 Impedance matching

For a source with internal electrical impedance $Z_s$, conjugate matching $Z_L=Z_s^{\ast }$ maximizes delivered mean power when the source is fixed. For a purely resistive source and equal load electrical resistance $R$, the load sees half the open-circuit voltage. A Johnson-Nyquist noise source with open-circuit mean-square voltage $4k_{B}TRd\nu$ therefore delivers $k_{B}Td\nu$ to the matched load, rather than $4k_{B}Td\nu$.

Impedance matching is a technique used in electrical engineering and telecommunications to ensure that the impedance of a load (such as an antenna or a speaker) matches the impedance of the source (such as an amplifier or a transmission line). The main goal of impedance matching is to maximize the power transfer from the source to the load and to minimize signal reflection, which can degrade the performance of a circuit or system.