Hardware Design Of Magnetic Induction Tomography Based On Quadrature Phase Detection

Magnetic Induction Tomography (MIT) is a non-contact,non-invasive medical imaging technology,this paper focuses on the hardware design of the measurement system. The main job of the paper is the design and implement of a single channel MIT system and the paper also does some study on the multi-channel system. Specific content are as follows :(1)A new type of sensor coils is designed.Both exciton coils and detection coils used in the system are planar spiral coils based on PCB technology. A comb style shield is added on both sides of the coils and it can reduce the capacitive effect of the system and reduce the disturbance from the external environment.(2) Quadrature phase detection method is used in phase measurement.A phase shifter is added in the signal channel and the phase of the detection signal can be shifted to be in quadrature with the refer signal.And then a phase detector was used to measure the phase variation between the two quadrature signals.The advantages of this method is to improve the sensitivity of the system.The phase shifter is a full-pass filter composed of resistors,capacitors and a operational amplifier.In order to fit the measurement of multi-channel system a phase adjustable component is added on the phase shifter.(3)An electronic switch is used as the phase detector,and this method is not reported in MIT until now.Experiments results show using a switch as the phase detector can make the system have a high performance.(4)The paper also do much work on the excitation circuits,the pre-amplifier circuits and the control circuits.Finally a 16-channel system was build.This multi-channel system consists of excitation circuits,phase detection circuits and control circuits and the the signals are switched by relays.The test results of the single channel system show that when working at the frequency of 5MHz,the phase noise of the system is 1 millidegree and the phase drift during 3 hours is 6 millidegree.The experiments of the single channel system show that the variation of the output of the phase detection circuits has a good linearity with the conductivity of the measured object and this prove the correction of the phase detection method used in the paper.