Hannes Toepfer - Academia.edu (original) (raw)
Papers by Hannes Toepfer
Tagung Kryoelektronische Bauelemente (KRYO 2011), Autrans, Frankreich, 02.10.2011 – 04.10.2011, 2011
Informatyka Automatyka Pomiary w Gospodarce i Ochronie Środowiska, 2018
In this paper, the method of images is used to model the effects of enclosure made of high-permea... more In this paper, the method of images is used to model the effects of enclosure made of high-permeability material on magnetic field of square coils. Closed-form description for the images, along with the case study involving square Helmholtz coils, is provided.
2014 11th International Workshop on Low Temperature Electronics (WOLTE), 2014
ABSTRACT Large arrays of superconducting radiation sensors require a multiplexed readout. One imp... more ABSTRACT Large arrays of superconducting radiation sensors require a multiplexed readout. One implementation of the promising code division multiplexing technique uses current steering switches (CSSs) based on superconducting quantum interference devices (SQUIDs). We pursue the concept of utilizing rapid single flux quantum (RSFQ) electronics to control these switches, where each SQUID of a CSS is inductively coupled to the storing loop of a delay flip-flop. The internal state of this digital logic element is represented by the presence of a magnetic flux quantum, which is destined to control the CSS.
Serbian Journal of Electrical Engineering, 2014
In this paper, method of current images is used to calculate magnetic field of a rectangular loop... more In this paper, method of current images is used to calculate magnetic field of a rectangular loop in presence of high-permeability material. We provide closed form description for the images of the current loop placed between two semi-infinite blocks of high-permeability material, in the cases when the plane of the loop is parallel or perpendicular to the surfaces of blocks. A case study of using the method of images to calculate magnetic field of rectangular loop inside cube made of high-permeability material is also provided.
Superconductor Science and Technology, 2010
... superconducting π-phaseshifters and possible applications Olaf Mielke1, Thomas Ortlepp1,Juerg... more ... superconducting π-phaseshifters and possible applications Olaf Mielke1, Thomas Ortlepp1,Juergen Kunert2, Hans-Georg Meyer2 and Hannes Toepfer1 ... Phys. 94 5405–7 [6] Majer JB, Butcher JR and Mooij JE 2002 Simple phase bias for superconducting circuits Appl. Phys. ...
Superconductor Science and Technology, 2012
As the complexity of Rapid Single Flux Quantum (RSFQ) circuits increases, both current and power ... more As the complexity of Rapid Single Flux Quantum (RSFQ) circuits increases, both current and power consumption of the circuits become important design criteria. Various new concepts such as inductive biasing for energy efficient RSFQ circuits and inductively coupled RSFQ cells for current recycling have been proposed to overcome increasingly severe design problems. Both of these techniques use ground plane holes to increase the inductance or coupling factor of superconducting integrated circuit wires. New design tools are consequently required to handle the new topographies. One important issue in such circuit design is the accurate calculation of networks of inductances even in the presence of finite holes in the ground plane. We show how a fast network extraction method with InductEx and FastHenry is used to calculate the inductances of a set of SQUIDs with ground plane holes of different sizes. The results are compared to measurements of physical structures fabricated with IPHT's 1kA cm-2 RSFQ niobium process to verify accuracy. We then do a parameter study and derive empirical equations for fast and useful estimation of the inductance of wires surrounded by ground plane holes. We also investigate practical circuits and show excellent accuracy.
