What is Attenuation: Definition and 133 Discussions

In physics, attenuation or, in some contexts, extinction is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variable attenuation rates.
Hearing protectors help reduce acoustic flux from flowing into the ears. This phenomenon is called acoustic attenuation and is measured in decibels (dBs).
In electrical engineering and telecommunications, attenuation affects the propagation of waves and signals in electrical circuits, in optical fibers, and in air. Electrical attenuators and optical attenuators are commonly manufactured components in this field.

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  1. J

    Linear attenuation coefficient

    Homework Statement This i self study! Hi, How thick should a foil made from absorber II be to give the same absoption as 1mm thick foil made from absorber I for xrays with energy 5X106 xray beam passing through an absorption material it is attenuated , this is given by I/Io e-ax io...
  2. X

    What is potential barrier against the photon penetration

    It is known that the penetration depth of photon into a material depends on the energy of the photon, density and atomic number of the material; because the photon energy is normally smaller than the potential against the penetration of photon, which is the potential barrier, so the incident...
  3. D

    Wave Attenuation: Struggling in Course? Resources to Help

    For my waves and diffraction course we have had a completely incompetent lecturer. We were looking at standing waves and then all of a sudden he spent a lecture looking at attenuation, not mentioning where it would apply or explaining it particularly well. I have tried to find a textbook to...
  4. D

    Why is light attenuation not linear?

    I was wondering why light transmission through a solution decreases exponentially and not linear with the concentration of the absorbing compound in solution. I know the Beer-Lambert law, but I do not really understand the reason for this logarithmic rather than linear dependence. Can anyone...
  5. laramman2

    Calculating Thickness of PTFE Membrane Air Filter

    Homework Statement Is there any way we can measure the thickness of an exposed PTFE membrane air sampling filter? An unexposed filter (from the filter datasheet) has a thickness of 40μm. We have 5 ambient air exposed filters with the following mass concentrations: 1μg/m3 (filter 1), 20.1 μg/m3...
  6. N

    Attenuation numerical instability via numerical diss. nonlinear ODE

    Hi, I'm solving a problem numerically that takes the form Q_{ij} \ddot{y}_j +S_{ijk}\dot{y}_j\dot{y}_k +V_i=0, where (Q_{ij},S_{ijk},V_i) are all functions of the dependent variables y_i. The dependent variables are all functions of the variable t. The resolution of this spectral...
  7. C

    Mass attenuation problem, protecting the lunar base against radiation?

    Homework Statement To protect the lunar base against space and sun radiation, astronauts covered it with 4m thick layer of regolith (moon soil). However, they found that they level of radiation was still 50% higher than on the Earth's surface, which they want to match. How many more meters of...
  8. C

    What do the I's stand for in attenuation and power loss equations?

    I'm revising attenuation and power loss logarithmic equations. The exam formula I'm given is attenuation = 10 log (I1/I2) I'm trying to confirm what each I stands for. Some of the examples I'm looking at seen to give input/output power, some seem to reverse it. Which is right? What do they...
  9. N

    Attenuation finding distace and amplitude

    Homework Statement problem 1 A 20 Hz seismic wave traveling at 3 km/s propagates for 2000 m from point X to point Y through a medium with an attenuation rate of 0.5 dB/λ. What is the ratio between the amplitude of the wave measured at X and the amplitude of the wave measured at Y (i.e., AX/AY)...
  10. S

    Radiological physics - linear attenuation co-efficient

    I am completing a radiological physics experiment about attenuation and half value thickness. I'm struggling to understand linear attenuation coefficient and what it means when it says its and exponential relationship. I understand that attenuation is the reduction in intensity of an...
  11. S

    Sound Wave Attenuation: Why Does Water Attenuate More?

