I hope many people might feel little awkward to see this question. But I feel this is important. Because in my place where I am living I can get a radio (Audio Receiver) very cheaply. I don't know till what extent they allow the audio frequency ranges. I guess they use ICs for Frequency Demodulators, Frequency Clippers, etc. If the Frequency demodulator doesn't work properly and allows all the frequencies that comes through air then its going to be a big problem to the humans. Can somebody answer which are all the frequency ranges that are available and which causes human hazards?
Electronic – Frequency ranges that causes a hazard to humans
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I've learned recently that lower frequency radio waves travel farther and have better object penetration than their higher frequency counterparts.
Then you learned poorly. This is simply not correct. Different frequencies go thru different materials differently, but it is not true that lower frequencies (longer wavelengths) "travel farther" somehow.
Think of really high frequencies, like light. Here we can discern different wavelength with our bare eyes as colors. Surely you must realize that red light doesn't always "travel farther" than blue light.
What does happen is different wavelength react differently to different size objects that they can't go thru. There are three basic effects going on, reflection, absorption, and diffraction.
How much a certain material absorbs EM radiation is very material-dependent, and often not monotonic with wavelength. Think of color filters. A green filter blocks both red and blue light but lets green light thru, even though its wavelength is between red and blue.
Big things relative to the wavelength will block the radiation. However, waves also diffract along the edges of objects. This is sortof a wave bending along to follow the object. This happens only along a thin layer near the object, with the thickness of this layer proportional to the wavelength. Long waves, like 1 MHz commercial AM can bend around the edges of hills and the curvature of the earth better on a human scale than 100 MHz commercial FM, for example. This may give the impression that these longer waves "go further", but that's not what's going on.
Short wavelength don't bend around the same object as well as long wavelengths, but they can slip thru smaller holes in objects or between objects. Again, this is proportional to wavelength. A 10 m hole will easily let 3 m (100 MHz) signals thru, but mostly block 300 m (1 MHz) signals. This is probably why the shorter wavelengths work better between decks of a ship. They bounce around better and eventually make their way thru doors and the like, which longer wavelengths can't.
This is a intentional radiator. That means, in the US at least, a FCC certification number must be available on the package somewhere. Look up that number to get the details of what frequency and power the transmitter is permitted to use.
I expect there is a similar mechanism in other jurisdictions.
Best Answer
The short answer is that unless you are dealing with professional power levels in the several watts range, RF is very difficult to cause injury with.
Long answer
RF doesn't affect humans directly unless there is a tremendous amount of power. Effects are typically thermal, when a particular chemical bond is struck just-so, it will absorb a photon, moving it slightly. Enough heating will damage cells by denaturing or "cooking" proteins.
Particular wavelengths (2.4 GHz) are well absorbed by water and fat, but absorption is still very diffuse so it would take a tremendous dose to cause enough heating in any one area to cause damage. The FCC safe exposure limit is 1.6 W absorbed per kilogram (as per one source), and 4 W/kg (in following link) for the entire body.
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Atomic nuclei can also also respond to RF, allowing for nuclear magnetic resonance spectroscopy (or MRIs), but this is a strictly nuclear effect and has no influence on chemical bonds.
IR and light obviously can cause burns, but only at sufficient power. IR lasers can be particularly hazardous to eyes, as it invisible it will not trigger a blink or aversion reflex, allowing a large, damaging dose to be absorbed before noticing.
Higher energy photons, UV, X-ray, and gamma, are able to ionize atoms when they strike them, causing unexpected chemical reactions to occur which can destroy, damage, or mutate cells.
These are all forms of "radiation", but the layperson couldn't tell what the implications of non-ionizing versus ionizing radiation are, which causes all sorts of unfounded fears of these invisible phantoms that carry our cell phone calls and webpages.