Wideband electrical impedance tomography

Abstract

This paper addresses the augmentation of a conventional single frequency electrical impedance tomography (EIT) system to form a wideband EIT system. This extends the system to provide spectral information, but with the essential capability to match process dynamics. The underlying opportunity for this study is that process materials may show considerable change in their electrical properties in response to an injected signal over a wide frequency range. This concept is used in the paper to demonstrate the construction of tomographic images for a range of frequency bands that can provide a deeper understanding and interpretation of a process under investigation. This paper describes a trial simulation of this approach and an experimental study. To provide measurements over the required frequency range a linear chirp is used as the excitation signal. Corresponding peripheral measurements have been synthesized using a 2D model in association with the EIDORS forward solver. The measurements are then analysed using an algorithm based on the wavelet transform to reveal spectral band datasets. In the presented feasibility trial a single-channel EIT chirp excitation was implemented, in essence simulating a real-time parallel data collection system, through the use of pseudo-static tests on foodstuff materials. The experimental data were then analysed and tomographic images were reconstructed using the frequency-banded data. The qualitative feasibility results illustrate the promise of this composite approach in exploiting sensitivity to variations over a wide frequency range. They indicate that the described method can augment an EIT sensing procedure to support spectroscopic analysis of the process materials.

A Review on Electrical Impedance Tomography Spectroscopy

“…An absolute imaging method, also called static imaging, is used when the reconstruction is made for measurements on one moment in time and no comparison is made between different frequencies. This method is used in [ 73 ], where a wideband EITS system is developed using a linear chirp as excitation frequency and the absolute image can be then obtained for each frequency of interest. However, this absolute imaging can be sensitive to forward modeling errors [ 54 ], which could be cancelled with difference imaging.…”

A Simultaneous and Continuous Excitation Method for High-Speed Electrical Impedance Tomography with Reduced Transients and Noise Sensitivity

“…Yet, the reason for using multiple sinusoidal signals in EIS and MF-EIT is different from that for the ONE-SHOT method. In EIS or MF-EIT, usage of wideband excitation signal avoids the repetition of the same EIT frame acquisition protocol at different AC frequencies [ 12 ]. The ONE-SHOT method employs composite of multiple sinusoidal waves in order to reduce the number of steps in the EIT frame acquisition protocol thus making multiplexing superfluous.…”

System Description and First Application of an FPGA-Based Simultaneous Multi-Frequency Electrical Impedance Tomography

“…For mfEIT, injecting multiple sine wave currents at different frequencies is necessary; this can be achieved by: injecting two single currents of different frequencies at two separated electrode pairs simultaneously [ 19 ]; injecting single sine currents at different frequencies sequentially [ 20 , 21 ]; injecting a swept-frequency (chirp) waveform [ 22 , 23 ]; injecting a mixed waveform current, composed of multiple sine waves of different frequencies simultaneously [ 19 , 24 , 25 ]. …”

“…Injecting a sweep of frequencies (method 3) seems promising, gaining the complete spectrum of frequencies in only one measurement. However, since this signal is non-stationary, the precise extraction of the amplitude and phase from the data is difficult [ 23 ]. Moreover, averaging the measurement over multiple periods for better signal-to-noise ratio (SNR) is not possible.…”