Non-invasive circuit and material imaging using the electric potential sensor
The work presented in this thesis constitutes major developments in the use of the ultrahigh
input impedance electric potential sensor (EPS). The EPS acts like a near perfect
voltmeter, which detects the surface spatial potential distribution of a sample without
making electrical contact to it (i.e. non-invasively). The EPS design is based on a
commercial operational amplifier, to which electronic guarding and novel feedback
techniques have been applied to increase dramatically the input impedance.
Four areas of the EPS are discussed:
Firstly, the exposed tip of the input-electrode defines the spatial resolution of the EPS.
A new technique to develop coax input-electrodes with sharp, mechanically polished
inner- conductors (tips) is examined.
Secondly, the EPS is used to image carbon fibre composite samples with microscopic
step size interval. The intention is to detect faults on the underside of these carbon fibre
composite samples. This will provide a new approach for detecting unseen faults in
carbon fibre composite applications as well as those based on other structurally
Thirdly, an array of 8 ultra-high input impedance EPS has been developed. The aim is
to explore the feasibility of using an EPS array, to reduce the length of time taken by a
single EPS to image samples.
Lastly, a high frequency version of the ultra-high input impedance EPS (up to lOOMHz)
is studied. The objective of this high frequency EPS version is to measure noninvasively
propagation time delays of pulses in real digital integrated circuits (ICs). This
will provide a new technique to investigate high-speed digital systems, in particular
when the ICs in these systems are operating close to their maximum frequency