A Low-Cost Environmental Nitrate Sensor

Nitrates are nutrients important to commercial, residential, and agricultural applications. However, nitrate loss from these applications, and animal manures, is a major source of water pollution, leading to algae blooms and hypoxic dead zones in coastal waterways. Low-cost nitrate sensors would aid in preventing over application of nitrate based fertilizers and in monitoring the environment for nitrate based water pollution. Printed circuit board (PCB) technology is being used to realize a variety of low-cost environmental sensors. Here, a capacitive PCB sensor was swept in frequency, yielding a distinctive equivalent capacitance versus frequency signature with a characteristic resonant peak. Concentrations of three different nitrate solutions were evaluated with the sensor, producing resonant peaks that decrease in magnitude and frequency with increasing concentration. The data was used to define equations that map nitrate concentration to either resonant peak frequency or magnitude, with R
²
values greater than 0.95.