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General One-Ports

An arbitrary interconnection of $ N$ impedances and admittances, with input and output force and/or velocities defined, results in a one-port with admittance expressible as

$\displaystyle \Gamma(s) =
\frac{b_0 s^N + b_1 s^{N-1}
+ \cdots + b_N}{s^N + a_1 s^{N-1} + \cdots + a_N}
\isdef \frac{B(s)}{A(s)}

In any mechanical situation we have $ b_0 = 0$, in principle, since at sufficiently high frequencies, every mechanical system must ``look like a mass.''8.3 However, for purposes of approximation to a real physical system, it may well be best to allow $ b_0\neq 0$ and consider the above expression to be a rational approximation to the true admittance function.

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