In electronics, impedance matching is the practice of designing the input impedance of an electrical load (or the output impedance of its corresponding signal source) to maximize the power transfer or minimize reflections from the load.
In the case of a complex source impedance ZS and load impedance ZL, maximum power transfer is obtained when
where * indicates the complex conjugate. Minimum reflection is obtained when
The concept of impedance matching was originally developed for electrical engineering, but can be applied to any other field where a form of energy (not necessarily electrical) is transferred between a source and a load. An alternative to impedance matching is impedance bridging, where the load impedance is chosen to be much larger than the source impedance and maximizing voltage transfer (rather than power) is the goal.
Read more about Impedance Matching: Theory, Power Transfer, Impedance-matching Devices, Power Factor Correction, Transmission Lines