Code-Division-Multiplexing Using Orthogonal Codes for Fast Electrical Impedance Tomography

Electrical impedance tomography (EIT) is used to determine the spatial conductivity distribution of a measurement environment, what involves several applications in the area of process engineering or medical science. In common systems a measurement environment is usually stimulated by defined current patterns in a serial time-multiplexing manner. Higher measurement rates can be achieved with code-multiplexed (CDM) excitations for parallel measurements. In order to optimize channel separation and dynamic range, orthogonal Walsh-Hadamard codes have been implemented on a fast EIT system. The crosstalk between different channels has been analyzed for 9 parallel coded excitation signals. Furthermore reconstructed conductivity distributions have been compared to reconstruction results obtained from frequency-multiplexed (FDM) measurements (root mean square difference of 0.02%).