Magnetic field sensors [sic]

We’re immersed in the earth’s magnetic field, but most of the time we’re unaware of its presence unless we see a spectacular auroral display, or a solar-event-induced field imbalance disturbs the power grid, or we use a compass to find our way home. Magnetic fields cause problems in the test lab by affecting CRT-display alignment and color purity. Helmholtz coils provide a magnetic-field-free space for accurate evaluation of display performance.

In the June 1999 issue of Test & Measurement World, Jim Ericson described how to construct a magnetic-field immunity tester from PVC pipe, plywood, and a few additional components. A search for “Magnetic Field (Gauss/Tesla) Meters” on www.tmworld.com reveals that the 2008 Buyer’s Guide listed several manufacturers of measurement instruments.

Straying further afield for measuring magnetism, how about using…cows? According to an article appearing in the Proceedings of the National Academy of Sciences (see sidebar), domestic cattle and certain deer species orient their bodies in a north-south direction while grazing or resting. Using satellite photos, field observations, and analysis of body impressions left by resting deer in snow fields, the authors eliminated ambient light and wind as possible influences and arrived at the earth’s magnetic field as a statistically valid predictor of body orientation.

Before you purchase a herd of four-legged test instruments, though, be aware that certain maintenance requirements—power supply and by-product-disposal considerations—may present problems in an urban setting. On the other hand, availability of fresh dairy products would greatly enhance the average office’s coffee break.

Anecdotes of exceptional feats of animal navigation abound. Homing pigeons seek their lofts, magnetotactic bacteria align themselves with the local magnetic field, and Monarch butterflies travel thousands of miles to their wintering grounds. Biologists pose various theories to account for these navigation feats, but devising an instrument for, say, butterfly telemetry remains a formidable challenge.

The next time you drive past a herd of cattle, check your dashboard GPS display and marvel at Mother Nature’s equivalent. The chips are in the field—not the cows.