Magnetometer Design

Findings

Types of Magnetometers

General site about magnetomters: http://www.sensorsmag.com/articles/1298/mag1298/main.shtml

Alternating Gradient Magnetometer

http://www.princetonmeasurements.com/agmvartmpb.htm

Anisotropic Magnetoresistance (AMR)

Made of Permalloy, a thin nickel-ironfilm deposited on silicon. The film changes resistance (2-3%) in the presence of a magnetic field.
http://www.sensorsmag.com/articles/0399/0399_18/main.shtml

Giant Magnetoresistance (GMR)

Hall Effect Sensor

Moving Coils

Proton Precession Magnetometer (PPM)

When molecules are aligned by a field and the field is then removed, the molecules precess at a frequency proportional to the ambient field strength.
Solenoidal or toroidal configuration.
http://www.portup.com/~dfount/proton.htm
http://www.diamondjim.bc.ca/Proton%20Precession%20Magnetometers.PDF

Superconducting Quantum Interference Devices (SQUID)

http://www.2genterprises.com/pdf/Model581DCSquid.pdf

Vector/Scalar Helium Magnetometer (VSHM) & Optically Pumped Magnetometer

http://www.sp.ph.ic.ac.uk/cassini/vshm.html

 

Final Considerations

Fluxgate Magnetometer

PDF of Professor Gill Pratt's Masters Thesis: A Blind Man's Compass

Magnetoinductors

Magnetoinductive magnetometers are relatively new, with the first patent issued in 1989. This sensor is simply a single winding coil on a ferromagnetic core that changes permeability within the Earth's field. The coil is the inductance element in a L/R relaxation oscillator. The oscillator's frequency is proportional to the field being measured. A static DC current is used to bias the coil in a linear region of operation (see Figure 3). As the sensor is rotated 90º from the applied magnetic field, the observed frequency shift can be as much as 100%. The oscillator frequency can be monitored by a microprocessor's capture/compare port to determine field values. These magnetometers are simple in design, inexpensive, and have low power requirements. Their temperature range is -20ºC to 70ºC, and they are repeatable to within 4 mG. Automatic assembly and axis alignment are difficult due to the sensor's small size and its physical configuration.

Materials

Mu Metal

Permalloy

http://www.hpmetals.com/pdfs/MOLYPERMA.pdf

© Olin College NASA Study 2004