Core Loss Density Research Articles

Reliability Testing on a Multilayer Chip Inductor Fabricated From a Ferrite With a 350 °C Curie Point

As more electronics are used in down-hole energy exploration, under the hood automotive applications, and in other environments where temperatures exceed 200 °C; there is a need for compact passive magnetic components that operate reliably at elevated temperatures. Most ferrites used to make multi layer ceramic inductors have Curie temperatures in the 100–200 °C range. As temperatures rise above the Curie point ferrites lose their magnetic properties and become paramagnetic. This means that traditional multi-layer ceramic inductors suffer severe performance degradation when operated at elevated temperatures. Therefore, ferrite materials with higher Curie temperatures need to be developed to increase device performance and reliability at these high temperatures. In this work inductors were made from a low-temperature, co-fire compatible, ferrite with a Curie temperature of 350 °C. The inductors were first subjected to a 1000 hour life test at 300 °C during which the electrical parameters were found to change no more than 4 %. The inductance, resistance, core loss, and saturation flux density of the inductors were measured at various temperatures. Additional testing focused on the effect of temperature on the device's frequency profile and performance changes under thermal cycling and thermal shock.

An automated measurement system for core loss characterization

This paper describes an automated measurement system for core loss characterization. This system can accomplish these aims, within specified magnetic induction and frequency ranges, and at different temperatures, with high accuracy, due to the techniques used in the acquisition and computation of the waveforms involved in loss calculation. The core loss characterization, obtained by fitting the core loss density (per unit volume) versus frequency and magnetic induction, permits the use of an equation, which is a very useful tool for the design optimization of high frequency magnetic components, such as transformers and inductors for switched mode power supplies.

Using parallel complex permeability for ferrite characterization

The authors address topics related to the characterization of linear ferrite materials using real and imaginary components of parallel permeability. Significant advantages are found in using the parallel rather than the usual series form of complex permeability to represent the performance of high-permeability ferrite cores. The findings include independence of the number of turns, a new equation for core loss density, a more direct examination of ferrite properties, and a reinterpretation of Snoek's limit. It is concluded that the parallel components of complex permeability provide direct measures of the inherent ferrite material properties. >

The effects of substructure on the high density core loss properties of commercial grain-oriented 3% SiFe

Commercially-produced grain-oriented 3% SiFe is batch annealed in coil form thereby generating single crystal grains with slight amounts of misorientation as measured from grain edge to grain interior. When heat flattened, lattice bending occurs along with the generation of a dislocation substructure, the quantity and arrangement of which depend on deformation rate, amount of deformation and stress relief annealing temperature. The 60 Hz core losses at 1.5 and 1.7T were found to be very sensitive to the latter two parameters. Core losses were modeled as a function of dislocation substructure. A strong linear correlation between supplemental losses, which are associated with 90° domain wall motion, and dislocation density was found without regard to dislocation arrangement. A weaker correlation was found between the interaction of 180° domain walls and dislocation density, perhaps indicating that dislocation arrangement is important here.

Inductor Size vs. Q: A Dimensional Analysis

Equations are derived and curves are plotted showing the change in Q of an inductor as a function of a change in size. The approach used is to assume the existence of a model having a fixed inductance and operating under a fixed set of conditions. A change in size is introduced by a magnification-type enlargement or shrinkage of all outline dimensions by the factor "a." Assuming a constant effective permeability and readjusting the number of turns to maintain inductance constant results in the elimination of "n," the relative number of turns. With the further assumption of a constant copper space factor, the relative copper losses (in the absence of core losses) determine the relative Q as a function of relative size. Copper losses with skin effect and with solid conduction are considered. The same approach is used to derive equations of relative size vs relative Q for a pure core-loss inductor. For this purpose, core losses are approximated by a straight-line equation between the logarithm of flux density and the logarithm of core-loss density. This turns out to depend upon the properties of magnetic materials. Although under certain conditions core losses may actually go down as size goes down, the broader considerations (not treated mathematically in this paper) of combined copper and core losses make such a condition untenable. At least, the equations and curves can provide the basis for a judicious estimate of the effect of miniaturization on inductor Q in any specific application.