    Why does water attenuate sound waves more than air? Is it because of it's bulk modulus? This is what I understand. Speed through a medium is determined by the elastic component over the inertial component. Since water has a much greater bulk modulus (elastic component) than air, it makes the...
  12. M

    Acoustical diffusion, scattering, attenuation

    This is killing me; not sure if I'm over-complicating or under-complicating it. I’m trying to understand if there is any difference between acoustic scattering and diffusion, and how that differs from attenuation. When particles collide, a small amount of heat is created, since the collision...
  13. D

    Finding attenuation, phase constant, and velocity

    Homework Statement Find the attenuation constant alpha, phase constant β, and phase velocity v if the conductivity of the material is σ=ωε the material parameters are μr=1, εr =2.5, and the wavelength in free space is λ naught = 30cm Homework Equations The Attempt at a Solution So...
  14. P

    Relation between units of attenuation

    Homework Statement It is customary to express fibre loss in units of dB/km: \alpha(dB/km) = \frac{10log(P_{in}/P_{out})}{L(km)} where P_{in} is the power entering the fibre and P_{out} is the power leaving the fibre. Show that \alpha(dB/km) = 4343\alpha(m^{-1}) The Attempt at a Solution...
  15. V

    Solving Nuclear Attenuation Problem - Thickness of Aluminium

    Homework Statement I've attached the problem and my attempt at it as a picture attached. I've done part b.i) although I'm not sure if it's entirely correct. I'm struggling with the last part b.iii). This is where I have to calculate the thickness of aluminium instead. I'm given the atomic...
  16. R

    Attenuation of em waves- unknown relationship help.

    Sorry if this is in the wrong place. Was not sure what it is categorised as. I have come across the following:e^{-\frac{\omega}{c} nkz}, referring to attenuation of a wave. It was found here...
  17. iVenky

    What is the reason for the square attenuation?

    I have seen this concept in many places like electrical field, gravitational field, brightness from a distant star or in satellite communication. That is, they seem to be inversely proportional to the square of the distance from the source of that field. What's the reason behind it?
  18. M

    How Do You Calculate Signal Power After Attenuation?

    Hi, I have a question regarding frequency, power... Let's say I have signal with power level of X dBm and the signal has been attenuated by Y times. What is the correct formula to use to get the final power ? Thank You
  19. M

    Confusion between Attenuation and Intesity change

    Dear All, I am basically from Bio background and doing research in Insect Physiology as Phd. Currently I am given a task to generate artificial insect songs using a software. I did it with 3 v Noise stimuli(1.5 peak to peak) and fed it to amplifier and I heard it on Amplifier. So now the...
  20. O

    How does fixed line level attenuation work?

    hello all first post here and I'm interested in some info you people may hold :smile: in layman's terms I'm trying to understand how a fixed line level can attenuate. according to wikis line level page the 'the signal out or line out remains at a constant level, regardless of the current...
  21. J

    Sound attenuation barrier height (trigonometry)

    Homework Statement http://img543.imageshack.us/img543/4598/photosfr.jpg Find dss, dsr and thus hs. Homework Equations trig The Attempt at a Solution dss = hs/(sin[θ]) dsr = hs/(sin[∅]) dss = 3.059/(cos[θ]) dsr = 47.191/(cos[∅]) θ = arctan(hs/3.059) ∅ = arctan(hs/47.191) I have tried...
  22. F

    TEM plane waves, decay and attenuation

    I've been trying to get reantiquated with electormagnetics to understand RF communications better. I have a question about TEM plane waves. The funtions which describe the plane waves in the z dirrection are: e-α cos(ωt-βz) ; in the time domain where is the rate of decay. In free...
  23. T

    Near field path loss with attenuation

    Homework Statement I have a 2 wireless cards with a power output of 0dBm, two 5dBi gain antennas, and a 30dB attenuator connected to each antenna. I need to figure out what the path loss will be in this scenario, so I can therefore determine the maximum distance possible between the...
  24. L

    Attenuation coefficient of water

    I have read that the attenuation of water (for ultrasound) is 0.0472 Np m–1 (MHz)–2. What is this in dB/cm/MHz^-2 ? What is Np? thanks
  25. FOIWATER

    Regarding the matching of a signal attenuation to source/load.

