Preliminary characterization of a one-axis acoustic system

The acoustic fields and levitation forces produced along the axis of a single-axis resonance system were measured. The system consisted of a St. Clair generator and a planar reflector. The levitation force was measured for bodies of various sizes and geometries (i.e., spheres, cylinders, and discs). The force was found to be roughly proportional to the volume of the body until the characteristic body radius reaches approximately 2/k (k = wave number). The acoustic pressures along the axis were modeled using Huygens principle and a method of imaging to approximate multiple reflections. The modeled pressures were found to be in reasonable agreement with those measured with a calibrated microphone

A magnetic bearing based on eddy-current repulsion

This paper describes a new type of electromagnetic bearing, called the Eddy-Current Bearing, which works by repulsion between fixed AC-electromagnets and a conducting rotor. The following advantages are expected: inherent stability, higher load carrying capacity than DC-electromagnetic bearings, simultaneous radial, angular and thrust support, motoring and generating capability, and backup mode of operation in case of primary power failure. A prototype is under construction

A sublimation heat engine

Heat engines are based on the physical realization of a thermodynamic cycle, most famously the liquid–vapour Rankine cycle used for steam engines. Here we present a sublimation heat engine, which can convert temperature differences into mechanical work via the Leidenfrost effect. Through controlled experiments, quantified by a hydrodynamic model, we show that levitating dry-ice blocks rotate on hot turbine-like surfaces at a rate controlled by the turbine geometry, temperature difference and solid material properties. The rotational motion of the dry-ice loads is converted into electric power by coupling to a magnetic coil system. We extend our concept to liquid loads, generalizing the realization of the new engine to both sublimation and the instantaneous vapourization of liquids. Our results support the feasibility of low-friction in situ energy harvesting from both liquids and ices. Our concept is potentially relevant in challenging situations such as deep drilling, outer space exploration or micro-mechanical manipulation

On the Static Pull-In of Tilting Actuation in Electromagnetically Levitating Hybrid Micro-Actuator: Theory and Experiment

This work presents the results of the experimental and theoretical study of the static pull-in of tilting actuation executed by a hybrid levitation micro-actuator (HLMA) based on the combination of inductive levitation and electrostatic actuation. A semi-analytical model to study such a pull-in phenomenon is developed, for the first time, as a result of using the qualitative technique based on the Lagrangian approach to analyze inductive contactless suspensions and a recent progress in the calculation of mutual inductance and force between two circular filaments. The obtained non-linear model, accounting for two degrees of freedom of the actuator, allows us to predict accurately the static pull-in displacement and voltage. The results of modeling were verified experimentally and agree well with measurements

Numerical and Experimental Investigation of Bridge Currents of an Induction Machine Equipped with Bridge Configured Winding

An eccentric rotor motion imbalances the magnetic field distribution in the air-gap region. Due to this uneven flux density distribution, a net radial force called Unbalanced Magnetic Pull (UMP) is in action towards the shortest air-gap. This UMP can degrade the machine’s performance. UMP can be controlled by a special kind of winding called Bridge Configured Winding (BCW). The BCW winding is a single set of winding which is used to produce the torque as well as the controllable force. The main contribution of this paper is to inspect the flow of bridge currents in the bridges when the machine is having rotor eccentricity or unbalance. The bridge currents in the presence of rotor eccentricity with the stator of an In­duction machine model has been analyzed by using an Electromagnetic Finite Element (FE) solver called Opera 2D/RM solver (Rotation Motion Analysis). The bridge currents have been measured for two different cases., (i) Induction machine model with zero eccentricity, (ii) Induction machine model with 10% static eccentricity of the air gap. Experimental re­sults are presented for the validation of Opera 2D/RM results. A modified 37kW Induction machine has been used for this study. A known mass unbalance is introduced in the perfo­rated disc in order to create the unbalance in the system purposefully. The bridge currents have been measured and compared with and without unbalance present in the system. The comparison of measured bridge currents for all the cases are given in the frequency domain

