Broadband electric field sensing and its application to material characterisation and nuclear quadrupole resonance
The aim of this project is to address the challenges associated with extending the radio frequency capability of Electric Potential Sensors to greater than 10 MHz. This has culminated in a single broadband sensor, with a frequency range of 200 Hz to greater than 200 MHz.\ud \ud The use of Electric Potential Sensors for the measurement of electric field with minimal perturbation has already been demonstrated at Sussex. These high impedance sensors have been successfully employed in measuring signals with frequencies in the range 1 mHz to 2 MHz. Many different versions of these sensors have been produced to cater for specific measurement requirements in a wide variety of experimental situations. From the point of view of this project, the relevant prior work is the acquisition of a 2 MHz electric field nuclear magnetic resonance signal, and the non-destructive testing of composite materials at audio frequency.\ud \ud Two very distinct electric field measurement scenarios are described which illustrate the diverse capabilities of the broadband sensor. Firstly, an electric field readout system for nuclear quadrupole resonance is demonstrated for the first time, with a sodium chlorate sample at a frequency of 30 MHz. Nuclear quadrupole resonance is an important technique with applications in the detection of explosives and narcotics. Unlike nuclear magnetic resonance a large magnet is not required, opening up the possibility of portable equipment. The electric field readout system is shown to be simpler than the conventional magnetic readout and may therefore contribute to the development of portable devices. Secondly, a broadband, high spatial resolution microscope system for materials characterisation with four different imaging modes is described. This includes; the surface topography of a conducting sample; the dielectric constant variation in glass/epoxy composite; the conductivity variation in a carbon fibre composite; and the electrode pixels inside a solid state CMOS fingerprint sensor.
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