Towards Wireless Characterization of Solvated Ions with Uncoated Resonant Sensors
semanticscholar(2020)
摘要
Uncoated resonant sensors are presented here
for wireless monitoring of solvated ions, with progress made toward monitoring nitrates
in agricultural runoff. The sensor, an open-circuit Archimedean coil, is wirelessly
interrogated by a portable vector network analyzer (VNA) that monitors the
scattering parameter response to varying ionic concentrations. The sensor
response is defined in terms of the resonant frequency and the peak-to-peak
amplitude of the transmission scattering parameter profile (|S21|). Potassium
chloride (KCl) solutions with concentrations in the range of 100 nM – 4.58 M
were tested on nine resonators having different length and pitch sizes to study
the effect of sensor geometry on its response to ion concentration. The
resonant sensors demonstrated an ion-specific response, caused by the
variations in the relative permittivity of the solution, which was also a
function of the resonator geometry. A lumped circuit model, which fit the
experimental data well, confirms signal transduction via change in solution
permittivity. Also, a ternary ionic mixture (composed of potassium nitrate (KNO3),
ammonium nitrate (NH4NO3), and ammonium phosphate (NH4H2PO4)) response surface was constructed by testing 21 mixture variations
on three different sensor geometries and the phase and magnitude of scattering
parameters were monitored. It was determined that the orthogonal responses
presented by resonant sensor arrays can be used for quantifying levels of target
ions in ternary mixtures. Applications of these arrays include measuring the concentration
of key ions in bioreactors, human sweat, and agricultural waters. Preliminary
results are shown for calibration standards and real waterway samples in Iowa,
USA.
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