IEEE Transactions on Applied Superconductivity, 2014
For spectroscopic and imaging applications in the submillimeter wavelength band, superconducting ... more For spectroscopic and imaging applications in the submillimeter wavelength band, superconducting radiation sensors are widely used. Thereby, sensor arrays with a rising number of pixels require multiplexing techniques in order to reduce the number of wires leading to the cryogenic stage. A current steering switch (CSS) provides the basis for one kind of promising code division multiplexers. It is composed of two identical superconducting quantum interference devices (SQUIDs) in parallel current paths. Switching one of them from the superconducting into the normal state, which is controlled by the applied magnetic flux, alters the signal path; thus, they can act as a polarity switch for analog signals. In this paper, we describe a method that uses rapid single-flux quantum (RSFQ) electronics for controlling these switches. Therefore, their SQUIDs are inductively coupled each to the storing loop of an RSFQ delay flip-flop (DFF); hence, the state of the analog switch can be controlled by means of digital RSFQ signals. As a first step, we show the change in the critical current of the SQUIDs by the coupled operating digital circuit. For a wider operating range of the CSS, we developed a DFF, which is able to store a larger quantity of magnetic flux to make it possible to apply more flux to the coupled SQUID. For further improvements, we tested asymmetric SQUIDs to reduce the required magnetic flux. The results of the simulations and measurements are discussed.
IEEE Transactions on Applied Superconductivity, 2011
A digital SQUID magnetometer measures the magnetic field amplitude by counting integer magnetic f... more A digital SQUID magnetometer measures the magnetic field amplitude by counting integer magnetic flux quanta within its superconducting input loop. Although resolution is limited in comparison to analog SQUID systems, the digital SQUID is able to outrange its analog counterpart with regard to parameters such as slew rate and dynamic range. In this work we evaluate the performance of a digital SQUID based on a three-level logic. Due to this basic principle, we face a combination of two comparator grayzones leading to hysteretic behavior of the sensor that produces a "dead zone" in the signal reversal point. The dependence of the comparator threshold on design parameters is investigated by simulation studies and reconfirmed by experimental results. We were able to reach a total dynamic range of more than 540,000 flux quanta (about 19 bit) with a linearity error of about 5 bit due to the mentioned hysteretic behavior. We discuss the results of our investigations and provide guidelines to extend dynamic range and linearity for future sensor designs.
IEEE Transactions on Applied Superconductivity, 2013
ABSTRACT In Europe, the FLUXONICS Foundry develops fabrication processes and design kits for supe... more ABSTRACT In Europe, the FLUXONICS Foundry develops fabrication processes and design kits for superconductor digital and mixed-signal circuits. We describe the implementation of the “European Roadmap for Superconductor Electronics” into the recent foundry process for superconductor digital electronics. Following the hierarchical cell-based design strategy, we developed a design kit with basic cells. We present experimental results of the process quality, the verified operation margins of the library cells, and the results of low- and high-speed investigations of test circuits. The process is suitable for the integration of complex digital and mixed-signal circuits for smart multichannel superconductor sensor applications with a digital interface.
Physica C: Superconductivity, 2006
The roadmap gives an overview on status and future developments in Superconducting Digital Electr... more The roadmap gives an overview on status and future developments in Superconducting Digital Electronics (SDE). Key areas in SDE under focus are applications, circuit simulation and design, circuit fabrication, interfacing and testing, cooling and system aspects, and new devices and materials. Care was taken to establish the vital link between research and development on the one hand and the industrial view on the other hand. The present roadmap is based on extensive input from the roadmap working group on SDE established by SCENET-the European Network for Superconductivity, intensified by the activities of the FLUXONICS Network-the European Foundry for Superconducting Electronics. It is the result of many years of discussion in the group and of consultations with experts in the field, on the way to bring together industrial expectations and visionary extrapolation and current status of technology.
