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Electromagnetic sensing has been found an interesting technique for the characterization of woody biomass. The knowledge of the dielectric properties is useful for this characterization and to improve the understanding of the dielectric behavior of the material. This study presents the dielectric properties of woody biomass at a center frequency of 555 MHz. A measurement system, previously developed, to determine the water content of biomass was used. This system uses a reflection method and measures a biomass volume of about 0.11 m³. The dielectric properties were extracted from attenuation and velocity of the electromagnetic waves in three types of woody biomass with varying water content.

The aim of this study is to determine the dielectric constant of woody biomass at different water contents and describe its behavior with a dielectric mixing model. The use of the model for determination of water content is also verified. Dielectric constants were calculated from the travel times of electromagnetic waves with a center frequency of 555 MHz through collected biomass samples. The power law, Maxwell-Garnett, and Polder van Santen mixing models were applied to the experimental data. In the models, biomass was considered as a mixture of three phases: a solid solution composed of wood cellular material and bound water, free water, and air. The experimental data was found to be better described by the Maxwell-Garnett model. The use of this model along with an independent validation set for the determination of volumetric water content resulted in a root mean square error of prediction of 0.03 within the investigated volumetric water content range of 0.07-0.29.

Peanut-hull pellets are obtained from a waste product, peanut hulls, which after pelleting can have several uses, namely as a renewable fuel. Rapid and nondestructive characterization of peanut-hull pellets is important for industrial utilization of this resource. Properties such as moisture content and bulk density are important for quality control and pricing and control of the energy conversion process. The dielectric properties of peanuthulls pellets can be used for the development of rapid and nondestructive sensors. In this study, the dielectric properties of peanut-hull pellets were measured at frequencies between 5 and 15 GHz, for moisture contents between 4% and 13%, temperatures between -15 °C and 38 °C, and bulk densities between 0.54 and 0.69 g·cm^-3.

The aim of this paper was to measure the broadband dielectric properties of sawdust. Knowledge of dielectric properties is important in improving understanding of a material and can lead to the development of methods for determining physical properties such as moisture and salt content. The broadband dielectric properties of sawdust were measured with an open-ended coaxial-line dielectric probe. Measurements on granular materials with the dielectric probe are dependent on the density of the measured region, which may differ from the average density of the sample. In this paper, a method was developed for determining the actual density for measurements with the dielectric probe. It consists of measurement of the dielectric constant with a different method (in this instance, a free-space transmission method) at a frequency common to both methods and identifying a relationship between the measured dielectric constant and density. The dielectric properties of sawdust samples with moisture content levels between 13% and 45% are presented for frequencies between 0.5 and 15 GHz.