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September 2014: Let’s Get Weird

It’s time to take a break from the world of architectural acoustics and get weird. Whether you know it or not, acoustical phenomena extend far into every discipline imaginable. So as we shrug off the dog days of August and watch kids head back to school, it’s time to get educated as well, this time on some acoustical weirdness.

Weird Fact 1: Did you know that Mother Nature has a long distance telephone line in the ocean that both whales as well as humans communicate along? The SOFAR channel (Sound Fixing and Ranging channel) is a layer of water in the ocean that encapsulates sound waves through complete internal reflection, much like a fiber optic cable transmits light. The SOFAR channel axis lies between 2000-4000 feet below the ocean surface. Low frequency sound can be heard in the channel sourced from across the entire Atlantic and Pacific Oceans. It plays an important role in submarine warfare and studies have shown that fin whales seek out the channel in order to communicate long distances with friends and family.

Sound Waves Diagram

Sound speed profile (left) and sound wave refraction (right) in the SONAR channel. 

Weird Fact 2: Speaking of the ocean, there are two tiny animals that live at the bottom of the sea that fight and kill prey with acoustics. The pistol shrimp (Alpheidae) has a large claw that can snap so fast that its shockwave literally rips apart water at 218 decibels. This in turn causes cavitation bubbles that reach temperatures approaching that of the surface of the sun through a process known as sonoluminescence. Another crustacean, the mantis shrimp (Stomatopod), has claws than can punch prey at 60 mph which causes an impact force of 1,500 Newtons. This is enough force to break aquarium glass. The mantis shrimp’s punch also causes cavitation bubbles similar to that of the pistol shrimp. I wonder who would win in a fight.

Shrimp Picture

The mantis shrimp taking a break from being the Mike Tyson of the sea.

Weird Fact 3: Cavitation bubbles not only help sea bugs fight enemies, they can help doctors fight diseases. For many years, kidney stones have been broken apart by use of shockwave lithotripsy which is basically a process of shooting ultrasound at kidney stones which inherently have very tiny bubbles attached to them. The shockwaves cause the bubbles to undergo cavitation, which acts like a microscopic hammer on the kidney stones. During the most recent meeting of the Philadelphia Regional Chapter of the Acoustical Society of America, Dr. Carr Everbach spoke about medical therapies just on the horizon that utilize acoustics together with bubbles to target internal medical conditions. It has been shown that if microscopic bubbles filled with medicine are entered into the bloodstream, they can be popped with sound once they reach their target, thus allowing the medicine to be delivered more directly and efficiently than more traditional treatments.

Bubbles

A bubble as it undergoes sound induced cavitation. Notice the last graphic shows the “microscopic hammering”.

There is plenty more acoustical weirdness out there such as how spiders tune their webs, acoustical levitation, the ghostly moaning of the NYC Freedom Tower, and Ben and Jerry’s acoustical ice cream freezer. So get out there and get your weird on with acoustics.

October 2014: The Wheels on the Bus
August 2014: Acoustical Sustainability