docs: def feedback_results_to_impedance_frame(feedback_result):
      '''
      Extract computed impedance data from `FeedbackResults` instance into
      `pandas.DataFrame`.
      '''
      index = pd.Index(feedback_result.time * 1e-3, name='seconds')
      df_feedback = pd.DataFrame(np.column_stack([feedback_result.V_actuation()
                                                  .filled(np.NaN),
                                                  feedback_result.capacitance()
                                                  .filled(np.NaN),
                                                  feedback_result.Z_device()
                                                  .filled(np.NaN)]),
                                 columns=['V_actuation', 'capacitance',
                                          'impedance'],
                                 index=index)
      df_feedback.insert(0, 'frequency', feedback_result.frequency)
      df_feedback.insert(1, 'voltage', feedback_result.voltage)
      return df_feedback