Electromechanical impedance: Analogs and duality

It is felt that 4-terminal network theory is potentially of great value in the analysis of problems in the non-electrical realm and problems which are only partially electrical. In attempting to apply 2-port theory however,1,2 some perplexing difficulties arise. These appear to the author basically to be due to somewhat loose habits of thought in defining impedance and admittance on the basis of purely electrical concepts without due regard for their significance in other domains.