A six-ring probe for monitoring conductivity changes

Numerical Evaluation of Complex Capacitance Measurement Using Pulse Excitation in Electrical Capacitance Tomography

Electrical capacitance tomography (ECT) is a technique of imaging the distribution of permittivity inside an object under test. Capacitance is measured between the electrodes surrounding the object, and the image is reconstructed from these data by solving the inverse problem. Although both sinusoidal excitation and pulse excitation are used in the sensing circuit, only the AC method is used to measure both components of complex capacitance. In this article, a novel method of complex capacitance measurement using pulse excitation is proposed for ECT. The real and imaginary components are calculated from digital samples of the integrator response. A pulse shape in the front-end circuit was analyzed using the Laplace transform. The numerical simulations of the electric field inside the imaging volume as well as simulations of a pulse excitation in the front-end circuit were performed. The calculation of real and imaginary components using digital samples of the output signal was verified. The permittivity and conductivity images reconstructed for the test object were presented. The method enables imaging of permittivity and conductivity spatial distributions using capacitively coupled electrodes and may be an alternative measurement method for ECT as well as for electrical impedance tomography.

Optimum design of electrode structure and parameters in electrical impedance tomography

In electrical impedance tomography (EIT) the electrode structure and parameters significantly influence measurement sensitivity and image quality, so how to optimize the electrode structure and parameters is one of the key problems in research today. This paper presents a method to optimize the EIT electrode structure and parameters based on coercive equipotential node models. The coercive equipotential mode of the compound electrode has been established based on that of the line electrode. A simulation study for the line electrode and the compound electrode of EIT has been made on a simulation software platform. The influences of different electrode structures and parameters on measurement sensitivity and the image reconstruction quality are studied. For line electrode simulation studies, two important conclusions are drawn. First, a narrower electrode is helpful in improving the imaging quality. Second, although it is known that a wider electrode is beneficial in decreasing the contact impedance, using a too wide electrode causes the measurement sensitivity to decrease. Furthermore the electrode width that leads to the best measurement sensitivity is different for different measurement depths. The compound electrode has four parameters: the excitation electrode width, the measurement electrode width, the space between the excitation electrode and the measurement electrode, and the distance between two adjacent compound electrodes. These parameters have mutual restrictions and complex influences on each other. It is unwise to optimize the design of a compound electrode by only using the overlay rate of electrodes. A simulation study of EIT electrode structure and parameter influences can be carried out according to this paper to determine the optimum design of the electrode structure and its parameters.