Characterization of conductor by alternating current potential-drop method with a four-point probe

A method of determining material parameters associated with a conductor using four points includes injecting and extracting alternating current into the plate using current-carrying wires operatively connected to two of the four points, measuring potential drop between the remaining two of the four points, and calculating the material parameters. The conductor can be of a homogenous material, a stratified material, or other type of material. The conductor can have any number of geometries, including that of a plate, a cylinder, a tube, a stratified cylinder or other shape

Negative Refractive Index Composite Metamaterials for Microwave Technology

Materials that exhibit negative index (NI) of refraction have several potential applications in microwave technology. Examples include enhanced transmission line capability, power enhancement/size reduction in antenna applications and, in the field of nondestructive testing, improved sensitivity of patch sensors and detection of sub-wavelength defects in dielectrics by utilizing a NI superlens

Design of interdigital spiral and concentric capacitive sensors for materials evaluation

This paper describes the design of two circular coplanar interdigital sensors with i) a spiral interdigital configuration and ii) a concentric interdigital configuration for the nondestructive evaluation of multilayered dielectric structures. A numerical model accounting for sensor geometry, test-piece geometry and real permittivity, and metal electrode thickness has been developed to calculate the capacitance of the sensors when in contact with a planar test-piece comprising up to four layers. Compared with a disk-and-ring coplanar capacitive sensor developed previously, the interdigital configurations are predicted to have higher signal-to-noise ratio and better accuracy in materials characterization. The disk-and-ring configuration, on the other hand, possesses advantages such as deeper penetration depth and better immunity to lift-off variations

Comment on “Finite-element modeling method for the study of dielectric relaxation at high frequencies of heterostructures made of multilayered particle” [J. Appl. Phys. 102, 124107 (2007)]

The article of Fourn et al. [J. Appl. Phys. 102, 124107 (2007) ] uses the numerical finite-element method to study the dielectric relaxation of a square array of coated cylinders. The comment here shows that similar results can be calculated immediately from the appropriate analytical expression. Our results are also compared to some figures in the article of Fourn et al. [J. Appl. Phys. 102, 124107 (2007) ]

Effects of parameter variations on negative effective constitutive parameters of non-metallic metamaterials

Analytical expressions describing the variability of effective constitutive parameters of non-metallic metamaterials, as a function of the constituent geometric and material parameters and their variations, have been developed from the total differential of Clausius-Mossotti expressions (using Mie dipole polarizabilities) for the effective (bulk) constitutive parameters of the metamaterial. In practice, these expressions are important for estimating the performance of a metamaterial with particular variations in the parameters of its constituents that arise during the fabrication process, and can be used to guard against extinction of desired double negative (DNG) behavior. With the derived expressions, the effects of parameter variations on effective constitutive parameters of non-metallic metamaterials have been analyzed for three types of metamaterials: (i) cubic arrays of identical magnetodielectric spheres; (ii) cubic arrays of dielectric spheres with equal radius but two different permittivities; and (iii) cubic arrays of dielectric spheres with equal permittivity but two different radii. These effects are evaluated in terms of the calculated variations in values of the effective constitutive parameters of the metamaterial in the vicinity of the DNG or single negative (SNG) band for particular geometric and material parameters and their variations. Results show that variation in the following parameters impacts DNG bandwidth. Listed in order from greatest to least influence: (i) sphere radius; (ii) sphere permittivity and permeability; (iii) lattice constant of the array; and (iv) the constitutive parameters of the array medium, all impact the width of the achievable DNG band. For particular cases studied here, results also show that the DNG behavior may be extinguished if there are 0.78%, 0.016%, and 0.016% variations in all parameters of metamaterial types (i), (ii), and (iii), respectively, as defined above. For the design of non-metallic metamaterials with inclusions, having arbitrary material parameters, in either periodic or random arrangement, the presented results can give a qualitative guide on the level of fabrication tolerances that should be achieved in order to observe the predicted SNG or DNG behavior experimentally

