Neper

The neper (Np) is a logarithmic unit for ratios of field quantities, defined as the natural logarithm of the ratio between two values. For power quantities, one neper corresponds to a power ratio of e².

Natural logarithm: The logarithm to base e, the inverse function of the exponential function. The neper measures a field-quantity ratio by taking this logarithm.
Signal attenuation: The reduction of a signal's amplitude or power as it travels through a medium or system. Attenuation along a path can be expressed as a negative neper value.
John Napier: A Scottish mathematician who introduced logarithms in the early seventeenth century. The unit's name honors the mathematician whose work established logarithms.
Decibel: A logarithmic unit equal to one tenth of a bel, commonly used for power and field-quantity ratios. Decibels are more common in practice, though the two units convert by a fixed factor.
Field quantity: A physical quantity whose square is proportional to power in a given context. The neper's defining ratio is formed from quantities of this kind.
Propagation constant: A complex quantity describing how a wave's amplitude and phase change with distance. Its real part measures amplitude change per unit distance in nepers.
International System of Units: The internationally agreed system of measurement units and their definitions. The neper is a non-SI unit accepted for use with the SI.
Amplitude ratio: The quotient of two amplitudes, such as two voltages or sound pressures. A neper is the natural logarithm of an amplitude ratio.
Power quantity: A physical quantity proportional to power, such as electrical power or intensity. A power ratio is expressed in nepers using half the natural logarithm of that ratio.
Fiber-optic communication: Communication that transmits information as light through optical fibers. Fiber losses and amplifier gains can be stated as logarithmic amplitude ratios.

Linked from 1 page