Murat Sean McKeown

Dielectric properties-based method for rapid and nondestructive moisture sensing in almonds

ABSTRACT A dielectric properties-based method is presented for rapid and nondestructive determination of moisture content in almonds independent of bulk density. The method relies on measurements of the dielectric properties at microwave frequencies. The dielectric properties of almonds were measured between 5 and 15 GHz, at 1-GHz increments, for samples with moisture contents from 4.8% to 16.5%, wet basis, bulk densities from 0.565 to 0.7 g/cm3 and temperatures ranging from 5.2 to 45 °C. Moisture calibration equations are given for several frequencies, at room temperature (25 °C) and with temperature compensation for temperatures between 5.2 and 45 °C, along with their respective standard errors of performance, which ranged from 0.44% to 1.06% depending on frequency.

Microwave moisture sensing through use of a piecewise density-independent function

Microwave moisture sensing provides a means to determine nondestructively the amount of water in materials. This is accomplished through the correlation of dielectric properties with moisture in the material. In this study, linear relationships between a density-independent function of the dielectric properties and moisture content of minced Vidalia onions, with slope dependent on moisture range, is identified. This allows prediction of moisture contents between 6% and 92%. Results showed the prediction of moisture content with a coefficient of determination of 0.976. The measurements and techniques presented in this study constitute a foundation for the development of a stand-alone sensor.

Dielectric Properties for Prediction of Moisture Content in Vidalia Onions

Microwave Sensing provides a means to nondestructively determine the amount of moisture in materials by sensing the dielectric properties of the material. In this study, dielectric properties of Vidalia onions were analyzed for moisture dependence at 13.36 GHz and 23°C for moisture content between 6% and 92%. Dielectric properties were obtained using an open-ended coaxial-line probe connected to a network analyzer. Linear regression models were developed using the dielectric constant, dielectric loss factor, and a density-independent function. Models were evaluated for calibration effectiveness in predicting moisture content using coefficient of determination (R²) and standard error of calibration (SEC). In order to validate the models, a standard error of performance (SEP) was calculated from a set of observations that were not used in the calibration. Preliminary results showed use of a density-independent function was more effective in prediction of moisture content then using dielectric properties alone. The measurements and models presented in this paper constitute the foundation for the development of a sensor for determining the degree of curing an onion has undergone.

Dielectric characterization of bentonite clay at various moisture contents and with mixtures of biomass in the microwave spectrum

ABSTRACT This study assesses the potential for using bentonite as a microwave absorber for microwave-assisted biomass pyrolysis based on the dielectric properties. As bentonite is a hygroscopic material, the effect of bound water content on dielectric properties was addressed in this study. Dielectric properties of bentonite at different moisture contents were measured using a coaxial line dielectric probe and vector network analyser in the microwave frequency range from 0.2 to 4.5 GHz at room temperature. Further, dielectric properties of mixtures of bentonite with biomass were measured from 1.5 to 20 GHz as mixtures of bentonite with biomass could have microwave processing applications such as the thermochemical conversion of biomass to biofuel. Both dielectric constant and dielectric loss factor increased linearly with increasing moisture content. Measurements on biomass and bentonite mixtures show a quadratic increase in dielectric constant and loss factor with increasing bentonite content and with moisture contents ranging from 9.5% (pure bentonite) to 11.4% (pure biomass) wet basis. At 915 MHz, dielectric constant ranged from 2.0 to 6.2 and dielectric loss ranged from 0.2 to 2.7, respectively. At 2450 MHz, dielectric constant ranged from 1.8 to 5.1 and dielectric loss ranged from 0.7 to 2.6, respectively.

Open Transverse-Slot Substrate-Integrated Waveguide Sensor for Biomass Permittivity Determination

A novel open transverse-slot substrate-integrated waveguide sensor is presented. The sensor is designed and fabricated for dielectric measurements of sawdust at 8 GHz. Different configurations of the sensor were investigated by using simulation software and relationships between the simulated magnitude and phase of the reflection coefficient and dielectric properties. A suitable configuration was fabricated with a circuit board milling machine, and the performance was investigated through measurements of the magnitude and phase of the reflection coefficient from sawdust samples. The permittivity of the material was determined by fitting the voltage stand wave ratio and phase with a normalized 2-D polynomial with known dielectric values. The permittivity determination model was tested by using independent sets of training and validation measurements on sawdust at different bulk densities and moisture contents between 6.8% and 39%. The predicted dielectric properties values showed linear relationships with moisture content. Therefore, moisture content in sawdust can be determined from measurements of either dielectric constant or loss factor at a single microwave frequency without knowledge of the bulk density.

Effects of temperature and material on dielectric properties of pelleted wood-based biomass

The production of pelleted biomass represents a significant emerging industry in the United States. Solid biomass can be formed from the waste products of many different products. In this study, the effects of temperature and pellet material type on the dielectric properties were investigated. Temperatures of peanut hull pellets were increased in 10 °C increments ranging from 0 - 50 °C and dielectric properties at various moisture contents were determined. Further work was performed in investigating the dielectric properties of pine compared to those of peanut-hull pellets to determine whether a “unified” calibration for moisture content could be developed. Finally, the effect of pine-pellet degradation into sawdust was investigated to determine whether this would cause a change in the dielectric properties. Results showed that a temperature compensated calibration for moisture content could be developed for peanut-hull pellets. Additionally, a unified calibration for moisture content was achieved at 10 GHz.

Microwave Moisture Measurements of Flowing Biomass

Abstract. Production of pelleted biomass is a significant emerging industry in the United States. A primary quality attribute of pelleted biomass is moisture content. This parameter is critical in pricing, binding, combustion, and storage of pelleted biomass. In order to produce pellets of a high quality moisture content must be tightly controlled. In this study, a microwave system designed for moisture sensing on flowing bulk material was utilized to determine feasibility in sensing biomass. Two types of pelleted biomass derived from peanut hulls and pine were used for moisture content determination. Moisture contents from 5.4%-9.9% were tested for pine and 8.9% - 14.5% were tested for peanut hull pellets. At each moisture content three different material flow rates were tested and compared to the static measurement. Using a calibration function developed using static measurements; moisture content of flowing material was predicted. Standard error of calibration was computed for comparisons between reference moisture content, predicted static moisture content, and predicted flowing moisture content. Results showed that static and flowing measurements were comparable.