Analysis of Performance of Howland AC Current Source for Electrical Impedance Spectro-Tomography

Abstract

Electrical impedance tomography (EIT) is a technique that is able to deliver valuable information on conductivity distribution in a process. An extension to conventional EIT is electrical impedance spectro-tomography (EIST) which is offering spectroscopic information. Along with methodological advancement of EIST and to meet practical requirements, there are ongoing researches to develop proper high-quality EIST hardware. An important part of EIST hardware is voltage controlled current source which its design is appeared to be a challenging task. This paper addresses briefly the aspects of EIST system and discusses the effect of various factors and their joint impacts on commonly used Howland voltage controlled current sources for EIST application. To perform realistic simulations, practical load and electrode model are applied within sensing bandwidth. The simulation results revealed the considerable impact of resistors tolerance on reducing the output impedance of the current sources in low frequencies while increasing the operating frequency significantly reduces the impact of tolerance. The simulation also demonstrates that the load current relative error is directly proportional to the resistors’ tolerance and its value approaches the ideal state, with zero-tolerance resistors, by increasing operating frequency. This point can be employed to determine the minimum operating frequency in which the impact of resistors tolerance can be canceled. The results imply that by using resistors with a lower tolerance, it is possible to achieve wider bandwidth in EIST. It can also be concluded that dual op-amp Howland current source is a suitable choice for EIST application.