Gregory W. Donohoe

Dynamics of vortex core switching in ferromagnetic nanodisks

Dynamics of magnetic vortex core switching in nanometer-scale Permalloy disk, having a single vortex ground state, was investigated by micromagnetic modeling. When an in-plane magnetic field pulse with an appropriate strength and duration is applied to the vortex structure, additional two vortices, i.e., a circular and an antivortex, are created near the original vortex core. Sequentially, the vortex-antivortex pair annihilates. A spin wave is created at the annihilation point and propagated through the entire element; the relaxed state for the system is the single vortex state with a switched vortex core.

High Q Ni-Zn-Cu Ferrite Inductor for On-Chip Power Module

We fabricated 3 times 3 array of 1 mum thick Ni-Zn-Cu ferrite and air-core planar inductors (5 times 5 mm2 in size; 2.5, 3.5, and 4.5 turns of Cu coil) on 4 inch bare Si wafer and 300 nm thick SiO2/Si wafer, respectively. The ferrite inductor showed higher Q than that of air-core inductor in the range of 7 to 100 MHz. The Q (= 19.5) of 4.5 turn ferrite inductor is 3.3 times higher than that (= 5.9) of 4.5 turn air-core inductor at 10 MHz, and inductance (L) increased by 10%. The Q-factors were found to be about 50 at 2.3 MHz and 20 at 10 MHz, respectively, for the ferrite inductor.

Low-power reconfigurable processor

The reconfigurable data path processor (RDPP) is a multi-processing integrated circuit under development for data intensive, streaming applications aboard spacecraft. It is targeted to an ultra-low-power, radiation-tolerant CMOS technology. The RDPP implements a synchronous data flow computational model with conditional data flow instead of conditional branching. In addition to the processor chip, a suite of support software is being developed.

Microdeformations in Sands by Digital Image Processing and Analysis

Laboratory experiments are typically performed on particulate media to study stress-deformation behavior and to verify or calibrate computer models from controlled or measured boundary stresses and displacements. However, such data do not permit the formation of shear bands, displacement fields within flowing granular media, and other smallscale localized deformation phenomena to be identified. Described are two semiautomated computer vision techniques for accurately determining the two-dimensional displacement field in granular soils from video images obtained through a transparent planar viewing window. The techniques described are applicable for studying the behavior of particulate media under plane strain and certain axisymmetric test conditions. Digital image processing and analysis routines are used in two different computer programs, Tracker and Tracer, Tracker uses a graphical user interface that allows individual particles to be selected and tracked through a sequence of digital video images. A c...

Teaching digital image processing with Khoros

As digital image processing has moved into the electrical engineering mainstream, it has become a popular course in the undergraduate curriculum. Since visual perception is a key component of image processing, an effective first course should emphasize laboratory experience. The Khoros software system offers an interactive environment to facilitate such a course.

High-Quality Factor Ni-Zn Ferrite Planar Inductor

Ferrite and air-core planar inductor arrays were fabricated on 4 inch Si wafer to characterize inductor performance. Three micron thick Ni0.5Zn0.5Fe2O4 film was deposited by a low temperature electrophoresis ferrite deposition process. All ferrite inductors in the array showed 35% higher inductance (L) and 130% higher quality factor (Q) than air-core inductor. The maximum Q of ferrite inductor was found to be 53 at 2 MHz. The superimposed DC current and the rated power were measured to be about 3 A and 15 W, respectively, for a 5% drop in L. The fabricated ferrite inductor has a higher current capability than the air-core inductor. In addition, the power efficiency of the buck DC-DC converter was predicted to be 94.3% at 1.93 W.

Integrated Ferrite Film Inductor for Power System-on-Chip (PowerSoC) Smart Phone Applications

An array of ferrite and air-core inductors was fabricated on silicon wafer to characterize inductor performance. The 1 μm and 2.5 μm thick ferrite films for the fabrication of inductors were prepared by dc magnetron sputtering. The inductance of the ferrite inductor increased with the thickness of ferrite film from 45.5 nH for 1 μm thick ferrite to 50 nH for 2.5 μm thick ferrite. The maximum Q-factor was obtained to be 59 at 2.87 MHz from 2.5 μm thick ferrite inductor, which is higher than 49.3 at 2.26 MHz for 1 μm thick ferrite inductor and 23.2 at 1.56 MHz for air-core inductor. Superimposed dc current of 1 μm and 2.5 μm thick ferrite inductors was estimated to be 2.5 A and 2.15 A, respectively, corresponding to a 5% drop in L at 10 MHz. In addition, the power efficiency of the buck dc-dc converter based on the studied ferrite inductors was calculated to be 91.7% for 2.5 μm thick ferrite inductor and 90.1% for 1 μm thick ferrite inductor at load current of 0.647 A.

Optimized Design of Low Voltage High Current Ferrite Planar Inductor for 10 MHz On-chip Power Module

In this paper, design parameters of high Q (> 50), high current inductor for on-chip power module were optimized by 4 Xs 3 Ys DOE (Design of Experiment). Coil spacing, coil thickness, ferrite thickness, and permeability were assigned to Xs, and inductance (L) and Q factor at 10 MHz, and resonance frequency ( fr) were determined Ys. Effects of each X on the Ys were demonstrated and explained using known inductor theory. Multiple response optimizations were accomplished by three derived regression equations on the Ys. As a result, L of 125 nH, Q factor of 197.5, and fr of 316.3 MHz were obtained with coil space of 127 μm, Cu thickness of 67.8 μm, ferrite thickness of 130.3 μm, and permeability 156.5. Loss tan δ = 0 was assumed for the estimation. Accordingly, Q factor of about 60 is expected at tan δ = 0.02.

Micromagnetic configurations and switching mechanism in Pac-man-shaped submicron Ni80Fe20 magnets

Micromagnetic modeling analysis and magnetic force microscopy studies were performed in order to characterize the magnetization configuration and magnetic switching behavior in two types, PM I and PM II, of submicron Pac-man-shaped Ni80Fe20 magnetic elements. It was found that a slight variation in the shape of the elements has a striking influence on the internal magnetic structures and switching field distribution. In particular, the vortex-formation driven switching is replaced by quasicoherent reversal by removing the central core part at the center of element. The sensitive dependence of remanent magnetic configuration and switching behavior on sample geometry is discussed in terms of the competition between the exchange and demagnetizing energy terms.

Micromagnetic domain structures and magnetization switching mechanism in submicrometer thin-film elements

Magnetization configuration and magnetic switching behavior in two types, P-I and P-II, of submicrometer Pac-man-shaped Ni/sub 80/Fe/sub 20/ magnetic elements are studied using both magnetic force microscopy (MFM) and numerical simulation. It was found that a slight variation in the shape of the elements has a striking influence on the internal magnetic structures and switching field distribution. In particular, the vortex-formation-driven switching is replaced by quasi-coherent reversal by removing the central core part at the center of element. The sensitive dependence of remanent magnetic configuration and switching behavior on sample geometry is discussed in terms of the competition between the exchange and demagnetizing energy terms.