Concentric coplanar capacitive sensor for nondestructive evaluation

A concentric coplanar capacitive sensor includes a charged central disc forming a first electrode, an outer annular ring coplanar with and outer to the charged central disc, the outer annular ring forming a second electrode, and a gap between the charged central disc and the outer annular ring. The first electrode and the second electrode may be attached to an insulative film. A method provides for determining transcapacitance between the first electrode and the second electrode and using the transcapacitance in a model that accounts for a dielectric test piece to determine inversely the properties of the dielectric test piece

An interdigital capacitive sensor for quantitative characterization of wire insulation

An interdigital capacitive sensor has been developed to characterize the permittivity of wire insulation. A theoretical model has been developed to calculate the capacitance of such a sensor that is in intimate contact with the surface of a double-layer cylindrical dielectric surrounding a conductive core. The cylindrical form of the electrostatic Green’s function due to an exterior point source is utilized, with the final capacitance value being calculated using the Method of Moments. Example calculations are performed and a field optimization method is developed to improve the sensing efficiency of the electrodes

Aging Mechanisms and Monitoring of Cable Polymers

Aging mechanisms of two polymeric insulation materials that are used widely in nuclear power plant low-voltage cables; cross-linked polyethylene (XLPE) and ethylene propylene rubber/ethylene propylene diene terpolymer (EPR/EPDM), are reviewed. A summary of various nondestructive methods suitable for evaluation of cable insulation is given. A capacitive sensor capable of making local nondestructive measurements of capacitance and dissipation factor on cable polymers, and potentially suitable for in situ cable monitoring, is introduced. Correlating values of elongation-at-break, indenter modulus, capacitance and dissipation factor measured on a set of 47 aged flame-resistant EPR samples shows a higher correlation between indenter modulus and dissipation factor than between indenter modulus and elongation-at-break

Dielectric measurement of low-concentration aqueous solutions: assessment of uncertainty and ion-specific responses

Excessive amounts of chemicals and ions flowing into water sources cause serious environmental and human-health related concerns. The lack of affordable and real-time monitoring systems for these contaminants limits effective conservation and management strategies. To establish a basis for developing an effective, fast, real-time, and affordable sensing system, dielectric spectroscopy method has been employed to characterize aqueous solutions of sodium chloride (NaCl), sodium nitrate (NaNO3), and sodium sulphate (Na2SO4) at environmentally-relevant (low) concentrations. Dielectric spectra were measured over the frequency range from 200 MHz to 20 GHz, at temperature 25 ± 0.01 °C and for concentrations 0 to 20 mmol/L. The measured spectra were fitted with a Debye model using a non-linear, weighted, least-squares analysis. A method of judiciously exploiting the resulting fitting parameters is proposed, that allows the concentration and type of ions to be uniquely determined. Uncertainties due to random and systematic errors that contribute to the measured dielectric spectra and become critical in the context of low concentration aqueous solutions have been assessed. Furthermore, two methods of calculating associated uncertainties of the indicator parameters, viz. covariance matrix and Monte Carlo methods have been performed. The results show the numerical approach taken by Monte Carlo method, while yielding the same estimates, reduces the tediousness accompanied by analytical covariance matrix method

Analysis of a concentric coplanar capacitive sensor using a spectral domain approach

Previously, concentric coplanar capacitive sensors have been developed to quantitatively characterize the permittivity or thickness of one layer in multi‐layered dielectrics. Electrostatic Green’s functions due to a point source at the surface of one‐ to three‐layered test‐pieces were first derived in the spectral domain, under the Hankel transform. Green’s functions in the spatial domain were then obtained by using the appropriate inverse transform. Utilizing the spatial domain Green’s functions, the sensor surface charge density was calculated using the method of moments and the sensor capacitance was calculated from its surface charge. In the current work, the spectral domain Green’s functions are used to derive directly the integral equation for the sensor surface charge density in the spectral domain, using Parseval’s theorem. Then the integral equation is discretized to form matrix equations using the method of moments. It is shown that the spatial domain approach is more computationally efficient, whereas the Green’s function derivation and numerical implementation are easier for the spectral domain approach