Application of the body of revolution finite-element method in a re-entrant cavity for fast and accurate dielectric parameter measurements

In dielectrometry,traditional analytical and numerical algorithms are difficultly employed in complex resonant cavities.For a special kind of structure(a rotating resonant cavity),the body of revolution finite-element method(BOR-FEM)is employed to calculate the resonant parameters and dielectric parameters.In this paper,several typical resonant structures are selected for analysis and verification.Compared with the resonance parameter values in the literature and the simulation results of commercial software,the error of the BOR-FEM calculation is less than 0.9%and a single solution time is less than 1 s.Reentrant coaxial resonant cavities loaded with dielectric materials are analyzed using this method and compared with simulation results,showing good agreement.Finally,in this paper,the established BOR-FEM method is successfully applied with a machined cavity for the accurate measurement of the complex dielectric constant of dielectric materials.The test specimens were machined from polytetrafluoroethylene,fused silica and Al_(2)O_(3),and the test results showed good agreement with the literature reference values.

Fast Measurement of Dielectric Conductivity for Space Application by Surface Potential Decay Method

Surface potential decay of polymers for electrical insulation can help to determine the dark conductivity for spacecraft charging analysis. Due to the existence of radiation-induced conductivity, it decays fast in the first few hours after irradiation and exponentially slowly for the remaining time. The measurement of dark conductivity with this method usually takes the slow part and needs a couple of days. Integrating the Fowler formula into the deep dielectric charging equations, we obtain a new expression for the fast decay part. The experimental data of different materials, dose rates and temperatures are fitted by the new expression. Both the dark conductivity and the radiation-induced conductivity are derived and compared with other methods. The result shows a good estimation of dark conductivity and radiation-induced conductivity in high-resistivity polymers, which enables a fast measurement of dielectric conductivity within about 600 rain after irradiation.

Wide-Temperature-Range Dielectric Permittivity Measurement under High Pressure

Two measurement systems are developed for in-situ dielectric property measurement under high pressure in a wide-temperature range from 77K to 1273 K. The high-temperature system ranging from room temperature up to 1273K is equipped with a hexahedron anvils press, while the low-temperature system ranging from liquid nitrogen temperature to normal condition is equipped using the piston cylinder setup with a specially designed sample chamber. Using these configurations, the dielectric property measurement of ferroelectrie BaTiO3 and multiferroie Tm0.5Gd0.5MnO3 compounds are demonstrated, which proves the validity of the systems through the tuning of the polarization and phase transition boundary by high pressure. These two systems will be equally applicable to a wide variety of electronic and transport property measurements of insulators, semiconductors, as well as battery materials.

Evaluation of myocardial viability during cold storage by measurement of myocardual dielectric properties tanδm in radio frequency

Objective To study the mechanism of myocardial dielectric property changes in radio frequency during hypothermic preservation and explore myocardial viability evaluative method. Methods Hybrid young pigs ( 20 - 30 kg) were used in the experiment. Heart arrest was in-

Dielectric and physico-chemical behavior of single thermally thick wood blocks under microwave assisted pyrolysis

Pyrolysis of thermally thick beech wood blocks with a size of around 2.5×8×6 cm^(3)(width×length×height)was carried out in a lab scale microwave reactor with a frequency of 2.45 GHz,operated,both,at 300 W and 600 W under inert conditions,using N_(2) at around 400 mbar absolute pressure.The microwave cavity had a size of 20×20×20 cm^(3).The specific energy supply referred to the untreated wood block was 4-8 W/g,with slight variations depending on the initial water content.The mass loss and the reflected microwave power were in-situ monitored during the experiments.The sample surface and chamber temperatures were measured with a pyrometer and a thermocouple,respectively.Physico-chemical and dielectric properties of the produced solids were investigated and compared to those of chars produced under conventional pyrolysis using the same raw materials.It is shown that the complex dielectric permittivity of the solid products changed drastically during the pyrolysis process,with increasing heating properties as the conversion process evolved.This was easily achieved using 60o W without susceptors.However,300 W was not enough to achieve a high conversion degree,independently of the irradiation time.This,together with the physico-chemical analyses of the solids,hinted to the importance of the transport kinetics in thermally thick materials,although further investigationis still required.

Synthesis and Controllable Growth Dynamics of Third Order Nonlinear Optical Material of 2-Amino-4-Methylpyridinium 2-Chloro 4-Nitro Benzoate Electro-Mechanical Investigation and Device Fabrication

An organic nonlinear optical material 2-Amino-4-methylpyridinium 2-chloro 4-nitro benzoate (AMPCNB) was synthesized and large size single crystals were grown by slow evaporation solution growth method. Single crystal X-ray diffraction study showed that the title compound belongs to monoclinic crystal system with P21/n space group. A powder XRD study was performed to ascertain its phase. The UV–VIS-NIR study was performed to investigate the transparency window and lower cutoff wavelength of the compound, no absorption has been observed between 318 and 1100 nm. The third harmonic efficiency of the title compound has been studied using the Z-scan technique using continuous-wave Nd:YAG laser to confirm its saturable absorption and self-defocusing effect. The photo conducting and charge transport properties are analyzed using photoconductivity and dielectric measurements. Theoretical calculation of molecular polarizability, which is helpful in device fabrication, was carried out from Penn gap, Clausius-Mosotti equations and the obtained results were compared. Mechanical properties of the grown crystal were investigated by Vicker’s microhardness study.

