Compute the capacitance of the DMF device _(i.e., dielectric and
        droplet)_ based on the computed impedance value.

        Note: this assumes impedance is purely capacitive load.
        TODO: Is this assumption ok?

def capacitance(self, filter_order=None, window_size=None, tol=0.05):
        '''
        Compute the capacitance of the DMF device _(i.e., dielectric and
        droplet)_ based on the computed impedance value.

        Note: this assumes impedance is purely capacitive load.
        TODO: Is this assumption ok?
        '''
        C = np.ma.masked_invalid(1.0 / (2.0 * math.pi * self.frequency *
                   self.Z_device(filter_order=filter_order,
                                 window_size=window_size, tol=tol)))
        C.fill_value = np.nan
        C.data[C.mask] = C.fill_value
        return C