Study On Imaging Method And System For Magnetic Induction Tomography

Magnetic induction tomography (MIT) is a new non-contact electrical impedance imaging technique for biological tissue. This technique is based on the principle of eddy current inspection, and an excitation coil is used to apply a high frequency magnetic field, which induces eddy currents in the material to be studied. The magnitude of eddy currents is related to the electrical impedance of material, and the magnetic field produced by eddy current disturbs the magnetic excitation field, then the magnetic field will be detected by sensing coils to reconstruct image of electrical impedance distribution of material, using some reconstruction methods. Comparing to ultrasonic, X-ray, CT and MRI imaging, the equipment and detection cost of MIT is much lower and it is a real-time, noninvasive and contactless technique. MIT has important application values and widespread prospects no matter in the field of biomedical or industrial applications.According to previous research results and the theory of MIT, a measurement system has been designed and fabricated in this paper. The system is made up of two parts:software and hardware. In hardware part, every circuit components has been fabricated, such as high frequency stability signal source based on DDS, power amplification circuit, differential amplifier circuit, high frequency phase detection circuit and main control circuit. In phase detection, this paper also tries to use I/Q demodulation method to detect phase besides using direct phase detect, In software part, using C#language, the upper computer software is programed. The software provides a user interface for system control and data acquisition, and mainly performs hardware connection, initializes the setting of hardware, changes frequency of excitation signal, selects signal channel, displays real-time data and draws real-time curve.In order to test the performance of the system, this paper designs a series of experiments. The results indicate that:first, in the condition of the steady stage of system and no experiment object, maximum phase drift is less than0.1°; second, sensitivity of phase is better than that of magnitude; third, material of different conductivity can be distinguished; finally, in the case of the same conductivity, the larger the size of the material object, causing the change in the measurement result greater. After system performance tests, the preliminary imaging results were also provided in this paper. At last, the paper gives some possible advice on improving system.