Dielectric loss

About: Dielectric loss is a research topic. Over the lifetime, 20296 publications have been published within this topic receiving 349254 citations.

Complex permittivity of some ultralow loss dielectric crystals at cryogenic temperatures

Abstract: Whispering gallery modes were used for very accurate permittivity and dielectric loss measurements of ultralow loss isotropic and uniaxially anisotropic single crystals. Several materials including sapphire, YAG, quartz, and SrLaAlO4 were measured. The total absolute uncertainty in the real part of permittivity tensor components was estimated to be ±0.1%, limited principally by the uncertainty in sample dimensions. Imaginary parts of permittivities were measured with uncertainties of about 10%, limited by the accuracy of Q-factor measurements of whispering gallery modes. It has been observed that, for most crystals, dielectric losses can be approximated by a power function of absolute temperature only in limited temperature ranges. At temperatures between 4-50 K, losses are often affected by impurities, which are always present in real crystals.

Fluoro-Polymer@BaTiO3 Hybrid Nanoparticles Prepared via RAFT Polymerization: Toward Ferroelectric Polymer Nanocomposites with High Dielectric Constant and Low Dielectric Loss for Energy Storage Application

Abstract: Polymer nanocomposites with high energy density and low dielectric loss are highly desirable in electronic and electric industry. Achieving the ability to tailor the interface between polymer and nanoparticle is the key issue to realize desirable dielectric properties and high energy density in the nanocomposites. However, the understanding of the role of interface on the dielectric properties and energy density of polymer nanocomposites is still very poor. In this work, we report a novel strategy to improve the interface between the high dielectric constant nanoparticles (i.e., BaTiO3) and ferroelectric polymer [i.e., poly(vinylidene fluoride-co-hexafluoro propylene)]. Core–shell structured BaTiO3 nanoparticles either with different shell thickness or with different molecular structure of the shell were prepared by grafting two types of fluoroalkyl acrylate monomers via surface-initiated reversible addition–fragmentation chain transfer (RAFT) polymerization. The dielectric properties and energy storage c...

Electromagnetic and microwave absorbing properties of multi-walled carbon nanotubes/polymer composites

Abstract: The preparation and characterization of CNTs/polymer (PET, PP, PE and varnish) composites were studied for microwave absorption applications in the range of 2–18 GHz. The results indicated the position of reflectivity peak moves to a lower frequency and the loss factors of composites increase with increasing CNTs concentrations. When CNTs concentration was above 4 wt%, there was a sharp increase of loss tangent. 4 wt% CNTs/PET and 8 wt% CNTs/varnish composites had considerable absorbing peak at 7.6 GHz, 15.3 GHz and achieved maximum absorbing value of 17.61 dB, 24.27 dB, respectively. In addition, the frequencies range for absorbing values exceeding 5 dB of CNTs/(PET, PP, varnish) composites are 13 GHz, 10 GHz and 6 GHz, respectively. The microwave absorption of CNTs composites can be mainly attributed to the dielectric loss rather than magnetic loss.

Electromagnetic Wave Absorption Properties of Reduced Graphene Oxide Modified by Maghemite Colloidal Nanoparticle Clusters

Abstract: Graphene is highly desirable as an electromagnetic wave (EM) absorber because of its large interface, high dielectric loss, and low density. Nevertheless, the conductive and electromagnetic parameters of pure graphene are too high to meet the requirement of impedance match, which results in strong reflection and weak absorption. In this paper, we report a facile solvothermal route to synthesize reduced graphene oxide (RGO) nanosheets combined with surface-modified γ-Fe2O3 colloidal nanoparticle clusters. The obtained two-dimensional hybrids exhibit a relatively low EM reflection coefficient (RC) and wide effective absorption bandwidth, which are mainly attributed to the unique microstructure of colloidal nanoparticle clusters assembled on RGO. The nanoparticle clusters have more interfaces. The interfacial polarization within nanoparticle clusters and conductivity loss of RGO plays an important role in absorbing EM power. The minimum RC reaches −59.65 dB at 10.09 GHz with a matching thickness of 2.5 mm. T...

Porous Co-C Core-Shell Nanocomposites Derived from Co-MOF-74 with Enhanced Electromagnetic Wave Absorption Performance.

Abstract: The combination of carbon materials and ferrite materials has recently attracted increased interest in microwave absorption applications. Herein, a novel composite with cobalt cores encapsulated in a porous carbon shell was synthesized via a facile sintering process with a cobaltic metal–organic framework (Co-MOF-74) as the precursor. Because of the magnetic loss caused by the Co cores and dielectric loss caused by the carbon shell with a unique porous structure, together with the interfacial polarization between two components, the ferromagnetic composite exhibited enhanced electromagnetic wave absorption performance compared to traditional ferrite materials. With the thermal decomposition temperature of 800 °C, the optimal reflection loss value achieved −62.12 dB at 11.85 GHz with thin thickness (2.4 mm), and the bandwidth ranged from 4.1 to 18 GHz with more than 90% of the microwave that could be absorbed. The achieved performance illustrates that the as-prepared porous Co–C core–shell composite shows ...