Variational Mode Decomposition-based Synchronous Multi-Frequency Electrical Impedance Tomography.

Electrical impedance tomography (EIT) can provide the system structure and functional imaging ability needed to map the distribution of and changes in plant root zones in a non-invasive, low-cost, safe, fast, and simple manner. Multi-frequency EIT solves the problem that single-frequency EIT can only carry impedance information corresponding to a single given excitation frequency. However, performing EIT at multiple frequencies simultaneously remains challenging. To address this problem, a mixed signal in which multiple frequencies are superimposed is injected into the object to be measured. Essentially, the aim of this approach is to separate the measured mixed voltage signals and thus acquire electrical impedance information simultaneously and quickly at various frequencies. Because the measured signal is a multi-frequency signal, decomposing this signal affects the imaging accuracy directly. To acquire more accurate data, the variational mode decomposition (VMD) method is used to decompose the measured multi-frequency signal. Accurate amplitude and phase information can be obtained simultaneously via multi-frequency excitation, and these data are then used to reconstruct the electrical impedance distribution. Results show that the proposed method can achieve the expected imaging effect. Use of the VMD method to process the multi-frequency signal data is more accurate and gives a better imaging effect than previous methods. The proposed method can be applied to multi-frequency electrical impedance imaging in practice.