Mixed energy-domain multipoles and multiports

Though the notions of multipoles and multiports come from electrical engineering, even there they are usually used in a rather vague way. The paper proposes rigorous physics-based definitions of both notions as well as of their relationship, and extends them towards the dynamic systems of mixed energy-domain nature. In this way, multipoles and multiports can provide unified physical-level models applicable to a wide variety of contemporary engineering systems giving circuit theory the opportunity to expand to other engineering disciplines as an interdisciplinary engineering tool.