Understanding radiation impedance through animations Free

It is very common for students to struggle to grasp a conceptual understanding of radiation impedance. Often graduate students need exposure to impedance concepts in more than one course before they start to understand its importance and meaning. Instructors commonly suggest that impedance can be thought of as a resistance, ignoring the imaginary part of the impedance (the reactance), and the word “sloshing” is sometimes used to describe what the radiation reactance represents. This paper will describe animations that have been developed in MATLAB to help students visualize the motion of a spherical source and a baffled circular piston along with the corresponding radiated sound pressure near these surfaces. These animations utilize the relevant physical equations to observe the phase relationship of the pressure to the surface velocity. Thinking of radiation impedance as the ratio of a potential quantity to a flow quantity can be helpful, with this ratio having an in phase component and a component where the two quantities are 90 degree phase shifted. Quotes from several acoustics textbooks on this subject are collected in this paper as well.