Radio and microwave safety

 

I have a long standing interest in research and understanding of radio frequency (RF) safety. As in many complex technical fields where vested interests are active, there is contradictory data, underfunded experiments, fraud and alleged fraud, speculation, mixed with hard-won scientific data and theories. Separating the wheat from the chaff is a big challenge. Approaching the subject with preconceived ideas, there’s always enough evidence around to support your supposition and reject others. The vast amount of contradictory and ambiguous data obfuscates the truth.


For example, cell phone transmitters were touted by some as the cause of mysterious “colony collapse disorder” that is wiping out honey bees around the world. Bee populations are being decimated, and cell phone usage is increasing, but correlation does not imply causation (and there’s not even correlation). Our ranch has thriving populations of honey bees (both captive and wild), in close proximity of cell towers.  The most likely cause of bee colony collapse I believe are neonicotinoid insecticides -- a conclusion the agri-chemical companies continue to fight. Most neonicotinoids were banned in Germany in 2008, and restricted in France even earlier, due to their impact on bees. But they are still widely used in the USA and elsewhere. 2014 Update: http://www.sciencemag.org/content/346/6211/806.full.

2016 Update: Neonics at 1.5-4 ppb reduce sperm count in bees: http://rspb.royalsocietypublishing.org/content/283/1835/20160506.


An experimental result is usually considered statistically significant if the likelihood of it occurring by chance is <5%. Thus you could expect 5% or 1 in 20 studies to (falsely) show “significant” results even if no effect were present. Also consider that studies showing a positive result are more likely to get published. These biases, along with strong economic pressure to minimize regulation and restriction of RF, add confusion to the confusion. Truth and certainty remain illusive.


One uncontroversial aspect of RF safety is that RF power decreases with the square of the distance from the source, at least after a few wavelengths. At our site, we strive for RF levels less than 1% of FCC occupational limits at all points on the ground. RF emissions beyond 100’ from the towers are typically much less than those within a foot of a hand-held transmitter (walkie-talkie).


http://www.fcc.gov/oet/rfsafety/ -- is the  official US government site on RF safety.

http://www.osha.gov/SLTC/radiofrequencyradiation/safety.html -- is the corresponding page on the Occupational Safety and Health Administration (OSHA) US government site.

http://www.arrl.org/news/rfsafety/ -- is the safety site for the nonprofit National Association for Amateur Radio.


State of the art technical papers are published widely, pubmed is a good searchable bibliography.



Low-Frequency Electromagnetic Fields


Often confused with RF safety are extremely low frequency (ELF) fields which emanate from 60 Hz power lines, electric blankets, infant incubators, etc. Mechanisms for biological effects are likely quite different, as these low frequency fields (mainly magnetic fields) couple to biology different than does electromagnetic radiation oscillating at millions, billions, or trillions of times per second. A collection of articles on ELF is:


D Hafemeister (Ed) “Biological effects of low-frequency electromagnetic fields”, AAPT, ISBN 0-917853-89-X.


Engels S et al. (2014) “Anthropogenic electromagnetic noise disrupts magnetic compass orientation in a migratory bird”, Nature 509, 353-356. This study seems to show, with double-blind standards, that ambient EMFs from 50kHz-5MHz disrupt birds compass sense. Hopefully it will be followed up, as the mechanism is rather mysterious.