4 research outputs found
Optimization of sensor design for Barkhausen noise measurement using finite element analysis
The effects of design parameters for optimizing the performance of sensors for magneticBarkhausen emission measurement are presented. This study was performed using finite element analysis. The design parameters investigated include core material, core-tip curvature, core length, and pole spacing. Considering a combination of permeability and saturation magnetization, iron was selected as the core material among other materials investigated. Although a flat core-tip would result in higher magnetic flux concentration in the test specimen, a curved core-tip is preferred. The sensor-to-specimen coupling is thereby improved especially for materials with different surface geometries. Smaller pole spacing resulted in higher flux concentration
Valley degeneracy in biaxially strained aluminum arsenide quantum wells
This paper details a complete formalism for calculating electron subband
energy and degeneracy in strained multi-valley quantum wells grown along any
orientation with explicit results for the AlAs quantum well case. A
standardized rotation matrix is defined to transform from the conventional-
cubic-cell basis to the quantum-well-transport basis whereby effective mass
tensors, valley vectors, strain matrices, anisotropic strain ratios, and
scattering vectors are all defined in their respective bases. The specific
cases of (001)-, (110)-, and (111)-oriented aluminum arsenide (AlAs) quantum
wells are examined, as is the unconventional (411) facet, which is of
particular importance in AlAs literature. Calculations of electron confinement
and strain in the (001), (110), and (411) facets determine the critical well
width for crossover from double- to single-valley degeneracy in each system.
The notation is generalized to include miscut angles, and can be adapted to
other multi-valley systems. To help classify anisotropic inter-valley
scattering events, a new primitive unit cell is defined in momentum space which
allows one to distinguish purely in-plane inter-valley scattering events from
those that requires an out-of-plane momentum scattering component.Comment: 17 pages, 4 figures, 2 table