A Load Invariant and High-Speed IoT-Based Electrical Impedance Tomography System

Electrical impedance tomography (EIT) systems are widely used in various IoT-related fields as they yield real-time performance for two-dimensional (2D) and three-dimensional (3D) image reconstruction, are low-cost, and are not invasive. One of their most critical components is the current source that must deliver a constant amplitude AC electric current within the typical range of 10 kHz to 1 MHz, regardless of the load impedance. A slight fluctuation of the electric current would cause a deviation from the simulated Jacobian matrix, thereby yielding inaccurate image reconstruction. Thus, in practice, EIT is limited to applications where the process medium is highly conductive. This would neglect the load impedance, mitigating the fluctuations in the amplitude of the generated electric current. Consequently, many EIT systems were applied for processes dominantly comprising water, the conductivity of which ranges from 5 S/m for seawater to 5.5 x 10-6 and 5 x 10-3 S/m for pure and drinking water, respectively. Thus, even in the case of high water-cut fluid, unless the water is very salty, the usage of EIT may not be adequate. Indeed, even if the conductivity of the medium is known and high, the gross conductivity formed between a given pair of measuring electrodes depends heavily on the phases distribution pattern between them and can be excessively low, causing high electric current fluctuations. Changes in the contact impedance between the electrodes and the process are another major source of current amplitude fluctuations. The paper has two contributions. First, it experimentally assesses the effect of the electrical current fluctuations on the accuracy of the EIT image reconstruction using three different cutting-edge and most widely current sources designs. To the authors best knowledge, this study is the first of its kind, as all other prior works assume that the electrical current is constant in the formulation of the EIT forward and inverse problems. The paper also suggests a new cost-effective measurement circuit design that overcomes fluctuations while providing high-speed data acquisition throughput of up to 2,800 frames/s (fps). Extensive system assessment was conducted experimentally, and the associated results show the higher accuracy of the suggested design when using the Gauss-Newton (GN) method in terms of mean-squared error, which was decreased by 75%.