LCR Bridge Research Articles

Laboratory measurement of dielectric constant and loss tangent of Indian rock samples

The data on dielectric properties of Indian rock samples are very sparsely reported in the literature. Keeping this in view, we have carried out laboratory measurements of the dielectric constant and loss tangents of some samples of sandstone, quartzite, limestone, marble, dolerite and basalt. LCR bridge and Q-meter have been employed for measurements in the frequency range 10 - 10' Hz. The results have been presented in the form of variation of these parameters with frequency which show characteristic features. Observations on the effect of moisture content of these samples on the dielectric properties have also been reported. Further, correlation of petrographic studies of rock samples with measured variations of dielectric properties has been attempted.

Static Dielectric Studies of Two Nematogenic Compounds

Static dielectric constants of two nematogenic compounds viz., (i) 1-hexyl-4-(4-isothiocyanatophenyl) bicyclo [222] octane and (ii) 4′-(pentyloxy)-4-biphenyl carbonitrile, have been measured at different temperatures using a sensitive LCR bridge. Using these data the dipole moment associated with the molecules is estimated. The validity of this approach is discussed by comparing the order parameter S obtained from the refractive index data with the values of S computed from the predications of the mean-field theories. Boardewijk's theory is applied here with appropriate molecular parameters, to compute dipole-dipole correlation factors.

Aplicación de un puente LCR en la caracterización de superficies de níquel tratadas voltamperométricamente en medio ácido en ausencia y presencia de ion cloruro

Impedance spectra for nickel electrodes at his corrosion potential after voltammetric treatment in acid media has been obtained. A LCR bridge has been used, controlling the applied potential by means of a potentiostat. The passive layer, generated after successive potential scans, has been characterized by means of the interfacial double layer capacitance and the faradaic impedance. The generalized corrosion, and also the localized attack, have been observed by means of scanning electron microscopy (SEM), whilst the scanning tunnelling microscopy (STM) has been used in order to realize the morphological analysis of the surfaces. In this way we want to correlate the morphological changes in the electrode surface after the successive scans in the acid media in absence and in presence of chloride with the impedance electrochemical response of the interface. When chloride is present in the acid media the charge transport across the interface is less impeded. The localized corrosion damages the passive layer electrogenerated after successive scans.

Microhardness and radiation damage studies of proton irradiated Kapton films

Kapton films were irradiated with a 3 MeV proton beam at different fluences. The microhardness, and electrical properties were studied using microhardness tester and LCR bridge, respectively. It is observed that hardness of the film increases significantly as fluence increases. The true bulk hardness of the film was obtained at loads greater than 400 mN . There is an exponential increase in the conductivity with frequency but effect of irradiation is not significant. The dielectric loss and dielectric constant are observed to change significantly due to irradiation.

Growth, properties and electrooptical applications of single crystal La3Ga5SiO14

The growth of single crystal La 3 Ga 5 SiO 14 (LGS) is briefly introduced. The transmission spectra show that the UV absorption edge is as low as 236 nm for the colorless LGS crystal sample. The dielectric constants, piezoelectric strain constants and elastic compliance constants are determined using LCR bridge, interferometric and resonance methods, respectively. The linear electrooptic coefficients γ 11 and γ 41 are measured to be 2.3 and 1.8 pm/V respectively by the interferometric method. A new kind of electrooptic Q-switch is designed by using the LGS crystal. The half-wave voltage of the Q-switch is 2250 V, and the single pulse output energy of 200 mJ is obtained with a pulse width of 9.4 ns. The damage threshold is about six times as large as that of a LiNbO 3 Q-switch under the same conditions.

A technique to investigate inhomogeneity in materials: An arrangement of microtip and scanning electron microscope

Amorphous and polycrystalline materials show different electrical properties when the contact area is in the submicron range. A large number of instruments (such as combinations of scanning electron microscope and scanning tunneling microscope) have been employed for such an investigation. A distinct disadvantage of these instruments is that they are rather expensive. In view of this, we have developed an instrumentation, which can be used to measure electrical behavior of any material in the submicron scale. This was achieved by installing a simple tip-holding arm in the scanning electron microscope; electrical meters (picoammeter and an LCR bridge) were used to investigate the behavior. We have studied amorphous carbon films grown in our laboratory, using this technique.

