A 19-channel d.c. SQUID magnetometer system for brain research

A 19-channel d.c. SQUID magnetometer system for neuromagnetic investigations is under constuction. The first-order gradiometers for sensing the signal are placed in a hexagonal configuration. D.c. SQUIDs based on niobium/aluminium technology have been developed, leading to a field sensitivity of about 5 fT/ Hz. SQUID read-out is realized with a resonant transformer circuit at 100 kHz. The multichannel control and detection electronics are compactly built

The UT 19-channel DC SQUID based neuromagnetometer

A l9-channel DC SQUID based neuromagnetometer is under construction at the University of Twente (UT). Except for the cryostat all elements of the system are developed at the UT. It comprises 19 wire-wound first-order gradiometers in a hexagonal configuration. The gradiometers are connected to planar DC SQUIDS fabricated with a Nb/Al, AlOx/Nb technology. For this connection we developed a method to bond a Nb wire to a Nb thin-film. The SQUIDs are placed in compartmentalised Nb modules. Further, external feedback is incorporated in order to eliminate cross talk between the gradiometers. The electronics basically consist of a phase-locked loop operating with a modulation frequency of 100 kHz. Between SQUID and preamplifier a small transformer is used to limit the noise contribution of the preamplifier. In the paper the overall system is described, and special attention is paid to the SQUID module (bonding, compartments, external-feedback setup, output transformer)

Filtering techniques for noise suppression in quasi-balanced circuits

Filtering techniques for noise suppression in quasi-balanced circuit

Power electronics for a 1-kilowatt arc jet thruster

After more than two decades, new space mission requirements have revived interest in arcjet systems. The preliminary development and demonstration of new, high efficiency, power electronic concepts for start up and steady state control of dc arcjets is reported. The design comprises a pulse width modulated power converter which is closed loop configured to give fast current control. An inductor, in series with the arcjet, serves the dual role of providing instantaneous current control, as well as a high voltage arc ignition pulse. Benchmark efficiency, transient response, regulation, and ripple data are presented. Tests with arcjets demonstrate that the power electronics breadboard can start thrusters consistently with no apparent damage and transfer reliably to the nondestructive high voltage arc mode in less than a second

Fully integrated millimeter-wave CMOS phased arrays

A decade ago, RF CMOS, even at low gigahertz frequencies, was considered an oxymoron by all but the most ambitious and optimistic. Today, it is a dominating force in most commercial wireless applications (e.g., cellular, WLAN, GPS, BlueTooth, etc.) and has proliferated into areas such as watt level power amplifiers (PA) [1] that have been the undisputed realm of compound semiconductors. This seemingly ubiquitous embracement of silicon and particularly CMOS is no accident. It stems from the reliable nature of silicon process technologies that make it possible to integrated hundreds of millions of transistors on a single chip without a single device failure, as evident in today’s microprocessors. Applied to microwave and millimeter wave applications, silicon opens the door for a plethora of new topologies, architectures, and applications. This rapid adoption of silicon is further facilitated by one’s ability to integrate a great deal of in situ digital signal processing and calibration [2]. Integration of high-frequency phased-array systems in silicon (e.g., CMOS) promises a future of low-cost radar and gigabit-per-second wireless communication networks. In communication applications, phased array provides an improved signal-to-noise ratio via formation of a beam and reduced interference generation for other users. The practically unlimited number of active and passive devices available on a silicon chip and their extremely tight control and excellent repeatability enable new architectures (e.g., [3]) that are not practical in compound semiconductor module-based approaches. The feasibility of such approaches can be seen through the discussion of an integrated 24GHz 4-element phased-array transmitter in 0.18μm CMOS [2], capable of beam forming and rapid beam steering for radar applications. On-chip power amplifiers (PA), with integrated 50Ω output matching, make this a fully-integrated transmitter. This CMOS transmitter and the 8-element phased-array SiGe receiver in [5], demonstrate the feasibility of 24GHz phased-array systems in silicon-based processes

A high-input impedance differential millivolt meter for use with solid ceramic oxygen electrolyte cells

Design factors are given for a high-input impedance differential millivolt meter designed, built, and tested as an inexpensive solid-state electronic system for use in measuring the electromotive force from solid ceramic oxygen electrolyte cells. A schematic diagram is included

Aircraft electromagnetic compatibility

Illustrated are aircraft architecture, electromagnetic interference environments, electromagnetic compatibility protection techniques, program specifications, tasks, and verification and validation procedures. The environment of 400 Hz power, electrical transients, and radio frequency fields are portrayed and related to thresholds of avionics electronics. Five layers of protection for avionics are defined. Recognition is given to some present day electromagnetic compatibility weaknesses and issues which serve to reemphasize the importance of EMC verification of equipment and parts, and their ultimate EMC validation on the aircraft. Proven standards of grounding, bonding, shielding, wiring, and packaging are laid out to help provide a foundation for a comprehensive approach to successful future aircraft design and an understanding of cost effective EMC in an aircraft setting

Numerická analýza a simulace Rogowského cívky

This work illustrates an analysis of Rogowski coils for power applications, when operating under non ideal measurement conditions. The developed numerical model, validated by comparison with other methods and experiments, enables to investigate the effects of the geometrical and constructive parameters on the measurement behavior of the coil and we also study the behavior of Rogowski coils coupled with bar conductors under quasi-static conditions. Through a finite element (FEM) analysis, we estimate the current distribution across the bar and the flux linked by the transducer for various positions of the primary conductor and for various operating frequencies. Simulation and experimental results are reported in the text.Tato práce ilustruje analýzu rogowských cívek pro energetické aplikace při provozu v podmínkách bez ideálního měření. Vyvinutý numerický model, ověřený porovnáním s jinými metodami a experimenty, umožňuje zkoumat vliv geometrických a konstrukčních parametrů na chování měření cívky a také studujeme chování rogowských cívek spojených s tyčovými vodiči za kvazi-statických podmínek . Pomocí analýzy konečných prvků (FEM) odhadujeme rozložení proudu přes tyč a tok spojený snímačem pro různé polohy primárního vodiče a pro různé provozní frekvence. Simulační a experimentální výsledky jsou uvedeny v textu.410 - Katedra elektroenergetikydobř