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A fast method for microwave processing and measurement of dielectric and thermal properties of materials as a function of temperature has been developed (MW-DETA). Unlike previous approaches, the method provides totally new quantitative measurements of the thermal parameters, which are fundamental for calculating the specific heat and in particular, the energy requirements of electrification of materials processing via microwave heating. The in-situ measurement of dielectric properties of the sample with temperature, together with the precise numerical modelling of the thermal process, provided the necessary information to quantify the thermal and microwave losses and, therefore, the precise amount of power delivered to the sample that is converted into heat. Compared to conventional calorimeters, microwave heating reduces the experimental time and improves the uniformity of heating, which leads to a fast and reliable method to determine the thermal properties of the material under test with different operation modes, either constant or variable heating rates. The functionality of the thermal parameters measurement system has been demonstrated by heating and measuring a ceramic sample of Macor up to 400 °C. Accuracy reached in the thermal process has been validated by comparison with a conventional DSC analysis. [Display omitted] • A novel fast microwave calorimeter with quantitative energy measurement is developed. • Energy consumption in the calorimeter including thermal and microwave losses is evaluated. • EM coupled with thermal simulation determines heat transfer and temperature distribution. • 0D model accurately predicts temperature evolution and thermal parameters. • Comparison with DSC measurements validates the proposed microwave calorimetry method. [ABSTRACT FROM AUTHOR]

Accurate determination of permittivity is a crucial factor for successfully developing new food processing technologies at radio frequencies. An improved measurement test fixture based on an open-ended coaxial probe was developed to determine the permittivity of lossy food products at radio frequencies as a function of temperature. In order to increase the sensitivity of the permittivity measurements at these frequencies, especially when using a vector network analyzer as a measuring device, the dimensions of the coaxial cell were carefully modeled to consider the range of dielectric losses estimated for food materials. The electromagnetic model was used to retrieve permittivity values from reflection measurements where the entire geometry of the test fixture was considered assuming there was no open radiation or infinite flanges and without the need of reference materials to calibrate the probe. The new cell was validated through permittivity measurements of six saline solutions and then, employed to determine the dielectric properties of cheese sauces and commercial milk samples at 40.68 MHz up to 120 °C. The ionic content and temperature had a limited influence on the dielectric constant but highly determined the loss factor. • A test fixture was developed for improved temperature-dependent permittivity measurements of foodstuffs at radio frequencies. • It used an open-ended coaxial probe achieving more than 6 times the response of previous designs reported in the literature. • Permittivity of milk and cheese food sauces were measured at 40.68 MHz up to 120 °C. [ABSTRACT FROM AUTHOR]