An Current Source Using a Negative Impedance Converter (nic) for Electrical Impedance Tomography (eit)

The purpose of this paper is to improve the output impedance of a current source used for Electrical Impedance Tomography (EIT) by using a Negative Impedance Converter (NIC). A Monopolar Howland Current Source(MHCS) and NIC circuits were implemented and then the output impedance was measured by a Data Acquisition (DAC) board of 12 bits resolution. A resistive load was used for investigating the performance of the MHCS with and without the NIC circuit when driving a constant ampitude sinusoidal current at 125 kHz through a single cable, a coaxial cable, or a coaxial cable plus a 32-channel multiplexer. Output impedance higher than 10.0 MΩ was measured for the single cable configuration without using the NIC circuit. Output impedance decreased to 13.6 kΩ when the MHCS was multiplexed and connected to a coaxial cable of approximately 90 cm long. However, when the NIC circuit was connected to the MHCS circuit the output impedance increased to approximately 3.0 MΩ.. These results show that accurate measurements can be achieved in single-frequency EIT systems.