On Wed, Jul 29, 2015 at 9:15 PM, Harold Hallikainen wrote: > > > Thus far, I'm not a believer. The power, of course, spreads over an area > that increases with the square of the radius. As you move away, the power > drops off pretty quickly. So, to get any power at the receiver, you have > to transmit quite a bit of power which I don't think is that safe. They > keep saying it's safe because it's used in medical imaging. A quick searc= h > does not reveal how much power medical ultrasound imaging systems use, bu= t > I suspect it's fairly low. One thing that surprised me is the frequencies= : > 2MHz to 15MHz. I wonder what absorbtion of air is at these frequencies. Ultrasound is not perfectly harmless. Consider the sinister way it affects fetal brain development: http://onlinelibrary.wiley.com/doi/10.1002/uog.9055/pdf I have the same reaction as Harold. The claim about medical imaging weakens the case in my mind. I am always dismayed at how poorly media people understand physics, even basic stuff like power levels. --=20 Regards, Mark markrages@gmail --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .