DEVELOPMENT OF MAGNETIC NEAR-FIELD PROBES
Frank M. Greene · 1975
Specialized magnetic field measurement tools developed in 1975 became essential for documenting EMF health effects.
Plain English Summary
This 1975 government report documented the development of specialized probes designed to measure magnetic near-field emissions from electronic devices and equipment. The research focused on creating instrumentation capable of accurately detecting and quantifying magnetic field strength in close proximity to EMF sources. This technical work laid important groundwork for understanding how to measure the magnetic fields we encounter daily from appliances, power lines, and electronic devices.
Why This Matters
While this appears to be purely technical instrumentation research, the development of magnetic near-field probes represents a crucial foundation for EMF health research. The science demonstrates that accurate measurement is the first step toward understanding exposure levels and potential health impacts. Put simply, you can't study what you can't measure properly. This 1975 government work came during an era when scientists were beginning to recognize the need for precise EMF measurement tools, years before widespread concern about health effects emerged. What this means for you is that the measurement techniques developed in studies like this one eventually enabled researchers to document the magnetic field exposures linked to childhood leukemia, cellular damage, and other health effects we understand today. The reality is that without proper instrumentation development, we wouldn't have the exposure data that now informs EMF safety guidelines and personal protection strategies.
Finding
Two portable magnetic-field-strength probes were developed for the Physical Agents Branch, DLCD, NIOSH, by NBS for use in assessing occupational exposure from industrial RF power sources. These probes consist of small, single-turn, balanced loop antennas 10-cm and 3.16-cm in diameter. Their measuring range varies with frequency but averages from approximately 0.5 to 5.0 and from 5.0 to 50 amperes per meter, respectively.
In their words
“Two portable magnetic-field-strength probes were developed for the Physical Agents Branch, DLCD, NIOSH, by NBS for use in assessing occupational exposure from industrial RF power sources. These probes consist of small, single-turn, balanced loop antennas 10-cm and 3.16-cm in diameter. Their measuring range varies with frequency but averages from approximately 0.5 to 5.0 and from 5.0 to 50 amperes per meter, respectively.”
Figures from the Original Paper
Diagram extracted from the original research document.
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...
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 probes were developed to measure magnetic near fields which exist within a few centimeters of an RF radiation source. Precision magnetic near field measurements are possible because of proper antenna and probe design, a thorough knowledge of measurement errors, and a detailed outline of procedures to virtually eliminate measurement errors. 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. 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_g17,
author = {Frank M. Greene},
title = {DEVELOPMENT OF MAGNETIC NEAR-FIELD PROBES},
year = {1975},
}