SEARCH · Engineering Papers

Results for “Permittivity”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

472 records · Page 27

All sources NASA NTRS DOE OSTI

DOE OSTI2021

Phase coexistence at the first-order Mott transition revealed by pressure-dependent dielectric spectroscopy of κ - (BEDT-TTF) 2 - Cu 2 (CN) 3

The dimer Mott insulator kappa - (BEDT-TTF) 2 - Cu 2 (CN) 3 can be tuned into metallic and superconducting states on applying pressure of 1.5 kbar and more. We have performed dielectric measurements (7.5 kHz to 5 MHz) on kappa - (BEDT-TTF) 2 - Cu 2 (CN) 3 single crystals as a function of temperature (down to T = 8 K) and pressure (up to p = 4.3 kbar). In addition to the relaxor-like dielectric behavior seen below 50 K at p = 0, that moves toward lower temperatures with pressure, a second peak emerges in ε 1 (T) around T = 15 K. When approaching the insulator-metal boundary, this peak diverges rapidly reaching ε 1 ≈ 10 5 . Our dynamical mean-field theory calculations substantiate that the dielectric catastrophe at the Mott transition is not caused by closing the energy gap, but due to the spatial coexistence of correlated metallic and insulating regions. We discuss the percolative nature of the first-order Mott insulator-to-metal transition in all details.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2023

Dielectric Relaxation by Quantum Critical Magnons

We report the experimental observation of dielectric relaxation by quantum critical magnons. Complex capacitance measurements reveal a dissipative feature with a temperature-dependent amplitude due to low-energy lattice excitations and an activation behavior of the relaxation time. The activation energy softens close to a field-tuned magnetic quantum critical point at H = H c and follows single-magnon energy for H > H c , showing its magnetic origin. Furthermore, our study demonstrates the electrical activity of coupled low-energy spin and lattice excitations, an example of quantum multiferroic behavior.

1-dimensional spin chains↗

NASA NTRS2017

Micromechanics of Composite Materials Governed by Vector Constitutive Laws

The high-fidelity generalized method of cells micromechanics theory has been extended for the prediction of the effective property tensor and the corresponding local field distributions for composites whose constituents are governed by vector constitutive laws. As shown, the shear analogy, which can predict effective transverse properties, is not valid in the general three-dimensional case. Consequently, a general derivation is presented that is applicable to both continuously and discontinuously reinforced composites with arbitrary vector constitutive laws and periodic microstructures. Results are given for thermal and electric problems, effective properties and local field distributions, ordered and random microstructures, as well as complex geometries including woven composites. Comparisons of the theory's predictions are made to test data, numerical analysis, and classical expressions from the literature. Further, classical methods cannot provide the local field distributions in the composite, and it is demonstrated that, as the percolation threshold is approached, their predictions are increasingly unreliable. XXXX It has been observed that the bonding between the fibers and matrix in composite materials can be imperfect. In the context of thermal conductivity, such imperfect interfaces have been investigated in micromechanical models by Dunn and Taya (1993), Duan and Karihaloo (2007), Nan et al. (1997) and Hashin (2001). The present HFGMC micromechanical method, derived for perfectly bonded composite materials governed by vector constitutive laws, can be easily generalized to include the effects of weak bonding between the constituents. Such generalizations, in the context of the mechanical micromechanics problem, involve introduction of a traction-separation law at the fiber/matrix interface and have been presented by Aboudi (1987), Bednarcyk and Arnold (2002), Bednarcyk et al. (2004) and Aboudi et al. (2013) and will be addressed in the future.

micromechanics↗

DOE OSTI2020

Interdigital Capacitance Sensor for Cable Insulation Test and Monitoring

A substantial body of work suggests feasibility to measure cable jacket and insulation conditions using various forms of interdigital capacitance (IDC) sensors. The sensors can either be used to manually test local cable conditions or as permanently installed sensors. Eligible cables subject to these measurements do not include shielded cables but the set of candidate cables is expanded from only unjacketed cables by the ability to assess insulation condition through the jacket. Dual gap IDC sensors are confirmed to be able to sense the insulation condition beneath a polymer jacket and, moreover, the IDC is the only known way to assess the insulation condition through the jacket. PNNL has filed a patent for this approach and is exploring commercial partnerships to exploit IDC technology for actionable field measurements.

NDE, cable, IDC, capacitance, permittivity, insula↗