BH Looper

BH Looper Senior Project 2006

The Applied Magnetics research group sponsored 4 undergraduate students in their ECE senior design project to build a BH-looper for the Applied Magnetics Laboratory. These students designed and built the entire device from the ground up.


What is a BH-looper?

BH Looper Block Diagram

A B-H looper measures the hysteresis loop (Flux Density B versus Field Intensity H) of a thin magnetic film sample by applying a field to the sample and measuring the magnetic field produced by the sample's magnetization.

This is an essential tool for the applied magnetics lab to characterize magnetic thin films for use in devices. Commercial versions of the B-H looper are available for many thousands of dollars.

From the hysteresis loop, one can determine:

  • Saturation: Amount of Field (H) required to align domains in the magnetic sample. This is the maximum flux density (B).
  • Coercivity: Amount of field required to reduce the Flux Density to zero.
  • Retentivity: Amount of flux density remaining in the sample at zero applied field strength.

Design Specifications

BH Hysteresis loop captured with our BH looper.
  • Thin Film Sample: 1cm x 1cm x 1nm
  • Test Frequency: 3260 Hz
  • Maximum Field Strength: 200 Oe
  • Field Uniformity: >98%
  • User Interface: Labview

Design Areas

BH Looper DeviceDesign of the BH-looper was approached from a theoretical perspective, modeling all the relevant components as they were designed. Since most design parameters were coupled (one parameter, affected other parameters), the Matlab tool was used to effectively compare different design parameters and examine the theoretical performance of the device before any construction was started.

There were three main design aspects to the BH-Looper project:

  • Excitation System: high current power amplifier design and construction; helmholtz coil pair design and construction
  • Pick-up system: pick-up coil pairs design and construction; sense amplifier design
  • Control system: LabView programming for test-logic and data analysis

Design Group

Group Members From Right to Left:
Simon Ghionea, Ram Ravichandran, Emory Albers, Monica Kempsell


We would like to thank Lakeshore Cryogenics Inc. for their donation of a Model 450 Gaussmeter.