Replies

"If I remember the test questions correctly, at a given power level, the lower the frequency, the more dangerous it is."

It's the other way around. The absorption ends up as heat and efficiency of absorption depends on the relationship of half wavelength to say radius of part absorbing.

If the energy in the field at your location is diddly and couldn't raise the temperature of a thimble full of water one degree in an hour(like a cell phone), it's harmless. RF, radar and IR are heat radiation. Efficient antennas for them depend on their length in comparison with their wavelength. Light ends up being absorbed as heat. Turn off the light in a closed room and it gets dark fast. The flying photons get absorbed and the room gets a few nanodegrees warmer. UV and X are ionizing rad.

Those familiar with the fundamental concepts of quantum theory will remember our old friend Planck's law, which describes the essential concept of the quanta of electromagnetic energy. Planck's law states that the quantum of energy, E, associated with an electromagnetic field is given by E = hv, where h is Planck's constant and v is the frequency of the electromagnetic radiation. If you express Planck's constant in joule-seconds and the frequency in hertz, the energy units fall out in joules.

Anything in the frequency of x-rays and above produces ionization directly through absorption or scattering of the incident photon, which is harmful, in sufficient quantities, to biological systems, because of the inhibiting of essential biochemical reactions, and the breakdown of long-chain molecules. Direct ionization requires incident energy quanta sufficient to remove electrons from the atoms they are bound to. Below a given threshold, ionization will not occur, but thermal effects, as noted in earlier posts, can be significant if field strengths are high enough. RF can produce ionization (like in the ion bottles of accelerators) but that is essentially a thermal effect. The free electrons are accelerated to high velocities by the oscillating field and collisions eventually strip other electrons from their associated atoms.

"It's the other way around. The absorption ends up as heat and efficiency of absorption depends on the relationship of half wavelength to say radius of part absorbing. "

It's the "Magnetic" portion at lower frequencies......It's the "Electro" portion at higher frequencies. At least that's what the standard on electromagnetic exposure says.....