Study on the Staggered Electrodes for 3D Electrical Capacitance Tomography

Electrical capacitance tomography (ECT) has received attention in
fluidized bed measurement for many years as a safe, economic, and non-intrusive
measurement technique^1-3. ECT is based on the
measurement of the variation of capacitance of sensors composed of excitation
and detection electrodes, which are normally installed externally of the
fluidized bed vessels⁴. Compared with 2D ECT, 3D ECT
can provide information concerning flow pattern and bubbles directly from the
volumetric images of fluidized beds⁵.

Low image
quality, however, possesses a serve challenge for 3D ECT because of the
sensitivity of sensors on the one hand and the non-linear ill-posed nature of
image reconstruction on the other hand. For 3D ECT, the traditional rectangular
sensors have been commonly used, in which the measured signal of the
capacitance between electrodes in the layers far from each other would be
extremely week compared to that between electrodes in the adjacent layers,
causing low signal to noise ratio (SNR).

In this work, we
studied the ECT sensors with staggered electrodes, in particular the shape of
electrodes with regard to its effect on the image quality. Three different
shapes of electrodes, including the diamond, circular and hexagon shape, were
studied. We studied the quality of reconstructed images with both numerical
simulations and experiments for static objects, and analyzed quantitatively the
image errors and correlation coefficients. The results show that the precision
of the sensors with staggered electrodes are higher than that with rectangle
electrodes. In addition, image quality obtained by sensors with staggered
electrodes is superior than that by rectangle electrodes. This provides a
potential way to improve the image quality for 3D ECT. The application of the
staggered electrodes for 3D ECT in fluidized bed measurement was also
illustrated.

References

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3.   Wang
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Volume Tomography for Characterization of Gas-Solid Slugging Fluidization with
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W. Design of electrical capacitance tomography sensors. Meas Sci Tech. 2010;21:042001.

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