Path: utzoo!attcan!uunet!husc6!linus!necntc!mit-eddie!mit-amt!mit-caf!fritz
From: fritz@mit-caf.MIT.EDU (Frederick Herrmann)
Newsgroups: sci.electronics
Subject: Re: ??: computer-controlled engines
Message-ID: <1212@mit-caf.MIT.EDU>
Date: 5 Aug 88 21:49:52 GMT
References: <7200006@silver> <1202@mit-caf.MIT.EDU>
Reply-To: fritz@mit-caf.UUCP (Frederick Herrmann)
Organization: Microsystems Technology Laboratories, MIT
Lines: 26

In <1202@mit-caf.MIT.EDU> I described electromagnetic compatibility
testing at GM.  I received a question about my use of the term
`anechoic' chamber, but was unable to reply to the sender, so am
posting this reply to him and anyone else who might have been
wondering:

Sorry, anechoic means no-echo.  The walls and ceiling of the room have
cones of conductive foam all over.  The cones are quite pointy, so
incident waves should reflect into the next cone instead of back into
the room, and after a few reflections the energy should be dissipated.
The walls are heavily shielded behind the cones, so that nothing gets
in and nothing gets out.  Fiber optic cables are used to get signals
from various instruments on the inside to computers on the outside.
GM's EMC group has two such chambers (one big enough for a truck cab),
and several shielded rooms (without the cones).

That describes an electromagnetic anechoic chamber; acoustical anechoic
chambers are similar, built with cones of a suitable material... I saw
one when I toured GM's noise and vibration lab.

Hope that answers your question...

				- Fritz
				  fritz@mit.caf.edu

Repeated disclaimer: I worked at GM for one summer, I didn't speak for
them then and I don't now.