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)

Development of Cryogenic Current Comparators with DC Squid Readout for the Calibration of Electrical Standards

For the realization of the electrical quantum metrology triangle (V-A-Ω) a device to amplify very small currents with high precision is needed. The cryogenic current comparator (CCC) is by far the best instrument to do this. In order to make a very current sensitive CCC for calibration of electrical standards, we have developed optimum dc Superconducting QUantum Interference Devices (SQUIDs). The design, fabrication and characterisation of these devices is presented. The measurements concern the flux-to-voltage transfer and the noise properties, especially the input current noise. The optimisation of the flux transformer circuit that links the CCC with the SQUID will be treated. In addition, typical fabrication aspects of the CCC as the wires and tube assembly, the shields and the support system will be addressed

Experimental studies of static torque/rotor position characteristics of stepper motors

W artykule podano definicję charakterystyki kątowej momentu statycznego silnika skokowego i zamieszczono klasyfikację stanowisk do badań charakterystyk kątowych. Opisano zbudowaną w Politechnice Warszawskiej automatyczną stację pomiarową do badania charakterystyk statycznych silników skokowych, skonstruowaną z wykorzystaniem wieloletnich doświadczeń autorów w dziedzinie badania właściwości mikromaszyn elektrycznych. Opisano schemat budowy stanowiska pomiarowego, podano konfigurację systemu pomiarowego. Scharakteryzowano program komputerowy do sterowania pomiarami i prowadzenia akwizycji wyników oraz ich graficznej wizualizacji. Na zakończenie zamieszczono przykładowe charakterystyki silników otrzymane opisanym urządzeniem i ich interpretację.In the introduction of the paper there is justified a need of using modern and effective test stands for studying stepper motors with regard to automation of their manufacturing processes and mass production of these motors. A definition of static torque/rotor position charac-teristics of a stepper motor as well as a definition of its static stability zone and angular deviation of the rotor position while loaded with an external torque are given. There is included a classification of test stands for studying angular characteristics of stepper motors (Fig. 1), and there is described an automatic measurement station for studying static characteristics of stepper motors, built at the Warsaw University of Technology, designed on the basis of a long-standing experience of the authors in the field of studying properties of electric micromachines. A schematic of a structure of the measurement station is shown (Fig. 2), and a configuration of the measuring system is presented (Fig. 3). In Tab. 1 the basic functional parameters describing the device are collected and its essential metrological features are given. In the further part of the paper there is characterized a computer program for controlling measurements and performing data acquisition related to results of the measurements as well as their graphical visualization. An algorithm of the program operation is also presented (Fig. 5). At the end there are presented exemplary static torque/rotor position characteristics of a hybrid motor supplied in a standard way (Fig. 6) and not supplied (no current flow) - Fig. 7, obtained by means of the described system. The summary describes shortly the content of the paper and provides interpretation of the obtained results of measurements. The references consist of an extensive list of publications related to the problem of studying characteristics of stepper motors, issued over a period of many years

Bonding of a niobium wire to a niobium thin film

A method for bonding a niobium wire to a niobium thin film is described. The bonds are to be used as superconducting connections between wire-wound gradiometers and thin-film coupling coils on DC SQUIDS. The method is characterized by two steps. Firstly, the hardness of the niobium wire is reduced by a heat treatment. Secondly, the niobium film is covered with a thin layer of palladium to prevent it from oxidizing. Superconducting bonds were realized using an ultrasonic bonding technique. The authors tested the bonds and measured supercond. (to a sensitivity level of 6 * 10-15 W) with currents up to 80 micro A, which is equiv. to 10 times the dynamic range of the DC SQUID systems. Even at 80 micro A, limited by the measuring set-up, the crit. current of the bonds is not reached. [on SciFinder (R)

Changes in electromyographic signals and skin temperature during standardised effort in volleyball players

The state of athletes’ muscles is not constant, but it differs depending on the stage of sports training, which is associated with different degrees of muscle fatigue. There is thus a need to find a non-invasive and simple method to assess muscle fatigue. The aim of the study was to determine the relationship between muscle fatigue due to physical effort and changes in skin temperature, measured using a thermographic camera. Methods: The study involved 12 volleyball players. The participants were to maintain 70% of peak torque in the joint for as long as possible. We measured peak torque and the time of maintaining 70% of its value (tlim) as well as continuously recording skin temperature and electromyographic (EMG) signals in the region of the belly of the rectus femoris. The measurements were taken twice: before and after a series of squats. Results: The study found that tlim decreased when isometric contraction was performed after physical effort. Pre- and post-exercise skin temperature did not differ significantly, however, the increase rates of temperature and the root mean square (RMS) of the EMG signals grew significantly. In most of the players, skin temperature also correlated with the RMS, median frequency (MDF), and mean frequency (MF) of the EMG signals. Conclusions: Measuring the time of maintaining submaximal torque during isometric contraction and the slope coefficient for the increase in temperature recorded using a thermographic camera can be a simple, cost-effective, and non-invasive method of assessing fatigue and efficiency decreases in the muscles in volleyball players