[SOLVED] RF radiation effects on human

[VJKris]

Hi Experts,

I am new to the RF field and I have some serious doubts on the RF level which will be hazardous to humans.

This is the lab setup wherein a radio transmitter equipment(RE) is only about 0.5-1 meter distance to a person who is using it and it seems to emit 32 dbm in a lab environment.The antenna of the RE is connected to a spectrum Analyzer.

Will there be a serious health issue if we are there for a long duration in the above setup? :---(

What are the safety precautions to be taken care?
If affected what needs to be done?..any remedies...?

Note: the radio equipment is an outdoor type(like the one mounted on poles)

Regards,
VJKris

 

[chuckey]

In civilized countries there very stringent rules on the level of exposure to RF radiation which is based on its heating effect. This means that at low frequencies its based on a field strength measured in V/M at high frequencies its based on mW/cm^2. I'll see if I can find some via Google. Yes loads on the web , try this :- http://www.rfsafetysolutions.com/RF Radiation Pages/Standards_Regulations.html
Frank

 

[flatulent]

In general, high fields that cause problems are from transmitters in the above 5 W radiated area. In your case the wiring will not be a good antenna and the radiated energy will be in the below 1 W region.

 

[albbg]

There are many studies that try to understand the relationship between EM field and health.
Many countries accept the guidelines written by ICNIRPS while others adopt more restrictive levels on the basis on a precautionary principle.
However it's still a controversal matter; someone only takes into account the thermal effects on biological tissue and other authors suggest also different mechanisms.

In Italy, as far as I remember, the electric field limit is Emax=6.3 V/m (but probably not applicable to the whole frequency spectrum).
The relation between electric field E and effective radiated power P from an antenna (Amplifier power+antenna gain), at a distance d is E=7*sqrt(P)/d.
This is valid only in far field.
If for instance we have a transmitter with an EIRP=2W (32 dBm) at a distance of meter, the electric field will be E=10 V/m: This is valid if we are in far field; in near field will be less bu difficult to estimate.
However you said that the antenna is connected to a spectrum analyzer, so I think your bench is:

TX--cable---attenuator--cable--Spectrum analyzer

In this case the radiated power will be that escaping from the cable (and connectors and attenuator) shielding, that is very low. If you equipment is open (i.e. the shield is removed) the radiated power will be higher but much less than 2W.

 

[vfone]

In civilized countries there very stringent rules on the level of exposure to RF radiation

In "uncivilized" countries are the same rules...for example guys in "uncivilized" countries never use 100W radiated power in their GSM mobile phones...

 

[VJKris]

Thanks for the response.
Yes,the setup is as you have mentioned and the Radio transmitter is shielded and all the equipments are in close proximity.
The antenna transmitter is at UHF band
So less than 2W shouldn't be a problem?

 

[E Kafeman]

Many years ago was I working with testing RF-shielded chambers to check for any leakage.
A spectrum analyzer was placed inside the chamber as a listener and outside the chamber had I a handheld antenna connected to a 1kW transmitter.
By moving the antenna close to any critical points in chamber construction could leakages be localized.
A problem was that the antenna quick did become very hot to hold, even if gloves was used. The fingers could be real swollen after a full day.
It was same kind of heat that can be felt when doing electrical welding or staying in the sun too long (I doing both).
This was long before cellphones and RF limits existed.
The thermal effect was obvious and I assume it was equal dangerous as any EM-source in that power range including strong glow-bulbs.

Better safe then sorry, do RF measurement in darkness for compensating those 2 Watt of energy or else can you get burnt fingers, but with 2 Watt as heat-source will it take some time.
There is no scientific prof for any thing else then the thermal effect.
We can collect that heat and verify that no energy is lost in any unknown dimension.
It is actually one method to measure RF radiation, by measuring how fast it can melt ice.
Set its power level in proportion to other things, soldering pen, LCD screen, indoor electrical heating element, kitchen range...
When color TV was new was it said that twice watching distance then for B/W TV-set was recommended due to increased radiation as the color tube did emit higher voltages.
Else was it high risk for impotence. Anyone know if it was true?
Not so long ago was same kind of tubes used as PC screens, and a lot of people was sitting real close of it for hours.
There must be a lot of useless men in that generation.