STRUCTURAL AND FERROELECTRIC PROPERTIES OF A NEW NIOBATE: Sr_6FeNb_9O_(30)

A new niobate Sr6FeNb9O30 was synthe-sized in the ternary system SrO-Fe2O3-Nb2O5 for the first time. The crystal structure was determined by X-ray diffraction and dielectric measurement, and it belongs to orthorhombic tungsten bronze structure at room tem perature with unit cell parameters a=1.7554(1) nm, b=1.7534 (1) nm, c=0. 77870(6)nm. Dielectric constants measure-ment show that Sr6FeNb9O30 has two phase transitions, paraelectric to ferroelectric at 185 C and ferroelectric to ferroelastic at 70 ℃.

An Improved Modeling of TDR Signal Propagation for Measuring Complex Dielectric Permittivity

Time domain reflectometry（TDR） is a measurement technique based upon transmission line theory. The solutions of transmission line equations are reformulated in terms of independent physical properties, instead of coupled per-unit-length circuit parameters. The complete TDR response is effectively modeled by a non-uniform transmission line using the non-recursive ABCD matrix approach. Approaches to calibrate line parameters and perform TDR measurements based upon such model are introduced with an example on dielectric spectroscopy. TDR modeling in terms of decoupled physical parameters and non-recursive algorithm allows more convenient calibration of line parameters and facilitates interpretation of TDR measurements.

Evidence of a third kind of Johnscher’s like universal dielectric response

Polymer/metal composites(PMC)comprising of polyvinylidene fluoride/nanocrystalline nickel with varying volume fractions of nickel(fcon)prepared under cold press show an insulator to metal transition(IMT)at percolation threshold(f_(c)=f_(con)=0:27).The two kinds of generalized Johnscher’s universal dielectric response(UDR)laws on both sides of IMT hold good,while for the percolative sample,none of the two laws hold good.Neither the concept of dipolar relaxation nor anomalous low frequency dispersion stands valid for f_(c)=0:27,while a completely different,neutral and competing electrical behavior is observed over the entire range of frequencies.The emerged third kind of Johnscher’s like UDR for fc is observed and the relaxation law has been formulated as the ratio of imaginary and real parts of dielectric constant remains constant over the entire range of frequency starting from dc to any higher frequency.The value of the constant is attributed to depend on the PMC,the dielectric constant of the polymer,the differences of conductivity and fractions of the components of the PMC and also on their connectivity arising due to the difference of their process conditions.The emerged unique dielectric relaxation consists of multiple relaxations arising due to the combination of other relaxations(arising due to the two different types of species)present in the sample,f_(con)=0:27.This novel material may be suitable for certain specific applications in electrical and electronics engineering.

Spectroscopic analysis and temperature-dependent dielectric properties of bulk Ni-Zn ceramics

In the present work,series of Zn ion-doped Ni_(1-x)Zn_(x)Fe_(2)O_(4)(0:0≤x≤0.5)ceramics were prepared by the double sintered solidstate reaction route to find out the influence of Zn2t ions on the crystal structure,lattice structure and dielectric behavior of parent NiFe_(2)O_(4).X-ray diffraction(XRD)study favors that all the prepared compounds belong to the cubic spinel structure.Lattice parameters found to have increasing value with increased Zn^(2+)ion substitution.The Raman scattering measurement discerns optical-active modes with blue shift as the doping increases.The dielectric constant(ε′)and dielectric tangent loss(tanδ)decrease with an increase in frequency and at higher frequency,both become constant.Dielectric parameters observe nonlinear behavior with increasing Zn^(2+)ion substitution.Room temperature dielectric constant of 10%Zn ion-doped NiFe_(2)O_(4)[Ni_(0.9)Zn_(0.1)Fe_(2)O_(4)]is much higher as compared to other prepared ceramics.The room temperature ac conductivity is found to increase with increase in frequency and temperature-dependent ac conductivity increases with increase in temperature.

Refractive index measurement of dielectric samples using highly focused radially polarized light(Invited Paper)

In this Letter, a refractive index measurement of a dielectric sample using highly focused radially polarized light is reported. Through imaging analysis of the optical field at the pupil plane of a high numerical aperture （NA） objective lens reflected by the sample under study, the Brewster angle is found. Employing a high NA objective lens allows the measurement of multiple angles of incidence from 0° to 64° in a single shot. The refractive index of the sample is estimated using the measured Brewster angle. The experimental results are compared with the theoretical images computed with the Fresnel theory, and a good agreement is obtained.

Measurement on Spot Size Dependence of Dense WDM Dielectric Multilayer Filters

We present the spot size dependence of dielectric multilayer filters for use in dense WDM systems. We found large dependences of filter performances on the spot size and the incident angle of input light, which should be important for miniaturizing multi-channel add/drop filters.

The Mobility of Threadedα-Cyclodextrins in PR Copolymer and Its Influences on Mechanical Properties

The methylated polyrotaxane （MePR） copolymer was prepared via the methylation of hydroxyl of threaded α-cyclodextrin （α-CDs） in polyrotaxane （PR） copolymer by CH3I/NaH. Its structure was characterized by GPC, IR and NMR. The WXRD and TGA measurements showed the destruction of channel-like crystalline structure in MePR copolymer. The sliding of threaded α-CDs along PEG axis in PR and MePR copolymers was demonstrated by their dielectric spectra that also evidenced the presence of rotating of threaded α-CDs around PEG axis in MePR eopolymer. The frequent and vigorous molecular mobility in MePR and PR copolymers was also verified by dynamic mechanical analysis （DMA） and rheological measurement, which was possibly assigned to the sliding and rotating of threaded α-CDs. DMA and rheological results showed that the mobility of α-CDs could simultaneously strengthen and toughen PR copolymer proved by stress-stain curves. In this paper, we report the CD mobility in PR and MePR copolymers. The macroscopic behaviors of PR copolymer, such as mechanical properties in solid state, were also found to be benefited from CD mobility.