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Microwave and Dielectric Drying
Published in Arun S. Mujumdar, Handbook of Industrial Drying, 2020
The temperature dependence of a dielectric constant is quite complex, and it may increase or decrease with temperature depending upon the material. (See discussion concerning water and polymers in Section 2.4.) In general, however, a material below its freezing point exhibits lowered dielectric constant and dielectric loss. Above freezing the situation is not clear-cut, and since moisture and temperature are important to both drying and dielectric properties, it is important to understand the functional relationships in materials to be dried. Wood, for example, has a positive temperature coefficient at low moisture content (5); that is, its dielectric loss increases with temperature. This may lead to runaway heating, which in turn will cause the wood to burn internally if heating continues once the wood is dried.
Fundamentals of an Antenna
Published in Rajveer S. Yaduvanshi, Gaurav Varshney, Nano Dielectric Resonator Antennas for 5G Applications, 2020
Rajveer S. Yaduvanshi, Gaurav Varshney
Dielectric constant is defined as “the ratio of the amount of electrical energy stored inside the material when an external voltage is applied to that of the energy stored in a vacuum.” It is denoted as ϵr. The dielectric constant of a material concentrates on the electrostatic lines of flux under the given conditions. Dielectric material supports the E-field when energy is dissipated in the form of heat energy minimally. The net electric flux density (D) can be expressed mathematically as follows: () D=εOE+P () P=εOχE () D=εO(1+χ)E
Capacitance-Based Humidity Sensors
Published in Ghenadii Korotcenkov, Handbook of Humidity Measurement, 2019
One should note that, despite the weak dependence of the parameters of capacitive sensors on temperature, temperature is one of the main sources of errors in measuring the humidity (Rotronic 2014). Sensor hygroscopic properties vary with temperature. An RH instrument relies on the assumption that the relationship between the amount of moisture present in the sensor hygroscopic material and RH is constant. However, in most hygroscopic materials, this relationship varies with temperature. In addition, the dielectric properties of the water molecule are affected by temperature. At 20°C, the dielectric constant of water has a value of approximately 80. This constant increases by more than 8% at 0°C and decreases by 30% at 100°C. Sensor dielectric properties also vary with temperature. The dielectric constant of most dielectric materials decreases as temperature increases. Fortunately, the effect of temperature on the dielectric properties of most plastics is usually more limited than in the case of water. However, they exist. All this can lead to errors in the measurement. Therefore, humidity values reported by the electronics must compensate for the impact of temperature on the sensor. Failure to do so can result in large measurement errors, sometimes up to 8% RH or more. It is also necessary to consider that any difference between the ambient temperature and the sensor temperature also causes an error. For example, at 20°C and 50% RH, a difference of 1°C between the ambient temperature and the sensor temperature results in an error of approximately 3%.
Dielectric properties of Sphenarium purpurascens at 2.4 GHz
Published in Journal of Microwave Power and Electromagnetic Energy, 2023
Tejinder Kaur, Jose Luis Olvera-Cervantes, Roberto Rojas-Laguna, Maria Elena Sosa-Morales, Alonso Corona-Chavez
In this paper, we have shown the dielectric properties of edible grasshoppers (S. purpurascens) using the cavity perturbation technique at 2.4 GHz and at different temperatures. It was seen that the resonant frequency increases linearly as temperature increases. In addition, the dielectric constant decreases when temperature is rising. This is due to water evaporation at higher temperatures. Moreover, quality factor decreases linearly as temperature rises, this causes the dielectric losses to increase linearly with increasing temperatures. This is caused by ionic conduction, where losses increase due to higher mobility of ions. When the samples are left to cool, the dielectric constant stabilizes at ε = 7.7 and the dielectric loss at ε = 5.4j. Furthermore, the penetration depth was calculated in a range from 10.8 mm at 25 °C to 3.5 mm at 80 °C. For optimum microwave heating processes, the maximum insect bed should be chosen as dp = 3.5 mm.
Determination of ionic strength due to magnesium sulfate heptahydrate in water by means of its permittivity in the microwave range
Published in Journal of Microwave Power and Electromagnetic Energy, 2020
Edel Serafín Hernández Gómez, José-Luis Olvera-Cervantes, Benito Corona Vásquez, Alonso Corona Chávez, Laura Sol Perez Flores, Tejinder Kaur Kataria
The dielectric constant is defined as the measure of the ability of a material to store electromagnetic energy. The dielectric loss factor is characterized by the amount of electromagnetic energy converted into heat in a material (Coronel et al. 2008). The loss factor due to dipolar rotation () and the loss factor due to ionic conduction () are the two mechanisms that contribute to the dielectric permittivity in the microwave frequencies (Pradhan et al. 2008). The loss factor and are related as follows: where
Blue-phase liquid crystal display with insulating protrusion
Published in Liquid Crystals, 2018
Yuqiang Guo, Yifei Wang, Chi Zhang, Qihui Mu, Xiaoshuai Li, Yubao Sun, Hu Dou, Qionghua Wang
Figure 9 shows the VT curves of D-P structures with various relative dielectric constants (κ). The effects of protrusion’s height on performances of BPLCD are investigated in the ahead discussion parts. If the higher dielectric constant materials [38] are used to make the protrusion with h = 5 μm, the saturation voltage can be further reduced [39]. The electric displacement vector is continuous in space, so the electric field strength is in inverse proportion to the dielectric constant [40]. There is a little part of electric field in the protrusion if a high dielectric constant material is used, just like the electric field in protrusion is excluded into the BPLC. The saturation voltage is lower than 10 V when the dielectric constant is 1000, as shown in Figure 9. However, the high dielectric constant ceramics (BaTiO3, κ > 3000) are usually opaque and fragile which cannot be utilised as a thin layer with special shapes. Composite materials with high dielectric constant are translucent and flexible, it is available for protrusion after some substantive modifying, such as, enhancing transmittance, film-forming and stability.