Loss Tangent Measurements Research Articles

Dielectric Properties of the Human Red Blood Cell

The dielectric properties of the erythrocyte were studied. Experimental methods and results of measuring the dielectric properties of individual human erythrocyte are presented. The method is theoretically justified. It is found that values of the complex permittivity of the erythrocyte, electrical capacitance, dielectric loss tangent remain almost constant despite significant changes in conductivity and the content of NaCl in the cell suspension. These values reflect the stability of the studied parameters of erythrocytes under conditions of changes within a wide range of the environment in which the cells are located. Complex cell permittivity and cell dielectric loss tangent are promising parameters for objective diagnostics of human diseases. The introduction of measurements of cell permittivity and cell dielectric loss tangent into medical practice will likely allow us to characterize the process of individual cell self-regulation in more detail.

Sub-Terahertz Complex Permittivity Measurement Method Using Cavity Switches

New method of measurement of dielectric constant and loss tangent for small samples of lossy dielectrics, including plain semiconductors, using non-oversized resonators being parts of the recently developed cavity switches for sub-terahertz bands is proposed. Strong influence of the tangent loss value to the Q-factor of the resonator is calculated and observed in experiments. A simple monosemantic algorithm to retrieve explicit mathematical expressions for the complex permittivity from the experimental data is demonstrated. The advantage of the new method over the known ones is much lower (up to million times) volume of the sample needed to analyze.

Compositional variations along the route of Chang\u2019e-3 Yutu rover revealed by the lunar penetrating radar

Using the high-frequency lunar penetrating radar data obtained by the Chang’e-3 mission, we apply the frequency-shift method to calculate the decay rate of the electromagnetic wave in the regolith-like ejecta deposits of the Ziwei crater. The radar data are divided into segments according to the navigation points along the traverse route of the Yutu rover. For each segment, we calculate the bulk loss tangent of materials within the top ~ 50 ns of the radar data based on the frequency decreasing rate of the electromagnetic wave. The loss tangent varies from ~ 0.011–0.017 along the route of Yutu, and it is within the range of the measured loss tangent of Apollo regolith samples. Using the empirical relationship between loss tangent and TiO2 + FeO content derived from the Apollo lunar samples, we estimate the TiO2 + FeO content for the bulk regolith along the route of Yutu, which is ~ 23–30 wt.%. This value is comparable with that estimated using both orbital reflectance spectral data and in situ observation made by the Yutu rover. The loss tangent derived along the route of Yutu is larger than the average value of returned lunar samples, which is mainly caused by the larger content of TiO2 + FeO at the landing site compared to the global average. Variations of the TiO2 + FeO content along the route of Yutu are mainly due to the excavation of the Ziwei crater. The TiO2 + FeO content map derived by the radar has a much higher spatial resolution compared to orbital observation, testifying the feasibility of this technique for regional geology study.

Towards large area CVD diamond disks for Brewster-angle windows

Abstract In the frame of the EUROfusion Work Package Heating and Current Drive (WP HCD) of the Power Plant Physics and Technology (PPPT) program, CVD diamond disk Brewster-angle windows for gyrotron operation at multi-megawatt RF power levels and long pulses are under development. These windows allow for frequency step-tuneable operation. The Brewster-angle of 67.2° for diamond leads to an elliptical connection of the disk to the copper waveguides (WGs), requiring an advanced joining process. For proper transmission of the RF power, the disk consists of low loss CVD diamond of optical grade. The current target for the WG aperture of DEMO is 63.5 mm. It allows for an RF power transmission of 2 MW, but it requires a disk diameter of 180 mm for the 67.2° angle. In addition, a thickness of approximately 2 mm is needed to achieve the proper mechanical stability. State of the art microwave plasma reactors are not capable of growing disks of such size. The maximum available diameter of a polycrystalline CVD diamond disk suited to microwave applications is currently 140 mm. Thus, the industrial partner Diamond Materials GmbH (Freiburg, Germany) is doing extensive diamond growth experiments. A first of its kind, 180 mm thermal grade, crack-free, diamond disk was produced in the microwave plasma reactor with an average unpolished thickness of about 2 mm. First loss tangent measurements have been also performed. This paper describes the steps and the first results of this non-straightforward path, a challenging new field for diamond manufacturers and a major breakthrough for future frequency step-tuneable operation.

