A Novel Digital Demodulation Method for MFEIT Based on APFFT

Electrical Impedance Tomography requires a high precision demodulator to estimate Amplitude and phase. Conventional digital quadrature demodulation performs well in single frequency Electrical Impedance Tomography. Because digital quadrature demodulator can only demodulate one single frequency signal at one time, it faces many problems when using in multi-frequency Electrical Impedance Tomography systems, multiple demodulators are needed or much more processing time is needed. The paper proposes a novel method All Phase Fast Fourier Transform demodulation for EIT system. All Phase Fast Fourier Transform algorithm improves the accuracy of Fast Fourier Transform Algorithm by using a special data truncation window. All Phase Fast Fourier Transform can get all the amplitudes and phases of different frequencies after one procedure. Then the performances of All Phase Fast Fourier Transform demodulator and digital quadrature demodulator are compared. According to the results, All Phase Fast Fourier Transform demodulation behaves better in amplitude and phase demodulation, especially in phase demodulation. In multi-frequency Electrical Impedance Tomography systems taking consideration of accuracy performance chiefly, All Phase Fast Fourier Transform demodulator should be the first choice.