Design of Quadrature Demodulator for EMT System and Image Reconstruction

According to the nonlinear interaction of distortion field which is between excitation field and measured field in the existing electromagnetic tomography system, and the condition that the detection signal can´t be simply considered as a linear superposition in the sensitive field. Combined with the the traditional Electromagnetic Tomography (EMT) system, above all, the paper designs a quadrature demodulator that is using direct digital synthesizers, and gets the output of the detection signal by adjusting the demodulating vector. Then, on the base of hardware system design, combined with image algorithm, the image reconstruction has been realized. Four kinds of experiment results show that the quadrature demodulator designed possesses a high detection resolution and reliability as well as good stability, and improves the original system´s phase and amplitude deviation effectively.