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 important materials. 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 specification.