Where is the object cross-sectional area projected onto a plane perpendicular to the incident beam (e.g. We may define efficiencies for extinction, scattering and absorption Īre extinction, absorption and scattering cross sections with dimensions of area. These energy flow rates are linearly dependent on incident wave intensity. Last term is a consequence of an interference between incident and scattered fields. Time averaged Poynting vector can be represented as (we omit here index for complex vectors and ) If object is embedded in nonabsorbing environment, is the rate at which energy is absorbed by object. If, energy is absorbed within the volume confined by surface. We construct imaginary closed surface around the object the net rate at which electromagnetic energy crosses this surface is Here we consider how to estimate energy scattered and absorbed by object. Consider arbitrary object illuminated by harmonic incident wave.įield in the medium surrounding the object can be represented as superposition of incident and scattered fields:
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