In 1982, I was standing on the deck of a Navy frigate watching the first attempt to launch a missile from the forecastle of our ship. Nearly the instant it came into sight, the missile exploded with a flash of light. A shock wave hit my body like a slap. A few seconds later, I realized that I couldn't hear a thing.
I was lucky. My hearing returned within a couple of hours, and there was no other damage. The missile exploded due to a structural failure, but not with the full force of a bomb. For people who are near such explosions, the result can be significant injury or even death.
That's the situation that a new patent from Boeing is intended to prevent. Despite the hype that accompanied some accounts of Dr. Brian Tillotson's invention, this isn't the kind of force fields or shields you saw in Star Wars and Star Trek. Instead, the Boeing scientist has developed a way to block the force of a shock wave created by an explosive device before it can hurt someone or cause damage.
The technology works by heating a small region of air to the point that it changes the speed of sound in the area being heated. This effectively redirects the shock wave (which is similar to a sound wave except that it moves faster) so that it misses the people or objects it's protecting. Depending on the characteristics of the heated area, the result is that the intensity of the shock wave is attenuated.
"Shockwaves are a high-intensity version of sound waves, and sound waves travel faster in a hotter gas," Tillotson explained in an email.
"Changing the shockwave's speed lets us change its direction—just as the speed of light is different in glass than in air, and that lets glass refract (or bend) light when the light enters or leaves the glass, our shockwave refracts as it enters and leaves the hot region. It enters moving in one direction (say, toward a soldier) and it leaves moving in a different direction (missing the soldier)."
Creating that hot region of air so that it can refract the shock wave is the tricky part. For this to work, the device needs to detect an explosion and then create the hot air fast enough that it happens before the shock wave hits whatever it is that's being protected.
The heart of Tillotson's design is a collection of sensors that can detect the explosion through its electromagnetic radiation (this is usually a flash of light) and then act within milliseconds.
That action, as described in the patent, consists of firing a group of lasers into the region of air between the explosion and the target. The lasers create a temporary plasma region that is very hot.