Yo Sakaki

Relationship among eddy current loss, frequency, maximum flux density and a new parameter concerning the number of domain walls in polycrystalline and amorphous soft magnetic materials

A new approach is presented for understanding the frequency and flux density dependence of eddy current losses in polycrystalline and amorphous soft magnetic materials by introducing an experimentally derived parameter which is thought to be proportional to the number of active domain walls. The relationship among eddy current loss, frequency, flux density and the new parameter is described by simple formulas and the result derived from these formulas agrees well with the Pry and Bean equation qualitatively and will offer an effective way to appreciate the mechanism governing eddy current loss.

An approach estimating the number of domain walls and eddy current losses in grain-oriented 3% Si-Fe tape wound cores

A method is presented for estimating the number of domain walls in grain-oriented 3% Si-Fe tape wound cores under sinusoidal flux conditions by extending the method developed in a study of the dynamic behavior of 50% Ni-Fe square-loop cores. The results show that the number of domain walls increases approximately with exciting frequency as f^{0.4 \sim 0.5} . The calculated eddy current loss based on the modified Pry and Bean equation and the obtained number of domain walls agree well with the measured loss.

Hysteresis losses in Mn-Zn ferrite cores

In this paper a cause of difference for the Steinmetz constant between polycrystalline Mn-Zn ferrite cores and other materials is qualitatively discussed by considering both irreversible domain wall motion and wall extinction.

Formula for dynamic power loss in ferrite cores taking into account displacement current

A formula for dynamic power loss taking into account the displacement current effect is introduced. The calculations based on the formula and the variation of core parameters, i.e., frequency dependence of resistivity, permeability, and permittivity, are compared values measured from 10 kHz to 10 MHz. In this frequency range the resistivity has a more dominant influence on the power loss than the other parameters. >

Physical meaning of equivalent loss resistance of magnetic cores

The equivalent loss resistance of magnetic cores is analyzed on the basis of magnetic domain theory. The hysteresis resistance due to hysteresis loss is dependent on the variation of the Steinmetz constant. The eddy current resistance due to eddy current loss is strongly affected by the change of domain configurations and is described by an experimental parameter that depends on the number of domain walls, the resistivity of the material, and the dimensions of the core, all of which control the mechanism generating eddy current losses. >

Very low loss ultrathin Co-based amorphous ribbon cores

Ultrathin Co‐based amorphous ribbons with a thickness of 6–10 μm were fabricated by a single roller quenching method in vacuum. The compositions of the alloys were zero magnetostrictive: Fe4.7Co70.3Si15B10 and (Fe0.05Co0.95)71(Si0.5B0.5)29. The ribbons obtained had good smoothness and dimensional uniformity. The core loss of toroidal samples 15 mm in diameter was measured after annealing. The loss decreased with decreasing ribbon thickness. In the case of 6.4‐μm‐thick (Fe,Co)71(Si,B)29 amorphous ribbon, the values at 100 kHz and 1 MHz were 40 mW/cm3 and 1.8 W/cm3 for Bm=0.1 T, respectively. The former was 1/4 that of Mn‐Zn ferrites or 1/2 that of 5‐μm‐thick Supermalloy tape wound core loss. The latter was (2)/(3) that of 5‐μm Supermalloy tape wound core loss. In addition, the initial permeability beyond 100 kHz was also markedly improved by thickness reduction. The values of 6.4‐μm‐thick (Fe,Co)71(Si,B)29 ribbon measured at 1 and 10 MHz were about 7000 and 1000 for Hm=2 mOe, respectively.

100 KHz-10 MHz iron loss measuring system

A very high frequency iron loss measuring system, the upper limit of frequency of which is 10MHz, is newly developed. This new system is helpful for elucidation of the mechanism generating power losses in magnetic cores used for MHz switching power supplies.

Possible mechanism of biomagnetic sense organ extracted from sockeye salmon

A new candidate for a biomagnetic sense organ has been discovered in the foreheads of sockeye salmon. This candidate is an elliptical cell encircled by many magnetic particles. The procedures for extracting the cells are described, and TEM (transmission electron microscopy) pictures are shown. The minor and major axes of the cells are about 0.65-0.75 mu m and 1.3-1.8 mu m, respectively, and the diameters of the magnetic particle range from 50 to 100 nm. The cell also includes a number of round organelles. A possible mechanism for how this organ senses magnetic field, that is, a relationship between the motion of magnetic particles and the applied field, is discussed using a simplified model. >

Large signal eddy current losses beyond 100kHz

Eddy current losses under large flux excitation in Mn-Zn ferrite cores and both polycrystalline and amorphous metallic cape cores of thickness 4μm to 28μm are measured in the frequency range up to 1MHz. Beyond 100kHz, the complex behaviors of magnetization in metallic cores as seen in the lower frequency range disappear and eddy current losses are only proportional to the square of both frequency and flux density. It is attributed to the conclusion that all of the nuclei of domains nucleate and the number of domain walls reaches a constant maximum value n max In order to obtain cores with less eddy current losses in the high frequency range, not only the values of conductivity and dimensions should be small but also the value of n max should be as large as possible. The ultra thin Supermalloy cores are superior to conventional ferrite cores in the dynamic characteristics.

Discussion on eddy current loss under square wave voltage excitation

The eddy current loss under square-wave voltage excitation is theoretically and experimentally investigated. It is shown that the loss is smaller than under sinusoidal voltage excitation when the peak induction is the same. This decrease strongly depends on the behavior of domain structure.<<ETX>>