Improvements in gelatin cold water solubility after electrospinning and associated physicochemical, functional and rheological properties

A major limitation of gelatin feedstocks for industrial food and pharmaceutical applications is the lack of solubility at room temperature, necessitating use of drum/dry blending processes, combined with additives. Herein, electrospinning is investigated as an alternative route for producing cold water soluble 100% gelatin feedstock in place of powders. The physicochemical, rheological and functional properties of electrospun gelatin and an industrially available gelatin powder feedstocks were compared. Optimal conditions for producing gelatin nanofiber sheets were found to be 25% (w/v) polymer concentration in a binary solvent system of acetic acid: water (3:1 v/v), a spinning voltage of 25 kV, a flow rate of 0.5 ml/h and a tip-to-collector distance of 150 mm. The production of nanofibers from gelatin powder did not change the nature of the material. The glass transition temperature of gelatin nanofibers was lower than gelatin powder. Conversion of gelatin powder into nanofiber sheets also increased the dissolution rate in water at ambient temperature and promoted emulsion and foam forming ability, as well as increasing foam stability. Loss tangent measurements revealed that the gel formed by the gelatin nanofibers could be characterized as a weak gel. No difference was observed in the Young's modulus of samples made from gelatin nanofibers and powder, and the 0.2% (w/v) gelatin nanofiber sample yielded a higher viscosity than the 0.1% (w/v) concentration. Gelatin nanofibers have promising potential to be used as feedstock in food technology when cold water solubility and improved control of physical, functional and textural properties are required.

Dielectric properties of the human red blood cell

The dielectric properties of the erythrocyte were studied. Experimental methods and results of measuring the dielectric properties of individual human erythrocyte are presented. The method is theoretically justified. It is established that values of the complex permittivity of the erythrocyte, capacitance, tangent of dielectric losses remains almost constant despite significant changes in conductivity, the content of NaCl of the cell suspension. These values reflect the stability of the studied parameters of erythrocytes under conditions of changes within a wide range of the environment in which the cells are located. Complex cell permittivity and cell dielectric loss tangent are promising parameters for objective diagnostics of human diseases. The introduction of measurements of cell permittivity and cell dielectric loss tangent into medical practice will probably allow us to characterize the process of individual cell self-regulation in more detail.

Monitoring structural variation on Gd ratio of La modified bismuth ferrite ceramics with enhanced magnetization

Critical structural variation and dielectric properties were investigated in Lanthanum and Gadolinium co-substituted bismuth ferrite (Bi0.9La0.1Fe1-xGdxO3 (x = 0.01, 0.03, 0.05, 0.07, 0.1, and 0.15). Conventional solid state reaction technique was used to synthesize ceramic samples. To investigate the influence of co-substitution on the phase formation and crystal structure, X-ray diffraction method (XRD), Scanning electron microscopy (SEM) and Raman spectroscopy were utilized. Probing the structural properties by changing Gd ratio was carried out to ensure single phase of rhombohedral R3c structure. Hence, the exploration of dielectric properties of single phase modified BiFeO3 (BFO) ceramic was executed by room temperature capacitance and loss tangent measurements. It was found that by substitution of 10 mol% La for Bi and up to 5 mol% Gd for Bi, perovskite structure of rhombohedral symmetry and R3c space group were formed. This possessed enhanced magnetization and reduced dielectric loss compared to pure BFO.

Precision measurement of relative permittivity of aluminum oxide for a high power resonant waveguide window with low return loss

An iterative method of estimating permittivity and window thickness with high precision is developed for half wavelength resonant waveguide windows for use in a lower hybrid launcher for DIII-D. The high Q factor of half-wavelength windows results in extreme sensitivity of return loss on small deviations in permittivity. Permittivity and loss tangent measurements of Morgan AL-995 99.5% aluminum oxide ceramic using a waveguide resonant cavity per ASTM D2520-13 determine variation of permittivity with frequency. Measurement of window resonant frequency in conjunction with the slope of permittivity from waveguide cavity measurements determine required thickness of a resonant window within 5 MHz of the desired resonant frequency. Methods to improve measurement accuracy of resonant peaks on a vector network analyzer are discussed. A sensitivity study to dimensional variations in window or sample rod geometry, and shift in resonant frequency due to RF heating of the window material is conducted.

