High Frequency Conductance Research Articles

High-frequency conductance measurement of the skin surface hydration state of dry skin using a new probe studded with needle-form electrodes (MT-8C).

When high-frequency conductance measurements are performed on dry scaly skin such as atopic xerosis, senile xerosis or psoriasis, the values recorded with a flat surfaced ordinary probe tend to be lower, indicating a reduced hydration state, than the actual one, because the rough and firm skin surface prevents close contact with the hard and flat surface of the applied probe. We evaluated the usefulness of an MT-8C probe (Measurement Technologies Cincinnati, USA), whose skin-attaching portion is studded with 8 needle-like electrodes instead of a flat surfaced type, for measurments on dry skin. The MT-8C probe yielded conductance values slightly higher than those recorded with the flat surfaced probe attached to Skicon in measuring the hydration state of moderately dry skin surface such as atopic xerosis and senile xerosis. It seems to be comparable or more sensitive than the capacitance recording with the Corneometer. The recorded values obtained with the MT-8C probe showed more variations than the latter because of its higher sensitivity and much smaller contact area, that makes it difficult to touch to the same spots repeatedly. No such a difference was observed on severely dry skin and thickly scaly psoriatic lesions.

Inclusion Compounds of Tetracyano Complexes and Their Electrical Properties

The presence of iodine and iodide ions in tetracyanonickelates inclusion compounds with the general formula Ni(B)mNi(CN)4 . n H2O (B = NH3 or ethylenediamine) changes the properties of these compounds. High frequency conductance measurements in the range of 10 - 105 Hz show that the products with ethylenediamine ligands have a higher electrical conductivity than those with NH3 ligands. The differences in the electrical properties between the compounds studied are mainly caused by chemical composition, structure and morphology.

High frequency properties and conductance of [formula omitted] microstructures

Fluctuations of the conductance, microwave photoconductance and photovoltage in mesoscopic GaAs AlGaAs heterostructures are studied. It is observed that their behaviour in a strong magnetic field (ω cτ ⪢ 1) is quite different for quasi two-dimensional and quasi one-dimensional devices.

Interactions of Electromagnetic Radiation with Electrolytes at High to Ultra-High Frequencies

Abstract At frequencies above one megahertz, the behaviour of electrolytic solutions changes from an ionic conductor to a lossy dielectric. High frequency conductance measurements of aqueous electrolytes (Na2SO4 and KCl) have been made by continuous wave and pulse admittance methods, in cells with immersed, shiny Pt electrodes to study this transition. Peak conductance frequencies as a function of concentration did not conform to the classical circuit representation of a resistance and capacitance. Measured phase angles indicate that relatively concentrated electrolytes (0.001 − 1 M) exhibit inductance due to electromagnetic and perhaps mass (inertial) effects. Modelling was possible with a constant value of the inductance, L, and capacitance, C, using a simple RLC equivalent circuit. Ion and solvent perturbations in high frequency electrical fields first are discussed in terms of a damped harmonic oscillator model, whose macroscopic response is self-consistent and equivalent mathematically to RLC network...

Some Aspects of the High Frequency Conductance of Electrolytes

The high frequency conductances (0.5‐25 MHz) of three binary electrolytes , , and have been measured in aqueous solution by a commercial network analyzer. The cell used for the experiments is a capacitive cell, or so‐called condenser‐type cell. A theoretical circuit model, which incorporates the Debye‐Falkenhagen dispersion in a rigorous manner, has been developed for this type of cell and low field conditions. A maximum conductance at a specific high frequency has been observed at a certain concentration for each electrolyte due to the bulk circuit elements interaction and an expression has been derived that enables comparison of the experimental data with numerical solutions. The calculations, based on the classical interpretation of ionic conductance, are in satisfactory agreement with experimental results for the lower concentrations only. Some aspects of the high frequency conductance in capacitive cells, such as the role of the Debye‐Falkenhagen effect which has been ignored or misrepresented previously, are clarified in this paper.

The preparation of tetracyanonickelates showing electrical conductivity

The tetracyanonickelates Ni(NH3)2Ni(CN)4·1.9 H2O (1), Ni(NH3)1.65(C4H8O2)0.2Ni(CN)4·0.8 C4H8O2·0.35 H2O (2) and Ni(en)3Ni(CN)4·H2O (3) exhibit, after contact with a solution of iodine (I2/KI), appreciable weight gains. According to thermal analysis, IR spectra and chemical analysis the new products contain intercalated iodine and iodides with the highest iodine content found in the product formed from (3). The results of high frequency conductance measurements of this product showed the highest value of electrical conductivity σ (10−6 S cm−1). Other compounds show relatively low values of σ (10−8–10−11 S cm−1).

