Further developments in an ac-based capacitance tomography system

An ac-based electrical capacitance tomography (ECT) system has been develop ed at UMIST, with sinusoidal excitation and phase-sensitive demodulation (P SD). In this article the overall system design is briefly described and the n discussed in detail are the key design features, needed to achieve a high signal-to-noise ratio and a high data acquisition rate, including transien t process analysis of the first stage, design of an analog Butterworth low- pass filter and optimization of the data acquisition process. The experimen ts show that the ac-based system has signal variance 19 times better than t he previous design, the charge/discharge ECT system, and that a data acquis ition rate of 140 frames per second is achieved for a 12-electrode system. (C) 2001 American Institute of Physics.