IMPEDANCE FILTERS

Impedance filters are a special class of minimum-phase filters that model energy-conserving devices and media. The real part of the Fourier transform of an impedance filter is positive. Impedances play a basic role in mathematical physics. There are simple ways of making complicated mechanical systems from simple ones, and corresponding mathematical rules allow construction of complicated impedances from simple ones. Also, impedances can be helpful in stabilizing numerical calculations.

Logically, a chapter on impedance filters belongs here, but I have little to add to what is already found in FGDP and IEI. FGDP describes the impedance concept in sampled time and its relation to special matrices called ``Toeplitz'' matrices. IEI describes impedances in general as well as their role in physical modeling and imaging with the wave equation.