Measurements on the resonator have revealed frequency hysteresis, in which the resonator response ‘jumps’ between high-amplitude and low-amplitude solutions (and vice versa) during frequency sweeps. Moreover, the type of nonlinear dynamic... more
Measurements on the resonator have revealed frequency hysteresis, in which the resonator response ‘jumps’ between high-amplitude and low-amplitude solutions (and vice versa) during frequency sweeps. Moreover, the type of nonlinear dynamic behaviour depends on the excitation parameters of the system, as is depicted in Fig. 2 (measurement) and Fig. 3 (simulation). A transition from hardening to softening is observed for increasing Vdc-values.
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At low frequencies, biological media are characterized by extremely high permittivities. As a result, the most commonly used simulation methods, i.e. finite-difference time domain (FDTD), finite element method (FEM), and domain integral... more
At low frequencies, biological media are characterized by extremely high permittivities. As a result, the most commonly used simulation methods, i.e. finite-difference time domain (FDTD), finite element method (FEM), and domain integral equations (DIE), suffer from severe limitations in accuracy. These limitations are caused by the round-off errors in finite-precision floating point operations. Finite precision causes error accumulation in FDTD due to the large number of time steps required to simulate one period and to maintain stability. In FEM, finite precision causes the numerical derivative to collapse due to the dependence on the mesh size. While the DIE is hardly influenced by the mesh size, the extreme permittivities cause a large difference in the order of magnitude of the various terms in the DIE.
Research Interests: Geophysics, Physics, Radiation, Finite element method, Instrumentation, and 8 moreLow Frequency, Modelling and simulation, Finite Difference, Computer Networks and Communications, Finite Difference Method, Statistics and Probability, Finite Difference Time Domain, and Finite Difference Time Domain Method
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Abstract Objective: In High Dose Rate Brachytherapy for prostate cancer there is a need for a new way of increasing cancer cell kill in combination with a stable dose to the organs at risk. In this study, we propose a novel ThermoBrachy... more
Abstract Objective: In High Dose Rate Brachytherapy for prostate cancer there is a need for a new way of increasing cancer cell kill in combination with a stable dose to the organs at risk. In this study, we propose a novel ThermoBrachy applicator that offers the unique ability to apply interstitial hyperthermia while simultaneously serving as an afterloading catheter for high dose rate brachytherapy for prostate cancer. This approach achieves a higher thermal enhancement ratio than in sequential application of radiation and hyperthermia and has the potential to decrease the overall treatment time. Methods: The new applicator uses the principle of capacitively coupled electrodes. We performed a proof of concept experiment to demostrate the feasibility of the proposed applicator. Moreover, we used electromagnetic and thermal simulations to evaluate the power needs and temperature homogeneity in different tissues. Furthermore we investigated whether dynamic phase and amplitude adaptation can be used to improve longitudinal temperature control. Results: Simulations demonstrate that the electrodes achieve good temperature homogeneity in a homogenous phantom when following current applicator spacing guidelines. Furthermore, we demonstrate that dynamic phase and amplitude adaptation provides a great advancement for further adaptability of the heating pattern. Conclusions: This newly designed ThermoBrachy applicator has the potential to revise the interest in interstitial thermobrachytherapy, since the simultaneous application of radiation and hyperthermia enables maximum thermal enhancement and provides maximum efficiency for patient and organization.
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A scalable, wideband downtilt demonstrator has been realized on a single printed circuit board (PCB). The system improves the efficiency and reconfigurability of antennas in base transceiver stations (BTS) and meets adaptive downtilt... more
A scalable, wideband downtilt demonstrator has been realized on a single printed circuit board (PCB). The system improves the efficiency and reconfigurability of antennas in base transceiver stations (BTS) and meets adaptive downtilt requirements. The downtilt beamsteering system is implemented as a four-element phased array fed by a feed network that generates a power taper of 1 : 3 : 3 :1 over the elements. The concept allows for beamsteering by applying phase shifts in low power branches only, using a two-bit switched line implementation (30°/bit). A fractional bandwidth of 40% is realized around the center frequency of 2.0 GHz. Hard-wiring of the phase shifter bits is used to demonstrate the operation of the concept. The measured gain varies less than 1:76 dB over the total bandwidth and scan range and is in agreement with the expected values, calculated from individual building blocks. Simulation and measurement results for the co- and cross-polarization performance match well and are in line with state-of-the-art requirements.
