2017
Sample holder
Vectorial magnetotransport measurements are at the heart of spintronics, a vastly growing field in solid state physics that includes, but is not limited to, the investigation of the interplay of magnetization in ultrathin layers (few nm thickness) and electrical currents send directly through them or through an attached normal metal. Key ingredients for such measurements are an external magnetic field to control the orientation of the magnetization of the magnetic layers, a spatially compact rotational stage where the sample can be placed onto, and electrical transport equipment to sense resistive effects that give access to a variety of characteristics of the sample under investigation. Conventionally, this is realized using electromagnets that consist of two coils with iron yokes in their core that point towards each other leaving a so called pole gap. In order to achieve high magnetic fields, which is desirable to control the magnetization of a large variety of magnetic materials, this pole gap needs to be small (usually 1-2 cm). This, in turn, demands a sophisticated rotational stage and electrical contact procedure. The latter has been optimized within the project presented here. While traditionally, any sample had to be placed onto the rotational stage and its fixed Cu bond pads, we realized a 2-part printed circuit board (PCB) solution. In particular, a socket and a carrier PCB has been designed. While the socket PCB, hosting electrical receptacles, is constantly fixed to the rotational stage, the second (carrier) PCB, can be inserted into the socket via its matching electrical pins. The carrier PCB hosts the sample and is connected to it via bond wires. By this, the sample can constantly stay connect to the carrier PCB, since it can be removed together with the carrier PCB. The bond wires remain alive and thus we allow for less sample damage due to less remount procedures if a sample had to be repluged for further measurements. This becomes particularly important for mechanically fragile samples and those that are highly sensitive to electrical discharges. With this, we realized an easy “plug-and-measure” PCB solution.
Arc Rotation Detector
In high voltage substations, common switching operations such as short-circuit interruption and load transfer regularly produce electric arcs at currents in the kiloampère range, typically contained inside specially designed devices. One of the challenges of these switching cases is the erosion of the contact material at temperatures reaching 15’000K and higher. At ETH Zürich’s High Voltage Laboratory (HVL), a novel method of reducing this contact erosion was developed for a particular application in future gas insulated high voltage dc substations. Multiple sets of rare earth magnets are arranged in precalculated locations near the annular contacts in order to generate a Lorentz force acting on the charged particles forming the switching arc. As a result, the electric arc travels at high speeds on the contacts in order to minimize localized heating and thus reduce contact erosion. To correlate different influences and arc speeds, a means of measuring the position of the electric arc as well as its speed over time was designed: The Arc Rotation Detector. Eight identical hall effect sensors transduce the magnetic field perpendicular to the sensor surface into voltage signals which are recorded with digital storage oscilloscope. Since the electric arc in this application is generally constricted to a cross-sectional area in the range of a few square millimeters to a few square centimeters, the approximate location of an arc in space can be calculated from the eight measured magnetic fields and the known positions of the sensors – as long as the noise levels are low. Furthermore, a peak finding algorithm can be used to track the arc’s approximate path and its speed by tracking which sensor is closest to the arc at a given point in time even in noisy applications. Using the Arc Rotation Detector, well over 100 measurements at currents ranging between 250-2500A were successfully analyzed with regard to their arc rotation speeds before the cumulative stress from radiative and convective heating of the arc became too great for the PCB.
LightProbe
The LightProbe is a hand-held ultrasound probe for medical imaging, which integrates the entire frontend in the probe handle and is equipped with a high-speed optical link.
DZ designed the motherboard of the system, which serves as the base-board for an Artix-7 FPGA module and contains a 64-channel receiver frontend and a 26.4 Gb/s optical connector.
DZ also designed a power supply sub-module of the LightProbe system, which generates in a very compact form-factor the required high-voltage supplies (+-50V) for the ultrasound transmit frontend.