Talk:Attenuation

Attenuation constant
Changed to -10*log_10(Output power / input power). Reference in [7] is wrong. When discussing attenuation in optics, the quantity should be negative. That formula gives a dB gain. New reference needed. —Preceding unsigned comment added by 169.234.12.117 (talk) 21:53, 30 January 2010 (UTC)

Wrong! attenuation is a positive quantity, and is implemented normally in formula, similar to I_0=exp(-alpha*z) —Preceding unsigned comment added by 169.234.3.206 (talk) 05:27, 1 February 2010 (UTC)

Wrong units in the formula
In the section on attenuation in optics it states that the units of intensity are Watts (W). This is simply wrong.

Intensity is Power per Area, so ither it should be Intensity (W/m^2) or Power (W). In both cases the formula can be used as the area is the same. So power or intensity are fine, but the units should not be mixed. — Preceding unsigned comment added by 134.3.129.103 (talk) 18:41, 11 August 2016 (UTC)

This Article's Existance Here
Shouldn't this be in Wiktionary? I propose either moving or copying the article there. --Falsifian Come to think of it, there are too many pages that link here. I'll copy it over if it's not already there. --Falsifian 16:30, 2004 Nov 22 (UTC)


 * A copy over to 'tionary is a great idea, but this subject is certainly worthy of a wikipedia article. Here's hoping someone fleshes it out. --Joel D. Reid 22:10, 13 July 2006 (UTC)
 * Woo hoo! That didn't take long&mdash;Fleshed out indeed. I love this place. -- Joel D. Reid 18:50, 20 July 2006 (UTC)

Attenuation relating to Biology/Genetics
I think that a seperate article should be created relating Attenuation to the process of RNA termination

A sentence or two could be added to describe the diffuse attenuation coefficient of downward propagatin radiation, as it is used in limnology, e.g. k(d)=-1/z ln (Iz/I0) [ see Kirk - Light and photosynthesis in aquatic ecosystems ] —Preceding unsigned comment added by 193.170.92.170 (talk) 10:52, 25 January 2011 (UTC)

disambiguiation
a disambiguation page is needed, for people like me who arrive at the physics attenuation page but are looking for attenuation (biology)

Attenuation

Values for attenuation coefficients
should the value for lung really be twice that of bone? i should think it would be the other way round or similar Rtcoles 16:43, 29 April 2007 (UTC)


 * How so? You haven't mistaken the frequency coeficient of attenuation for a mere attenuation, have you?  Jim.henderson 02:33, 3 May 2007 (UTC)


 * I think I might have - maybe the difference could be made more clear in the article? why does lung attenuate twice as much as bone at this particular frequency, for example? Rtcoles 18:28, 12 May 2007 (UTC)


 * This particular coefficient isn't so much about how attenuation varies among media at a particular frequency. It's more about the slope of the curve of attenuation vs frequency in each particular medium.  However, to address the question rather than the coefficient, grip your knife in your teeth.  Press the tip against the rail.  Hear the Iron Horse when it is still half a day's walk away.  Solids conduct sound better than liquids, and liquids better than air.  Don't tap your finger on the wall of the fish tank; you'll deafen the fish because they don't have air attenuating the sound.   Jim.henderson 00:05, 13 May 2007 (UTC)

The last reference link is not working. Does anyone know which university was originally referenced, and what their URL is now? Ackbeet 15:03, 11 September 2007 (UTC)

I'm worried about the values of the attenuation coefficients for water (and also the units and naming) - Kinsler, in "Fundamentals of acoustics" (3rd ed.) says that acoustic attenuation coefficients (a) are measured in Nepers/m (Np/m) and absorption coefficients (alpha) in dB/m. Using his eqn 7.52 (and experimental data in fig 7.5) gives an absorption coefficient of 0.21dB/m at 1MHz. This is very different to the value of 23dB/m at 1MHz found in this table. Comments please? —Preceding unsigned comment added by 152.78.32.144 (talk) 16:40, 9 September 2010 (UTC)

I've updated the values for attenuation constants using a more recent reference, which itself is a compendium of measurements from the literature. As the previous commenter noticed, there was a typo in the value for water in the previous table, which listed a value two orders of magnitude larger than the correct value probably due to a meter/cm unit mistake (Nepers/m vs Nepers/cm). Other values have shifted as well, but by a factor of ~2 or less. David s graff (talk) 14:48, 7 October 2010 (UTC)

Power versus amplitude
" Attenuation of a signal's power by n decibels is equivalent to attenuating its amplitude by 2n decibels." Shouldn't this be the other way around? If $$ P=UI=\frac{U^2}{R} $$, then an attenuation of n decibels in voltage will cause an attenuation of 2n decibels in signal power. Or what is meant by amplitude? — Preceding unsigned comment added by 141.2.242.226 (talk) 08:11, 20 September 2011 (UTC)

Ultrasound Attenuation Formula

 * $$ \text{Attenuation} = \alpha [\text{dB}/(\text{MHz} \cdot \text{cm})] \cdot \ell [\text{cm}] \cdot \text{f}[\text{MHz}]$$

Shouldn't this be f^2? This paper: http://rennes.ucc.ie/~bill/repository/2013-IEEE_IUS-1432.pdf indicates that the attenuation of ultrasound through air is related by the square of the frequency.

Answer written on December 18, 2013: It can be $$f^\nu$$ with $$\nu$$ typically between 1 and 2 depending on the medium. For biological tissue it is often assumed to be close to 1. Please see e.g. http://en.wikipedia.org/wiki/Acoustic_attenuation


 * Having a look at one of the articles referenced, it seems pretty clear the dependence on air is indeed closely quadratic with the frequency. I can provide the data I have extracted, and a python notebook with the regression. Nevertheless, nothing stops you from defining an "alpha" in which you divide by the frequency. Only, do not expect this number be constant ! This should be clearly stated, I am deleting the "linear relationship" sentence since it is simply not true. --Daniel (talk) 11:11, 21 November 2018 (UTC)

Table of attenuation coefficients
I think the table should be under Attenuation coefficient instead of (or in addition to) here. Mintz l (talk) 15:35, 23 May 2014 (UTC)

Assessment comment
Substituted at 08:33, 29 April 2016 (UTC)

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