The so-called secular equation for a plane wave in piezoelectric medium can be written as f(c,α)=0. (and sometimes f(c,α,ω)=0). It is written in the literature that "for a given apparent wave speed c and angular frequency ω, Eq. (18) is a polynomial of ten orders about α. The solutions of this polynomial stand for all possible wave modes".

The question is how do I choose "wave speed c and angular frequency ω"?

Some portions of articles are attached below.