neper (Np)

The neper (Np), named for the mathematician James Napier, is a unit used to express the ratio of quantities such as current or voltage. Thus the ratio N, in nepers, of current I1 and I2 is N = ln(I2/I1). The neper is thus the natural logarithmic equivalent (see logarithm) of the decibel. Power ratios, say of powers P1 and P2, can also be expressed in nepers; here N = ½ ln (P2/P1), and 1 neper = 8.686 dB.