Image reconstruction algorithm for capacitively coupled electrical
resistance tomography
Baoliang Wang, Wuhao Tan, Zhiyao Huang
n
, Haifeng Ji, Haiqing Li
State Key Laboratory of Industrial Control Technology, Department of Control Science and Engineering, Zhejiang University, Hangzhou 310027, PR China
article info
Available online 17 July 2014
Keywords:
Electrical tomography
Inverse problem
Image reconstruction algorithm
C
4
D
Two-phase flow
abstract
Capacitively Coupled Electrical Resistance Tomography (CCERT), which is on the basis of Capacitively
Coupled Contactless Conductivity Detection (C
4
D), is a novel electrical tomography technique. As a
developing technique, more research work should be undertaken. This work focuses on the study of
image reconstruction algorithm of CCERT. Combining Tikhonov regularization principle and Simulta-
neous Iterative Reconstruction Technique (SIRT), a new hybrid image reconstruction algorithm is
proposed. Tikhonov regularization is introduced to obtain the initial reconstructed image. SIRT is used
to obtain the final reconstructed image. With a 12-electrode CCERT prototype, image reconstruction
experiments are carried out. Experimental results show that the images reconstructed by the proposed
image reconstruction algorithm are satisfactory and are in accord with the actual distributions of two-
phase flows. The research work also indicates that the proposed image reconstruction algorithm is more
suitable for image reconstruction of CCERT, comparing with the conventional image reconstruction
algorithms of Electrical Capacitance Tomography (ECT) and Electrical Resistance Tomography (ERT).
& 2014 Elsevier Ltd. All rights reserved.
1. Introduction
Electrical Resistance Tomography (ERT) ca n implement the para-
meter measurement of conductive two-phase flows by providing
cross-sectional images and has broad application pr ospects in many
industrial fields, such as petroleum, chemical engineering, environ-
ment pro tection, etc. [1–4]. However, the conventional ERT systems
are on the basis of contact conductivity det ection technique, the
electrodes are directly in contact with the conductive fluid, that may
result in electrochemical erosion effect and polarization effect of the
electrodes. Meanwhile, unpredictable measurement errors will arise,
if the electrodes ar e con taminat ed. Th ese drawbacks limit the
practical applications of the conventional ERT systems.
Capacitively Coupled Contactless Conductivity Detection (C
4
D)
was proposed by Zemann et al. [5] and da Silva and do Lago [6]
independently in 1998. Its measurement principle is shown in
Fig. 1. A typical C
4
D sensor consists of an insulating pipe, two
metal electrodes (an excitation electrode and a detection elec-
trode) placed cylindrically around the outer surface of the insulat-
ing pipe, an AC source and an AC current pick-up unit, as shown in
Fig. 1(a). The electrodes, the insulating pipe and the conductive
fluid can form two coupling capacitances C
1
and C
2
, and the
conductive fluid between the two electrodes can be equivalent
to a resistor R, that forms an alternating current path. Fig. 1
(b) shows the equivalent circuit of the C
4
D sensor. If an AC voltage
is applied to the excitation electrode, an AC current which contains
the information of the conductivity of the fluid can be obtained
from the detection electrode.
Obviously, C
4
D is a contactless conductivity detection techni-
que and can avoid the electrochemical erosion effect and the
polarization effect. So, C
4
D has received great attention of scientific
researchers since it appeared. Unfortunately, C
4
D is still a devel-
oping technique. Up to date, it is mainly studied and used in the
research field of analytical chemistry for ion concentration or
conductivity detection [7–9]. Few research works concerning the
application of C
4
D in process tomography are reported.
Currently, by introducing C
4
D into the research field of process
tomography, our research group has proposed a novel electrical
tomography, Capacitively Coupled Electrical Resistance Tomogra-
phy (CCERT). Based on a mathematical model of CCERT, the
sensitivity fields have been obtained by Finite Element Method
(FEM) simulation. A 12-electrode CCERT prototype has been
developed with its data acquisition system designed on the basis
of the Phase-Sensitive Demodulation (PSD) method. With the
prototype, the feasibility of CCERT has been verified by Linear-
Back Projection (LBP) algorithm [10]. The influence of three main
parameters (the angle of the electrodes, the permittivity and the
thickness of the pipe wall) on the measurement performance of
CCERT sensor has been studied and an optimized CCERT sensor has
been designed [11]. However, compared with Electrical
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Flow Measurement and Instrumentation
http://dx.doi.org/10.1016/j.flowmeasinst.2014.07.006
0955-5986/& 2014 Elsevier Ltd. All rights reserved.
n
Corresponding author. Tel.: þ8657187952145; fax: þ8657187951219.
E-mail address: zyhuang@iipc.zju.edu.cn (Z. Huang).
Flow Measurement and Instrumentation 40 (2014) 216–222