Health issues when amplifying a low-power radar

[oyvdahl]

I am working with a low-power radar (-15dBm) which we are going to amplify as much as we can by using of-the-shelf components to see how far we can extend the range.

For this project I am looking into the health issues of sending out more power (probably less than 50-100W). As I understand it, there are no proven health issues when there is no significant thermal heating in the tissue. Therefor I am trying to find out how much power which is needed to cause a significant thermal heating on humans.

Given a person's distance from the radar and the radar's emitted power, is there any simplified calculations that I can do to get a brief overview of the hazard of "significant thermal heating"?

Any links, google search words or any clues at all is appreciated.

Best Regards
Oyvind

 

[FvM]

Suggested limit values have been defined by the ICNIRP (International Commission on Non-Ionizing Radiation Protection)

Some references can be found e.g. here:
EMF limits - ICNIRP basic restrictions

 

[biff44]

Opinions vary, but some researchers are getting suspicious of cell phone power levels!

I would definately not let that sort of power beam into my eyes, as I would be worried about cataracts.

After that, I would want to compute the dosage absorbed by the human body, and see if it conforms to the radiation limits for the country you reside in. There is a maximum power density in watts/cm² that you should not go above.

And remember that if you have any antenna gain, your effective power inside of the main beam will be much higher than 100 watts (could be killowatts)

here are some resources:
Safety and Health Topics: Radiofrequency and Microwave Radiation

 

[G0HZU]

With radar you have to look at both peak power and mean power.

Is the 100W the peak power or mean power? There is a significant difference.

Also, as mentioned by biff44 you have to take into account the ERP from the antenna as this could be far higher.

 

[oyvdahl]

Thanks for the link. And thanks for the tip about antenna gain.

The problem is that I really don't know how to calculate the SAR value. I have found the equation on Wikipedia, but I have to admit that I don't understand how to actually use it.
By searching google I have found some papers, but they are very specific in calculating SAR for a human eye or in a fetal.

Is there no shortcut here to just get a sense of if the emitted power will create a "significant thermal heating" in a person standing for instance one meter in front of it?

G0HZU: I have not found any 100W amplifiers yet, the highest so far has been 35W. And I don't know if it was peak or mean power.

 

[vfone]

You have to know the peak and mean power not only for SAR calculation, but also for choosing your Power Amplifier.
The maximum output power of a linear amplifier should be the peak power of the signal, because if you chose mean power, the peaks will be limited.

**broken link removed**

 

[oyvdahl]

I have read a lot and I think I have managed to calculate power density by following this article: https://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/pwr-dens.pdf
I will figure out the peak/mean power, but for now I used max output power of the amplifier to be sure I was not calculating a value too low.

I did not manage to calculate the SAR value, but from table 6 in **broken link removed** a reference value was given in Wm^-2 which I used instead.

Please let me know if anyone suspects I have misunderstood something.

Thanks for your help!


Regards
Oyvind