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ARS Home » Southeast Area » Athens, Georgia » U.S. National Poultry Research Center » Quality and Safety Assessment Research Unit » Research » Publications at this Location » Publication #340350

Title: Open-ended half-mode substrate integrated waveguide sensor with ground flange for complex permittivity measurement

item JULRAT, SAKOL - Oak Ridge Institute For Science And Education (ORISE)
item Trabelsi, Samir
item NELSON, STUART - US Department Of Agriculture (USDA)

Submitted to: IEEE Sensors Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2018
Publication Date: 4/1/2018
Citation: Julrat, S., Trabelsi, S., Nelson, S.O. 2018. Open-ended half-mode substrate integrated waveguide sensor with ground flange for complex permittivity measurement. IEEE Sensors Journal. doi:10.1109/JSEN.2018.2801316.

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. Moisture testers for rapidly measuring the moisture content of agricultural crops such as grain and oilseeds are practical examples. 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 for sensing the microwave dielectric properties of materials, which might be developed for rapid sensing of quality factors in agricultural and other products. It involves microwave device 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 open-ended waveguide aperture. Measurements were successfully completed that provided accurate determination of the dielectric properties of aqueous solutions of methanol, saline solutions, gelatin, and samples of canola seed, small spherical seeds. The results agreed very well with values obtained by conventional techniques for measuring the dielectric properties of these materials. 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 novel open-ended half-mode substrate integrated waveguide (HMSIW) sensor with ground flange for measuring complex permittivity of liquids, semisolids, and granular and particulate materials is presented. The open-ended HMSIW is designed and fabricated on FR4 substrate. The ground flange was customized to achieve good matching with the open-ended HMSIW. The sensor model is described by using the aperture admittance model of open-ended waveguide. The complex permittivity of a given material is determined from measurement of the one-port reflection coefficient. For accurate measurement of the complex permittivity the well-known three-material (air, distilled water, and 25% ethanol aqueous solution) calibration method was used. Complex permittivity of ethanol and 50% and 76% ethanol aqueous solutions measured with the HMSIW were in good agreement with those obtained by using an open-ended coaxial-line probe. In addition, results of measurements on saline solutions, gelatin samples and canola seed samples of different moisture contents are shown.