Stefan Goetz

Stefan Goetz
Duke University | DU

About

91
Publications
9,059
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,302
Citations
Citations since 2016
48 Research Items
1086 Citations
20162017201820192020202120220100200300
20162017201820192020202120220100200300
20162017201820192020202120220100200300
20162017201820192020202120220100200300

Publications

Publications (91)
Article
The temporal shape of a pulse in transcranial magnetic stimulation (TMS) influences which neuron populations are activated preferentially as well as the strength and even direction of neuromodulation effects. Furthermore, various pulse shapes differ in their efficiency, coil heating, sensory perception, and clicking sound. However, the available TMS...
Preprint
Objective. Transcranial magnetic stimulation (TMS) with monophasic pulses achieves greater changes in neuronal excitability but requires higher energy and generates more coil heating than TMS with biphasic pulses, and this limits the use of monophasic pulses in rapid-rate protocols. We sought to design a stimulation waveform that retains the charac...
Article
Full-text available
Precisely timed activation of genetically targeted cells is a powerful tool for the study of neural circuits and control of cell-based therapies. Magnetic control of cell activity, or ‘magnetogenetics’, using magnetic nanoparticle heating of temperature-sensitive ion channels enables remote, non-invasive activation of neurons for deep-tissue applic...
Article
Background: Motor-evoked potentials (MEP) are one of the most prominent responses to brain stimulation, such as supra-threshold transcranial magnetic stimulation (TMS) and electrical stimulation. Understanding of the neurophysiology and the determination of the lowest stimulation strength that evokes responses requires the detection of even smalle...
Article
Full-text available
Implantable bioelectronic devices for the simulation of peripheral nerves could be used to treat disorders that are resistant to traditional pharmacological therapies. However, for many nerve targets, this requires invasive surgeries and the implantation of bulky devices (about a few centimetres in at least one dimension). Here we report the design...
Article
Objective: We present a combination of a power electronics system and magnetic nanoparticles that enable frequency-multiplexed magnetothermal-neurostimulation with rapid channel switching between three independent channels spanning a wide frequency range. Approach: The electronics system generates alternating magnetic field spanning 50 kHz to 5...
Article
Full-text available
Neuromuscular magnetic stimulation is a promising tool in neurorehabilitation due to its deeper penetration, notably lower distress, and respectable force levels compared to surface electrical stimulation. However, this method faces great challenges from a technological perspective. The systematic design of better equipment and the incorporation in...
Article
Objective Investigate the variability previously found with cortical stimulation and handheld transcranial magnetic stimulation (TMS) coils, criticized for its high potential of coil position fluctuations, bypassing the cortex using deep brain electrical stimulation (DBS) of the corticospinal tract with fixed electrodes where both latent variations...
Article
Full-text available
The past 50 years witnessed the inventions of more than one thousand power electronic topologies. However, we still lack a common standard to compare and classify various topologies. Moreover, topologies are often created through intuition rather than systematic approaches. The intuition of voltage and current sharing, along with modularity and sca...
Article
Full-text available
Modular cascaded circuits offer attractive qualities in reconfigurable battery applications, including improved fault tolerance and flexibility. In contrast to conventional hard-wired dc battery packs, however, cascaded topologies, such as modular multilevel circuits (MMC) with serial or serial and parallel connectivity, load modules with substanti...
Article
Full-text available
Electric vehicle (EV) charging infrastructure will play a critical role in decarbonization during the next decades, energizing a large share of the transportation sector. This will further increase the enabling role of power electronics converters as an energy transition technology in the widespread adoption of clean energy sources and their effici...
Preprint
Neuromuscular magnetic stimulation is a promising tool in neurorehabilitation due to its deeper penetration, notably lower distress, and respectable force levels compared to electrical stimulation. However, this method faces great challenges from a technological perspective. The systematic design of better equipment and the incorporation into moder...
Preprint
Background: Motor-evoked potentials (MEP) are one of the most prominent responses to brain stimulation, such as supra-threshold transcranial magnetic stimulation (TMS) and electrical stimulation. Understanding of the neurophysiology and the determination of the lowest stimulation strength that evokes responses requires the detection of even smaller...
Preprint
Objective Persons with tetraplegia can use brain-machine interfaces to make visually guided reaches with robotic arms. Without somatosensory feedback, these movements will likely be slow and imprecise, like those of persons who retain movement but have lost proprioception. Intracortical microstimulation (ICMS) has promise for providing artificial s...
