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Q: How far radiofrequency waves penetrate into the human body ( Answered,   2 Comments )
Subject: How far radiofrequency waves penetrate into the human body
Category: Science > Instruments and Methods
Asked by: spitz1-ga
List Price: $20.00
Posted: 18 Oct 2006 00:36 PDT
Expires: 16 Nov 2006 23:36 PST
Question ID: 774598
I would like to know if there is any literature or proof as to how far
radiowaves penetrate into the human body

Request for Question Clarification by hedgie-ga on 20 Oct 2006 03:27 PDT
Hello spitz

   There is enormous body of literature, some theoretical and technical,
   some repporting measurements for specific range and organs ...

At this price it would help to narrow it a bit, and indicate a technical level
you want.

e.g.  is this one 

An electromagnetic wave passing through the human body declines in
intensity as it heats tissues ... Signal attenuation is minimal below
~1 MHz (Eqn. 6.32). ... 

too technical, too  theoretical,..   or just right?

Are you at home with terms like: 

  attenuation? - a definition from
If Av is the voltage attenuation in decibels, Vs is the source signal
voltage, ... Let us know. Send your comments to

 Decibell: dB? 
The decibel (dB) is considered the baseline by which all ... A 3 dB
attenuation requirement would translate to 50% of the signal power
being lost along a ...

  The reason we would need those terms is that

   there is no sharp cutoff. If you know the  input intensity, attenuation,
   and select the 'detectable treshold' - then you can easily calculate where 
   the wave 'disappers'  or if it passes without much effect. Just
using a scientific calculator (calculator with log and exp functions).

 Both will effects (total abssorption, and passing trouhgh) will 
hapen acroos the range.

      Under 1 MHz 'wet bodies'  are transparent.
see also

 So, please, clarify the question.
 I will check thisa in a week  or so,


Clarification of Question by spitz1-ga on 22 Oct 2006 18:28 PDT
Hi, What I would specifically like to know is - if 434mhz was applied
to a human being at a rate of 1.5mw/cm2 how deep into the body would
the application be if the application occured for 20 minutes (don't
know if time makes a difference - perhaps tissue heating over time may
affect depth?)

Mark Spitz - 7 Gold

Clarification of Question by spitz1-ga on 24 Oct 2006 01:21 PDT
Hedgie - I thought I ought to also say that I am willing to pay more
if you are able to provide validated and accurate calculations and
using a recognized source document(name of author/s,name of
journal/volume and #/page/title of article - basically a citation).

If you can do that quote a price.

Thanks again
Subject: Re: How far radiofrequency waves penetrate into the human body
Answered By: hedgie-ga on 28 Oct 2006 02:16 PDT
Hi Spitz

      From your clarification I conclude that it would be useful to start with

SEARCH TERM:  extinction coefficient

e.g. this

  You do not need to understand all the equations there, but this one

dI/dz = -alfa * I
 Beer-Lambert law  is essential (and not difficult to get).

It says that Intensity of electromagnetic wave (emg) in media decreases 
according to exponential curve (same rule applies for light as for radio frequency)

 That curve is shown here under heading 

Exponential decay of intensity

The  curve shows decrease of intensity with depth of penetration. Article also
describes other factors, angle of incidence, polarization, etc. 

As I briefly mentioned before in my RFC, question 'how deep it
penetrates'  depends on what is considered 'negligible intensity'.

Exponential never reaches zero:  for function  y=  10^(-x)  we have

 x              y
 2               .01
 5               .00001
 10              1.e-10 

  etc.    So, if we consider .00001 to be 'really zero'  penetration would be 5
but for some super sensitive effect it can be 10. So, to determine
penetration depth the threshold need to be specified. If effect of the
emg is heating, then threshold would be estimated from assuming 
increase of 2 degree C to negligible.

Here, the length of exposure and also particular organ may be
relevant, as ability to carry away the heat (density of blood vessels)
will play a role in total
increase in temperature.  (see BHP example below).

So, general conclusion is with present specification, you cannot
expect exact numbers.

Some specific numbers for different organs and frequencies are here:

Note below Fig 2 and 3  

' Between 10MHz and 1GHz both the quantities are complex. In the
GHz-THz band, a complex conductivity implies both significant
attenuation (from the real part of the conductance) and scattering of
EM waves with a gradual transition from attenuation to scattering as
frequencies increase. In the band between 10MHz and 1GHz, with both
the quantities being complex, it is difficult to solve the Maxwell's
equations to determine behavior because of the multiple cross terms. A
numerical simulation is probably an easier alternative...'

shows that in 'your range' behavior is complex (both absorbtion and transmission).

This work quotes authoritative source:

 However, short duration exposure to RF-induced thermal load will
usually not cause damage and the heat will be dissipated. For this
reason, RF radiation exposure is not cumulative, unlike ionizing
radiation exposure. The biological effects of RF radiation are
thoroughly treated in textbooks such as CRC Handbook of Biological
Effects of Electromagnetic Fields.20-21

That handbook is expensive, but available in most college libraries.

This critical report qutes considerable bibliography

By the way 434mhz  really means  434 milli Hertz,  I assume you mean 
           434 MHz  434 Mega Hertz - part of FM radio spectrum (shown here)

 Capitalization is relevant in SI units.

I want to mention in conclusion one specific medical application of emg induced
hyperthermia . When temperature in a tissue exceeds 45C cells start dying and here
the duration of exposure is ,of course,  significant.  Typical treatment for BHP
lasts about 20 minutes.

 Heating experiment using agar phantom showed the hot spots to be
distributed at 0.5-3 cm from the catheter surface. Heating experiment
using canine prostates demonstrated that an intraprostatic temperature
of > 48 degrees C could be achieved while the urethral and rectal
temperatures had not exceeded 36 and 40 degrees C respectively.
Histological examination immediately after the experiment showed the
urethral mucosa to be preserved while coagulation necrosis of the
periurethral prostate accompanied with congestion and hemorrhage of
small blood vessels were observed at 5-8 mm from the urethra.

and image

Whole range of frequencies, from radio to microwave to UV can be used, as effect
depends on  induced temperature, not the frequency itself. 

Here is a bibliography of recent scholarly articles

I will stop here since I do not know  which way to focuse.  You can
ask for clarification or (preferably) post another question more still
more specific.
Are you interested in thermal ablation described above, for therapy, safety , ??
If you want me to continue the search, you may add 'for Hedgie' to
your second question. That method is preferable to me  guessing the
cost of more detailed search. The more background of your interest and
more details (sketch of the
transmitter and application) outside of body, on the skin, inside the body, ...
and purpose you can describe, the easier it is to find relevant citations. 

Subject: Re: How far radiofrequency waves penetrate into the human body
From: pinkfreud-ga on 18 Oct 2006 12:41 PDT
This report may be of interest to you:
Subject: Re: How far radiofrequency waves penetrate into the human body
From: spitz1-ga on 18 Oct 2006 19:09 PDT
Thank you Pinkfreud - the info is not exactly what I was looking for
but is useful and interesting. I appreciate your thoughts on this

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