Methods and systems for improving the sensitivity of a variety of
conductivity sensing devices, in particular capacitively-coupled
contactless conductivity detectors. A parallel inductor is added to the
conductivity sensor. The sensor with the parallel inductor is operated at
a resonant frequency of the equivalent circuit model. At the resonant
frequency, parasitic capacitances that are either in series or in
parallel with the conductance (and possibly a series resistance) is
substantially removed from the equivalent circuit, leaving a purely
resistive impedance. An appreciably higher sensor sensitivity results.
Experimental verification shows that sensitivity improvements of the
order of 10,000-fold are possible. Examples of detecting particulates
with high precision by application of the apparatus and methods of
operation are described.