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Based on a full-wave simulation model, we investigate how various optimization methods perform on a sensitive problem of a high-Q, nine-pole rectangular waveguide filter system with respect to its multi-mode scattering parameters
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This paper gives a general overview of the work of the Eindhoven University of Technology that is carrier out within PANAMA European project. This project addresses the future communication needs in Europe related to increased e??ciency... more
This paper gives a general overview of the work of the Eindhoven University of Technology that is carrier out within PANAMA European project. This project addresses the future communication needs in Europe related to increased e??ciency and energy saving in applications such as cellular handsets, base stations and mobile satellite communications. Additionally, the paper describes the need for adaptive beamforming for downtilt in base transceiver stations and the novel approach to tackle this issue using phase shifters based on RF MEMS.
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For electromagnetic simulations in the field of neurostimulation, excitations typically range up to kHz frequencies. The Finite Element Method (FEM) is often used in such situations. Here we show that the accuracy of FEM solvers does not... more
For electromagnetic simulations in the field of neurostimulation, excitations typically range up to kHz frequencies. The Finite Element Method (FEM) is often used in such situations. Here we show that the accuracy of FEM solvers does not benefit from mesh size refinement and that this results in an optimal mesh size that is well above the desired mesh size from a practical point of view (mm-sized voxels)
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Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are the most commonly studied non-invasive brain stimulation treatment options. Over the past years, modeling and simulation of stimulation-induced... more
Transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS) are the most commonly studied non-invasive brain stimulation treatment options. Over the past years, modeling and simulation of stimulation-induced electric fields have received increased attention. Modeling can take place at three different levels of abstraction. Although some validation of these models has taken place at these levels separately, coupling between the levels through a multi-scale approach and experimental validation of the overall approach has only recently started. This specific coupling might be an important step to unravel the mechanism of action and to ultimately improve the clinical efficacy of non-invasive brain stimulation.
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Conventional transcranial electric stimulation(tES) using standard anatomical positions for the electrodes and standard stimulation currents is frequently not sufficiently selective in targeting and reaching specific brain locations,... more
Conventional transcranial electric stimulation(tES) using standard anatomical positions for the electrodes and standard stimulation currents is frequently not sufficiently selective in targeting and reaching specific brain locations, leading to suboptimal application of electric fields. Recent advancements in in vivo electric field characterization may enable clinical researchers to derive better relationships between the electric field strength and the clinical results. Subject-specific electric field simulations could lead to improved electrode placement and more efficient treatments. Through this narrative review, we present a processing workflow to personalize tES for focal epilepsy, for which there is a clear cortical target to stimulate. The workflow utilizes clinical imaging and electroencephalography data and enables us to relate the simulated fields to clinical outcomes. We review and analyze the relevant literature for the processing steps in the workflow, which are the fo...
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Research Interests: Hyperthermia and Medicine
Integration of vibration energy harvesters (VEHs) with small-scale electronic devices may form an attractive alternative for relatively large batteries and can, potentially, increase their lifespan. However, the inherent mismatch between... more
Integration of vibration energy harvesters (VEHs) with small-scale electronic devices may form an attractive alternative for relatively large batteries and can, potentially, increase their lifespan. However, the inherent mismatch between a harvester's high-frequency resonance, typically in the range 100−1000 Hz, relative to the available low-frequency ambient vibrations, typically in the range 10–100 Hz, means that low-frequency power generation in microscale VEHs remains a persistent challenge. In this work, we model a novel electret-based, electrostatic energy harvester (EEH) design. In this design, we combine an out-of-plane gap-closing comb (OPGC) configuration for the low-frequency oscillator with an in-plane overlap comb configuration for the high-frequency oscillator and employ impact for frequency up-conversion. An important design feature is the tunability of the resonance frequency through the electrostatic nonlinearity of the low-frequency oscillator. Impulsive normal...
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Assisting visually impaired people to see again using technology is quite challenging, especially for cases where most of the visual pathway is damaged. The only viable option is to stimulate the visual cortex directly. Sending the... more
Assisting visually impaired people to see again using technology is quite challenging, especially for cases where most of the visual pathway is damaged. The only viable option is to stimulate the visual cortex directly. Sending the stimulation data to electrodes on the visual cortex is preferably done wirelessly to avoid infections and to ease mobility. The receiver on the implant poses a challenge in design, as the power supply is limited. In this paper, vital system requirements for this communication link are discussed. A low power system-level approach is presented which seeks to avoid power hungry components. This leads to the consideration of a bandpass sampled phase shift keying scheme via an inductive link. We propose a non-coherent digital demodulator, which relaxes the need for low phase noise oscillators which consume more power and, also avoids the use of phase locks loops. The overall communication system has a potential to deliver stimulation data to the implant side i...
