  Biological cells can be treated as composites of graded material inclusions.
  In addition to biomaterials, graded composites are important in more
traditional materials science. In this article, we investigate the
electrorotation (ER) spectrum of a graded colloidal suspension in an attempt to
discuss its dielectric properties. For that, we use the recently obtained
differential effective dipole approximation (DEDA) and generalize it for
non-spherical particles. We find that variations in the conductivity profile
may make the characteristic frequency red-shifted and have also an effect on
the rotation peak. On the other hand, variations in the dielectric profile may
enhance the rotation peak, but do not have any significant effect on the
characteristic frequency. In the end, we apply our theory to fit experimental
data obtained for yeast cells and find good agreement.