    I recently did an experiment where I had a T-type attenuator. It was connected to a 50 ohm load, and as such I used a function generator with an internal impedance of 50 ohms. Doing the correct calculations, I found the source and load impedance were matched to the attenuator at 50 ohms...
  26. M

    Understanding Attenuation Lengths for Radioactive Materials in Hollow Spheres

    Hello, I am reading this article in wikipedia http://en.wikipedia.org/wiki/Attenuation_length about attenuation lengths and there is something I'm hoping someone here can explain to me. Lets say I have one small solid sphere and one big hollow sphere. And let's say I put the small sphere...
  27. A

    Radio wave attenuation and scattering and absorption

    I am trying to understand why radio waves are not greatly attenuated by the atmosphere due to scattering or absorption? I have tried searching the internet and can't find any satisfactory answers. Please help. Oh and does this property somehow relate to why they are used to transmit information...
  28. A

    E-Field Attenuation: Causes & Effects

    Do electric fields attenuate in space? If so what causes the attenuation?
  29. T

    Radiation & nuclear physics, linear attenuation Co-60, Cs-137-

    Hello there. I've been struggling with this one for quite a long time now and decided to ask if any of you people could point out what I'm missing here. There are actually three problems which are related to each other. I managed to solve the first and the second one, but the third is where I...
  30. J

    Investigating Attenuation of X-Ray Photons with Al Thickness

    Hi Would anyone help/advise me? I've done 2 experiments as part of my radiography degree. One was to investigate the effect of the ISL on a beam of x-ray photons. I could understand this, produced 2 graphs (Mean reading against distance (uGy) and Mean reading against 1/d squared) and wrote a...
  31. amylase

    Why does attenuation coefficient decrease with increased energy?

    Hello. Not sure if this is the right board to post. This is not homework. I am just self-teaching quantum physics as I read a book on the topic of X-ray Physics. It has about 30 chapters in total and so far I find myself having about 3 questions per chapter. Hope you guys don't mind me asking...
  32. M

    Wave attenuation, complex e

    Consider a wave propagating in a medium with complex epsilon (e). Show that the ratio of decay length to wavelength is roughly Re(e)/Im(e) when the decay length is long compared to the wavelength. --- I could attempt this if I knew where to start... not much help, but could anyone...
  33. E

    Plane waves: sign of Re(ε), Re(μ) in passive media, attenuation angle

    Hello, I'm having some issues with plane waves propagating through a medium which is: - linear - spatially and temporally homogeneous - spatially non-dispersive - isotropic - temporally dispersive - passive I know that permittivity, permeability and the k-vector are complex in...
  34. O

    Photoelectric mass attenuation coefficient data

    Homework Statement I see graphs for the total mass attenuation coefficient such as this all over the web:http://scientificsentence.net/Radiations/images/attenuation_coefficients.jpg However, I can't find data on the individual attenuation coefficients such as the photoelectric or Compton...
  35. O

    How Does Photon Energy Influence Exponential Attenuation in Matter?

    I am researching how photon intensity attenuates within matter and am a bit confused by what I have come across. Several sources state that the attenuation of photon intensity within matter is exponential (as a function of depth). The explanation is that photon interactions with electrons in...
  36. O

    Electromagnetic Attenuation Conceptual Question

    Hello, Why does electromagnetic wave intensity attenuate exponentially with depth from its incident intensity in an object? Why is the relationship exponential? I just need a nudge in the right direction or more if you are willing. Thank you for any help!
  37. N

    Linear attenuation coefficient.