Electrical and optical response of lithium ion irradiated polyimide (kapton)

Optical and electrical response of polyimide (Kapton1) has been studied after irradiation with a 50 MeV7Li+3 ion beam. The ion fluences ranging from 1.28 × 1011 to 1.48 × 1014 ions cm−2 have been used for irradiation in order to study the fluence dependence of optical and electrical changes in polyimide. The optical response was studied using UV-Visible spectroscopy. The electrical a.c. frequency response was studied using a LCR bridge and the low voltage d.c. response was studied using a regulated d.c. power-supply and a nano-ampere meter. The irradiated samples clearly show a decrease in the absorption with increasing fluence. The increase in d.c. conductivity with increasing fluence; a significant change in a.c. response and a decrease in the magnitude of tan δ and a change in relaxation frequency have been observed due to the heavy ion irradiation.

50 MeV lithium ion beam irradiation effects in poly vinylidene fluoride (PVDF) polymer

Irradiation effects of 50 MeV7Li+3 ion beam induced in bulk PVDF polymer have been studied with respect to their optical, chemical, structural and electrical behaviour by using UV-visible, FT-IR spectroscopy, XRD technique and electrical frequency response using LCR bridge. The ion fluences ranging from 1.27 X 1011 to 2.15 X 1013 ions cm-2 have been used to study dose effects of irradiation in PVDF. The recorded UV-visible spectra clearly shows five characteristic peaks at 315, 325, 360, 425 and 600 nm. Due to irradiation, the optical absorption initially decreases but then increases with higher fluences. In the FT-IR spectra, no appreciable change has been observed after irradiation, indicating that this polymer is chemically stable. There is exponential increase in admittance with log of frequency but the effect of irradiation is not quite appreciable. The value of tan δ and relaxation frequency are changed appreciably due to irradiation. The diffraction pattern of PVDF indicates that this polymer is in semi-crystalline form; a decrease in the crystallinity and crystallite size has been observed due to irradiation

Study of Dielectric Anisotropy of an Ester/Biphenyl Mixture Exhibiting an Induced Smectic Phase

In this paper we present dielectric investigations of the binary mixtures of 4-n-pentyl 4′cyanobiphenyl (5CB) and 4-n-pentyl 4-n′ hexyloxy benzoate (ME60.5) at different compositions which show an induced smectic phase. Physical properties from different experimental observations have been reported earlier. We have undertaken this study to have information relating the macroscopic anisotropy and the molecular properties. Mixtures with different mole fractions of ME60.5 were prepared and their transition temperatures were observed under polarising microscope. Δϵ was measured using a digital LCR bridge at 10 kHz. A cell was constituted by means of two plane parallel tin oxide coated conducting glass plates separated by thin glass spacer. Sample was aligned by external magnetic field. Δϵ for smectic phase is found to be less than nematic phase. Results in detail will be discussed.

AC Conductivity of Amorphous CuInTe2 Thin Films

The ac conductivity of amorphous CuInTe 2 thin films was measured at various temperatures (66.7 to 99.8 K) and at various frequencies (100 Hz to 100 kHz) using ANDO AG2311 LCR bridge. The log-log plot of the normalized true ac conductivity σ R (ω)/σ(0) with reduced frequently ω/σ(0) exhibits two straight lines with slopes 2 and 0.76 at low and high frequency regions, respectively. This agrees fairly well with the predictions of the Extended Pair Approximation (EPA) model due to Summerfield and Butcher.