IEEE Transactions on Magnetics, 2015
IEEE Topical Meeting on Electrical Performance of Electronic Packaging, 2000
A superconducting sampling measurement system is a highly useful tool for analyzing ultrahigh spe... more A superconducting sampling measurement system is a highly useful tool for analyzing ultrahigh speed electrical signals in cryogenic environments, due to a time resolution at ps levels with low current levels of μA. The digitizing sampling system is composed of a Josephson sampling circuit, digital delay line, feedback signal detection circuit and a computer. The Josephson sampling circuit is designed
IEEE Transactions on Magnetics, 2015
We propose a procedure to determine optimal magnet systems in the framework of the nondestructive... more We propose a procedure to determine optimal magnet systems in the framework of the nondestructive evaluation technique Lorentz force eddy current testing. The underlying optimization problem is clearly defined considering the problem specificity of nondestructive testing scenarios. The quantities involved are classified as design variables, and system and scaling parameters to provide a high level of generality. The objective function is defined as the absolute defect response signal of the Lorentz force resulting from an inclusion inside the object under test. Associated constraints are defined according to the applied force sensor technology. A numerical procedure based on the finite element method is proposed to evaluate the nonlinear objective and constraint functions, and the method of sequential quadratic programming is applied to determine unconstrained and constrained optimal magnet designs. Consequently, we propose a new magnet design based on the Halbach principle in combination with high saturation magnetization iron-cobalt-alloys. The proposed magnet system outperforms currently available cylindrical magnets in terms of weight and performance. The corresponding defect response signal is increased up to 180% in the case of small defects located close to the surface of the specimen. The combination of active and passive magnetic material provides an increase of the absolute defect response signal by 15% compared to magnet designs which are built solely from permanent magnet material. The proposed procedure provides a highly adaptive optimization strategy in the framework of Lorentz force eddy current testing and proposes new magnet systems with inherently improved characteristics.
IEEE Transactions on Magnetics, 2015
ABSTRACT We propose a framework of nonintrusive polynomial chaos methods for transcranial magneti... more ABSTRACT We propose a framework of nonintrusive polynomial chaos methods for transcranial magnetic stimulation (TMS) to investigate the influence of the uncertainty in the electrical conductivity of biological tissues on the induced electric field. The conductivities of three different tissues, namely, cerebrospinal fluid, gray matter (GM), and white matter, are modeled as uniformly distributed random variables. The investigations are performed on a simplified model of a cortical gyrus/sulcus structure. The statistical moments are calculated by means of a generalized polynomial chaos expansion using a regression and cubature approach. Furthermore, the results are compared with the solutions obtained by stochastic collocation. The accuracy of the methods to predict random field distributions was compared by applying different grids and orders of expansion. An investigation on the convergence of the expansion showed that in the present framework, an order 4 expansion is sufficient to determine results with an error of <1%. The results indicate a major influence of the uncertainty in electrical conductivity on the induced electric field. The standard deviation exceeds values of 20%–40% of the mean induced electric field in the GM. A sensitivity analysis revealed that the uncertainty in electrical conductivity of the GM affects the solution the most. This paper outlines the importance of exact knowledge of the electrical conductivities in TMS in order to provide reliable numerical predictions of the induced electric field. Furthermore, it outlines the performance and the applicability of spectral methods in the framework of TMS for future studies.
IEEE Transactions on Magnetics, 2015
The present paper provides the 3-D time-dependent analytical solution of the electromagnetic fiel... more The present paper provides the 3-D time-dependent analytical solution of the electromagnetic fields and forces emerging if a coil or a permanent magnet moves with a sinusoidal velocity profile relative to a conducting slab of finite thickness. The results can be readily used in application scenarios related to electromagnetic damping, eddy current braking, energy harvesting or nondestructive testing in order to efficiently analyze diffusion and advection processes in case of harmonic motion. The study is performed for rectangular and circular coils as well as for cuboidal and cylindrical permanent magnets. The back reaction of the conductor and therewith associated inductive effects are considered. The solutions of the governing equations and the integral expressions for the time-dependent drag-and lift-force are provided. The analytical results are verified by a comparison to numerical simulations obtained by the finite-element method. The relative difference between the analytically and numerically evaluated force profiles was < 0.1%. Exemplary calculations show that the waveforms of both force components strongly depend on the level of constant nominal velocity v0, the magnitude of the velocity oscillation amplitude v1 and the underlying oscillation frequency fv. His current research interests include numerical simulations and visualization of electromagnetic fields, with applications to forward/inverse problems in nondestructive evaluation, bioelectromagnetics, small electrical machines, and magnetic fluid dynamics.
