Hi Dave, Thanks a lot for your reply. But I don't agree with what you said: "Acoustics is a vector phenomena and it follows the same Maxwell equations as electromagnetic waves."
I guess what you meant was that Acoustic waves follow Helmholtz wave equation which Electromagnetic waves also follow. The Helmholtz wave equation is a scalar equation. Maxwell equations are a set of vector equations. One of the fantastic conclusions people could have drawn pure mathematically from Maxwell equations was that Electromagnetic phenomena could become electromagnetic wave that is a solution of Helmholtz wave equation with propagation velocity of c. Acoustic phenomena has nothing to do with Maxwell equations. Thank you. Please correct me. Best Regards, Barry Ma ------------- Original Text From: "George, David L" <[email protected]>, on 10/5/98 11:43 AM: To: Cc: Barry: It is true about acoustics. A company called NCT makes a good living with it. Some airplanes use noise canceling to make the passenger areas more comfortable. There is a noise buster head set which cancels the low frequency noise. Acoustics is a vector phenomena and it follows the same Maxwell equations as electromagnetic waves. There has been some noise cancellation work done in the ELF range during the ELF magnetic field craze but it is not easy. Regards, Dave George ---------- From: Bailin Ma [SMTP:[email protected]] Sent: Wednesday, September 23, 1998 5:46 PM To: [email protected] Subject: re: Doubt on Measuring with Spectrum Analyzer Hi, >Ed Price said: "I have heard of active cancellation equipment which can generate a phase shifted image of the offending signal and locally radiate this signal so as to create a limited "null" zone. How big of a null zone, the uniformity of cancellation, the stability and agility of the cancellation and the cost/complexity of the equipment are all unknown to me. >I wonder if any in our group has every tried active cancellation?" A friend of mine told me a few years ago that the active cancellation technology was successfully applied in Acoustics. IF it is true, I guess the difficulty to transplant it to Electromagnetic is that Acoustic field is scalar, whereas EM fields are vectors. Best Regards, Barry Ma ------------- Original Text From: "Muriel Bittencourt de Liz" <[email protected]>, on 9/22/98 1:35 PM: Hello all, I'm doing my measurements of conducted emissions using a Spectrum Analyser, but my site isn't shielded, i.e. some interferences ( radio stations ) appear at the screen of the SA. So, i'm doing this: i record the signal with the product tested at "off" and when i turn the product "on", i subtract the signal of "on" minus the signal of "off". this means that i subtract the "ambient noise" from the noise being generated by the product itself. What i really want to know is: is this procedure correct? am i doing a nonsense thing? Any comments will be welcome. thanks Muriel -- ================================================== Muriel Bittencourt de Liz INEP - Instituto de Eletronica de Potencia Universidade Federal de Santa Catarina Caixa Postal - 5119 88.040-970 - Florianopolis - SC - BRASIL Phone: +55.48.331.9204 - Fax: +55.48.234.5422 e-mail: [email protected] Homepage: http://www.inep.ufsc.br ================================================== --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