Conference Paper
Full-text available
Preprint
Objective: This article presents a novel transcranial magnetic stimulation (TMS) pulse generator with a wide range of pulse shape, amplitude, and width. Approach: Based on a modular multilevel TMS (MM-TMS) topology we had proposed previously, we realized the first such device operating at full TMS energy levels. It consists of ten cascaded H-bridge...
Preprint
Objective We present a power electronic system and magnetic nanoparticles for multiplexed magnetogenetic neurostimulation with three channels spanning a wide frequency range and rapid channel switching capability. This enables selective heating of magnetic nanoparticles with different coercivity using various frequency–amplitude combinations of the...
Article
Full-text available
Cascaded-bridge converters (CBCs) and modular multilevel converters (MMCs) enjoy growing popularity mostly due to modularity and scalability. Conventionally, their submod-ules allow only serial and bypass operation so that the use of low-voltage components for high-voltage output becomes possible. Dually, submodule parallelization adds switched-cap...
Preprint
Full-text available
Precisely timed activation of genetically targeted cells is a powerful tool for studying neural circuits and controlling cell-based therapies. Magnetic control of cell activity or "magnetogenetics" using magnetic nanoparticle heating of temperature-sensitive ion channels enables remote, non-invasive activation of neurons for deep-tissue application...
Preprint
Full-text available
Precisely timed activation of genetically targeted cells is a powerful tool for studying neural circuits and controlling cell-based therapies. Magnetic control of cell activity or “magnetogenetics” using magnetic nanoparticle heating of temperature-sensitive ion channels enables remote, non-invasive activation of neurons for deep-tissue application...
Article
After approximately a decade of electric vehicles entering the mainstream car market, technological developments and coordinated efforts from private and public sectors are shaping a healthy ecosystem. A growing charging infrastructure offers a wide spectrum of charging options, allowing to accommodate various profiles of EV drivers. This paper pro...
Article
This work aims to reduce the acoustic noise level of transcranial magnetic stimulation (TMS) coils. TMS requires high currents (several thousand amperes) to be pulsed through the coil, which generates a loud acoustic impulse whose peak sound pressure level (SPL) can exceed 130 dB(Z). This sound poses a risk to hearing and elicits unwanted neural ac...
Article
The large-scale deployment of grid-tied power elec-tronic converters in renewable generation, electric motor drives, and energy storage systems, speeds up the global energy transi-tion. However, the stability problems faced by power converters in weak grids, which feature large and variable grid impedances, stand as a serious challenge that has puz...
Article
Since the introduction of modular multilevel converters (MMC), various additional features have been intro-duced for MMCs, among them parallel inter-module connectivity. However, such a parallel mode requires appropriate modulation and switching strategies to ex-ploit its full potential. Low-frequency switching modula-tion is widely used with half-...
Article
Full-text available
In more-electronics power systems, grid-forming power converters regulate the grid frequency and voltages in replacement of synchronous generators. Notably, grid impedances greatly influence the small-signal and voltage stability of grid-forming converters. As such, prior knowledge of grid impedances can be very helpful for controller design. Howev...
Preprint
Objective: This work aims to reduce the acoustic noise level of transcranial magnetic stimulation (TMS) coils. TMS requires high currents (several thousand amperes) to be pulsed through the coil, which generates a loud acoustic impulse whose peak sound pressure level (SPL) can exceed 130 dB(Z). This sound poses a risk to hearing and elicits unwante...
Article
Full-text available
H-bridge-based multilevel converters (e.g., cascaded H-bridge converters) benefit from modularity and scalability. However, they suffer from the complexity and costs associated with a large count of semiconductor switches, together with their drivers and peripheral circuits, as well as higher conduction losses as compared to half-bridge-based count...
Article
Full-text available
This paper proposes a novel bipolar-type dc system suitable for both distribution and transmission systems based on Modular Multilevel Series/Parallel Converters. The system features decoupled operations of each pole of the bipolar system, being able to operate in both asymmetrical and regenerative modes. This enables two independent dc systems by...
Article
Although existing interleaved discontinues pulse width modulation (IDPWM) maintains the minimum switching loss and line current ripples, it introduces a larger zero-sequence circulating current (ZSCC). For the application with a larger current, it is desirable to reduce the ZSCC of IDPWM while maintaining minimum switching times and line current ri...