Serbian Journal of Electrical Engineering, 2014
Tagung Kryoelektronische Bauelemente (KRYO 2011), Autrans, Frankreich, 02.10.2011 – 04.10.2011, 2011
Informatyka Automatyka Pomiary w Gospodarce i Ochronie Środowiska, 2018
In this paper, the method of images is used to model the effects of enclosure made of high-permea... more In this paper, the method of images is used to model the effects of enclosure made of high-permeability material on magnetic field of square coils. Closed-form description for the images, along with the case study involving square Helmholtz coils, is provided.
2014 11th International Workshop on Low Temperature Electronics (WOLTE), 2014
ABSTRACT Large arrays of superconducting radiation sensors require a multiplexed readout. One imp... more ABSTRACT Large arrays of superconducting radiation sensors require a multiplexed readout. One implementation of the promising code division multiplexing technique uses current steering switches (CSSs) based on superconducting quantum interference devices (SQUIDs). We pursue the concept of utilizing rapid single flux quantum (RSFQ) electronics to control these switches, where each SQUID of a CSS is inductively coupled to the storing loop of a delay flip-flop. The internal state of this digital logic element is represented by the presence of a magnetic flux quantum, which is destined to control the CSS.
Serbian Journal of Electrical Engineering, 2014
In this paper, method of current images is used to calculate magnetic field of a rectangular loop... more In this paper, method of current images is used to calculate magnetic field of a rectangular loop in presence of high-permeability material. We provide closed form description for the images of the current loop placed between two semi-infinite blocks of high-permeability material, in the cases when the plane of the loop is parallel or perpendicular to the surfaces of blocks. A case study of using the method of images to calculate magnetic field of rectangular loop inside cube made of high-permeability material is also provided.
Superconductor Science and Technology, 2010
... superconducting π-phaseshifters and possible applications Olaf Mielke1, Thomas Ortlepp1,Juerg... more ... superconducting π-phaseshifters and possible applications Olaf Mielke1, Thomas Ortlepp1,Juergen Kunert2, Hans-Georg Meyer2 and Hannes Toepfer1 ... Phys. 94 5405–7 [6] Majer JB, Butcher JR and Mooij JE 2002 Simple phase bias for superconducting circuits Appl. Phys. ...
Superconductor Science and Technology, 2012
As the complexity of Rapid Single Flux Quantum (RSFQ) circuits increases, both current and power ... more As the complexity of Rapid Single Flux Quantum (RSFQ) circuits increases, both current and power consumption of the circuits become important design criteria. Various new concepts such as inductive biasing for energy efficient RSFQ circuits and inductively coupled RSFQ cells for current recycling have been proposed to overcome increasingly severe design problems. Both of these techniques use ground plane holes to increase the inductance or coupling factor of superconducting integrated circuit wires. New design tools are consequently required to handle the new topographies. One important issue in such circuit design is the accurate calculation of networks of inductances even in the presence of finite holes in the ground plane. We show how a fast network extraction method with InductEx and FastHenry is used to calculate the inductances of a set of SQUIDs with ground plane holes of different sizes. The results are compared to measurements of physical structures fabricated with IPHT's 1kA cm-2 RSFQ niobium process to verify accuracy. We then do a parameter study and derive empirical equations for fast and useful estimation of the inductance of wires surrounded by ground plane holes. We also investigate practical circuits and show excellent accuracy.
