Measurement of the dielectric properties of sawdust between 0.5 and 15 GHz

Authors: PAZ, ANA MARTA - Swedish University; Trabelsi, Samir; Nelson, Stuart; THORIN, EVA - Swedish University

Submitted to: IEEE Transactions on Instrumentation and Measurement
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/28/2010
Publication Date: 10/20/2011
Citation: Paz, A., Trabelsi, S., Nelson, S.O., Thorin, E. 2011. Measurement of the dielectric properties of sawdust between 0.5 and 15 GHz. IEEE Transactions on Instrumentation and Measurement. 60(10):3384:3390.

Interpretive Summary: Dielectric properties are electrical properties that determine how materials interact with electric fields such as those of high-frequency and microwave electromagnetic energy. Therefore, the dielectric properties of materials determine how rapidly they will heat in microwave ovens and lower radio-frequency dielectric heating equipment. Dielectric properties are also important in low power applications, such as the rapid measurement of moisture content in grain and other commodities. Biofuels are an attractive alternative source of energy to fossil fuels. Moisture content of solid biofuels is an important factor in pricing, conditioning for combustion, and storage management. This paper discusses the measurement of dielectric properties at microwave frequencies between 5 and 15 GHz for pine sawdust, a waste product of the lumber industries that can be used as a biofuel. The moisture contents of pine sawdust samples were adjusted to various levels and their dielectric properties were measured at different bulk densities by two different techniques over moisture contents from 13% to 45%, as determined by standard methods. Analysis of the variations of the dielectric properties of the sawdust with moisture content and bulk density revealed promise for using the microwave dielectric properties for sensing moisture content.. The new data on pine sawdust are of interest to engineers and scientists working on biofuels applications. The microwave measurement method, based on dielectric properties sensing, offers promise for the monitoring of moisture and bulk density in biofuels processing and utilization and can improve the energy efficiency in such applications.

Technical Abstract: Rapid, nondestructive, and subsurface sensing of material properties such as water content can be achieved through dielectric measurements. The interaction between the electromagnetic waves and the material is defined by the dielectric properties, which can be used to determine the physical properties of the material. In this study, an open-ended coaxialline dielectric probe was used for broadband measurements of the dielectric properties of sawdust. Measurements of 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 in measurements with the coaxialline probe. It consists of measurement of the dielectric constant with a different method at a frequency common to both methods and identifying a correlation between the measured dielectric constant and density. In this instance, a free-space transmission method was used for this purpose. The dielectric properties of sawdust samples with moisture contents between 13% and 45% are presented for frequencies between 0.5 and 15 GHz.