Dielectric properties of natural rubber Hevea brasiliensis latex were measured at frequencies 0.2 to 20 GHz, at temperatures of 2, 15, 25, 35, and 50oC and around 30-98% moisture content. Measurements were done using open-ended coaxial line sensor and automated network analyzer. As expected, results showed that dielectric constant increased with increasing moisture. From 0.2 to 2.6 GHz, the losses were governed by conductive losses but for frequencies greater than 2.6 GHz, these were mainly due to dipolar losses. The former is due to conducting phases in hevea latex, while the latter is mainly governed by the orientation of water molecules. The results were analyzed at 2.6, 10, and 18 GHz, respectively. These were then compared with the values predicted by the dielectric mixture equations recommended by Weiner, Bruggeman and Kraszewski. All the measured values were found to be within the Weiner’s boundaries and close to the upper limit of Weiner’s model. It is also close to the predicted values of Bruggeman’s model with a/b = 0.1. All the models including Kraszewski are suitable for predicting the dielectric properties of hevea latex for frequencies 2.6 to 18 GHz, moisture content 30 to 98% and temperatures 2 to 50oC.
This paper describes the development of a simple method to determine the permittivity and moisture content (m.c.) of
ginger. The measurement system consists of a microwave sensor, directional coupler and a PIC microcontroller. The
microwave sensor is a square flanged open-ended coaxial (OEC) sensor made from SMA stub contact panel with outer
diameter (O.D) 4.10 mm. The microwave oven drying method was used to determine the actual m.c. of the ginger. All data
acquisition, processing and display were accomplished using a PIC 16F690 microcontroller programmed using Flowcode
software. The actual values of the permittivity of ginger were obtained by using the Agilent (now Keysight Technologies)
85070B dielectric probe along with a HP 8720B Vector Network Analyzer (VNA). The results showed good relationships
between m.c., permittivity (dielectric constant (εʹ) and loss factor (ε̋)) and reflected voltage. The calibration equations
between reflected voltage and m.c. have been established for the sensor. The measurement system provides a simple, fast
and accurate technique to predict m.c., εʹ and ε̋ of ginger from reflected voltage measurements alone. The accuracy in
determination of m.c., εʹ and ε̋ in ginger was within 2.9%, 2.7%, and 3.6%, respectively.