IEEE Transactions on Applied Superconductivity, 2014
For spectroscopic and imaging applications in the submillimeter wavelength band, superconducting ... more For spectroscopic and imaging applications in the submillimeter wavelength band, superconducting radiation sensors are widely used. Thereby, sensor arrays with a rising number of pixels require multiplexing techniques in order to reduce the number of wires leading to the cryogenic stage. A current steering switch (CSS) provides the basis for one kind of promising code division multiplexers. It is composed of two identical superconducting quantum interference devices (SQUIDs) in parallel current paths. Switching one of them from the superconducting into the normal state, which is controlled by the applied magnetic flux, alters the signal path; thus, they can act as a polarity switch for analog signals. In this paper, we describe a method that uses rapid single-flux quantum (RSFQ) electronics for controlling these switches. Therefore, their SQUIDs are inductively coupled each to the storing loop of an RSFQ delay flip-flop (DFF); hence, the state of the analog switch can be controlled by means of digital RSFQ signals. As a first step, we show the change in the critical current of the SQUIDs by the coupled operating digital circuit. For a wider operating range of the CSS, we developed a DFF, which is able to store a larger quantity of magnetic flux to make it possible to apply more flux to the coupled SQUID. For further improvements, we tested asymmetric SQUIDs to reduce the required magnetic flux. The results of the simulations and measurements are discussed.
IEEE Transactions on Applied Superconductivity, 2011
A digital SQUID magnetometer measures the magnetic field amplitude by counting integer magnetic f... more A digital SQUID magnetometer measures the magnetic field amplitude by counting integer magnetic flux quanta within its superconducting input loop. Although resolution is limited in comparison to analog SQUID systems, the digital SQUID is able to outrange its analog counterpart with regard to parameters such as slew rate and dynamic range. In this work we evaluate the performance of a digital SQUID based on a three-level logic. Due to this basic principle, we face a combination of two comparator grayzones leading to hysteretic behavior of the sensor that produces a "dead zone" in the signal reversal point. The dependence of the comparator threshold on design parameters is investigated by simulation studies and reconfirmed by experimental results. We were able to reach a total dynamic range of more than 540,000 flux quanta (about 19 bit) with a linearity error of about 5 bit due to the mentioned hysteretic behavior. We discuss the results of our investigations and provide guidelines to extend dynamic range and linearity for future sensor designs.
IEEE Transactions on Applied Superconductivity, 2013
ABSTRACT In Europe, the FLUXONICS Foundry develops fabrication processes and design kits for supe... more ABSTRACT In Europe, the FLUXONICS Foundry develops fabrication processes and design kits for superconductor digital and mixed-signal circuits. We describe the implementation of the “European Roadmap for Superconductor Electronics” into the recent foundry process for superconductor digital electronics. Following the hierarchical cell-based design strategy, we developed a design kit with basic cells. We present experimental results of the process quality, the verified operation margins of the library cells, and the results of low- and high-speed investigations of test circuits. The process is suitable for the integration of complex digital and mixed-signal circuits for smart multichannel superconductor sensor applications with a digital interface.
Physica C: Superconductivity, 2006
The roadmap gives an overview on status and future developments in Superconducting Digital Electr... more The roadmap gives an overview on status and future developments in Superconducting Digital Electronics (SDE). Key areas in SDE under focus are applications, circuit simulation and design, circuit fabrication, interfacing and testing, cooling and system aspects, and new devices and materials. Care was taken to establish the vital link between research and development on the one hand and the industrial view on the other hand. The present roadmap is based on extensive input from the roadmap working group on SDE established by SCENET-the European Network for Superconductivity, intensified by the activities of the FLUXONICS Network-the European Foundry for Superconducting Electronics. It is the result of many years of discussion in the group and of consultations with experts in the field, on the way to bring together industrial expectations and visionary extrapolation and current status of technology.
