Electrical sensor development for the dielectric properties measurement and moisture content estimation of switchgrass and corn stover

Magalhaes de Souza, Augusto
Major Professor
Stuart J. Birrell
Committee Member
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Agricultural and Biosystems Engineering

The dielectric properties of material play a relevant role when developing moisture content sensors of agricultural products. However, little is known about the permittivity of switchgrass and corn stover in a wider frequency band. Thus, this research goal was to determine their dielectric constant and loss factor at different moisture contents and frequency range of 5 Hz to 13 MHz. Also, an electrical sensor system was developed to predict the amount of water in agricultural products with the material static and in movement.

The dielectric properties of switchgrass and corn stover were calculated by measuring their admittance using an impedance analyzer at three different moisture content levels, approximately between 9 and 30.5% and a fixed bulk density of 0.133 g/cm3.

Overall, it was observed that the dielectric properties of these materials increased with moisture content but decreased with frequency. Prediction models were developed using the data of a frequency range of 10 kHz to 5 MHz. These models R2's were higher than 0.90 in general; however, the R2 was 0.9811 for a model in a frequency range from 100 kHz to 5 MHz for the loss factor of switchgrass in movement.

A sensor system was designed to generate and read a super-imposed multi-frequency signal that was sent and received from a device under test (DUT) with switchgrass. These input and output signals were analyzed to estimate the moisture content at four levels.

Overall, the attenuation between the input and output waves increased with moisture. Two models were created to estimate water from switchgrass. They had an R2 of 0.7901 and 0.9976 for the material static and in movement, respectively.

The permittivity of switchgrass and corn stover were successfully estimated for the frequency range of 10 kHz to 5 MHz at three moisture levels. Additionally, the developed sensor system was capable of sensing the moisture of switchgrass, but more investigation is necessary. This study helps to comprehend the influence of the electric field at different frequencies on these materials.