|JULRAT, SAKOL - Oak Ridge Institute For Science And Education (ORISE)
Submitted to: Biosystems Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/2017
Publication Date: 4/24/2017
Citation: Julrat, S., Trabelsi, S. 2017. Density-independent algorithm for sensing moisture content of sawdust based on reflection measurements. Biosystems Engineering. 158:102-109.
Interpretive Summary: Dielectric materials are generally considered poor conductors of electricity. The permittivity of a dielectric material is the physical characteristic of that material that determines its interaction with electric fields, and it can be described by a complex number, the real part of which is commonly known as the dielectric constant and the imaginary part is known as the dielectric loss factor. Materials with high dielectric loss factors will absorb energy rapidly from electric fields of sufficient strength and sufficiently high frequencies. Heating of foods in a microwave oven is an example of this conversion of electric energy to heat energy. Permittivities or dielectric properties of materials can be correlated with other physical properties of those materials such as moisture content, the amount of water in the materials. If the desired properties of materials are well correlated with their dielectric properties, those properties can be determined nondestructively by sensing or measuring the dielectric properties with suitable electronic instruments. New techniques are needed for sensing or measuring the dielectric properties of materials to improve or provide new quality-sensing equipment for practical applications in agriculture and related industries. This paper describes a new technique and type of device, an open-ended haft-mode substrate-integrated waveguide (HMSIW) sensor, for sensing the microwave dielectric properties of materials. It involves microwave waveguide components fabricated from double sided substrate material (sheet of dielectric material copper-clad on both sides) similar to PC cards. It uses an open-ended waveguide aperture to sense the dielectric properties of materials placed in contact with the aperture. A density-independent algorithm for moisture content determination from dielectric properties was used. Excellent performance of this algorithm was demonstrated through measurement of the dielectric properties of sawdust over a range of moisture contents and bulk densities with the HMSIW sensor. Therefore, the novel technique offers promise for development of inexpensive sensors for practical use in sensing properties of agricultural products and other materials with portable instruments and in-line sensing devices.
Technical Abstract: A density-independent algorithm for moisture content determination in sawdust, based on a one-port reflection measurement technique is proposed for the first time. Performance of this algorithm is demonstrated through measurement of the dielectric properties of sawdust with an open-ended haft-mode substrate-integrated waveguide (HMSIW) sensor. For accurate measurement of the dielectric properties of sawdust, the HMSIW sensor was calibrated by using a three-material calibration technique, with air, water and 25% ethanol aqueous solution. For moisture determination, a density-independent calibration function expressed in terms of the dielectric properties was used. Both moist and dry bulk densities were considered for the complex-plane representation of the dielectric properties. Results of moisture prediction, relative to each complex-plane representation were found to be similar at 5 GHz and 23 °C with the standard errors of performance of 0.955% and 0.957%, respectively.