Article
Split-battery converters based on cascaded H-bridges (CHBs) are gaining popularity due to their excellent physical modularity. During operation, however, the batteries experience substantial current ripple. Conventional ripple-current reduction methods rely on bulky passive components or complicated control. This article presents modulation and com...
Article
This paper aims at reducing the root mean square (RMS) values of the zero-sequence circulating current (ZSCC). The analysis reveals that the ZSCC is determined by the duty ratios of the medium voltage vector and zero vector. Whereas the reference voltage fixes the duty ratio of the medium vector, the duty ratio of the zero-voltage vector depends on...
Article
Full-text available
Background Accurate data on the sound emitted by transcranial magnetic stimulation (TMS) coils is lacking. Methods We recorded the sound waveforms of seven coils with high bandwidth. We estimated the neural stimulation strength by measuring the induced electric field and applying a strength–duration model to account for different waveforms. Resul...
Preprint
Background Transcranial magnetic stimulation (TMS) is a noninvasive brain stimulation technique used for research and clinical applications. Existent TMS coils are limited in their precision of spatial targeting (focality), especially for deeper targets. Objective This paper presents a methodology for designing TMS coils to achieve optimal trade-o...
Article
Magnetic stimulation is a non-invasive neurostimulation technique that can evoke action potentials and modulate neural circuits through induced electric fields. Biophysical models of magnetic stimulation have become a major driver for technological developments and the understanding of the mechanisms of magnetic neurostimulation and neuromodulation...
Article
This paper presents a multi-objective real-time controller for a modular multilevel converter capable of parallel module connectivity, the so called modular multilevel series parallel converter (MMSPC). The MMSPC topology allows the batteries to be dynamically rewired in various series-parallel configurations, generating a wide range of output volt...
Conference Paper
Appropriate isolated supply solutions for recent power converters, such as distributed smartgrid units or modular multilevel converters, have to provide sufficient power reserve, but often suffer from low efficiency at partial load, causing unnecessary large power loss in the converter control unit. Particularly in modular multilevel converters, th...
Article
OBJECTIVE: To compare the strength–duration (S–D) time constants of motor cortex structures activated by current pulses oriented posterior–anterior (PA) or anterior–posterior (AP) across the central sulcus. METHODS: Motor threshold and input–output curve, along with motor evoked potential (MEP) latencies, of first dorsal interosseus were determined...
Conference Paper
A significant limitation of transcranial magnetic stimulation (TMS) is that the magnetic pulse delivery is associated with a loud clicking sound as high as 140 dB resulting from electromagnetic forces. The loud noise significantly impedes both basic research and clinical applications of TMS. It effectively makes TMS less focal since every click act...
Chapter
This chapter provides overview of the state of the art of transcranial magnetic stimulation (TMS) devices, including pulse sources with flexible control of the output waveform parameters and a wide variety of coil designs. It discusses technologies for accurate TMS targeting, including electric field models, frameless stereotaxy, and robotic coil h...
Article
Full-text available
To compare the strength-duration (S-D) time constants of motor cortex structures activated by current pulses oriented posterior-anterior (PA) or anterior-posterior (AP) across the central sulcus. Motor threshold and input-output curve, along with motor evoked potential (MEP) latencies, of first dorsal interosseus were determined at pulse widths of...
Article
Purpose We used a controllable pulse parameter transcranial magnetic stimulation (cTMS) device to assess whether adjusting pulse width and coil orientation would allow more selective stimulation of different neuronal populations. Methods Young healthy subjects participated in experiments involving single pulse stimulation over the hand motor area...
Conference Paper
We present a novel Modular Multilevel Parallel Converter (M2PC) technology that solves key issues in the application in frequency-variable direct-drive gas turbine systems with high rotational speed as stationary power supplies as well as in mobile setups on ships, cars, and airplanes. In contrast to conventional converters, the M2PC can operate wi...
Article
This paper introduces a novel modular multilevel series/parallel converter that allows switching modules dynamically not only in series, as in the traditional modular multilevel converter (M2C), but also in parallel. As in M2C, the semiconductor voltages do not exceed the module capacitor voltage for any module state. While the new topology is a ge...
Conference Paper
The dependency of energy systems on battery storage systems is constantly increasing, but there are still several unsolved problems. Current battery systems are inflexible, only cells with the same electrical parameters can be combined, and cell defects cause a high reduction of the overall battery lifetime or even a system black out. In addition,...
