Electrostatics | EPFL Graph Search

Electrostatics is a branch of physics that studies slow-moving or stationary electric charges. Since classical times, it has been known that some materials, such as amber, attract lightweight particles after rubbing. The Greek word for amber, ἤλεκτρον (), was thus the source of the word 'electricity'. Electrostatic phenomena arise from the forces that electric charges exert on each other. Such forces are described by Coulomb's law. There are many examples of electrostatic phenomena, from those as simple as the attraction of plastic wrap to one's hand after it is removed from a package, to the apparently spontaneous explosion of grain silos, the damage of electronic components during manufacturing, and photocopier & laser printer operation. Electrostatic forces play a large role at the nanoscale; for instance, the force between an electron and a proton, which together make up a hydrogen atom, is about 36 orders of magnitude stronger than the gravitational force acting between them.

Reliable MEMS Actuators for Driving Large Microsystems

Nicolas Bernard Golay

Nowadays many consumer electronic devices are using small engines (micromotors). Thanks to technological innovation, the components can be imbedded into numerous portable systems. The key factors for a nomadic integration are: reduction of power consumption, reliability, durability and manufacturing cost. From the perspective of an always denser integration, conventional fabrication techniques of motors are reaching their limits (windings, size of the permanent magnet). The technologies developed for the micro-electronics (thin film processes) offer new possibilities to create microscopic size motors. The potential for innovation in this field being very wide, many new concepts are based on this technology. Lots of research centers are trying to find new principles of actuation to increase the overall efficiency of motors. With the challenge of replacing a small "classical" motor by a micromotor based on thin film technologies, the electrostatic actuation is going to have a great potential in the future. Many problems are related to the compatibility of both technologies in terms of coexistence. This is mainly due to problems of dimensions and associated tolerances. The challenge of this research was to propose a solution for the creation of a micromotor including the following concepts: usable mechanical interface between an outer gear and the mechanical output torque of the micromotor (about 0:5 µNm), moderate energy consumption, relatively small chip size in relation to the required performances and finally ability to be easily implemented in a mechanism (module). This thesis presents the different aspects of the concept, design, simulation, fabrication and characterization of a MEMS based motor using silicon micro-technologies. The micromotor is constituted of a fixed base (stator) with an electrostatic actuator (force generator), a rotor and a protective cover (encapsulation). The principle of the electrostatic actuation is based on a comb inter-digitized configuration. A first interface (ratchet system) was developed to allow for the conversion of the back and forth movement of the linear type actuator to a circular motion of the silicon rotor. A challenge was to create an actuator able to deliver an electrostatic force of 500 µN with a applied potential of 40 V. To obtain this force, the actuator itself has an active area of over 10 mm2. The first concept has two large actuators representing 60% of the total area of the stator. In the second concept, the occupied area of the three actuators represents 40 % of the total area of the stator. Two systems were created during this work, based on the same principles of actuation and of actuator/rotor interfacing. The first system uses a crank mechanism to interface the silicon rotor and a metallic pinion. The encapsulation was achieved via a metal support on which a plastic lid was fastened. These two pieces were fabricated by conventional machining (milling) techniques. The micromotor module was made by assembling the different components. The second system was made based on a direct interface type (direct link between internal teeth of the silicon rotor and outer teeth of a metallic gear). The encapsulation concept uses only micro-technologies. The cover was made of a glass substrate on which a silicon spacer was bonded (anodic bonding process). The motor module was then achieved by assembling a silicon base (stator), a silicon rotor and a silicon/glass cover. In accordance with the specifications, the obtained results are very promising. The electrostatic force generated by the actuator is in the order of few hundreds of micronewton. The power consumption is in the order of few microwatts. Many innovative concepts have been studied and manufactured. Some of those have been patented, showing the interest of these new ideas. Experiments have demonstrated the functionality of a MEMS engine.