Preparation of barium/strontium titanate by solution route

Abstract As compared to the conventional solid-state route, solution routes have been reported to produce powders with better homogeneity and controlled morphology. A new solution-based method has been developed to produce fine powders of BaTiO3 and SrTiO3 of high reactivity. In this method an equimolar mixture of solutions of barium nitrate or strontium nitrate and titanium nitrate is heated with suitable amount of glycerol under controlled conditions to get a pasty mass, which was dried at 200†C and calcined at 500†C to get precursor powder, free from organic matter. On further heating the material transforms into single phase BaTiO3 or SrTiO3 having surface area of 6-8 m2/g. The pellets obtained by cold-pressing this powder, could be easily densified to 98% T.D. after sintering at 1250†C for a short duration. Phase analysis was done by X-ray diffraction. Thermogravimetry (TG) and Differential Thermal Analysis (DTA) experiments were done for the 200†C dried powder. The relative permittivity of the sintered BaTiO3 pellets was measured at different temperatures using an LCR bridge. The powder morphology and the particle size distribution were studied by scanning electron microscopy.

Bioimpedance spectroscopy and dielectric properties of biological tissues

Event Abstract Back to Event Bioimpedance spectroscopy and dielectric properties of biological tissues Igor Lackovic1* 1 University of Zagreb, Faculty of Electrical Engineering and Computing, Netherlands Aim: For accurate forward and inverse modelling in EEG and MEG head tissues dielectric properties are of utmost importance. The purpose of this presentation is: (i) to give an overview of impedance spectroscopy, a powerful method for characterizing dielectric properties and (ii) to present a survey of dielectric properties of various tissues. Methods: Biompedance spectroscopy, which is measurement of dielectric properties (electric conductivity and permittivity) as a function of frequency, requires special attention and careful calibration of measurement equipment. To interface the instrument (LCR bridge, impedance analyzer, network analyzer) to biological sample, various configurations of electrodes, impedance cells and open-end coaxial probes are used. When measuring dielectric properties at low frequencies (up to a few kHz) electrode polarization is the main problem since electric double layers that form at the electrode-electrolyte interface cause large capacitance which has to be corrected for. Electrochemical processes at electrodes are very complicated and depend on electrode material, state of electrode surface, current density, etc. On the other hand, biological tissue, as a measurement object, is very complex in terms of conduction/polarization mechanisms and is generally inhomogeneous (properties vary with space coordinates), anisotropic (properties are different for different directions of propagations), dispersive (properties depend on the frequency of the field) and nonlinear (properties depend on the intensity of the field). At low frequencies biological tissue is predominantly an electrolytic conductor since there are always free ions to migrate. At the same time, biological tissue, due to its complex structure, exhibits in the presence of electric field characteristics of dielectric materials such as polarization. Besides, tissue electrical properties are temperature dependent. Moreover, pathological processes (e.g. tumours) can alter tissue electrical properties. Additionally, as measurements cannot always be performed in vivo post-mortem tissue changes should also be considered. Results: Based on our experimental studies and literature data we illustrate all the above mentioned tissue characteristics (inhomogenity, anisotropy, dispersions, nonlinearity, post mortem changes etc.) and factors affecting accuracy of conductivity and permittivity measurements. We also present results from literature survey on various head tissue conductivities. Apart from results obtained by bioimpedance spectroscopy, which is the main focus of this presentation, we also cover recent magnetic resonance electrical impedance tomography (MR EIT) studies for imaging head tissues conductivity distribution. Conclusion: Results of this presentation may carry important information for EEG/MEG source imaging since accurate solution of EEG/MEG inverse problem depends on accurate values of head tissues conductivities. Conference: NeuroMath COST Action BM0601: Neurodynamic Insight into Functional Connectivity, Cognition, and Consciousness, Dubrovnik, Croatia, 27 Mar - 28 Mar, 2010. Presentation Type: Oral Presentation Topic: Talks Citation: Lackovic I (2010). Bioimpedance spectroscopy and dielectric properties of biological tissues. Front. Neurosci. Conference Abstract: NeuroMath COST Action BM0601: Neurodynamic Insight into Functional Connectivity, Cognition, and Consciousness. doi: 10.3389/conf.fnins.2010.05.00004 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 24 Jul 2010; Published Online: 24 Jul 2010. * Correspondence: Igor Lackovic, University of Zagreb, Faculty of Electrical Engineering and Computing, Atlanta, Netherlands, igor.lackovic@fer.hr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Igor Lackovic Google Igor Lackovic Google Scholar Igor Lackovic PubMed Igor Lackovic Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.