Development of Magnetic Near-Field Probes
Frank M. Greene · 1975
NIOSH's 1975 probe development work established critical measurement foundations for today's EMF health research.
Plain English Summary
This 1975 NIOSH technical report by Greene focused on developing specialized probes for measuring magnetic near-field emissions from various electromagnetic sources. The research aimed to create better tools for detecting and quantifying magnetic field exposures in occupational and environmental settings. This work laid important groundwork for modern EMF measurement techniques we rely on today.
Why This Matters
This foundational research represents a crucial moment in EMF science - the recognition that we needed better tools to actually measure what we were being exposed to. In 1975, NIOSH understood that magnetic near-fields required specialized detection equipment, not the crude instruments available at the time. What makes this significant is the timing: this was decades before cell phones, WiFi, and our current electromagnetic environment, yet researchers already saw the need for precise magnetic field measurement.
The reality is that without proper measurement tools, we can't assess health risks or set safety standards. This early work helped establish the technical foundation for detecting the very exposures we now know can affect biological systems. Today's debates about EMF health effects depend entirely on measurement capabilities that trace back to research like this.
Exposure Information
Specific exposure levels were not quantified in this study.
Study Details
To develop portable magnetic-field-strength probes for measuring hazard-level magnetic near fields in the frequency range from approximately 10 to 40 MHz for assessing occupational exposure from industrial RF power sources.
Two portable magnetic-field-strength probes were developed consisting of small, single-turn, balance...
The probes consist of small, single-turn, balanced loop antennas 10-cm and 3.16-cm in diameter. Thei...
The NBS magnetic-field probes respond essentially to only the magnetic-field component of an E-M radiation field. However, commercially available E-M survey meters have virtually no magnetic-field response. Consequently, a substantial magnetic-field could be present in an E-M radiation field and the commercially manufactured meters would indicate a negligible hazard. The development of these magnetic-field-strength probes was essential to the collection of magnetic-field occupational exposure data from RF power sources. No commercially produced survey instruments were available which could be used to make meaningful magnetic-field-strength measurements between 10 MHz and 300 MHz. Specialized magnetic-field-strength probes are mandatory to characterize the magnetic-field component of RF radiation sources operable from approximately 10 MHz to 300 MHz. The worst-case errors resulting from the electric-dipole response are proportional to frequency for a fixed-size of loop. At a frequency of 40 MHz this error is 8.3 percent for the 10-cm diameter loop and 2.6 percent for the 3.16-cm diameter loop. These errors can be essentially eliminated by following the experimental procedure outlined near the end of Section 2. The errors due to partial resonance are roughly proportional to the square of the frequency as can be determined from equation (16) or figure 9. At a frequency of 40 MHz this error is only 2 percent for the 10-cm diameter loop and 0.5 percent for the 3.16-cm diameter loop and can usually be considered negligible.
Show BibTeX
@article{development_of_magnetic_near_field_probes_g3859,
author = {Frank M. Greene},
title = {Development of Magnetic Near-Field Probes},
year = {1975},
}