Alice Köstinger

SMES Optimization Benchmark Extended: Introducing Pareto Optimal Solutions Into TEAM22

In 1996, a superconducting magnetic energy storage arrangement was selected to become a benchmark problem for testing different optimization algorithms, both deterministic and stochastic ones. Since the forward problem can be solved semianalytically by Biot-Savarts law, this benchmark became quite popular. Nevertheless, the demands on optimization software have increased dramatically since then. To give an example, methods looking for Pareto-optimal points rather than for a single solution only have been introduced by several groups. In this paper, a proposal for an extended version of the benchmark problem will be made and some results will be presented.

Spectroscopic 16 channel magnetic induction tomograph: The new Graz MIT system

Frequency differential magnetic induction tomography allows the reconstruction of images of relative conductivity spectra with the aid of magnetic AC fields and coil arrays. We describe a new 16-channel hardware with an analog bandwidth of 50 kHz – 1.5 MHz which covers a good part of the s-dispersion of many tissues. At each acquisition time 8 of the 16 excitation coils are simultaneously driven by individual power amplifiers with up to 3 Ass at multiple frequencies. These amplifiers are configured as current sources so that every coil termination is high enough so as not to perturb the field of all other coils. For encoding the excitation coils their individual carrier frequencies differ by 200 - 500 Hz. In this way every excitation frequency is split into 8 subcarriers within a bandwidth of 1.6 - 4 kHz so that they can be approximately considered as a single peak in the comparatively flat tissue spectrum. The magnetic fields are received by 16 planar gradiometers and the induced voltages are amplified by lownoise amplifiers before being fed into the ADC. The real and imaginary parts of the received signals are extracted efficiently with FFT.

Hidden metallic object localization by using giant magnetic resistor sensors

Purpose – The purpose of this paper is to achieve a very accurate localization of hidden metallic objects in human medicine applications.Design/methodology/approach – The proposed methodology takes advantage of the eddy current effect within a metallic object. Its magnetic reaction field will be measured, e.g. with giant magnetic resistor (GMR) sensors.Findings – A comparison of measurements and numerical results obtained by finite element computations demonstrate the reliability and positively gives a clue about the feasibility of the suggested method.Research limitations/implications – While measuring noisy signals, the use of a lock‐in amplifier is rather expensive; especially, in applications with a high number of GMR sensors the use of channel multiplexer must be considered, which again may generate noise.Originality/value – The paper shows how appropriate shielding of external fields in the measurement setup ensures results of satisfying quality.

Optimal design of a disk type magneto-rheologic fluid clutch

SummaryTo transmit a continuously adjustable torque from the main shaft to the move shaft electromagnetic clutches can be used in cars. In contrast to friction clutches, electromagnetic clutches transmit rotation by a magneto-rheologic fluid consisting of a base fluid mixed with numerous ferro-magnetic micro-sized particles. In the absence of a magnetic field a small basic torque is passed on only. Once the flux density is increased, the micro-sized particles start to form firmly tied chains increasing the transmitted torque. The magnitude of the torque can be regulated by the application of an appropriate magnetic field which is simulated by the Finite-Element-Method. The optimal design of the clutch requires a certain torque being transmitted while keeping the weight as small as possible. This task of multi-objective optimization is performed using a higher order Evolution Strategy, a stochastic optimization method.ZusammenfassungZur Übertragung eines stufenlos regelbaren Moments in einem Getriebe kann man elektromagnetische Kupplungen verwenden. Anders als bei normalen Druckkupplungen wird in diesem Fall das Moment mittels einer magneto-rheologischen Flüssigkeit übertragen. Diese besteht aus einer Trägerflüssigkeit, die mit unzähligen Mikropartikeln versetzt ist. Ist kein Magnetfeld vorhanden, überträgt die Kupplung lediglich ein geringes Grundmoment. Sobald allerdings die Flussdichte erhöht wird, beginnen die Mikropartikel, feste Ketten zu bilden. Damit erhöht sich auch das übertragene Moment. Das für die Übertragung verantwortliche Magentfeld wird mittels der Methode der Finiten Elemente simuliert. Ein optimales Design der Kupplung soll ein gegebens maximales Moment übertragen und dabei ein möglichst geringes Gewicht aufweisen. Diese Optimierungsaufgabe, einander widersprechende Ziele zu erfüllen, wird mit einer Evolutionsstrategie, einem stochastischen Optimierungsverfahren, gelöst.

Niching evolution strategy finding global and Pareto optimal solutions

Purpose – The purpose of this paper is to extend a (μ/ρ, λ) evolution strategy to perform remarkably more globally and to detect as many solutions as possible close to the Pareto optimal front.Design/methodology/approach – A C‐link cluster algorithm is used to group the parameter configurations of the current population into more or less independent clusters. Following this procedure, recombination (a classical operator of evolutionary strategies) is modified. Recombination within a cluster is performed with a higher probability than recombination of individuals coming from detached clusters.Findings – It is shown that this new method ends up virtually always in the global solution of a multi‐modal test function. When applied to a real‐world application, several solutions very close to the front of Pareto optimal solutions are detected.Research limitations/implications – Stochastic optimization strategies need a very large number of function calls to exhibit their ability to reach very good local if not t...

e‐Courseware authoring tools for teaching electrodynamics

Nowadays, there are strong movements towards development and usage of multimedia courseware as a means of knowledge transfer. Many authors of textbooks or lecture notes are now striving to redesign the supporting material for their major courses in a structured, highly efficient way, including interactive content and media. Thus, in order to avoid unnecessary work load resulting from updating and publishing various courseware versions, tools for improving document creation and conversion have been developed and are now being applied for the first time on a new “Electrodynamics”‐‐ courseware.