Differential measurements in electric field tomography: visualization of a test object from experimental data
Electric field tomography (EFT) is a method of quasistatic electromagnetic tomography enabling contactless investigation of the spatial distribution of the electrical properties in the object, when probing it with an alternating electric field. By switching the alternating voltage source sequentially between spatially distributed electrodes, it is possible to collect information on changes of the field phase using the remaining electrodes and to visualize the spatial distribution of the electrical properties of the object by solving the inverse problem for equations describing an electric field in an inhomogeneous medium. The main problem in the implementation of the EFT is the extraction of a useful signal (phase shift) caused by the Maxwell-Wagner relaxation in the object from the total measured change of the phase. An EFT system has been created with differential excitation and field measuring, which can significantly reduce the effect of measurement errors and noise on the results. A multichannel circular measuring system was used to implement this. A multichannel circular system was used, operating in the unipolar electric field tomography mode, on which visualization of test objects was previously successfully performed. The algorithm of its operation has been modified significantly to operate in the differential mode of excitation and data collection. The phase and amplitude of the difference signal between two adjacent electrodes was calculated programmatically. Successful visualization of the test object placed in the center of the system was achieved experimentally by the differential electrical tomography system using both phase and amplitude measurements.