Design of an electrochemical micromachining machine

Electrochemical micromachining (μECM) is a non-conventional machining process based on the phenomenon of electrolysis. μECM became an attractive area of research due to the fact that this process does not create any defective layer after machining and that there is a growing demand for better surface integrity on different micro applications including microfluidics systems, stress-free drilled holes in automotive and aerospace manufacturing with complex shapes, etc. This work presents the design of a next generation μECM machine for the automotive, aerospace, medical and metrology sectors. It has three axes of motion (X, Y, Z) and a spindle allowing the tool-electrode to rotate during machining. The linear slides for each axis use air bearings with linear DC brushless motors and 2-nm resolution encoders for ultra precise motion. The control system is based on the Power PMAC motion controller from Delta Tau. The electrolyte tank is located at the rear of the machine and allows the electrolyte to be changed quickly. This machine features two process control algorithms: fuzzy logic control and adaptive feed rate. A self-developed pulse generator has been mounted and interfaced with the machine and a wire ECM grinding device has been added. The pulse generator has the possibility to reverse the pulse polarity for on-line tool fabrication.The research reported in this paper is supported by the European Commission within the project “Minimizing Defects in Micro-Manufacturing Applications (MIDEMMA)” (FP7-2011-NMPICT- FoF-285614)

Selected Papers from 2020 IEEE International Conference on High Voltage Engineering (ICHVE 2020)

The 2020 IEEE International Conference on High Voltage Engineering (ICHVE 2020) was held on 6–10 September 2020 in Beijing, China. The conference was organized by the Tsinghua University, China, and endorsed by the IEEE Dielectrics and Electrical Insulation Society. This conference has attracted a great deal of attention from researchers around the world in the field of high voltage engineering. The forum offered the opportunity to present the latest developments and different emerging challenges in high voltage engineering, including the topics of ultra-high voltage, smart grids, and insulating materials

Electrochemical Safety Studies of Cochlear Implant Electrodes Using the Finite Element Method

Cochlear implants, amongst other neural prostheses, utilise platinum electrodes as an interface between the synthetic implant and the biological tissue environment. If excessive electrical charge is injected via these electrodes, injury to the tissue may result. Empirically derived stimulation limits have been defined to prevent tissue damage, however the injurious mechanisms are still unclear. Evidence suggests that the non-uniform distribution of charge on electrodes influences the electrochemical generation of toxic by-products. However, in vivo and in vitro techniques are limited in their ability to systematically explore the factors and mechanisms that contribute to stimulation-induced tissue injury. To this end, an in silico approach was used to develop a time-domain model of cochlear implant stimulation electrodes. A constant phase angle impedance was used to model the reversible processes on the electrode surface, and Butler-Volmer reaction kinetics were used to define the behaviour of the water window irreversible electrochemical reactions. The resulting model provided time-domain responses of the current density distributions, and net charge consumed by the hydrolysis reactions. This model was then used to perform systematic evaluations of various electrode geometries and stimulation parameters. The modelling results showed the current associated with irreversible reactions was non-uniform and tended towards the periphery of the electrode. A comparison of electrode geometries revealed interactions between electrode size, shape and recess depth. Stimulation mode, electrode position, and electrolyte conductivity were found to impact the shape of the electric field and the extent of irreversible reactions. This emphasised the influence of the physiological environment on the stimulation safety. In vitro experiments were conducted to validate the model. The implications of the results described in this thesis can be used to inform the design of safer electrodes

Charging and Discharging Mechanism of Polyimide under Electron Irradiation and High Voltage

Polyimide has been widely used as insulating and structural materials in spacecraft due to its excellent electrical, thermal and mechanical properties. However, its charging and discharging problem in harsh space environment has been a major limit to the development of high-voltage and high-power spacecraft. In this chapter, charging and discharging phenomena of dielectric materials under electron irradiation environment were presented. First, the electrical properties of polyimide consisting of dielectric properties, trap properties, conductivity and electrical breakdown properties were investigated, which have great influences on charging and discharging characteristics. Then, a surface charging model under relatively low-energy electron irradiation was proposed for polyimide, based on the synergistic effects of electron movement above surface and charge transport in surface layer. The DC surface flashover of polyimide under electron irradiation with different energies, fluxes and incident angles was investigated. Furthermore, a deep charging model under high-energy electron irradiation with the Fluence Model for Internal Charging (FLUMIC) spectrum was established. The effects of electron flux enhancement and operating voltage on charging characteristics were discussed in different grounding modes. It indicates that the processes of discharging under electron irradiation have a close link with the charge transport characteristics of polyimide

