Klaus Krüger

Modelling of lossy coils using fractional derivatives

Coils exposed to eddy current and hysteresis losses are conventionally described by an inductance with equivalent core-loss resistance connected in parallel. The value of the equivalent core-loss resistance depends on the working frequency and the external wiring. Thus the model is less than satisfactory. The authors propose to describe loss inductance using fractional derivatives containing both a loss term and a storage term.After introducing the theory of fractional derivatives, the operating mode of the fractional coil model is explained by the example of an RLC oscillating circuit. Subsequent measurements of a series resonant circuit with a lossy coil impressively confirm the theoretical model with regard to both the frequency and time domains.

Inkjet Printing of Piezoelectric Lead Magnesium Niobate-Lead Titanate Thick Films

This study shows the fabrication of lead magnesium niobate-lead titanate (PMN–PT) thick-films by inkjet printing on ceramic substrates for the first time. PMN–PT powder, prepared by mechanochemical synthesis, is dispersed in an organic solvent using a three roll mill to form a high-viscosity paste. For printing, the paste is thinned to a low-viscosity ink. Small amounts of ethyl cellulose in the ink prevent sedimentation. Glass particles are added to the paste to improve adhesion on the substrate surface. A two step inkjet-printing process forming homogeneous layers is introduced. After sintering at 950 °C for 2 h, piezoresponse force microscopy (PFM) is used to investigate the piezoelectric response of the printed films.