Effect of Cobalt Dopant on the Structural, Magnetic and Dielectric Properties of Fe3O4 Nanoparticles Prepared by Co-precipitation Method

Co-doped magnetite powders were successfully synthesized by the co-precipitation method. Structural, morphological, magnetic and electrical properties were investigated using x-ray diffraction (XRD), Fourier transform infrared (FT-IR), transmission electron microscopy (TEM), a vibrating sample magnetometer (VSM), ac conductivity and dielectric measurements. X-ray diffraction demonstrated that all the synthesized samples are cubic spinel structure with a space group of Fd3 m. Structural parameters such as crystallite size and lattice constant were calculated. FTIR analysis showed the two characteristic ferrite bands around 590 cm−1 and 405 cm−1 which are attributed to the stretching frequency of the tetrahedral and octahedral sites. TEM showed nearly homogeneous spherical shape particles with some irregularity in shape. VSM measurements of the powder exhibited ferromagnetic characteristics. The doping with Co2+ increases the coercivity (Hc) and remanance magnetization (Mr). The ac conductivity, dielectric constant and loss tangent measurements as a function of frequency and temperature show composition dependence.

Synthesis, structural, dielectric and domain properties of Al-doped KNbO3 single crystal

Single-crystal samples of Al-doped potassium niobate (KNbO3) [KN] were synthesized by a high-temperature flux technique. X-ray diffraction analysis of the crystal suggests that a single phase with an orthorhombic structure was formed. The dielectric studies of the KN single crystal as a function of temperature (from 30 to 500 °C) show that the compounds underwent a phase transition, which was confirmed by thermal analysis of the DTA curve. The measured loss tangent of the crystal, which is in good agreement with the dielectric studies. The ferroelectric property of the crystal was confirmed by studying the hysteresis loop. In this study, several parameters, like the coercive field and spontaneous polarization, were measured and calculated. The domain study was carried out using a trinocular microscope, which reported the formation of the 60° domain line and dislocation etch pits. The effects of the electric field on the domain of the Al-doped KN single crystal were discussed.

Water vapor permeable polyurethane films based on the hyperbranched aminoethers of boric acid.

The hyperbranched polymers have drawn intensive attention in the design of macromolecules and functional materials because of their unique physical and chemical properties resulting from the branched architecture and the high number of functional groups. In the present study, by means of light scattering, viscosimetry, thermomechanical analysis, tensile stress–strain, mechanical loss tangent and water vapor permeability measurements, we demonstrate the hierarchical macromolecular organization of organoboron polyurethanes synthesized using sterically hindered amino ethers (AEBA) of boric acid. It is shown that the water vapor permeability of polyurethanes obtained on the basis of sterically hindered aminoethers of boric acid is due to the peculiarities of the chemical structure of AEBA, which can exhibit an ionomeric nature and the presence of steric hindrances created in the hyperbranched structure of AEBA, which can lead to an increase in free volume in such polyurethanes.

Photosensitive Glass-Ceramics for Heterogeneous Integration

The push for heterogeneous integration requires very unique material properties with respect to processing, material constants, and integration capabilities with other materials (such as copper, II...