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Nonlinearities in MEMS silicon resonators are caused by different effects. Depending on the resonator layout, different nonlinearities may be dominant in the resonator response. A model for a clamped-clamped beam resonator is derived,... more
Nonlinearities in MEMS silicon resonators are caused by different effects. Depending on the resonator layout, different nonlinearities may be dominant in the resonator response. A model for a clamped-clamped beam resonator is derived, which contains both a mechanical and an electrical part. The dynamic behaviour of the resonator is investigated both numerically and experimentally in order to obtain a qualitative
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Introduction to design novel treatment combinations involving mild hyperthermia, pre-clinical trials are essential. These studies into treatment effectiveness require close monitoring of the temperature during testing . Invasive... more
Introduction to design novel treatment combinations involving mild hyperthermia, pre-clinical trials are essential. These studies into treatment effectiveness require close monitoring of the temperature during testing . Invasive thermometry restricts testing of the link between hyperthermia and immune responses, so MRI-compatibility is a necessity. Next to that, the applicator must heat locally, and secondary hot spots especially in vulnerable regions like the spinal cord must be prevented. Lastly, the system must be non-invasive, for disturbances in the tissues studied interfere with the accuracy of the research.With these goals in mind, we designed and built an applicator based on a novel water-embedded antenna design. In this study, we report the mode of operation for the head&neck region, but it can also be used for other tissues up to about 2 cm deep.MethodsA simulation-based approach was used to design the antenna element, and the surrounding system including the load. Simulat...
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The combination of interstitial hyperthermia treatment (IHT) with high dose rate brachytherapy (HDR-BT) for prostate cancer treatment and has the potential to improve clinical outcome, since it highly enhances the efficiency of cell kill,... more
The combination of interstitial hyperthermia treatment (IHT) with high dose rate brachytherapy (HDR-BT) for prostate cancer treatment and has the potential to improve clinical outcome, since it highly enhances the efficiency of cell kill, especially when applied simultaneously. Therefore, we have developed the ThermoBrachy applicators. To effectively apply optimal targeted IHT, treatment planning is considered essential. However, treatment planning in IHT is rarely applied since it is regarded difficult to accurately calculate the deposited energy in the tissue in a short enough time for clinical practice. In this study, we investigated various time-efficient methods for fast computation of the electromagnetic (EM) energy deposition resulting from the ThermoBrachy applicators. Initially, we investigated the use of an electro-quasistatic solver. Next, we extended our investigation to the application of geometric simplifications. Furthermore, we investigated the validity of the superp...
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There is a growing interest to improve the quality of life of blind people. An implanted intracortical prosthesis could be the last resort in many cases of visual impairment. Technology at this moment is at a stage that implementation is... more
There is a growing interest to improve the quality of life of blind people. An implanted intracortical prosthesis could be the last resort in many cases of visual impairment. Technology at this moment is at a stage that implementation is at sight. Making the data communication to and from the implanted electrodes wireless is beneficial to avoid infection and to ease mobility. Here, we focus on the stimulation side, or downlink, for which we propose a low-power non-coherent digital demodulator on the implanted receiver. The experimentally demonstrated downlink is on a scaled-down version at a 1 MHz carrier frequency showing a data rate of 125 kbps. This provides proof of principle for the system with a 12 MHz carrier frequency and a data rate of 4 Mbps, which consumes under 1 mW at the receiver side in integrated circuit (IC) simulation. Due to its digital architecture, the system is easily adjustable to an ISM frequency band with its power consumption scaling linearly with the carri...
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Computational modeling is increasingly used to design charging systems for implanted medical devices. The design of these systems must often satisfy conflicting criteria, and fast electromagnetic solvers are pivotal for enabling... more
Computational modeling is increasingly used to design charging systems for implanted medical devices. The design of these systems must often satisfy conflicting criteria, and fast electromagnetic solvers are pivotal for enabling multi-criteria optimization. In this paper, we look at wireless power transfer for implantable devices and the specific absorption rate and induced currents related to the implanted side of the design. We present an analytical model based on the quasi-static approximation as a fast, yet sufficiently accurate, alternative for full wave electromagnetic modeling. The analytic model was benchmarked against full-wave simulations to validate accuracy and improvement in computation time. Our analysis shows that the analytic model allows for feasible complete optimization of coil shapes, as the analytic model takes only 11 seconds to compute a single iteration, while the full-wave model takes 5 hours to compute the same case. The maximum difference with full-wave simulations was less than 25\% and the mean difference less than 2.3%. Adding a novel figure of merit into the multi-criterion optimization resulted in a 16% higher charging speed. The specific absorption rate and coupling factor were both experimentally verified to show that the measured results are within a 5~mm coil offset margin, which validates the simulation results.
