Design And Implementation Of Excitation Source For Brain Magnetic Induction Tomography And Study On Magnetic Excitation Field

Brain Magnetic Induction Impedance Tomography (BMIT) is a kind of contactless imaging technology for brain by measuring the perturbation of magnetic excitation field with detection coil. The technology is very significant in monitoring and diagnosing the encephalic pathological changes. The brain tissue in a certain frequency and intensity magnetic excitation field can induce eddy current for electromagnetic induction effect. Because magnetic field produced by eddy current disturbs the magnetic excitation field, there is a phase difference between detection signal of detection coil and reference signal. The phase difference increases in direct proportion to brain tissue's electrical conductivity, so we can obtain brain tissue's electrical conductivity by detecting the phase difference. In BMIT system the performance of excitation source has significant influence on the precision and sensitivity of phase detection. The output power of excitation source for BMIT designed by all work groups was not high, these groups hadn't analyzed the magnetic field of excitation coils deeply yet and their design of excitation coils was too simple. So we designed and implemented"voltage control current source (VCCS)"circuit with higher output power and three types of excitation coils, then detected the distribution of magnetic field of all types of coils. The experiment of cell phase detection showed that the new type excitation source for BMIT and discal focused coil could satisfy the requirement of BMIT. At 200 kHz, 1 MHz and 10 MHz, the output power range of the excitation source is 0.035 W～31.4 W, the peak value of steady output current is over 1 A, and the frequency stability of 10-9 and the THD amplitude of less -51 dB are taken. The focused discal excitation coil is most effective for phase detection with cells models. The main content of my work is as follows:1. Selected the optimum frequency standard source with high frequency stability and high precision.2. Designed a preamplifier circuit with adjustable gain and a voltage following circuit.3. Designed a power amplifier circuit to produce certain amplitude current driving excitation coils.4. Implemented 3 types of excitation coils.5. Obtained the optimal excitation coil by analyzing the magnetic field distribution.6. Proving the performance of the excitation source by neuron cell experiment.The excitation source can produce certain frequency sine wave, with higher frequency stability, lower THD and wider adjustable range of output power. According to the results of neuron cell experiment we decided to use the discal focused coil as the excitation coil, which is most effective for phase detection than other excitation coils and available for detecting brain tissue conductivity.