  We investigate the Fourier coefficients $b_k(T)$ of the net--baryon number
density in strongly interacting matter at nonzero temperature and density. The
asymptotic behavior of the coefficients at large $k$ is determined by the
singularities of the partition function in the complex chemical potential
plane. Within a QCD-like effective chiral model, we show that the chiral and
deconfinement properties at nonzero baryon chemical potential are reflected in
characteristic $k$-- and $T$-- dependences of the Fourier coefficients. We also
discuss the influence of the Roberge-Weiss transition on these coefficients.
Our results indicate that the Fourier expansion approach can provide
interesting insights into the criticality of QCD matter.