NEW WAVEGUIDE METHOD FOR DIELECTRIC PARAMETER MEASUREMENT

Perfect knowledge of dielectric parameters is necessary for its application in various devices. In spite of the whole range of measurement techniques, their practical implementation in the microwave frequency band runs into some difficulties. This article describes a new method for nonmagnetic dielectrics permittivity and loss tangent measurement in the microwave frequency band. A dielectric specimen slab is placed in the short-circuited waveguide section normal to its axis and fills the whole cross-section of the waveguide at approximately quarter wavelength from its short-circuited endpoint. By means of the vector network analyzer the waveguide section reflection factor is measured. Objective function is de-termined as difference between calculated and measured module and phase of the reflection factor. Specific code for ob-jective function calculation and its minimization is worked out. Minimization of this function by varying dielectric parameters makes it possible to find real values of these parameters. The method needs no de-embedding and can be used with non-calibrated waveguide-to-coax transitions. Also it is less sensitive to the noise component of reflected signal. The testing results show that new method’s error does not exceed 0.2 % for relative permittivity and 1% for dielectric loss tangent.

Electric Properties Measurement of Lentil

Abstract This paper contains the results of the electric properties measurement of lentil set. Electric measurements with use of these materials are of fundamental importance in relation to the analysis of quantity of absorbed water and dielectric heating characteristics. The aim of this paper was to perform the measurements of conductivity, dielectric constant and loss tangent on samples of lentil, the electrical properties of which had not been sufficiently measured. Measurements were performed under various moisture contents, and the frequency of electric field ranged from 1 MHz to 16 MHz, using a Q meter with coaxial probe. It was concluded that conductivity, relative permittivity and loss tangent increased with an increase in moisture content, and dielectric constant and loss tangent decreased as the frequency of electric field increased.

Synthesis and characterization of a potential bio-based dielectric fluid from neem oil seed

Vegetable oil with high percentage unsaturated fatty acid content are unstable to oxidation at elevated temperatures. However, epoxidation is an effective chemical reaction for chemical structural modification of such oil to eliminate unsaturated carbon–carbon double bond which is responsible for the instability of the oil. In this research, laboratory purified neem oil was epoxidized in situ in the presence of an acidic catalyst and the product was further transesterified. The purified (PNO), epoxidized (ENO) and transesterified (ENOE) oil samples produced were characterized by FTIR, Viscosity measurement using Brookfield Digital Viscometer, relative permittivity, loss tangent and ac conductivity measurements were made using a coaxial probe placed in a thermostatically controlled heat chamber and a frequency analyzer at varying frequency and temperature in the range 20 Hz to 20 kHz and 20 °C to 70 °C respectively. All three samples show Arrhenius type behavior for viscosity and ac conductivity. ENOE sample had least viscosity of 0.0254 Pa s at 40 °C. Both PNO and ENO had a.c conductivity of the order 10−10 S/m at 20 °C and power frequency and loss tangent of 0.0082 and 0.0191 respectively. The oil samples possess low loss in the temperature and frequency ranges considered and are suggested to be suitable candidate for potential natural ester insulating fluid in High Voltage equipment.

Microwave Permittivity of Trace sp2 Carbon Impurities in Sub-Micron Diamond Powders.

Microwave dielectric loss tangent measurements are demonstrated as a method for quantifying trace sp2-hybridized carbon impurities in sub-micron diamond powders. Appropriate test samples are prepared by vacuum annealing at temperatures from 600 to 1200 °C to vary the sp2/sp3 carbon ratio through partial surface graphitization. Microwave permittivity measurements are compared with those obtained using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron energy loss spectroscopy (EELS). The average particle size remains constant (verified by scanning electron microscopy) to decouple any geometric dielectric effects from the microwave measurements. After annealing, a small increase in sp2 carbon was identified from the XPS C 1s and Auger spectra, the EELS σ* peak in the C 1s spectra, and the D and G bands in Raman spectroscopy, although a quantifiable diamond to G-band peak ratio was unobtainable. Surface hydrogenation was also evidenced in the Raman and XPS O 1s data. Microwave cavity perturbation measurements show that the dielectric loss tangent increases with increasing sp2 bonding, with the most pertinent finding being that these values correlate with other measurements and that trace concentrations of sp2 carbon as small as 5% can be detected.

