Permittivity Measurements for Cypress and Rockrose Biomass Versus Temperature, Density, and Moisture Content

Abstract

Permittivity of materials is of utmost importance for microwave applicators’ design and to predict high-frequency dielectric heating of materials. In the case of aromatic plant biomass, however, there are few data that help researchers design microwave applicators for microwave-assisted extraction. In this work, the permittivity of cypress and rockrose biomass samples were measured versus temperature, density, and moisture content. A resonant technique based on a coaxial bi-reentrant microwave cavity was employed to obtain the complex permittivity of biomass samples as a function of those magnitudes around the 2.45 GHz ISM frequency. The obtained measurements show that large variations for permittivity values can be found with moisture content and density changes for both cypress and rockrose biomass. Temperature also has effects in a lesser degree, although it has an important influence on the cypress biomass loss factor. Polynomial expressions fitting the experimental data were provided in order to facilitate the estimation of intermediate values, which were not explicitly arranged in this work. As a general trend, the permittivity of cypress and rockrose biomass increases with increasing values of moisture content and density, whereas the biomass loss factor increases when temperature rises.

Postharvest Microwave Drying of Basil (Ocimum basilicum L.): The Influence of Treatments on the Quality of Dried Products

“…Literature studies on the behavior of plants, including the aromatic ones, such as Cymbopogon nardus (L.) Rendle, Eucalyptus spp., Piper aduncum L., Piper hispidinervum C. DC., Cupressus sempervirens L. and Cistus spp., show how their dielectric properties, even if they are not high such as pure water medium, allow rapid heating due to the presence of a mixture of ions, non-polar long chains and large polar molecules, typical chemical constituents of branches, leaves and inflorescences, that activate dissipative energy mechanisms [ 30 , 31 ]. In particular, water and salt content play a fundamental role: the greater the quantity of water present (and saline content) in the plant, the better the response to the applied electric field will be and, consequently, the faster the heating and the removal of moisture.…”

Detection of Anti-Counterfeiting Markers through Permittivity Maps Using a Micrometer Scale near Field Scanning Microwave Microscope

“…Permittivity is a fundamental property of dielectric materials describing their interaction with electromagnetic fields [ 10 ] and is the most studied parameter at microwave frequencies. Permittivity studies have historically been linked to telecommunications systems [ 11 ]; nevertheless, microwave techniques for non-destructive testing and evaluation have also been frequently employed for a good range of industrial and scientific applications [ 12 , 13 , 14 , 15 , 16 ].…”

Dielectric Characterization of Fabric Aggregates around the 2.45 GHz ISM Band under Various Humidity, Density, and Temperature Conditions

“…It was possible to relate the dielectric properties to the measured temperature data in a way similar to that described in [ 25 , 26 ] by comparing the temperature and permittivity time vectors. It should be mentioned that each complex permittivity value was calculated by averaging the results from three tests.…”

“…The sample temperature was measured in accordance with Newton’s law of cooling, which predicts that temperature decreases more rapidly at higher temperatures; as a result, more permittivity data was collected at lower temperatures than at higher ones. To acquire permittivity values with comparable temperatures, the averaged permittivity values within 1 °C temperature bins were again averaged [ 25 , 26 ].…”