If we have a more complex structure comprising several layers with different dielectric properties, such as a cell, these different layers manifest themselves in ways we can account for in our model.  As first elucidated by Ying Huang and Ronald Pethig (and based on prior work on dielectrics), the DEP force of  so-called "shelled spheroid" 

 

Dielectrically, cells can be reduced to an insulating membrane enclosing a conductive cytoplasm (possibly enclosed by a cell wall) (see figure). The cell nucleus has little effect unless it is over 50% of the cell volume.

 

Each component has its own resistance and capacitance –these combine, like little filters, to produce an overall value of polarisability relative to the suspending medium. If we can determine the dielectrophoretic spectrum of the cells of interest, then from theory we can determine the electrical properties of the different components by fitting a theoretical model to the spectrum (see figure).

From the dielectrophoretic response of cells, we can determine four parameters: