

Saturation (graph theory)

Fluxgate compass

Single domain

10.1063/1.2171121

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Citations (22)

Characterization of superparamagnetic Fe3O4 nanoparticles by fluxgate magnetorelaxometry for use in biomedical applications

Journal of Applied Physics (2008)

Frank Ludwig E. Heim Meinhard Schilling Keiji Enpuku

We have investigated the magnetorelaxometry (MRX) of various Fe3O4 nanoparticle suspensions utilizing a differential fluxgate setup. To estimate the distribution of the hydrodynamic size of the magnetic nanoparticles (MNPs) with organic shell, the cluster moment superposition model is applied. On a sample series of MNPs from the same batch diluted in water-glycerine mixtures of varying viscosity, it is demonstrated that the model is suited for the estimation of the distribution of the hydrodynamic size of MNPs and clusters. Since a MRX measurement lasts only a few seconds, it is also highly suited to study the aggregation kinetics. This is demonstrated on MNPs with silica shell suspended in 5% phosphate-buffered saline solution.

Superparamagnetism

10.1063/1.2840048

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Citations (22)

Precision X-Band RF Control System

Matthias Reukauff Daniel Kühn Markus Hoffmann Uroš Mavrič H. Schlarb

Source

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Tuning Excitation Field Frequency for Magnetic Particle Sensing using Superparamagnetic Quantifier

Journal of Biomedical Nanotechnology (2022)

Melissa Mathilde van de Loosdrecht Tamara Kahmann Frank Ludwig Lejla Alić

Nonlinear handheld detection of magnetic nanoparticles is used to assess the lymph node status of cancer patients. Joint sensitivity and resolving power of nonlinear handheld detection can be maximized by optimizing the frequency of the excitation field, which is strongly influenced by Brownian and Néel relaxation. The characteristic frequency of magnetic nanoparticles that defines sensitivity and resolving power is usually assessed by AC susceptometry. In this study, we used SPaQ data to predict handheld detection performance for magnetic nanoparticles with various particle sizes. SPaQ assesses dynamics by measuring the derivative of the magnetization originating from magnetic nanoparticles activated by an alternating excitation field. The ratio between the maximum signal difference and full-width-at-half-maximumis used to estimate the optimal excitation frequency. Thereupon, it was shown that a particle with a combination of Brownian and Néel relaxation is superior in nonlinear handheld detection compared to Brownian or Néel only particles. Moreover, the optimal excitation frequency is generally established at a slightly higher frequency compared to the characteristic frequency assessed by AC susceptometry. Consequently, this insight into the consequences of the dynamic behavior of magnetic nanoparticles under an alternating magnetic field enables the optimization of nonlinear handheld detection for specific clinical applications.

10.1166/jbn.2022.3406

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DEMONSTRATION OF A BPM WITH 5 MICRON RESOLUTION OVER A 10 CM RANGE

Kirsten Hacker V. Arsov Michael Bock M. Felber Patrick Geßler

At the Free electron LASer in Hamburg (FLASH), six distinct methods to measure the energy of the electron beam have been employed in and around the first bunch compressor chicane. First results from four of the six methods will be presented here and an attempt is made to benchmark all of the measurements against one another. The design and performance of RF phase measurement and EOM sampling schemes for the BPM in the dispersive section of the chicane are also presented in this context. The BPM is required to produce sub-5 um resolution over a 10 cm range, capable of resolving 2*10 -5

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Dipole-Sensitive Homogeneous-Field Compensated High- <inline-formula> <tex-math notation="TeX">$T_{c}$</tex-math></inline-formula> DC SQUID

IEEE Transactions on Applied Superconductivity (2014)

Alexandre Guillaume Frank Ludwig Denis Kajevic Jan M. Scholtyssek M. L. Schilling

Magnetic nanoparticles (MNPs) are of great interest for industrial and medical applications. Therefore, the properties of the particles must be well known. For the measurement of small amounts of particles, a sensor design with high dipole sensitivity is required, whereas homogeneous excitation fields must be shielded or compensated. The spatial dimensions need to be tuned to the sample size in order to maximize the coupling efficiency. In this paper, we present a new sensor design employing a high-T _c YBa ₂ Cu ₃ O ₇ superconducting quantum interference device (SQUID), which is inductively coupled to a surrounding superconducting compensation loop. We choose a square SQUID design that is positioned in the axis of symmetry of the compensation loop in order to compensate spatial homogeneous and first-order gradient magnetic fields. The SQUID is operated in a flux-locked loop (FLL) with bias reversal. We investigate the dependence of the performance on the compensation loop layout. Design limitations are demonstrated, and the SQUID noise is characterized with and without an applied magnetic field.

10.1109/tasc.2014.2359764

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Citations (3)

Dynamic behaviour in suspensions of magnetic nanoplatelets and their liquid crystalline hybrids

Hajnalka Nádasi Alexey Eremin Darja Lisjak Patricija Hribar Boštjančič Frank Ludwig

Ferromagnetic liquid crystalline suspensions of scandium-doped barium hexaferrite (Sc-BaHF) nanoplatelets exhibit intricate magnetic dynamics and robust magnetic response, making them promising for use in novel magnetooptical devices. We explore magnetic dynamics, optical properties and self-assembly of these liquid magnets employing optical imaging and magnetic susceptometry in oscillating (AC) fields. The dynamics of the optical response and the formation of magnetohydrodynamic patterns in AC magnetic fields were studied using optical microscopy. The observations are discussed in the light of magnetic dynamics and orientational order.

10.1117/12.3022290

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Comparison of Superparamagnetic Quantifier and Magnetic Particle Spectroscopy

Melissa Mathilde van de Loosdrecht Sebastian Draack Sebastiaan Waanders Hendrikus J.G. Krooshoop Frank Ludwig

Superparamagnetism

Quantifier (linguistics)

Particle (ecology)

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Citations (1)

Long-term stable microwave signal extraction from mode-locked lasers

Optics Express (2007)

Jungwon Kim Frank Ludwig M. Felber Franz X. Kärtner

Long-term synchronization between two 10.225 GHz microwave signals at +10 dBm power level, locked to a 44.26 MHz repetition rate passively mode-locked fiber laser, is demonstrated using balanced optical-microwave phase detectors. The out-of-loop measurement result shows 12.8 fs relative timing jitter integrated from 10 Hz to 10 MHz. Long-term timing drift measurement shows 48 fs maximum deviation over one hour, mainly limited by drift of the out-of-loop characterization setup itself. To the best of our knowledge, this is the first time to demonstrate long-term (>1 hour) 3 mrad-level phase stability of a 10.225 GHz microwave signal extracted from a mode-locked laser.

SIGNAL (programming language)

Mode-Locking

10.1364/oe.15.008951

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Citations (23)