Impedance Matching
The practice, in electronics, 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 signal reflection from the load.
Origin
British engineer Oliver Heaviside coined the term "impedance" in July 1886, providing the foundation for impedance matching. The concept found early application in telephone systems and older audio systems, where source and load resistances were matched at 600 ohms to maximize power transfer before amplifiers existed. The Smith chart, a key analysis tool, was independently proposed by Tōsaku Mizuhashi (1937) and Phillip H. Smith (1939). Bell Laboratories experiments in 1929 found that 30Ω and 77Ω optimized coaxial cables, leading to the widely adopted 50Ω compromise for high power and low loss.