EPFL2010

Micro- and nano-electrostatic force fields

Martin Jenke

Electro-static or electro-dynamic fields generated by micro- or nano-electrodes are today widely used in many different fields, such as micro- and nanogripping, "lab on a chip", and "lab in a cell", for the purpose of manipulation, separation, or analysis of micron-sized particles, cells, or single molecules. Commonly numerical simulations and Electrostatic Force Microscopy (EFM) methods, based on Atomic Force Microscopy (AFM), are used to study and predict the electrostatic force fields above produced structures. However, this measurement methods have several disadvantages. These disadvantages range from simple limitations (e.g. it is not possible to measure in three dimensions or expensive new equipment is needed) to much more serious disadvantages (e.g. missing compensation for known AFM problems, which results in wrong measurements). In this thesis we propose a new EFM method based on simple static force distance curves, which allows measuring accurately, and simultaneously the topography, vertical electrostatic force field and attraction forces. The method is numerical simulated in 3D to study in detail, with simulations and measurements, electrostatic force fields above nanoelectrodes. To do this, we show for the first time the fabrication of interdigitated nanoelectrodes with pitches down to 50 nm with gas assisted focused ion beam milling. We present as well for the first time the fabrication of Pt coated AFM tips with radii between 50 and 600 nm, together with their calibration. These tips not only close the gap between conventional tips with tip radii of about 10 nm and cantilevers with attached spheres. They show as well high mechanical stability, which solves a common problem in EFM, the mechanic stability of the tip. The shape of the tip greatly influences the measurement. We demonstrate this using numerical simulations, and show that already small tip discrepancies can change the measured force up to 50 %. Moreover, we proved that changes in the relative humidity result in electrostatic force changes of up to 45 %. We discovered that the resolution of EFM measurements on nanoelectrodes can be enhanced by using a tip radius of 2 to 2.5 times the pitch of the measured interdigitated nanoelectrode. Based on this and its influence on topography measurements, which are usually made before, in between or at the end of EFM measurements, we give hints for measurements with different tip radii. Beside these important general improvements, discoveries and hints for EFM, we show as well some applications of our new EFM method and the before obtained results. We show that our new method can distinguish the force field caused by trapped charges in SiO2 from the force field caused by nanoelectrodes below it. This enables to study the influence of charge trapping in future semiconductor chips, which use charge trapping to store information. Furthermore, we used our new EFM method and some gripping experiments to study electrostatic micro-and nanogripping. This experiments lead to some propositions for improvements in electrostatic micro-and nanogripping. Such as a new gripper design with gripping object size independent centering effect, which is studied using 3D numerical simulations.

EPFL2008

Analytical Methods for the Study and Design of Integrated Switched Oscillators and Antennas for Mesoband Radiation

Jose Felix Vega Stavro

This thesis was carried out within the framework of a scientific cooperation project entitled “Application of High Power Electromagnetics to Human Safety” developed by the EPFL, the National University of Colombia and Los Andes University, Colombia. The project was funded by the Swiss Agency for Development and Cooperation (SDC) through the EPFL Centre Coopéation & Développement (CODEV). The Scientific Cooperation aimed at the study and development of techniques for the generation of high power electromagnetic signals for the disruption or preemptive activation of Improvised Explosive Devices (IEDs) during humanitarian clearance activities. The results and conclusions of the thesis will be applied to the construction of a resonant radiator, which can be used for securing humanitarian demining operations in Colombia. The thesis is devoted to the analysis of a specific type of resonant radiators known as Switched Oscillators (SWO). An SWO is a radiator constituted by a high voltage charging circuit that drives a quarter-wave transmission line resonator connected to an antenna. An SWO can produce high-amplitude, short duration, electromagnetic fields, with a moderate bandwidth, when compared to the main resonance frequency. The outcome of the thesis can be also be used in electromagnetic compatibility applications, for the production of resonant, high power electromagnetic fields, with the aim of testing the immunity of electronic systems against Intentional Electromagnetic Interference (IEMI) attacks. The thesis is divided in three parts. The first part deals with the electrostatic design of an SWO. A method for producing an optimized design of the electrodes forming the spark gap of the SWO is presented. The method is based on the generation of a curvilinear coordinate space on which the electrodes are conformal to one of the coordinate axis of the space. Laplace equation is solved in the interelectrodic space, obtaining an analytical solution for the electrostatic distribution. Furthermore, using appropriate mathematical manipulations, we derive an analytical expression for the impedance of the transmission line formed by the proposed electrodes. The second part of the thesis is devoted to the analysis of SWOs in the frequency domain. An original analysis approach, based on the chain-parameter technique, is proposed in which the SWO and the connected antenna are described using a two-port network using which a transfer function between the input voltage and the radiated field is established. A closed form expression of the resonance frequency of the SWO is also obtained. The developed technique makes it possible to study the response of an SWO when connected to an arbitrary antenna with a frequency-dependent input impedance. The final part of the thesis presents the construction and test of an SWO prototype. The prototype design is based on the theoretical developments presented in the first two parts of the thesis. The realized SWO is experimentally characterized using different antennas. It is characterized by an input voltage of 30 kV and a resonance frequency of 433 MHz. Radiated electric fields using monopole antennas were in the order of 10 kV/m at a distance of 1.5 m. The prototype is used for testing the validity of the electrodynamic model for the analysis of SWOs connected to frequency dependent antennas. Different monopole antennas connected to the SWO are considered and the radiated fields are measured and compared with theoretical calculations. It is shown that the developed theoretical model is able to reproduce with a good accuracy the behavior of the SWO connected to a frequency dependent antenna.

EPFL2013