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The authors present a mathematical model that can be used to model the electromagnetic (EM) fields generated by a vertically oriented magnetic dipole (VMD) located above a conductive half-space, such as biological tissue. The model was... more
The authors present a mathematical model that can be used to model the electromagnetic (EM) fields generated by a vertically oriented magnetic dipole (VMD) located above a conductive half-space, such as biological tissue. The model was compared to a full-wave simulation in CST. The difference is shown to be below 8.1% on average for frequencies ranging from 13 MHz to 5 GHz. It executes over 800 times faster than a full-wave solver, using more than 20 times less memory, and can be adapted to model more realistic magnetic sources without much extra effort. This model can improve the design process of inductive or radiative links significantly, enabling rapid design iteration. It is well suited for biomedical applications. Extension to magnetic sources with arbitrary orientation, as well as electric sources, is possible.
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IntroductionCancer treatments remain a heavy load for the patient due to the many side effects. Mild hyperthermia, locally heating tissue to 42⁰ C, has proven to be a powerful treatment enhancer with no severe side effects. Recently, new... more
IntroductionCancer treatments remain a heavy load for the patient due to the many side effects. Mild hyperthermia, locally heating tissue to 42⁰ C, has proven to be a powerful treatment enhancer with no severe side effects. Recently, new potential applications of mild hyperthermia in cancer therapy were discovered. Converting these cell-culture based findings into clinical protocols requires pre-clinical investigation of the various strategies by clinical trials with small animals. For this goal, a site-specific head & neck hyperthermia applicator for murine models was developed. Hereto, we studied a design with an antenna array operating at 2.45 GHz embedded in a water bolus.Methodology A simulation-based approach was used to design the separate antennas operating at 2.45 GHz, and later on the antenna array. Simulation programs SEMCAD and CST are used, both of which use a Finite Difference Time Difference (FDTD) calculation methods. The design yields an air-water boundary between t...
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s Brain Stimulation 14 (2021) 1589e1707
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Brain-on-chip (BoC) models are tools for reproducing the native microenvironment of neurons, in order to study the (patho)physiology and drug-response of the brain. Recent developments in BoC techniques focus on steering neurons in their... more
Brain-on-chip (BoC) models are tools for reproducing the native microenvironment of neurons, in order to study the (patho)physiology and drug-response of the brain. Recent developments in BoC techniques focus on steering neurons in their activity via microfabrication and via computer-steered feedback mechanisms. These cultures are often studied through calcium imaging (CI), a method for visualizing the cellular activity through infusing cells with a fluorescent dye. CAlciumImagingAnalyser 2.0 (CALIMA 2.0) is an updated version of a software tool that detects and analyzes fluorescent signals and correlates cellular activity to identify possible network formation in BoC cultures. Using three previous published data sets, it was demonstrated that CALIMA 2.0 can analyze large data sets of CI-data and interpret cell activity to help study the activity and maturity of BoC cultures. Last, an analysis of the processing speed shows that CALIMA 2.0 is sufficiently fast to process data sets wi...
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ABSTRACT During a hyperthermia treatment, a tumour is locally heated for a defined period of time by focussing the energy of electromagnetic waves into it. Hyperthermia treatment planning (HTP) consists of finding optimal amplitudes and... more
ABSTRACT During a hyperthermia treatment, a tumour is locally heated for a defined period of time by focussing the energy of electromagnetic waves into it. Hyperthermia treatment planning (HTP) consists of finding optimal amplitudes and phases for the antenna array of the applicator to realize this objective. Current optimization methods for HTP are time-consuming and not very flexible. In this paper we present an automated refined eigenvalue-based approach for optimizing antenna parameters for hyperthermia treatments, that allows for fast and efficient calculation and near-realtime adjustments. The approach is demonstrated on a two-dimensional clinical case, yielding good results.
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Numerous excitation sources for disk vibrations are present in optical drives. For increasing rotation speeds, airflow-housing-induced vibrations have become more and more important. Currently, drives are designed in which rotation speeds... more
Numerous excitation sources for disk vibrations are present in optical drives. For increasing rotation speeds, airflow-housing-induced vibrations have become more and more important. Currently, drives are designed in which rotation speeds are so high that critical speed resonances may show up. The presence of these resonances depends on the layout of the inner housing geometry of the drive. The influence of the drive inner housing geometry is investigated systematically by means of a numerical-experimental approach. An analytical model is derived, containing disk dynamics and the geometry-induced pressure distribution acting as the excitation mechanism on the disk. The Reynolds’ lubrication equation is used as a first approach for the modeling of the pressure distribution. The model is numerically implemented using an approach based on a combination of finite element and finite difference techniques. An idealized, drive-like environment serves as the experimental setup. This setup r...