# absorption coefficient alpha

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In a dielectric with a relative permittivity given by εr and a relative permeability given by µr which is at unity, the admittance is given by y = (ε0εr/µ0)½ = Y εr½ = Y N = Y (n-ik). (13) As was the case for the impedance, the absorption coeﬃcient may be a function of frequency, and measurements over the frequency range of interest may be required. by the equation c=1/(µ0ε0)½. If λ is in nm, multiply by 10 7 to get the absorption coefficient in the units of cm-1. The absorption coefficient describes how much light of a given color is absorbed by a material of a given thickness. The more light a material absorbs, the higher its absorption coefficient will be. The absorption of light per unit length in a medium is often quantified with an absorption coefficient α, also called attenuation coefficient. Absorption and extinction coefficient theory. If a flux through a material decreases with distance. The sound power absorption coeﬃcient α for the test sample at a given frequency is given by α = 1 −R2 Π = 1 − (SWR −1)2 (SWR +1)2 = 4 SWR+ 1 SWR +2. If a plane wave of frequency (f) propagates through a solid with velocity (v) in a direction defined by (x), the electric field (E) is described by the following progressive wave equation: Where, (E0)is the incident electric field vector and. In the case of an absorbing material, the behaviour of a beam of radiation incident in a medium of refractive index n1 on an absorbing medium of complex refractive index n2 = n2-ik2, with an angle of incidence θ1, using Snell's law in complex form is then defined by: Coherence of multiple internal reflections, Find out more about our products and services, Find out more about our research interests, Spectral Characterisation of Infrared Optical Materials and Filters, Absorption and extinction coefficient theory. This equation is known as Bouguer's law or Lambert's law of absorption, by which radiation is absorbed to an extent that depends on the wavelength of the radiation and the thickness and nature of the medium. https://encyclopedia2.thefreedictionary.com/Absorption+Coefficient. α = I a / I i (1). Hence, ε0ε1E1 = ε0ε2E2 and µ0µ1H1 = µ0µ2H2. I i = incident sound intensity (W/m 2). From Maxwell's equations on electromagnetic theory, the speed of light in a vacuum c is related to the permittivity of free space ε0, (the degree to which a medium can resist the flow of charge, defined by the ratio of the electric displacement to the intensity of the electric field that produces it), and the permeability of free space µ0 (the ratio of the magnetic flux density in a solid to the external magnetic field strength inducing it, µ = B/H.) The velocity of propagation of a electromagnetic wave through a solid is given by the frequency-dependent complex refractive index N = n - ik where the real part, n is related to the velocity, and k, the extinction coefficient is related to the decay, or damping of the oscillation amplitude of the incident electric field. The optical properties of the solid are therefore governed by the interaction between the solid and the electric field of the electromagnetic wave. Additional optical properties of silicon are given in the page Optical Properties of Silicon. The absorption coefficient is therefore described as the reciprocal of the depth of penetration of radiation into a bulk solid, i.e., it is equal to the depth at which the energy of the radiation has decreased by the factor of e-αx, or alternatively, the intensity of the incident radiation is attenuated by the solid to 1/e of its initial value at a distance from the surface boundary defined by λ/4πk. I a = sound intensity absorbed (W/m 2). Absorption coefficient - α - for some common materials can be found in the table below: The optical impedance of a material is another useful parameter in considering reflection and transmission of electromagnetic waves across an interface, Z=Ex/Hy=Ey/Hx=(µ0µr/ε0εr)½. The absorption coefficient is measured in cm-1 or m-1, and it is traditionally called the absorption factor in spectrography and some other branches of applied optics. It has units of 1/cm (1/length), because it describes the amount of light absorbed per thickness of material. This requires the tangential components of E (electric field vector) and H (magnetic field vector) to be continuous across the boundary, and the normal components of D (electric displacement vector) and B (magnetic flux density vector) to also be continuous across the boundary. The effects of [D.sub.t] and [D.sub.f] on the sound absorption coefficient [alpha] are plotted in Figure 19. The optical admittance of free space, Y, is given by Y = 1/Z0 = (ε0/µ0)½ = 2.654x10-3Ω-1. The velocity of propagation of a electromagnetic wave through a solid is given by the frequency-dependent complex refractive index N = n - ik where the real part, n is related to the velocity, and k, the extinction coefficient is related to the decay, or damping of the oscillation amplitude of the incident electric field. The ratio of the sound energy absorbed by a surface of a medium or material to the sound energy incident on the surface. All content on this website, including dictionary, thesaurus, literature, geography, and other reference data is for informational purposes only.