latténuation

Attenuation, in French often written l'atténuation, is the gradual loss of intensity of a signal, wave, or particle as it travels through a medium or through space. The loss arises from absorption (conversion of energy to heat), scattering (redirecting energy away from the forward path), and geometric spreading (energy becoming distributed over a larger area with distance). In many disciplines, attenuation is quantified by an attenuation coefficient α (per unit length) or by the loss expressed in decibels (dB). For a wave traveling a distance x in a homogeneous medium, the remaining intensity is I(x) = I0 e^{-α x}. The corresponding transmission loss is L = 10 log10(I0 / I(x)) in decibels, or, in circuit terms, 10 log10(Pin / Pout).

Applications span optics, acoustics, telecommunications, and radiology. In optics and spectroscopy, the Beer-Lambert law describes absorption: I = I0 e^{-ε c x}. In acoustics, material absorption coefficients, along with reflection and scattering, determine sound level decay and reverberation time. In telecommunications and wireless propagation, attenuation characterizes cable and atmospheric losses; path-loss models often incorporate distance and frequency dependencies. In medical imaging, attenuation coefficients quantify how X-rays or gamma rays are absorbed by tissues, enabling contrast in CT scans. In astronomy and atmospheric science, attenuation by dust, gas, and aerosols alters observed brightness and spectra.

Measurement and units: attenuation length, the distance over which intensity falls by a factor e, equals 1/α. Attenuation is wavelength- and temperature-dependent; higher frequencies often experience greater loss in many media.