Fast Electrical Impedance Tomography Based on Code-Division-Multiplexing Using Orthogonal Codes

Abstract

Electrical impedance tomography (EIT) is used to determine the spatial conductivity distribution of a measurement environment that involves several applications in the areas of process engineering and medical diagnostics. In common EIT systems, the measurements are performed by means of current patterns which are injected into the measurement environment using a serial time-division-multiplexing (TDM) scheme for the excitation of different electrodes. The measurement rate can be increased by performing parallel excitation using orthogonal signals. In this paper, a code-divisionmultiplexing (CDM) measurement procedure is presented. To optimize the separation between different measurement channels and the dynamic range, orthogonal Walsh-Hadamard codes are used. The measurements are conducted with a fast EIT system with nine parallel excitation sources and 18 parallel measurement channels. The measured crosstalk rejection between different channels is larger than 98 dB. The maximum absolute deviation between different measurement sets for repeated measurements is less than 24 µV with a mean standard deviation of less than 8.2 µV. The dynamic range for impedance measurements based on different excitation procedures (TDM, frequencydivision-multiplexing, and CDM) has been determined. Furthermore, reconstructed conductivity distributions based on measurements with the different excitation procedures have been compared with each other for different measurement scenarios (a root mean square difference of less than 1.2%). Finally, the influences of frequency-dependent measurement objects on the excitation procedures have been discussed.

Hardware implementation of electrical resistance tomography for damage detection of carbon fibre–reinforced polymer composites

“…In order to assess whether the electrodes were realized successfully or not, deviations between the electrical resistance of the electrode pairs on a sample with a chemically cleaned surface (steps 2-6 in the above procedure) and on a sample without chemical cleaning (without steps 2-6) were measured. Excitation by current was conducted for each pair of electrodes according to the opposite stimulation pattern used (10-1, 11-2,., [9][10][11][12][13][14][15][16][17][18][19]. At the same time, voltage on these electrodes was measured.…”

“…The recently developed systems are primarily focused on speed. A fast tomography system developed by Gevers et al 12 on the principle of parallel excitation by orthogonal signals is very interesting, as is the fast tomography developed by Wang et al 13 A number of other tomography system have been developed in the field of medicine.…”

Super-sensing technology: industrial applications and future challenges of electrical tomography

“…All these multidimensional methods require extra system hardware design to allow multifrequency signal excitation and sometimes parallel excitation [59]. Software data fusion algorithms are also required to integrate the extra information acquired from all dimensions.…”

Development of a High-Speed Current Injection and Voltage Measurement System for Electrical Impedance Tomography-Based Stretchable Sensors

“…In [11], the authors use a frequency-division multiplexing approach; they simultaneously inject currents at different frequencies from all the electrodes and measure the resulting voltage. In [12], a similar approach is also presented, where a fast EIT system is achieved via parallel current excitation that uses orthogonal signals. The drive currents can be then isolated, as they present diverse frequencies.…”