What frequencies pass through the human body? - Page 1
Forum section: electronics / beginners

author: Mutad0r
author_rank: Contributor
timestamp: April 07, 2015, 09:05:36 pm
content: I have searched the internet, but haven't found any answer to a relatively simple question; what frequencies pass best/worst through the human body. In fact, I need to know which frequencies have the worst passing through the human body, as in which frequencies weaken the most. I'm going to go to school tomorrow and see what I can measure through my own body, but I cant go to very high frequencies, I'd like to atleast try up to a GHz. I found information that 1 MHz to 100 MHz is BEST at passing through the human body, but no reference to where that comes from.So if anyone with a fancypants oscilloscope and an RF generator could make a simple frequency/amplitude chard (like they have for filters) that would be like great.I know the school has an RF generator that can go to a couple of GHz, but the oscilloscopes arent that good, but I'll see what I can find out myself.

author: amyk
author_rank: Super Contributor
timestamp: April 07, 2015, 09:14:46 pm
content: With or without causing injury?If there is enough power,any"frequency" will...

author: retrolefty
author_rank: Super Contributor
timestamp: April 07, 2015, 09:16:40 pm
content: Maybe short research into microwave ovens would get you started on answers to your questions.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: April 07, 2015, 09:37:02 pm
content: Uneducated guess by me: Everything below Infrared light and above UV-Light will travel through a human body. There is a low end though: Once the wavelength is long enough, it doesn't really travelthroughthe body, it just goes around it/ignores it.A good place to start research might be RC model submarines. Using the normal RC frequencies, the boats rarely can dive below 5m because at that depth the water blocks the signal. The depth decreases with distance from the transmitter and increases with lower frequencies.

author: edavid
author_rank: Super Contributor
timestamp: April 07, 2015, 09:38:07 pm
content: You sure didn't search very hard...https://www.google.com/search?q=rf+absorption+human+bodygives this handy paper:http://www.adv-radio-sci.net/4/357/2006/ars-4-357-2006.pdf

author: Zero999
author_rank: Super Contributor
timestamp: April 07, 2015, 10:07:29 pm
content: If you're talking about being in direct contact with an electrical conductor, then mains frequencies are the most dangerous but at higher frequencies (above 10kHz or so) heating becomes the dominant mode of tissue damage through burns.As far as electromagnetic radiation is concerned, wavelengths significantly larger than the human body travel around the body, as mentioned above. Most RF frequencies are absorbed somewhat and cause heating, with increasingly higher frequencies (above 50GHz or so) being absorbed more at the surface. Some parts of the body such as the eyes, genitals and brain are very sensitive to even small increases in temperature which is why the radiation used in microwave ovens (2.45GHz) is so dangerous. In the visible and UV spectrum, it depends on your skin colour, which UV causing burns and cancer, especially in lighter people. Higher energy X rays and gamma rays pass straight through the body and also cause burns and cancer.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 08, 2015, 12:00:06 am
content: You can calculate based on the approximate bulk resistivity of meat, its thickness, and the skin* depth at the frequency. Frequencies below that are transmitted, frequencies above are absorbed more and more.*Referring to a "skin" of electrical current flow; nothing to do with the dermis, specifically.The skin depth at microwave frequencies is typically around an inch, i.e., if you stuff a pot roast into the microwave oven and give it ten minutes, it'll be well done on the outside, and completely raw inside.Other subjects of interest: frequency response of the nervous system (DC and line frequency AC are the most dangerous, stimulating muscle; above about 1kHz, you feel less and less shock, and thermal burns become a problem), conductivity of skin (wet and dry), fat, "wet" internal stuff (veins, muscle, organs..), amount of current required from point X to point Y to cause cardiac arrest, etc...Tim

author: Mutad0r
author_rank: Contributor
timestamp: April 08, 2015, 08:13:27 am
content: First of all, I never expected so many great answers, so THANKS!Second of all, I suppose I didn't use proper wording of the problem in google to find any results, what I got was mostly nonsense. That PDF was particularly useful.Third of all, GODDAMMITthe "The transmission loss increases with frequency..." part in that document was particularly dissappointing. I was hoping to use lower frequencies since I have no idea how to make a 800 MHz transmitter... At least the document only explored 100MHz to 1GHz, so I'll still make a measurement at school for frequencies below that, maybe theres a point where the signal drops off. Hopefully it's not too low though.