Very-Low-Frequency Electromagnetic Field Detector With Data Acquisition

Naturally occurring electromagnetic oscillating fields in the very-low-frequency (VLF) range of the spectrum, i.e., from 1 to 200 kHz, are weak and difficult to detect under normal conditions. These naturally occurring VLF electromagnetic events are observed during thunderstorms, in certain mountain winds, and during earthquakes. On the other hand, man-made VLF electromagnetic fields are stronger and have been suspected of causing negative health effects. Typical sources of these VLF emissions include television sets, video display terminals (VDTs), certain medical devices, some radio stations, and the ground-wave emergency network (GWEN) used for military communications. This paper describes the development of a triaxial ldquoVLF gaussmeter,rdquo which can be made portable. This electronic system can be used to monitor VLF electromagnetic radiation in residential and occupational environments. The ldquoVLF gaussmeterrdquo is based on a microcontroller with a built-in 10-bit A/D converter and has been designed to measure the magnetic flux density and frequency across the wide VLF bandwidth (BW). A digitized resolution of 0.2 mG is used for the 0-200-mG range, and 2-mG resolution is used for the range of 2-2000 mG. The meter has been designed to include the following features: 1) automatic or manual range selection; 2) data logging; 3) single-axis mode; 4) peak hold; 5) RS-232 communication port; and 6) analog recorder output.