Article
Magnetic stimulation is gaining importance as an alternative to electrical stimulation in neurorehabilitation because it offers deep penetration and low pain. However, presently available equipment is not ideal for this purpose and sometimes even unsuitable. Furthermore, it is not known what physical conditions a coil has to provide for efficient s...
Conference Paper
The new Modular Multilevel Parallel Converter (M2PC) for electrically driven vehicles is presented in this paper. The new M2PC upgrades the advantages of common Modular Multilevel Converters (M2C) through the ability to connect capacitors of nearby Submodules (SM's) not only serially but also in parallel. This leads to some further advantages like...
Conference Paper
A novel Modular Multilevel Parallel Converter (M2PC) for an optimized Hydrogen Gas Turbine Power Supply (HPU) is presented in this paper. This new M2PC improves the energy density, scalability and variance of the system voltage characteristics, in addition to the general advantages of the HPU concept. The basic operation modes of the M2PC topology,...
Article
Transcranial magnetic stimulation (TMS) is widely used for noninvasive activation of neurons in the brain for research and clinical applications. The strong, brief magnetic pulse generated in TMS is associated with a loud (>100 dB) clicking sound that can impair hearing and that activates auditory circuits in the brain. We introduce a two-pronged s...
Conference Paper
Neuromuscular magnetic stimulation is an auspicious tool in rehabilitation. It causes low distress and allows a more homogeneous activation without the problematic current concentration at electrodes as known from electrical stimulation. However, the performance of available technology is poor. For improvements of the coil technology, important mec...
Conference Paper
Recent studies revealed that transcranial stimulation with static magnetic field (SMF) at 0.1-0.15 T results in reduction of neural excitability in the human motor cortex. We explore the mechanisms of this phenomenon with patch-clamp recording in rat brain slices. Recording from layer II/III pyramidal neurons in motor cortex, we observed an increas...
Article
The association of magnetic nanoparticles with gene delivery vectors in combination with the use of gradient magnetic fields (magnetofection) enables improved and synchronised gene delivery to cells. In this paper, we report a system comprising rotating permanent magnets to generate defined magnetic field pulses with frequencies from 2.66 to 133 Hz...
Article
Full-text available
Magnetic stimulation is a standard tool in brain research and has found important clinical applications in neurology, psychiatry, and rehabilitation. Whereas coil designs and the spatial field properties have been intensively studied in the literature, the temporal dynamics of the field has received less attention. Typically, the magnetic field wav...
Data
Details on the used nominal axon model. (PDF)
Article
Objective: To demonstrate the use of a novel controllable pulse parameter TMS (cTMS) device to characterize human corticospinal tract physiology. Methods: Motor threshold and input-output (IO) curve of right first dorsal interosseus were determined in 26 and 12 healthy volunteers, respectively, at pulse widths of 30, 60, and 120 μs using a custo...
Article
Device technology for magnetic stimulation is still extremely limited regarding waveform dynamics and flexibility. Existing systems are well-known to be very inefficient from an energy perspective. In addition, neither a noninvasive analysis of different neuron dynamics nor an adjustment of the pulse waveform for a more specific stimulation is poss...
Article
Magnetic stimulation allows for painless and non-invasive extrinsic motor nerve stimulation. Despite several advantages, the limited coupling to the target reduces the application of magnetic pulses in rehabilitation. According to experience with electrical stimulation, magnetic bursts could remove this constraint. A novel burst stimulator was used...
Article
Magnetic stimulation is a key tool in experimental brain research and several clinical applications. Whereas coil designs and the spatial field properties have been intensively studied in the literature, the temporal dynamics of the field has received little attention. The available pulse shapes are typically determined by the relatively limited ca...
Article
Magnetic stimulation pulse sources are very inflexible high-power devices. The incorporated circuit topology is usually limited to a single pulse type. However, experimental and theoretical work shows that more freedom in choosing or even designing waveforms could notably enhance existing methods. Beyond that, it even allows entering new fields of...
Article
Full-text available
The input-output (IO) curve of cortical neuron populations is a key measure of neural excitability and is related to other response measures including the motor threshold which is widely used for individualization of neurostimulation techniques, such as transcranial magnetic stimulation (TMS). The IO curve parameters provide biomarkers for changes...