Let’s refer back to the Polish paper quoted in Havana Sonic Attacks — Addendum for techies only:
Roshchin and Dobroserdov indicated that levels of 90–110 dB within the range of lower frequencies (21kHz) and 110–115 dB within the range of higher frequencies (40kHz) constituted the limit of occurrence of functional changes .
Since we’re designing a weapon, let’s consider 120dB, at the head of Patient Zero, as an absolute minimum. Just inside the window, how much ultrasound intensity is required? Sengpiel Audio has a helpful page of calculators. Assume that the sound evenly spreads into one hemisphere, with Patient Zero sleeping 3 meters distant from the window,
120dB (sound pressure at head) = 137dB (sound power level 3 meters away)
Since 120dB (sound power level) = 1 watt,
137dB (sound power level) = 10^1.7 watts = 50 watts.
It turns out we need 50 watts. If only 5% makes it through the window, then we need 1000 watts hitting the window on the outside.
We chose a high ultrasound frequency to form the duct, between 140 and 400 kHz, specifically because it is rapidly absorbed in air, heating the air. But for the payload, we don’t want this to happen.
The AIRSTAR attenuation chart shows that for frequencies between 20 and 40 kHz, air absorbs hardly any of it. Most of it reaches the window. So let’s aim for those. Perhaps we need 4000 watts at the gadget to get 1000 watts on the window. It depends upon the efficiency of the duct scheme, and distance. So pad the estimate good.
What structures in the brain correspond to wavelengths of ultrasound in water? The speed of sound in water is 1500 meters/second. Capillaries are 10 microns and smaller, corresponding to frequencies in the megahertz range. These fade quickly in air, too fast to use. With increasing feature size, nothing sticks out. But at an ultrasound frequency of 30 kHz, the wavelength is 5 cm, about the distance between the dura mater (the “brain bag”) and the cerebral ventricles (the inner fluid-filled chambers.) It also corresponds to other major anatomical structures.
This sounds like CTE, in ultra-slow motion! Beginning with “punch drunk” boxers in the 1920’s, chronic traumatic encephalopathy has progressively extended in the direction of less significant brain trauma, more frequently incurred. Boxers got knocked out; after a number of knock-outs, they weren’t the same. In 2005, it was found in football players whose trauma history was very minor compared to boxers. The Russian references imply that the lower limit is very, very low. If the brain is shaken, in a comparatively gentle manner, for a long time, symptoms overlapping CTE can occur.
The blow that knocks out a boxer causes a large impulse, a change of momentum, to the head. However the head was moving before the blow, it moves differently the instant after. The brain doesn’t follow this change in one piece. Tiny tears in the tissue occur, as different pieces move in different directions.
How much energy is in the boxer’s fist? Not much at all. It won’t heat your coffee. It’s enough to drive a few nails into wood. The energy a sumo wrestler employs to force his opponent to another position is much greater. The power levels we just discussed are continuously applied. We should change the design of our gadget to apply concentrated pulses.
The approach is so far tenable. 4000 watts for an hour is about equal to 40 battery packs for a laptop, or a typical add-on pack. So maybe the operator has to sit in a car. But if the device could deliver short, powerful pulses, it would ruin somebody’s brain much faster, like Joe Louis’s fist. For example, if the gadget delivers a 15 kilowatt pulse for 10% of the time and loafs the rest, it uses only 37% of the power, and gets the job done much faster to boot.
We want a cymbal clash!, not the soft tone of the flute. We want to be the drummer next door you’d like to brain. Well, now’s your chance. The more unevenly a given amount of energy is applied, the more damage the gadget will inflict. This also means that if the power calculations are too optimistic, we can make it up with pulses. And this is just the start. With every new and improved brain fryer, we can up the pulse and lower the total power consumption. We can make it small, even stylish. Everybody will want one.
There is a beautiful, perfect world, Math-land, where this is an easy problem. Math-land has a celestial piano that can play all the notes in the universe. By combining the notes in just the right way, as discovered by Joe Fourier, we can make the pulse (the cymbal clash) we need. Back in the real world, it isn’t so easy. The real reason we want to make concentrated pulses is because it saves us energy. With pulses, the gadget only has to run full-tilt for short intervals. Then it rests. We call this “duty cycle.” Only very heavy machinery, like a power plant, is designed to run full power 24/7.
So the pulse idea is good, but only if it is practical, and saves energy. The Math-land scheme doesn’t work here. The idea of a celestial piano is just nonsense. As best, it serves as an inspiration. You build your gadget in Math-land first. Then you do it again, in the real world, where there is a budget for everything, including energy. Real gadgets can’t make pulses like that and work very long. For that, you need explosions.
So now we discover that back in the real world, there is no way to create the pulse we need. Life is sometimes cruel that way. There has to be an answer, so we can keep our lousy jobs. Relax, there is.
Next stop, the physics lab.
To be continued shortly.