Study Of Circuit And Signal Processing Of A Wide-frequency Band Emt

Electromagnetic Tomography (EMT), which has been developed since 1990s, is one kind of Process Tomography(PT) based on the law of Electromagnetic induction. It has advantages of non-invasion, non-contact and non-hazard, and it is capable of obtaining the distributions of both the conductivity and magnetic properties, so it has a large applicable potential in the fields of industry process monitoring and biomedical applications.EMT works based on the following principle. Firstly the imposed AC currents is applied into excitation coils to produced the excitation magnetic field; the magnetic and conducting materials in the sensing area will change the excitation magnetic field; Then the receiving signals can be detected using the measure coils, and the spatiotemporal distributions of the conducting and magnetic materials in the sensing field can be computed by the qualitative or quantitative image reconstruction algorithms. For materials with high conductivity, even low excitation frequency can produce an induced magnetic field that is strong enough for EMT to measure. But signals generated by low conductive materials are very small, so a EMT system needs to use higher excitation frequency. To apply EMT to wider areas, detecting the low conductivity materials and therefore developing a wider-frequency EMT is very important.The main contributions of this thesis can be summarized as follows:Firstly, change the excitation frequency of the EMT system through FPGA codes and design the circuits to evaluate the performance of the system when the excitation frequency varies between 10kHz-2500kHz.Secondly, employing the TINA simulating software, optimize the design to improve the circuit input to output characteristics in the context of wide-frequency EMT. Then the design was implemented and verify.Finally, problems like stray capacitance and screen caused by high frequency excitation was addressed. This thesis proposed to use a front-end circuit between the data acquisition unit and coils; which proves that the excitation signal can be transmitted and amplified accurately in the condition of wide-frequency excitation. Further experiments were carried out to investigate the performance using different conductivity materials.