Dust Density Waves in Weak Electric Fields: Effect of the Dust Number Density

We report on modifications of the dispersion relation, describing dust density waves in complex plasmas subjected to weak electric fields due to variations of the equilibrium dust densities. The calculations show the essentially different wave dispersion and predict the existence of cutoff wavenumbers, corresponding to aperiodically growing dust density perturbations. The theory explains the preferential range of wavenumbers where the dust density waves can be effectively excited.