Many researchers have investigated methods for describing systems with an infinite number of degrees of freedom and for finding their appropriate equivalents. The present work gives a comprehensive review of the methods available for finding analogues of waveguides in solids and gases, and in diaphragms, plates and air-gaps. Solutions and descriptions are given for various structures such as electromechanical filters, delay lines and acoustic systems. The book focuses on structures such as waveguides in solids and gases and discusses their analysis and gradual synthesis. The equivalent circuits of waveguides are based on a one-dimensional model, and solutions suitable for further analytical and numerical processing are examined. An analogue is provided with a wide range of applications for such systems; it allows the analysis or gradual synthesis of a whole series of more complex systems with reasonable accuracy. The book also tackles the dispersion problem in solid-state waveguides, and discusses some types of phase velocity approximations. The work is intended for electroacoustic and acoustic engineers and scientists, especially those working in the transducer field.