IEEE Transactions on Magnetics, 2015
IEEE Topical Meeting on Electrical Performance of Electronic Packaging, 2000
A superconducting sampling measurement system is a highly useful tool for analyzing ultrahigh spe... more A superconducting sampling measurement system is a highly useful tool for analyzing ultrahigh speed electrical signals in cryogenic environments, due to a time resolution at ps levels with low current levels of μA. The digitizing sampling system is composed of a Josephson sampling circuit, digital delay line, feedback signal detection circuit and a computer. The Josephson sampling circuit is designed
IEEE Transactions on Magnetics, 2015
We propose a procedure to determine optimal magnet systems in the framework of the nondestructive... more We propose a procedure to determine optimal magnet systems in the framework of the nondestructive evaluation technique Lorentz force eddy current testing. The underlying optimization problem is clearly defined considering the problem specificity of nondestructive testing scenarios. The quantities involved are classified as design variables, and system and scaling parameters to provide a high level of generality. The objective function is defined as the absolute defect response signal of the Lorentz force resulting from an inclusion inside the object under test. Associated constraints are defined according to the applied force sensor technology. A numerical procedure based on the finite element method is proposed to evaluate the nonlinear objective and constraint functions, and the method of sequential quadratic programming is applied to determine unconstrained and constrained optimal magnet designs. Consequently, we propose a new magnet design based on the Halbach principle in combination with high saturation magnetization iron-cobalt-alloys. The proposed magnet system outperforms currently available cylindrical magnets in terms of weight and performance. The corresponding defect response signal is increased up to 180% in the case of small defects located close to the surface of the specimen. The combination of active and passive magnetic material provides an increase of the absolute defect response signal by 15% compared to magnet designs which are built solely from permanent magnet material. The proposed procedure provides a highly adaptive optimization strategy in the framework of Lorentz force eddy current testing and proposes new magnet systems with inherently improved characteristics.
IEEE Transactions on Magnetics, 2015
ABSTRACT We propose a framework of nonintrusive polynomial chaos methods for transcranial magneti... more ABSTRACT We propose a framework of nonintrusive polynomial chaos methods for transcranial magnetic stimulation (TMS) to investigate the influence of the uncertainty in the electrical conductivity of biological tissues on the induced electric field. The conductivities of three different tissues, namely, cerebrospinal fluid, gray matter (GM), and white matter, are modeled as uniformly distributed random variables. The investigations are performed on a simplified model of a cortical gyrus/sulcus structure. The statistical moments are calculated by means of a generalized polynomial chaos expansion using a regression and cubature approach. Furthermore, the results are compared with the solutions obtained by stochastic collocation. The accuracy of the methods to predict random field distributions was compared by applying different grids and orders of expansion. An investigation on the convergence of the expansion showed that in the present framework, an order 4 expansion is sufficient to determine results with an error of <1%. The results indicate a major influence of the uncertainty in electrical conductivity on the induced electric field. The standard deviation exceeds values of 20%–40% of the mean induced electric field in the GM. A sensitivity analysis revealed that the uncertainty in electrical conductivity of the GM affects the solution the most. This paper outlines the importance of exact knowledge of the electrical conductivities in TMS in order to provide reliable numerical predictions of the induced electric field. Furthermore, it outlines the performance and the applicability of spectral methods in the framework of TMS for future studies.
IEEE Transactions on Magnetics, 2015
The present paper provides the 3-D time-dependent analytical solution of the electromagnetic fiel... more The present paper provides the 3-D time-dependent analytical solution of the electromagnetic fields and forces emerging if a coil or a permanent magnet moves with a sinusoidal velocity profile relative to a conducting slab of finite thickness. The results can be readily used in application scenarios related to electromagnetic damping, eddy current braking, energy harvesting or nondestructive testing in order to efficiently analyze diffusion and advection processes in case of harmonic motion. The study is performed for rectangular and circular coils as well as for cuboidal and cylindrical permanent magnets. The back reaction of the conductor and therewith associated inductive effects are considered. The solutions of the governing equations and the integral expressions for the time-dependent drag-and lift-force are provided. The analytical results are verified by a comparison to numerical simulations obtained by the finite-element method. The relative difference between the analytically and numerically evaluated force profiles was < 0.1%. Exemplary calculations show that the waveforms of both force components strongly depend on the level of constant nominal velocity v0, the magnitude of the velocity oscillation amplitude v1 and the underlying oscillation frequency fv. His current research interests include numerical simulations and visualization of electromagnetic fields, with applications to forward/inverse problems in nondestructive evaluation, bioelectromagnetics, small electrical machines, and magnetic fluid dynamics.
Serbian Journal of Electrical Engineering, 2014