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Purpose -The paper aims to study the variation of electrical properties like electrical resistivity and current noise of a polymer thick film resistor, namely, PVC-graphite thick film resistor, with parameters such as volume fraction, grain size, temperature and high voltage. Design/methodology/approach -A model is proposed to explain the observed variations, which assumes that the texture of the polymer thick film resistor consists of insulator granules coated with conducting particles and also having cavities. The resistivity of these resistors is controlled mainly by the contact resistance between the conducting particles and the number of contacts each particle with its neighbors. Findings -The variation of resistivity with temperature and high voltage is explained with the help of the model and it is attributed to the change in contact area and number of contacts. The current noise of these resistors is controlled mainly by the average relative resistance fluctuations between the conducting particles and the number of contacts each particle with its neighbors. Originality/value -The variation of current noise with high voltage has also been explained with the help of this model and it is attributed to the change in number of conducting particles and conducting layers.

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Rao et al.: Characterization and Ex Vivo studies of ItraconazoleItraconazole, an antifungal drug possess poor solubility, gastrointestinal irritation and first pass effect. Hence in the present work it was initially made as nanoparticles to facilitate absorption and at later stage nanoparticles loaded transdermal patches were developed using promising nanoparticles. Nanoparticles were prepared with Eudragit RL 100 by solvent displacement technique. Formulations F1 to F9 were prepared by using different concentrations of Eudragit RL 100 and polyvinyl alcohol and evaluated for drug content, drug release, entrapment efficiency and mean particle size. The selected formulation was lyophilized to incorporate these formed nanoparticles into transdermal patch by varying concentrations of hydroxy propyl methyl cellulose K100M, polyvinyl alcohol and polyethylene glycol 400. The obtained patches were evaluated for thickness, tensile strength, folding endurance, moisture absorption and moisture content and the drug release showed biphasic release. All the formulations followed first order kinetics, diffusion controlled and fickian release. Flux (ex vivo) studies on rat skin of optimized formulation have high flux of 63.24 µg/cm 2 /h compared with pure drug, prepared itraconazole ointment 39.15 µg/ cm 2 /h and prepared itraconazole gel 40.01 µg/cm 2 /h. The permeability of itraconazole nanoparticle loaded transdermal patch showed 2.63 folds enhancement compared to pure drug. Scanning electron microscopes clearly showed the drug loaded nanoparticle embedment in polymeric transdermal patch. Formulated nanoparticle loaded itraconazole transdermal patch can be successfully used as a carrier for enhancing transdermal permeation and the bioavailability.

Purpose -The purpose of this paper is to study the variation of the temperature coefficient of resistance (TCR) of polymer thick film resistors, namely, PVC-graphite thick film resistors, with parameters such as volume fraction, grain size, and high voltage. Design/methodology/approach -A model is proposed to explain the observed variations, which assumes that the texture of the thick film resistors consists of insulator granules coated with conducting particles. Findings -The paper finds that the TCR of these materials is controlled mainly by the contact resistance fluctuations between the conducting particles and the number of contacts each particle has with it neighbours. The variation of TCR with high voltage has also been explained with the help of this model and it is attributed to the changes in contact area and the number of contacts. Originality/value -The value of the paper is in showing that apparently the TCR of polymer thick film resistors can be controlled by the expansion properties of the insulating medium. The variation of TCR with high voltage is also due to change in number of contacts between the conducting particles. These types of material may find applications in thermal sensors or as temperature control elements.

The purpose of this paper is to study high voltage interactions in polymer thick film resistors, namely, polyvinyl chloride- (PVC-) graphite thick film resistors, and their applications in universal trimming of these resistors. High voltages in the form of impulses for various pulse durations and with different amplitudes have been applied to polymer thick film resistors and we observed the variation of resistance of these resistors with high voltages. It has been found that the resistance of polymer thick film resistors decreases in the case of higher resistivity materials and the resistance of polymer thick film resistor increases in the case of lower resistivity materials when high voltage impulses are applied to them. It has been also found that multiple high voltage pulse (MHVP) stressing can be used to trim the polymer thick film resistors either upwards or downwards.

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This paper deals with the investigations carried out on the variation of current noise (1/f noise) in polymer thick film resistors, when they are subjected to pulse voltage trimming. The current noise is measured in terms of noise index (micro volts of noise per volt of DC applied, in a decade of frequency) using Noise Meter Model 315 C manufactured by Quan‐Tech of New Jersey. It has been found that current noise decreases as the resistors are trimmed to lower values. An attempt has been made to explain the decrease in current noise with the trimming of resistors.