Outdoor Insulation and Gas Insulated Switchgears

This book focuses on theoretical and practical developments in the performance of high-voltage transmission line against atmospheric pollution and icing. Modifications using suitable fillers are also pinpointed to improve silicone rubber insulation materials. Very fast transient overvoltage (VFTO) mitigation techniques, along with some suggestions for reliable partial discharge measurements under DC voltage stresses inside gas-insulated switchgears, are addressed. The application of an inductor-based filter for the protective performance of surge arresters against indirect lightning strikes is also discussed

Development of prototype components for the Silicon Tracking System of the CBM experiment at FAIR

Das CBM-Experiment an der zukuenftigen Beschleunigeranlage FAIR wird die Eigenschaften von Kernmaterie unter extremen Bedingungen untersuchen. Das experimentelle Programm unterscheidet sich von den Schwerionen-Experimenten an RHIC (BNL) und LHC (CERN), die Kernmaterie bei hohen Temperaturen erzeugen. Im Gegensatz dazu kann die Untersuchung des QCD-Phasendiagramms, im Bereich der hoechsten Nettobaryonendichten und moderaten Temperaturen, die nur schwach untersucht wurden, mit hoher Praezision durchgefuehrt werden. Hierzu werden Kollisionen der verschiedenen Schwerionenstrahlen, bei Energien von 10-45GeV/Nukleon, mit nuklearem Target gemessen. Das physikalische Programm des CBM Experimentes umfasst die Messung sowohl der seltenen Sonden als auch der Mengenobservablen, die aus verschiedenen Zeitphasen des Zusammenstosses der Kerne stammen. Insbesondere kann der Zerfall von Teilchen mit Charm-Quarks durch Rekonstruktion des Zerfallsvertex, versetzt von dem primaeren Wechselwirkungspunkt um mehrere hundert Mikrometer, registriert werden. Hierzu ist praezises Tracking bei voller Ereignisrekonstruktion, mit bis zu 600 Spuren der geladenen Teilchen pro Ereignis innerhalb der Akzeptanz, noetig. Andere seltene Sonden erfordern den Betrieb bei einer Wechselwirkung von bis zu 10 MHz. Das Detektor-System, dass Tracking durchfuehrt, muss eine hohe Ortsaufloesung, auf der Ebene von 10 um leisten, mit hohen Arbeitsgeschwindigkeiten zu betreiben sein und ebenso ein strahlungstolerantes Design mit geringem Materialbudget besitzen. Das Silicon Tracking System (STS) wurde entwickelt um die Spuren geladener Teilchen in einem Magnetfeld zu rekonstruieren. Das System besteht aus acht Tracking Stationen, die sich in der Oeffnung eines Dipolmagneten mit 1T Feld befinden. Bei Spuren mit Impulsen ueber 1 GeV, betraegt die Impulsaufloesung bei einem solchen System etwa 1%. Um diese Aufgabe erfuellen zu koennen, ist eine sorgfaeltige Optimierung des Detektordesigns erforderlich. Insbesondere muss ein minimales Materialbudget erreicht werden. Die Herstellung eines Detektor-Moduls erfordert Aktivitaeten mit Bezug auf die Modul-Komponenten und deren Integration. Ein Detektor-Modul ist eine grundlegende funktionelle Einheit, die einen Sensor, ein Analogmikrokabel und Front-End-Elektronik umfasst, montiert auf einer Traegerstruktur. Das Ziel der Arbeit ist es, die Qualitaetssicherungstests der Prototyp-Modulkomponenten, zur Bestaetigung des Detektor-Modul-Konzeptes durchzufuehren, und um seinen Betrieb mit radioaktiven Quellen und Teilchenstrahlen zu demonstrieren. Die doppelseitigen Silizium-Mikrostreifendetektoren wurden als Sensortechnik fuer den STS, aufgrund der Kombination einer guten Ortsaufloesung, einer zweidimensionalen Koordinatenmessung mit geringem Materialbudget (0.3%X0), der hohen Auslesegeschwindigkeit und ausreichender Strahlungstoleranz gewaehlt. Mehrere Generationen von doppelseitigen Silizium-Mikrostreifendetektoren wurden zur Erkundung strahlenharter Konstruktionsmerkmale und des Konzepts, eines grossflaechigen Sensors und dessen Kompatibilitaet mit der Leiter-Struktur des Detektor-Moduls, hergestellt. Insbesondere wurden Sensoren mit doppelter Metallschicht auf beiden Seiten und aktivem Bereich von 62x62 mm2 produziert. Die elektrische Charakterisierung der Sensoren wurde durchgefuehrt, um die gesamte Bedienbarkeit sowie die Extrahierung der Geraeteparameter feststellen zu koennen. Strom und Kapazitaets-Spannungs-Charakteristiken sowie Interstreifenparameter wurden gemessen. Das Auslesen der Sensoren wurde mithilfe einer selbstgetriggerten Front-End-Elektronik getaetigt. Ein Front-End-Board wurde auf der Grundlage eines n-XYTER-Auslesechips mit datengesteuerter Architektur entwickelt, der geeignet ist bei Auslesegeschwindigkeit von 32MHz betrieben zu werden. Die Front-End-Platine enthaelt einen externen Analog-zu-Digital-Wandler (ADC). Die Kalibrierung des ADC wurde unter Verwendung von sowohl Roentgenquelle als auch eines Impulsgenerators vorgenommen. Die Schwellenkalibrierung und Untersuchung der Temperaturabhaengigkeit der Chip-Parameter wurden durchgefuehrt. Die ultraleichten Halterungsstrukturen wurden aus Kohlefaser entwickelt, diese haben die Steifigkeit, die Detektor-Module halten, und die minimale Coulomb-Streuung der Teilchenspuren einbeziehen zu koennen. Es wurden Analogmikrokabel mit Aluminiumleiterbahnen auf einem Polyimidsubstrat produziert - eine Kombination von guter elektrischer Verbindung und geringem Materialbudget. Die Mikrokabelstruktur umfasst mehrere Lagen optimiert fuer die niedrige Kapazitaet der Leiterbahnen und den damit verbundenen geraeuscharmen Betrieb. Es wurden Analog-Mikrokabel mit Aluminiumleiterbahnen auf einem Polyimidsubstrat produziert, also eine Kombination von guter elektrischer Verbindung und geringem Materialbudget. Die Mikrokabelstruktur umfasst mehrere Lagen optimiert fuer die niedrige Kapazitaet und den damit verbundenen geraeuscharmen