A COLE PHANTOM FOR EIT

A phantom was designed for testing and comparing multifrequency EIT data collection systems. The phantom simulates a cylinder of homogeneous conductor with 16 drive and 16 receive electrodes interleaved. Combinations of resistors and capacitors were used to simulate the complex impedance, Z*, of a typical tissue in the frequency range 8-2048 kHz obeying the Cole equation Z* = Z(infinity) + (Z(0) - Z(infinity))/[1 + (i f/f(c))((1-alpha))] where Z* is the complex impedance at frequency f, Z(0) and Z(infinity) are the limiting values of impedance at low and high frequencies, f(c) is the characteristic frequency and alpha is a constant. A practical phantom was then constructed on which four different sets of spectroscopic parameters could be selected: (i) alpha = 0.20, f(c) = 150 kHz, Z(0)/Z(infinity) = 3.31; (ii) alpha = 0, f(c) = 273 kHz, Z(0)/Z(infinity) = 2.64; (iii) alpha = 0, f(c) = 71.1 kHz, Z(0)/Z(infinity) = 1.36 and (iv) Z(0)/Z(infinity) = 1.00 with no dispersion.