    Why do we call the attenuation coefficient LINEAR? I(x)=Ioexp[-µx] why µ is called linear?
  38. A

    Waveguide - attenuation of power

    Homework Statement Show from general considerations that the attenuation of power in the rectangular waveguide (TE10 mode propagating in z-direction) is: P(z)=P(0)exp(-2k''z) where k'' is the imaginary part of the wavevector in the phasor exp(j(wt-kz)) Homework Equations power is...
  39. I

    Linear attenuation coefficient

    Homework Statement sphere r=1cm contains same density of H2O as surroundings with additional N=10^20 iodine atoms/cubic cm linear attenuation coeff (u) for water at 50keV = 0.2 /cm crosssection for interaction of 50kEV photon with iodine = c = 3.6x10^-22 /cm^2 a) calculate u for the...
  40. M

    Light vs Radio attenuation in water

    Hi all, I can't figure this one out, but I'm sure I'm probably missing something simple. Here's the problem I'm having: From what I've been told in my SCUBA class (as well as from online article's and forums) light is attenuated in water in the order red->violet (red being attenuated first)...
  41. C

    Kramers-Kronig relationship between ultrasonic attenuation and phase velocty

    Hi Forum, I am currently attempting to utilize http://bayes.wustl.edu/etj/articles/kramers-kronig.pdf" Unfortunately ... I have not been successful. I have tried for the past week and asked those around me. All help is appreciated. The equation is as follows: ( 1/c(w0) ) - ( 1/c(w) ) =...
  42. S

    Understanding EM Wave Attenuation in Conductors and Dielectrics

    Hi, I have been reading my textbook and online but I'm not sure if I understand. An EM wave attenuates in a conductor but not in a dielectric? If that is correct what does the impedance of a dielectric represent, since I thought impedance would be associated with an energy loss...
  43. T

    Neutron Attenuation 1st order ODE Interpertation

    Hi, I'm having some trouble interpreting an equation. In Lamarsh's Introduction to Nuclear Engineering. The formulae for neutron attenuation is: I(x) = I_{0} exp(-\Sigma_{t} x I am given the formulae \frac{-dI}{I(x)} = \Sigma_{t} dx This formulae has been described as "the probability of a...
  44. T

    Can a Photon be Attenuated? Scattering Theory Explained

    I know in scattering theory that a wave can be attenuated when it interacts with a dielectric sphere, it is partially scattered, partially absorbed. So, the scattering light has less flux density than was incident. However, if we use wave-particle duality then the same should be true for a...
  45. T

    Flux attenuation, given interaction cross section

    It strikes me that this may well be fairly easy, but i can't quite get my head round the correct way to lay this problem out (at least in a mathematical sense). If you are considering a neutron flux onto a fully understood material, and you also know the neutron interaction cross section of...
  46. S

    Understanding Attenuation Coefficient of X-rays: Gas, Liquid, or Solid State?

    During my A level physics class we were discussing the attenuation coefficient of x-rays and a question arose that I can't find an answer to anywhere. If someone could help answer what effect physical state (ie gas/liquid/solid ect) has on the attenuation coefficient of x-rays it would be much...
  47. T

    Linear attenuation coefficient

    is the linear attenuation coefficient named like it is because it is linearly proportional (inversely) to the energy? I have to read off the coefficient from a graph I have. I have the value for a 2MeV photon, if I want the value for a 1MeV photon is it simply twice the 2MeV value? Reading off...
  48. T

    Near and Far Field Attenuation Inverse Laws

    Homework Statement near-field distance attenuation follows an inverse cube law (1/d^3), while in the far-field it follows inverse law (1/d). Prove mathematically how we arrive at 60dB/decade from the inverse distance cube relation and 20dB/decade from the inverse distance relation...
  49. R

    Understanding X-ray Attenuation: Determining Absorption Probability and Depth

    Hi all, using the mass attenuation coefficient and density, one can determine the percentage of X-rays absorbed in a material for a given depth, using the Beer-Lambert Law. e.g. The intensity of a beam of 8 keV X-rays will be reduced by 68% after passing through 70 microns of Silicon...
  50. C

    Magnitude and Attenuation in Fields subject

    Dear folks, I'm a 3D computer graphics student, working on particles and fields area. As I'm a newer I have lots of doubts to clear on Physics topics. Please explain me what is Magnitude & Attenuation in Fields subject? I can see these two are common for most of the fields like air, drag...
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