Betrieb. Es wurde ein Demonstrator-Tracking-Teleskop gebaut und in mehreren Strahltests, einschliesslich 2.5 GeV Protonenstrahl an COSY (Juelich), betrieben. Drei Tracking-Stationen wurden mit Hodoskopen ergaenzt. Die Datenanalyse ergab Informationen ueber Analog- und Zeitverhalten sowie Strahlenprofil. So wurden Tracking- und Alignmentinformationen erhalten. Mit speziell entwickelten Monitoring-Tools wurde die Strahlstabilitaet bewertet. Als Ergebnis der Studien, wurde die Leistung der Modulkomponenten bewertet und die Anforderungen zum Detektormodul formuliert. Die genaue Definition des endgueltigen Detektormoduldesigns jedoch, war ausserhalb des Geltungsbereichs dieser Arbeit.The CBM experiment at future accelerator facility FAIR will investigate the properties of nuclear matter under extreme conditions. The experimental programm is different from the heavy-ion experiments at RHIC (BNL) and LHC (CERN) that create nuclear matter at high temperatures. In contrast, the study of the QCD phase diagram in the region of the highest net baryon densities and moderate temperatures that is weakly explored will be performed with high precision. For this, collisions of different heavy-ion beams at the energies of 10–45GeV/nucleon with nuclear target will be measured. The physics programme of the CBM experiment includes measurement of both rare probes and bulk observables that originate from various phases of a nucleus-nucleus collision. In particular, decay of particles with charm quarks can be registered by reconstructing the decay vertex detached from the primary interaction point by several hundreds of micrometers (e.g., decay length c Tau = 123 µm for D0 meson). For this, precise tracking and full event reconstruction with up to 600 charged particle tracks per event within acceptance are required. Other rare probes require operation at interaction rate of up to 10MHz. The detector system that performs tracking has to provide high position resolution on the order of 10 µm, operate at high rates and have radiation tolerant design with low material budget. The Silicon Tracking System (STS) is being designed for charged-particle tracking in a magnetic field. The system consists of eight tracking station located in the aperture of a dipole magnet with 1T field. For tracks with momentum above 1GeV, momentum resolution of such a system is expected to be about 1%. In order to fulfill this task, thorough optimization of the detector design is required. In particular, minimal material budget has to be achieved. Production of a detector module requires research and development activities with respect to the module components and their integration. A detector module is a basic functional unit that includes a sensor, an analogue microcable and frontend electronics mounted on a support structure. The objective of the thesis is to perform quality assurance tests of the prototype module components in order to validate the concept of the detector module and to demonstrate its operation using radioactive sources and particle beams. Double-sided silicon microstrip detectors have been chosen as sensor technology for the STS because of the combination of a good spatial resolution, two-dimensional coordinate measurement achieved within low material budget (0.3%X0), high readout speed and sufficient radiation tolerance. Several generations of double-sided silicon microstrip sensors have been manufactured in order to explore the radiation hard design features and the concept of a large-area sensor compatible with ladder-type structure of the detector module. In particular, sensors with double metal layer on both sides and active area of 62×62mm2 have been produced. Electrical characterization of the sensors has been performed in order to establish the overall operability as well as to extract the device parameters. Current-voltage, capacitance-voltage characteristics and interstrip parameters have been measured. Readout of the sensors has been done using self-triggering front-end electronics. A front-end board has been developed based on the n-XYTER readout chip with data driven architecture and capable of operating at 32MHz readout rate. The front-end board included an external analog-to-digital converter (ADC). Calibration of the ADC has been performed using both 241Am X-ray source and external pulse generator. Threshold calibration and investigation of temperature dependence of chip parameters has been carried out. Low-mass support structures have been developed using carbon fibre that has the rigidity to hold the detector modules and introduce minimal Coulomb scattering of the particle tracks. Analogue microcables have been produced with aluminium traces on a polyimide substrate, thus combining good electrical connection with low material budget. Microcable structure includes several layers optimized for low trace capacitance and thus low-noise performance. A demonstrator tracking telescope has been constructed and operated in several beam tests including 2.5GeV proton beam at COSY synchrotron (Jülich). Three tracking stations have been complemented with several beam hodoscopes. Analysis of the beam data has yielded information on analogue and timing response, beam profile. Tracking and alignment information has been obtained. Beam stability has been evaluated using specially developed monitoring tools. As a result of conducted studies, performance of the module components have been evaluated and requirements to the detector module have been formulated. Practical suggestions have been made with respect to the structure of the detector module, whereas precise definition of the final detector module design was outside of the scope of this thesis