Dynamics of Liquid Metal Drops Influenced by Electromagnetic Fields

Zusammenfassung Diese Arbeit ist den Effekten gewidmet, die an der Oberfläche von Flüssigmetall im Magnetfeld auftreten können. Im Prinzip erlauben Magnetfelder, Lorentzkräfte auf flüssiges Metall auszuüben und in seinem Innern Induktionswärme zu generieren. Es ist aber auch bekannt, dass Flüssigmetall-Oberflächen durch Magnetfelder dramatische Formänderungen oder Schwingungen erfahren können. Ein Verständnis dieser Phänomene ist wichtig für sämtliche metallurgische Anwendungen, bei denen freie Oberflächen vorkommen. Als repräsentatives Problem untersuchen wir einen Tropfen aus Flüssigmetall, der eine freie Oberfläche mit einem endlichen Volumen verbindet. Wir schliessen Temperatureffekte aus und konzentrieren uns auf die Wirkung der Lorentzkraft. Wir erarbeiten ein Schema zur Klassifikation von Tropfen-Magnetfeld-Problemen basierend auf der Frequenz des Magnetfeldes und dem Shielding-Parameter des Tropfens in diesem Feld. Anhand dieses Schemas wählen wir fünf Fallstudien aus und studieren das Tropfenverhalten im i) transienten, ii) hochfrequenten und iii) mittelfrequenten Magnetfeld. Die Untersuchungen sind vorwiegend analytischer Art, nur die Mittelfrequenz-Studie ist experimentell. Die beiden wichtigsten Probleme, welche die vorliegende Arbeit zum Gegenstand hat, sind das symmetrische Zusammendrücken oder Halten von Flüssigmetalltropfen einerseits und deren azimutale Verformungen andererseits. Für das transiente Magnetfeld werden zwei Studien präsentiert, jede zu einem der beiden Hauptprobleme. Eine Verbindung zwischen transientem und hochfrequentem Feld besteht darin, das mit beiden Feldtypen stationäre Kräfte im Metall erzeugt werden können. Ein wichtiger Unterschied ist jedoch, dass transiente Felder das Metall durchdringen können, während hochfrequente Felder vom Metall abgeschirmt werden, wodurch eine Kopplung zwischen Tropfenform und Magnetfeld entsteht. Die Effekte im hochfrequenten Feld sind daher schwieriger zu modellieren. Wir präsentieren eine Hochfrequenz-Studie, in der es um das Zusammendrücken und Halten von Tropfen in einem gegebenen Magnetfeld geht. Eine zweite Hochfrequenz-Studie beschäftigt sich mit longitudinaler Levitation. Dort geben wir als einfache Tropfenform einen Flüssigmetall-Zylinder vor und ermitteln das Magnetfeld, welches die vorausgesetzte Tropfenform tatsächlich ermöglichen würde. Im mittelfrequenten Feld bieten sich für theoretische Betrachtungen die grössten Schwierigkeiten, da das Magnetfeld den Tropfen nun partiell durchdringt und kaum noch vereinfacht werden kann. Dieser Bereich wurde daher durch die fünfte Studie experimentell erkundet. Dabei wurde eine Flüssigmetall-Scheibe verwendet, welche nur zweidimensionale Verformungen ausführen kann. Die Ergebnisse der Arbeit zeigen, dass insbesondere transiente Magnetfelder gangbare Wege der analytischen Modellierung bieten. Ebenso wie hochfrequente Magnetfelder eignen sie sich zum Formen und Stützen freier Flüssigmetall-Oberflächen. Für das Studium der azimutalen Verformungen hat sich die Scheiben-Geometrie als günstig erwiesen, sowohl analytisch als auch experimentell. Insgesamt zeigt sich, dass eine Fortführung der Arbeit auf dem Gebiet der Wechselwirkung zwischen Magnetfeldern und Flüssigmetall-Oberflächen lohnenswert ist.This work is devoted to the free surface effects that occur when liquid metal is placed in a magnetic field. Principally, magnetic fields allow to exert Lorentz forces on liquid metal and to generate induction heat inside it. But it is also known that liquid metal surfaces in magnetic fields can undergo dramatic shape changes or experience oscillations. An understanding of these phenomena is crucial to all metallurgical applications showing free surfaces. As a representative problem we examine a liquid metal drop that combines a free surface with a finite volume. We exclude heat effects and focus on the consequences of the Lorentz force. To this end, we elaborate a classification scheme for liquid metal drop - magnetic field problems comprising the frequency of the magnetic field and the Shielding parameter of the drop in this field. On that basis we select five case studies involving i) transient, ii) middle-frequency and iii) high-frequency magnetic field to explore the behavior of liquid metal drops in it. We mainly use analytical means - only the middle-frequency study is experimental. The major problems we tackle concern the symmetric squeezing and supporting of drops and its azimuthal deformations, respectively. Two studies are presented for the transient magnetic field, each accounting for one of the two problems. A connection between transient and high frequency magnetic field is the possibility to exert a steady force on the liquid metal. An important difference is that transient fields can penetrate the metal while high-frequent fields are shielded by the metal resulting in a coupling between surface shape and magnetic field distribution. Therefore, the effects of high frequency magnetic fields are more difficult to model. We present one high frequency study where we presuppose the magnetic field and ask for the resulting drop shape (forward problem) and another one where we presuppose a simple surface shape and ask for the best suited magnetic field to obtain it (reverse problem). The most difficulties arise in middle-frequent magnetic fields. Here we have partial shielding which makes it necessary to solve the magnetic diffusion equation and to account for the coupling between magnetic field and drop surface at the same time. In this field, the fifth study reports experimental results on the azimuthal deformations of a liquid metal disc in an inhomogeneous inductor field. The results of the work show that especially the transient fields provide feasible ways for analytical modeling. Like high frequency fields they are suited to shape and to support liquid metal surfaces. To study azimuthal deformations, the disc geometry has proven useful - both analytically and experimentally. Overall, it still seems worthwhile to further investigate the behavior liquid metal surfaces in magnetic fields