Not meant to joke, but set it in proportion to similar EM radiation sources that we have used for many years and our knowledge and experience from that.
I would not be surprised if it is dangerous to get the fingers half-boiled two days a week for a year, as I did 30 years ago, but so far no problems.

 

[albbg]

E Kafeman, I don't agree with you.
Probably the EM radiated by the VJKris are very small and not dangerous at all, however generally speaking I don't understand how can you be so sure about the safety to stay in front of an RF source if no heat can be reveald by the body.
First of all the regulations assume a saftey level, based only on thermal effects, taking into account a maximum permissible increase of temperature of the body (usually the brain) of 1 degC.
More over, even if there is no clear scientific evidence about non-thermal effects, they are reported in many studies, accepted from someone and rejected by others, due to many reasons.
However even if you want to focus on thermal effects, you have to take into account the mass of the tissue that is receiving the EM and the RF characteristics of that tissue at the frequency you want to consider. Onother factor is how deep the field penetrates inside the tissues: electrosurgery is based on the RF properties.

So it's a complex matter.

 

[biff44]

If you could be a little more precise about your situation, we might be able to comment. What do you mean "emit 32 dBm"? Do you disconnect the antenna, put a power meter in its place, and then measure +32 dBm? Do you have the antenna radiating, and 1 meter away in any position you can read 32 dBm off of a mobile test antenna?

 

[E Kafeman]

I don't understand how can you be so sure about the safety to stay in front of an RF source if no heat can be reveald by the body.

You are free to not understand but it is not so complex:
My body did react by registering the heat. Skin sensors are very sensitive for minor temperature variations.
If sensed heat from a RF power source is less=>less power level=> less effect due to EM waves.

More over, even if there is no clear scientific evidence about non-thermal effects, they are reported in many studies, accepted from someone and rejected by others, due to many reasons.

No one have succeed to proof, at an accepted scientifically level, anything else then thermal effects.
Real low absorbed thermal effects (<0.1 Watt) can be considered as marginal in a body that naturally produces more then 100 W of internal heat.
A very similar "minor effect" is to reduce our own body possibilities for heat convection by wearing clothes, and that seems accepted as healthy.

you have to take into account the mass of the tissue that is receiving the EM and the RF characteristics of that tissue at the frequency you want to consider.

Guess you is thinking about that human body is a poor attenuator for EM freq. below 10 MHz => most of the energy will pass thru a body without affecting anything, which gradually changes with increasing frequency, above 10 GHz => most energy is absorbed already at skin level.
We have similar effect for sound waves, high frequencies are more absorbed while low freq. easier is passing true a human body.
If it exist a generally more dangerous frequency range, in the range 10 MHz to 10 GHz, is it maybe around 50 MHz as it then could start a self-resonating effect due to human average length then is close to a quarter wave length, acting similar as a resonant vertical monopole antenna standing at earth. It is well known that a low power level of mechanical self resonance can destruct big things such as road bridges. However do conventional EM monopole antennas not seem to suffer of similarities to this mechanical self-destruction problem, as a result of a low RF power level. It is probably also valid for "human antennas".

Another factor is how deep the field penetrates inside the tissues

An EM wave becomes weaker with distance but there is no final deep or distance.

 

[albbg]

As you said no one succeded in proof the presence of non-thermal effects during the exposition of the human body to RF field. But also no one succeded in proof the absence of non-thermal effects during the exposition of the human body to RF field
However I think many papers and experiments have been produced; they are not widley accepted but they cannot be neglected. Have a look, for example, to:

http://www.ramazzini.it/ricerca/pdf...nd living matter_Eur J Oncol Library_2010.pdf
http://www.ncbi.nlm.nih.gov/pubmed/158900 (abstract only)
http://arxiv.org/ftp/physics/papers/0102/0102007.pdf

About the 100W power generated by the body, they are dissipated over the whole mass and not internally focused in some specific tissue. Furthermore is different the way in which the heat is generated.

 

[E Kafeman]

But also no one succeded in proof the absence of non-thermal effects

Non thermal effect due to that RF energy is absorbed, does probably not exist. It is a bit as turning off light-switch to investigate if someone is affected by the light. This kind of research is therapy for doctors that need to have a project to get subsidy.
Any RF energy, even real weak, have a thermal effect when absorbed by a resistor or human body.
For low power levels can it be hard to measure small variations in temperature but mathematically is it a linear function.

There is no RF energy "internally focused" even if a cellphone is held close against an ear. The human head dissipates a lot of heat, that is why an average cellphone RF power(~0.1W) only have a minor effect for total temperature situation.
Covering an ear with a dead cellphone for several minutes and temperature will rise with several degrees both in ear and cellphone. Conclusion is that no RF energy is needed at all to cause increased temperature with several degrees. It is no problem to measure this effect with a simple thermometer.
As result can it be a dangerous problem if remaining body is covered with isolating clothes, causing overheating in the brain, as it not can dissipate enough heat if also ears are covered.
The problem can be even worse as it not is uncommon that a cellphone emit 3-5 Watt due to internal losses while producing 0.1 Watt average RF power. Emitted mainly in infrared frequency range. Human body is a good absorber in that frequency range.

"different the way in which the heat is generated"
For a certain change of temperature is energy origin or production method of that energy not a parameter. It is frequency depending in that way that for low EM frequencies is human body a less good absorber.

 

[VJKris]

Setup: The Antenna is a remote radio head(eg: similar to shown in the picture https://www.fujitsu.com/global/services/telecom/product/rrh.html#id1) operating @ 2.375 GHz.
The output antenna port is connected to a agilent spectrum analyzer through RF cable to observe the spectrum.On this i observe 32 dbm as its power level.
The radio head,spectrum analyzer etc are placed at distance of 1 m from the engineer working.

 

[E Kafeman]

Is the remote radio connected to a spectrum analyzer or an antenna or both? Is the antenna omnidirectional?
If RF power only is connected ta a SA is there very low radiation level as most of the energy is burnt in an internal resistor in the SA.
If you is 1 meter away from an omnidirectional antenna is the body covering a small fraction of total radiation directions.
If you have a SA available, why not measure field-strength at 1 meter distance and calculate how much of the total radiated 2 Watt that you is able to absorb?
A guess is that the body is able to absorb 5% of total radiation (0.1Watt), evenly spread in a lot of body-mass.

 

[VJKris]

There is no antenna connected.Only the SA is connected to the output port on the radio head.

 

[E Kafeman]

If everything is shielded, there is no radiation, or very small levels due to non ideal shielding.
Your local FM broadcast station will probably cause much higher RF field levels in a radius of several kilometers.
As I not know if it exist a non hazardous level can I not tell if it is hazardous either.
My opinion is that if you can feel any heat, go away (+10 Watt or similar as the heat from a +10 Watt glow-bulb at near distance).
Most regulations says something in the range max 1-2 Watt RF radiation per kg body-mass (peak level in any body part). It is a synthetic level, no one really know if there is a is safe level as no one neither have succeeded to define the threat.
To get a relation to an EM radiation level that we have long experience from, the sun radiation, is radiation power level a clear day more then 1000 Watt per square meter.
Absorbing too much or too little radiation from the sun on our body can be less healthy is it said. It seems likely, I can feel the heat and can get burnt.
If you feel uncomfortable staying all day long near the RF leakage from the transmitter, maybe 0.01 Watt, take a walk in the sun..
I do so.