Generation of Large-Volume Diffuse Plasma by an External Ionization Wave From a Single-Electrode Plasma Jet

A non-thermal transient diffuse plasma can be generated remotely in a nonconductive reduced pressure chamber by an external guided fast ionization wave (FIW). We found that an atmospheric-pressure low-temperature plasma jet (APPJ) can be a source of FIW which transfers an enhanced electric field at the wave front across a reduced pressure Pyrex glass chamber with no electrical connection to the chamber. Here, we studied the formation and propagation of the APPJ plasma, the interaction of atmospheric-pressure guided FIW with a dielectric surface which forms the wall of the reduced-pressure system, and the formation and propagation of the reduce-pressure FIW inside a chamber. In this study, key characteristics of the transient diffuse plasma are discussed. The reduced pressure plasma parameters were measured by Langmuir probe and APPJ electrical measurements were carried out to elucidate the operational mechanisms of the guided FIW as an igniter of the reduced-pressure transient diffuse plasma. It was shown that the transient discharge in the reduced-pressure chamber was generated by an enhanced electric field (18.5 kV/cm when the APPJ applied voltage was 8.5 kV) inside the chamber that generated a bulk plasma with negative potential due to the nonconductive boundary. We used fast imaging of both APPJ plasma plume and the transient reduced-pressure FIW inside the Pyrex chamber. Fast images were taken by an intensified CCD to study the launching and propagation phases of both APPJ plasma and the transient reduced-pressure diffuse plasma as well as the incidence of the guided FIW on a dielectric surface. The APPJ plasma plume images revealed that the plasma plume created by guided FIW was in fact made of two discrete volumetric discharges (known as plasma bullet) per applied high-voltage pulse traveling at supersonic velocities up to 170 km/s. Since such a volumetric discharge was initiated by a surface discharge inside the APPJ hollow tube, it had a donut-shaped structure. We also used Optical emission spectroscopy (OES) to determine the physical and chemical characteristics of the APPJ plasma and the transient diffuse plasma. It was shown that the diffuse plasma was capable of producing first and second ionized nitrogen (N+ and N++), atomic oxygen (O), ionized nitrogen molecule (N2+), and OH• radicals in helium diffuse plasma (with air impurities) and in air diffuse plasma. The present research shows that this type of electrodeless non-thermal, large-volume diffuse plasma resembles a fast-growing transient glow discharge that lasts for several hundreds of nanoseconds. The electron density in such a plasma with the admixture of helium and air can reach up to 1012 cm-3 at a pressure around 1 Torr. A promising application of the large-volume diffuse plasma is in surface processing such as plasma-aided coating and etching processes with minimal contamination due to the clean environment inside the reduced-pressure system