Fall/Winter 2012

The Place to Go Where Sounds Stop

Inside the ARA Anechoic Chamber.

Everyday people experience noise that surrounds them.  Quite often it would be nice to find a place to go where there was no noise, a place to go where sounds stop. This is not only a wish by individuals but also by scientists.  Often crucial data can be tainted by the most minute noise that surrounds us.  A good example of the importance of no noise interference is with Askaryan Radio Array project by the Wisconsin IceCube Particle Astrophysics Center.  Recently, a chamber was built by the Physical Sciences Laboratory along with  WIPAC specifically for testing this project.  Previously the PSL was instrumental in building and testing of detectors for IceCube.  However, this project differs from IceCube in the way that it is trying to detect neutrino events.  ARA is trying to detect a radio pulse from the neutrino, unlike IceCube that was trying to detect a flash of blue light.

ARA scientist Mike Duvernois explains the science behind the building of the chamber. “ARA is a second generation radio neutrino experiment. It's the Askaryan Radio Array, named after the Russian physicist who first noted that charged particle showers in dense materials (sand, ice, or salt in particular) would generate a large, and detectable, radio pulse. This technique, when implemented at the South Pole, takes advantage of the extremely radio transparent, cold, deep Antarctic ice to allow individual stations in the ARA array to "see" neutrino events multiple kilometers away from the station, he said.” 

Recently at PSL , the Anechoic Chamber was unveiled.   “The anechoic chamber at PSL is a shielded room, a room that keeps >99.9999% of the radio power (from radio stations, computer clocks, spark discharges, etc.) out of the room, and then is lined with absorbing materials that prevent reflections of radio signals generated inside the chamber. (Anechoic means without echoes. There are chambers that look somewhat similar, but differ in their construction, that absorb sound.) For the ARA experiment we use this chamber in three different ways. First, we use it to test our antennas with known signals without outside noise contamination. The lack of echoes makes such measurements easier to interpret. Second, we use the chamber to measure the (low levels) of radio noise produced by our electronics to avoid contaminating our South Pole radio quiet environment. Finally, we use the chamber for careful calibrations of our radio frequency detector subsystems without external interference, and again with no echoes to confuse the measurements.

The chamber will also be available for measurements of the second sort, so called Electromagnetic Compatibility (EMC), for future extensions to IceCube or other experiments relying upon high speed digital electronics which as a byproduct tends to produce radio noise. Additionally other physics groups with antenna and radio frequency detector interest will be able to use this resource for their work and for the training of students.”


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