Electrical Determination of Water Content and Concentration Profile in a Simulation Model of In Vivo Stratum Corneum

Because of its efficient water-holding capacity, healthy stratum corneum (SC) can stay soft and flexible under any environmental conditions. There may be, however, a great difference in water content within the SC between the lowermost layer that faces the wet underlying living tissue and the superficial portion of the SC that is exposed to the relatively dry ambient atmosphere. To better understand the water profile of the SC and also to verify the accuracy of measurements of high frequency conductance used to evaluate the hydration state of the skin surface, we devised a simple and convenient in vitro model of the SC that stimulates the in vivo setting of the SC. It consists of an isolated sheet of SC whose lower surface covers a pad of water-saturated filter paper, and its upper surface is exposed to the ambient atmosphere. By placing this model in environments with different relative humidities (RH), we confirmed that the recorded conductance values correlated well with the actual water content of the SC (r = 0.94). Using a model having five layers of SC sheets, the water content of the innermost portion of the SC was estimated to be equivalent to about 90% of its dry weight; this level of water content remaining relatively constant over a wide range of ambient RH except in extraordinarily humid environments above 90% RH when water began to accumulate excessively in the whole SC. Using this five SC-sheet model, it was clearly demonstrated that there was an almost straight water concentration gradient from the lowermost layer to the uppermost layer of the SC. We also confirmed that the skin conductance of the high frequency current correlated well with the water content of the superficial portion of the SC as well as with that of the whole SC, therefore, it is a good parameter of the hydration state of the superficial layer of the SC.

Standing charge density waves driven by electron drift in patterned (Al, Ga)As/GaAs heterostructures

We have experimentally investigated the effect of electron drift on the plasma resonance of the 2-dimensional, (2-D), electron gas in submicron patterned (Al, Ga)As/GaAs heterostructures. Metal gratings were deposited on the surface of modulation doped heterostructures, and alloyed into the structure providing periodic “ohmic” contacts to the 2-D electron gas. 2-D plasma resonances were measured by sub-milimeter wave transmission spectroscopy from 300 to 3000 GHz. The effect of electron drift was detected by measuring the change in high frequency conductance caused by pulsed currents applied perpendicular to the grating lines. The drifting electrons caused the plasmon to either split or change frequency. The changes are an order of magnitude larger than expected from a model based on a cold classical plasma drifting under the grating. Alternatively, a standing charge density wave, induced by the current flow, can lead to either a splitting or frequency shift as seen experimentally.

High frequency titrimetry

High frequency titrations have been carried out with a crystalcontrolled oscillator at 5 Mc. A measure of the change in the high frequency conductance during a titration is obtained by determining the grid bias at resonant frequency with a vacuum tube voltmeter after each addition of titrating solution. The following monovalent phenols have been examined: phenol,o-, m- andp-cresol,α- andβ-naphthol and 2-retenol. Of the di- and trivalent phenols we have titrated pyrocatechol, resorcinol, hydroquinone, pyrogallol and phloroglucinol. The compounds (0.5–5 mg) have generally been dissolved in benzene-methanol 2∶1 and they have been titrated with potassium methoxide in benzene-methanol 10∶1. Each hydroxyl group in a molecule gives rise to a break in the titration curve. A number of mixtures of monovalent phenols have also been titrated. Each component in the mixture causes a break in the titration curve. This means that the component with the highest dissociation constant is first titrated, and then the others in order of decreasing dissociation constant.

High Frequency Conductance of Pyrex Glass in the Presence of Vapors

The electrical conductance of ``Pyrex'' brand glass 774 was measured at frequencies between 40 kc and 1000 kc in the presence of ethyl alcohol vapor and water vapor. Data were taken at 50°, 65°, 79° and 107°C. The relations between conductance, degree of saturation, and frequency were found to be of the same form at all temperatures. There is a distinct discontinuity in the curves of conductance vs. frequency at about 500 kc. Vapor pressures of alcohol up to 85 percent of saturation cause no change in the conductance of the test piece. However, above this degree of saturation the conductance increases rapidly with pressure, becoming very high if condensation occurs. Conductance decreased with increasing current unless the test element was aged in the vapor several hours. Surface conductivities for both alcohol and water vapor are computed. Those for water vapor agree, well within the limits of error, with the results found by Yager and Morgan. An unexplained resonance effect occurred when high currents were used to measure the conductance while the test element was in the presence of small amounts of either alcohol or water vapor. The effect shows the double resonance peak and many of the other characteristics of close coupling between oscillating circuits. However, the effect is in some way due to the energy absorbed in the test element in the presence of a minute amount of water or alcohol since either an increase or decrease of pressure will cause the disappearance of the phenomenon. It was impossible to produce the effect by the substitution of any combination of capacity and artificial leak.