Variable Temperature Broadband Microwave and Millimeter-Wave Characterization of Electrochromic (WO3/LiNbO3/NiO) Thin Films

This paper reports for the first time, the dielectric characterization of a new, electronically tuneable electrochromic (EC) thin-film material over the frequency range 1–67 GHz, at temperatures of 7 °C, 23 °C, and 50 °C. Test cells composed of a microstrip line terminated with coplanar waveguide (CPW) transitions were fabricated to facilitate on-wafer RF measurements and the application of different bias voltages using a standard CPW probe station. A precise curve-fitting technique based on full-wave simulations was used to extract the permittivity and loss tangent values of the material. The validity of the dielectric extraction technique was first demonstrated by employing a known material, silicon dioxide (SiO2). It is shown that the dielectric tunability of the EC material varies between 11.3% (1 GHz) and 7.5% (67 GHz) at 23 °C, and the measured loss tangent varies between 0.012 (OFF, 0 V, state) and 0.025 (ON, 6 V, state). Above room temperature, the devices exhibit higher values of dynamic tunability and a small increase in insertion loss. The results obtained for this first generation of tuneable EC material are encouraging, and many of the dielectric properties are shown to compare favourably with other, more mature bulk tuneable media, such as liquid crystals.

An approach to widen the electromagnetic shielding efficiency in PDMS/ferrous ferric oxide decorated RGO–SWCNH composite through pressure induced tunability

In the present era, the advanced technology demands for the fabrication of light weight and compressible high performance electromagnetic interference (EMI) shielding materials for adaptable shielding application in the area of modern electronic gadgets and telecommunication devices. This study highlights facile fabrication of such lightweight compressible porous polydimethylsiloxane (PDMS)/FRS [Ferrous ferric oxide (Fe3O4) decorated reduced graphene oxide (RGO)/single wall carbon nanohorn (SWCNH)] composite for tunable EMI shielding applications. The Fe powder used to reduce GO, was decorated on the SWCNH and RGO as Fe3O4 during the in situ reaction. FRS dispersed PDMS was allowed to soak and cured in a sugar cube, followed by leaching out of the sugar to obtain highly porous network structure with lightweight and compressible PDMS/FRS composite. The composite possessed an absorption-dominated good comprehensive EMI shielding performance, possibly due to both conductive dissipation and multiple reflections and scattering of EM waves by the inside 3D conductive RGO-SWCNH network with ferromagnetic Fe3O4 nanoparticles. The measurement of attenuation constant and loss tangent describe the absorption property of the composite. The shielding performance of the composite could be simply adjusted owing to its’ pressure induced compressible property, applicable as smart tunable EMI shielding material.

Dielectric and magnetic properties of CoFe2O4 prepared by sol-gel auto-combustion method

Cobalt ferrite powders were successfully synthesized by sol-gel auto-combustion method. Influence of sintering temperature on structural, magnetic and dielectric properties was studied. All the obtained samples are spinel ferrite with a cubic symmetry. As the sintering temperature increased from 900°C to 1300°C, the average grain size increased from 0.26μm to 0.83μm. The dielectric constant and loss tangent measurement showed strong temperature dependence at all frequencies. The maximum magnetization increased while the coercivity and remanent magnetization decreased with the increasing sintering temperature. The non-saturation at high fields may be related to the surface effects in CoFe2O4 samples. When sintered at 1300°C, the sample showed a maximum magnetization value of ∼87.32 emu/g at room temperature. The highest value of coercivity of all the samples was 1368.33Oe for the sample sintered at 900°C.

Dielectric properties of (Sr0.7Pb0.3)TiO3 ceramics with relaxor-like character

ABSTRACTDielectric properties of (Sr0.7Pb0.3)TiO3 ceramics were investigated up to 100 kHz down to −260 °C along with temperature dependent thermal strain, X-ray diffraction peaks, and hysteresis loops. The (Sr0.7Pb0.3)TiO3 ceramic showed almost frequency independent relative dielectric permittivity, the Curie point at 10 °C from the cubic to the tetragonal, and dielectric maxima with the second-order phase transition, more than 30000. The Curie-Weiss behavior showed deviation near the Curie point owing to microscopic polarization similarly observed in relaxor ferroelectrics. Loss tangent measurements showed low values in the paraelectric phase, less than 0.0005, and three anomalies in the ferroelectric phase.