def fft_signal(self, data_frame):
        """
            This method perform Fast Fourier Transform on the data frame using a \
            `hanning window <https://docs.scipy.org/doc/scipy-0.14.0/reference/generated/scipy.signal.hann.html>`_

            :param data_frame: the data frame
            :type data_frame: pandas.DataFrame
            :return: data frame with a 'filtered_singal', 'transformed_signal' and 'dt' columns
            :rtype: pandas.DataFrame
        """
        signal_length = len(data_frame.filtered_signal.values)
        ll = int(signal_length / 2 - self.window / 2)
        rr = int(signal_length / 2 + self.window / 2)
        msa = data_frame.filtered_signal[ll:rr].values
        hann_window = signal.hann(self.window)

        msa_window = (msa * hann_window)
        transformed_signal = fft(msa_window)

        data = {'filtered_signal': msa_window, 'transformed_signal': transformed_signal,
                'dt': data_frame.td[ll:rr].values}

        data_frame_fft = pd.DataFrame(data, index=data_frame.index[ll:rr],
                                      columns=['filtered_signal', 'transformed_signal', 'dt'])
        logging.debug("fft signal")
        return data_frame_fft
This method perform Fast Fourier Transform on the data frame using a \
            `hanning window <https://docs.scipy.org/doc/scipy-0.14.0/reference/generated/scipy.signal.hann.html>`_

            :param data_frame: the data frame
            :type data_frame: pandas.DataFrame
            :return: data frame with a 'filtered_singal', 'transformed_signal' and 'dt' columns
            :rtype: pandas.DataFrame