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Properties and applications of engineering materials
Published in Alan Darbyshire, Charles Gibson, Mechanical Engineering, 2023
Alan Darbyshire, Charles Gibson
Permittivity is a measure of a material’s ability to intensify an electric field such as that produced between the plates of a capacitor. The plates of a capacitor are separated by an insulating material known as a ‘dielectric’. Depending on the use and type of capacitor, air, waxed paper, plastics and ceramic materials are used as dielectrics. When a potential difference is applied across the plates of a capacitor, electrical charge is stored on them and an electric field is set up between them.
Flexible Nanogenerators
Published in Inamuddin, Mohd Imran Ahamed, Rajender Boddula, Tariq Altalhi, Nanogenerators, 2023
Syed Wazed Ali, Satyaranjan Bairagi, Swagata Banerjee
Permittivity is the ability of a material to polarize under an electric field which is related to dielectric constant. Permittivity of a material to permittivity of a vacuum is relative permittivity. When an electric field is applied, electronic, atomic and orientation polarizations occur due to the separation of positive and negative charges to behave like electric dipoles. Relative permittivity consists of real and imaginary parts which are dielectric constant and dielectric loss (tanδ). The relaxation time in a polymer is the cause for the inability of polarization process to follow the rate of change of oscillating-applied electric field which is dielectric loss.
Introduction to Nanosensors
Published in Vinod Kumar Khanna, Nanosensors, 2021
Electric displacement is the displacement of charge perpendicular to the direction of the field produced in an electric field per unit area. Permittivity is the ratio of electric displacement to electric field. Relative permittivity or dielectric constant of a material is its permittivity with respect to permittivity of free space. Displacement current is the rate of displacement of charge in an insulator (a material that does not allow current to flow through).
Coplanar capacitive sensors and their applications in non-destructive evaluation: a review
Published in Nondestructive Testing and Evaluation, 2023
T. Zhu, K. Wen, Z. Zhang, X. Yuan, W. Li, X. Yin
Equation (1) defines capacitance, for any pair of conductors of any shape, as the ratio of the charge stored on the conductors to the potential difference between them. For the conventional parallel-plate capacitor, the capacitance was experimentally found to be based on the permittivity, , of the medium between the plates known as a dielectric, the surface area, , between the plates and the dielectric, and the distance of separation, , between the plates, as shown in Equation (2). The permittivity (absolute permittivity), , is a property of insulators that shows their ability to allow an electric field to penetrate them. In other words, it is the opposition to the formation of an electric field in a medium. By comparing the permittivity of any material to that of a vacuum, , we obtain its relative permittivity, , as shown in Equation (3).
Influence of the molecular structure of compounds with terminal isothiocyanate group on the induction of the smectic A phase: Part II
Published in Liquid Crystals, 2023
Paulina Zieja, Marzena Tykarska, Przemysław Morawiak, Paweł Perkowski, Wiktor Piecek
The experimental results for A5.5 are shown in Figure 7(a), where the real part of permittivity perpendicular to the director is presented vs. temperature for four frequencies (1 kHz, 10 kHz, 100 kHz, 1 MHz). We observed that in the thin cell the crystallisation temperature is 40°C while the melting temperature found in POM observations is 89°C, so it supercools at almost 50 deg. We found many times in dielectric spectroscopy of nematics or smectics that the crystallisation temperature shifts down when dielectric properties are measured in thin cells, at the low cooling rate. The cell walls forcing the planar alignment often stabilise mesophases. Moreover, the temperatures of nucleation of nematic phase from isotropic liquid shift often up in thin cells with planar anchoring. During measurements, we did not use DC field because the A.5.5 compound has a (low) negative electric anisotropy thus it cannot be reoriented by DC field from HG to HT orientations. The permittivity is around 2.4 and it slightly decreases with temperature.
Three-dimensional numerical investigation of hybrid nanofluids in chain microchannel under electrohydrodynamic actuator
Published in Numerical Heat Transfer, Part A: Applications, 2023
Milad Amiri, Dariusz Mikielewicz
Where and refer to electric field strength vector (V/s) and charge density (C/m3), respectively. is dielectric permittivity (F/m). The first term represents the impact of the electric field on free charges, namely the electrophoresis or Coulomb force. The second and the third terms depict dielectrophoresis and electrostriction force densities, which are referred to as polarization forces induced in the field [69]. Due to the constant electric permittivity, the second and third terms on the right side of Eq. (10) become neglectable. As a result, the electrohydrodynamic force is limited to Coulomb force which is used as a source term in the momentum equation. The electrohydrodynamic governing equations were calculated as follows [40].