Wideband electrical impedance spectro-tomographic imaging

The underlying opportunity for this study is that process materials may show
considerable change in their electrical properties in response to an injected signal
over a wide frequency range. The use of this concept to demonstrate the
construction of tomographic images for a range of frequency bands is described.
These can then provide a deeper understanding and interpretation of a process
under investigation.
The thesis presents an in-depth review of the characteristics of the various
wideband signals that could be used for simultaneous spectral measurements.
This includes an objective selection process that demonstrates that a Chirp signal
form offers key advantages. It then addresses the details of the developed
method and algorithms for WElT systems that deploy a Chirp wideband excitation
signal and a further aspect of the method, based on the time-frequency
analysis, particularly wavelet transform, which is used to reveal spectral data
sets. The method has been verified by simulation studies which are described.
To provide measurements over a required frequency range a linear chirp is deployed
as the excitation signal and corresponding peripheral measurements are
synthesised using a 2D model. The measurements are then analysed using a
wavelet transform algorithm to reveal spectral datasets which are exemplified in
the thesis. The thesis then examines the feasibility of the presented method through
various experimental trials; an overview of the implementation of the electronic
system is included. This provides a single-channel EIT chirp excitation implementation,
in essence simulating a real-time parallel data collection system.
through the use of pseudo-static tests on foodstuff materials. The experimental
data were then analysed and tomographic images reconstructed using the
frequency banded data. These included results illustrate the promise of this
composite approach in exploiting sensitivity to variations over a wide frequency
range. They indicate that the described method can augment an EIT sensing
procedure to support spectroscopic analysis of the process materials.