  A novel wireless microstrip-based RF sensor designed for detecting changes in
ionic content of water and the addition of solid contaminant objects is
proposed and demonstrated. The sensor can be installed on the exterior wall of
dielectric containers and customized according to the material of the container
to enable wireless sensing. Its operation within the lower microwave frequency
range (670-730 MHz) serves to minimize signal attenuation in water and
streamlines circuitry design. The most significant feature of this sensor is
its unique design, rendering it impervious to its surrounding environment. This
not only shields it from environmental noise but also maximizes its sensitivity
by efficiently utilizing incoming power for sensing purposes. The sensor
exhibits remarkable sensitivity, capable of detecting solute concentrations as
low as 0.003125 M in water. It can also detect the insertion of foreign solid
objects into the container from the exterior wirelessly and distinguish them
from liquids being added. As a proof-of-concept demonstration, the sensor in
this study was optimized for a porcelain wall of 10-12 mm thickness. The
sensor's small size and the materials used for its fabrication make it
adaptable to a wide range of applications in industries such as food,
pharmaceuticals, and bathroom fixtures. The aforementioned properties position
the sensor as an ideal choice for various smart bathroom applications, where
accurate and reliable water use monitoring is essential for efficient water
conservation.
