Attenuation

Attenuation is the gradual loss of intensity or amplitude of a signal, radiation, or other quantity as it propagates through a medium or system. It results from interactions such as absorption, scattering, reflection, and geometric spreading, and it is a key concept across physics, engineering, and medicine.

In acoustics, sound attenuates as it travels through air or other media, due to spreading of the wavefront and energy loss to the medium. Higher frequencies are typically absorbed more strongly. Attenuation is quantified by an attenuation coefficient, often expressed in nepers per meter or decibels per meter, and by the measured decrease of sound pressure level with distance.

In optics, attenuation refers to the reduction of light intensity caused by absorption and scattering within a material. Beer's law describes an exponential decrease I = I0 e^{-α x}, with α the absorption coefficient that depends on wavelength. In fiber optics, propagation loss is typically given in decibels per kilometer.

In electronics and signal processing, attenuation denotes the reduction in signal strength from input to output. It is often expressed in decibels as 10 log10(Pout/Pin) for power or 20 log10(Vout/Vin) for voltage. Attenuation contrasts with gain and can be produced by attenuators, transmission lines, or radiation losses.

In medical imaging and radiography, tissues attenuate X-rays or gamma rays according to their composition, influencing image contrast. Attenuation coefficients underlie CT numbers and are wavelength dependent.