Simultaneous injection and measurement chirp division multiplexed Electrical Impedance Tomography and Spectroscopy

Abstract

Electrical Impedance Tomography and Spectroscopy produce cross-sectional images of objects based on the objects’ internal impedance distribution. It commonly uses time division multiplexing, frequency division multiplexing, or code division multiplexing. These multiplexing methods have limitations of temporal data inconsistencies when applied to fast-changing objects; spectral inconsistencies due to the application of different excitation frequencies on different electrodes and inability to achieve frequency difference imaging; and capacitive spikes due to abrupt signal changes, respectively. This paper proposes the novel use of orthogonal chirp division multiplexing to overcome these challenges. Orthogonal chirps are simultaneously injected at all electrodes mounted on the object and potentials measured concurrently. Mathematical formulations and development of a 16-electrode FPGA-based prototype system are presented. It achieves an excitation bandwidth of 1 MHz and 870 frames/second measurements. The system has a position error of 7.74 % and a size error of 3.84 % comparable to other methods.