Remote Water Salinity Sensor Using Metamaterial Perfect Absorber

Controlling water salinity plays a key role in farming efficiency. Current sensors are mostly expensive and need regular maintenance. In addition, they require electrical connections or extra power supply that leads to difficult and costly implementation in remote-sensing scenarios. In this article, an accurate and low-profile sensor is developed using a metamaterial perfect absorber (MPA) structure. The proposed sensor works based on the level and frequency of the absorbed signals. Hence, there is no need for electrical connections, which enables remote-sensing applications. Square-shaped channels have been created in a regular FR-4 substrate to facilitate sensing of water salinity levels. A $7 \times 7$ array with a total size of $140 \,\,\text {mm} \times 160 \,\,\text {mm}$ has been fabricated that shows a resolution of 10 MHz per percentage of water salinity. The absorption frequency shifts from $f=3.12$ to 3.59 GHz for salinity level from 0% to 50%. A strong correlation between measurement and simulation results validates the design procedure.