Magnetic modeling and characterization

Keywords:
Stoner-Wohlfarth model, Preisach model, vibrating sample magnetometer (VSM), magneto-optic Kerr effect (MOKE)

Modeling and characterizing magnetic materials for various applications using a Quantum Design VersaLab, a custom MOKE, a GMW + MMR Technologies Hall-effect setup. Current efforts include the following:

  • Inductive coil magnetic resonance detection
  • Magneto-optic switches
  • Microstrip transmission lines

Superconducting hysteresis

 
 

Keywords:
High-temperature superconductors, HTS degaussing, HTS cables

Type-II  superconductors,  including  high-temperature  superconductors,  are  characterized  by  the  coexistence  of  a normal-conducting  and  a  superconducting  behavior  in  a  mixed-state  region.  In  this  state,  the  superconductor  is  partially penetrated by quantized magnetic flux tubes or fluxoids, a phenomenon called flux pinning. Flux pinning is known to be the intrinsic  reason  for  hysteresis.

The  continuous  advancement  of  high-temperature  superconductors  (HTS)  technology  has  empowered  numerous military applications. Copper coils have been traditionally used to actively reduce the magnetic signature of a naval vessel, a process called degaussing. The U.S. Navy has recently started using HTS degaussing systems, reducing the size and weight requirements by a significant margin. Press releases in the last couple of years reveal the U.S. Navy’s plan to expand the use of HTS in the fleet through power transmission, power generation, and several other applications.  The proposed higher-level model provides a computationally-efficient tool capable  of predicting the hysteretic magnetization of  HTS, an increasingly-used technology on naval vessels.

Relevant links:
US Navy to order high temperature superconductor equipment


Magnetization, magnetostriction, and stress effects
Collaborators: Professor Della Torre (GWU) and Institute for Magnetics Research

Keywords: deperming, degaussing, Preisach, magnetic hysteresis

The interplay between the earth’s magnetic field, the navigation stresses, and the magnetism of a naval vessel continuously alter its magnetic signature, making it prone to detection by undersea mines. Our Preisach-type magnetic models, when coupled with FEM solvers, can predict the magnetic signature of non-trivial ferromagnetic geometries. 

Relevant links:
Degaussing and deperming
Preisach model applets

Magnetocaloric effect and magnetic refrigeration
Collaborators: Professor Bennett (GWU) and Institute for Magnetics Research

Keywords: gadolinium, Heusler alloys, magnetic transitions

Magnetic materials change their thermodynamic properties when subjected to a changing magnetic field. In particular, if the change happens under adiabatic conditions, the temperature of the material changes. The magnetocaloric effect (MCE) has a growing potential for efficient magnetic refrigeration near room temperature.

Relevant links:
G.E. develops an MCE-based fridge
H
istory of magnetic cooling


Actuation of ferromagnetic microrobots
Collaborators: Professors Firebaugh (USNA), Professor Piepmeier (USNA), and Professor Khalil (GUC)

 
 

Keywords: microrobot, magnetic actuation

Wireless microrobot control has a wide range of useful medical, biological, and industrial applications. We are developing a magnetic actuation and visual sensor system capable of controlling a microrobot in a three-dimensional fluidic environment.

Relevant links:
NIST microbotics challenge