A New Method Of Tomographic Imaging Using CDC

Electrical Capacitance Tomography(ECT)is a tomographic imaging technology with a great development prospect.It measures the capacitance data deployed between the electrode plates on the outer wall of the pipeline and visualized the permittivity distribution of the measured objects in the pipeline by image reconstruction algorithm.Therefore,capacitance measurement and image reconstruction algorithm become the key factors of ECT technology.In this paper,a new capacitance measurement circuit is designed based on the capacitor digital converter(CDC),which has high precision,high integration,strong anti-interference ability,stable performance and low cost.Firstly,Arduino and EVAL-AD7746 are used to realize single channel measurement,and it is found that the circuit can obtain high precision measurement results.In order to solve the range limitation of CDC chip,this paper uses the CDC range extension circuit and adds analog switch to realize the orderly and high-precision measurement of multi-channel capacitance.The electrodes of ECT system are respectively deployed on the outer wall of the pipe,and the measured two electrodes are selected by analog switch,and then the capacitance between the measured electrodes is measured by CDC circuit.The STM32 series integrated circuits realize communication between IIC bus and CDC circuit,and receive capacitance data collected.The capacitance data detected is transmitted to the computer terminal through the serial port.Due to the "soft field" nature of capacitive tomography,in order to obtain high-quality reconstructed images,a new image reconstruction algorithm is proposed in this paper,which uses the model of standard Tikhonov(STR)to model ECT image reconstruction by means of total variations(TV)normalization and second-order TV normalization.This paper uses Bregman algorithm to solve the proposed objective function,which can divide a complex problem into some simple problems.Numerical simulation of the target algorithm proposed in this paper is carried out and compared with the traditional algorithms,like STR algorithm and Landweber algorithm.The simulation results show that the proposed image reconstruction algorithm is feasible.