Abstract
Continuous and accurate sensing of water content in soil is an essential and useful measure in the agriculture industry. Traditional sensors developed to perform this task suffer from limited lifetime and also need to be calibrated regularly. Further, maintenance, support, and deployment of these sensors in remote environments provide additional challenges to the use of conventional soil moisture sensors. In this paper, a metamaterial perfect absorber (MPA) based soil moisture sensor is introduced. The ability of MPAs to absorb electromagnetic signals with near 100% efficiency facilitates the design of highly accurate and low-profile radio frequency passive sensors. MPA based sensor can be fabricated from highly durable materials and can therefore be made more resilient than traditional sensors. High resolution sensing is achieved through the creation of physical channels in the substrate integrated waveguide (SIW) cavity. The proposed sensor does not require connection for both electromagnetic signals or for adding a testing sample. Importantly, an external power supply is not needed, making the MPA based sensor the perfect solution for remote and passive sensing in modern agriculture. The proposed MPA based sensor has three absorption bands due to the various resonance modes of the SIW cavity. By changing the soil moisture level, the absorption peak shifts by 10 MHz, 23.3 MHz, and 60 MHz, which is correlated with the water content percentage at the first, second and third absorption bands, respectively. Finally, a 6 times 6 cell array with a total size of 312 ,hbox {mm} times 312 ,hbox {mm} has been fabricated and tested. A strong correlation between measurement and simulation results validates the design procedure.
Highlights
Landy introduced metamaterial perfect absorbers (MPA) in 2 0081
A large number of MPAs have been introduced as a sensor in terahertz frequencies[21,22,23,24]
It should be noted that the MPA needs to be calibrated prior to the sensing process
Summary
Landy introduced metamaterial perfect absorbers (MPA) in 2 0081. This specific classification of FSS metamaterial absorbs the incident waves with near-unity efficiency. A large number of MPAs have been introduced as a sensor in terahertz frequencies[21,22,23,24] Several restrictions, such as the complicated fabrication process, and the high cost of stable material in the terahertz spectrum, make implementing these sensors challenging. The structures, which take advantage of this method are mostly complicated and need one or two connections for sensing These characteristics could limit reported MPA sensors in large scale applications. Another reported technique to use MPA as a microwave sensor is adding an analyte layer to the MPA structure[28,29,30] In this method, an air gap can be added between the substrate and metal layer[31] or between two substrates[32,33]. Fabricating a multi-layer structure, including an air layer to place the sample in the metamaterial structure, is challenging
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