In accordance with one aspect of the present technique, a method is disclosed. The method includes identifying a first change in an excitation direction of a group of cells and determining a first set of characteristics of the group of cells corresponding to the first change. The method also includes identifying a second change in the excitation direction of the group of cells and determining a second set of characteristics of the group of cells corresponding to the second change. The second change in the excitation direction is opposite to the first change in the excitation direction. The method further includes determining a number of functional cells from the group of cells based on the first and the second set of characteristics.