Modeling the Barium–strontium-titanate-based Electrolyte Conductivity Sensor Impedance Parameters for a Four-electrode Configuration
Electronics
Abstract
A contactless electrolyte conductivity (EC) sensor with Pt interdigitated electrodes for the two-electrode configuration is developed and examined. As a covering insulating material (protective layer) on Pt metallic electrodes in the EC sensor, (Ba,Sr)TiO3 nano-films were used. For the fabrication of (Ba,Sr)TiO3 - based ceramic targets, in contrast to well-known traditional methods, a new cost effective method has been used: the High-Temperature SelfPropagating Synthesis (SHS) method and (Ba,Sr)TiO3 thin membranes as a covering insulator layer are fabricated by the PLD (pulsed laser deposition) method. The sensors were characterized by means of impedance-spectroscopy measurements in different commercially available electrolyte-conductivity standard solutions, ranging from 0.084 to 50 mS/cm and over the frequency range from 1 to 3 MHz. The theoretical simulations show that impedance becomes frequency independent for the experimentally measured different conductivity values when Cdl varies in the range of (200000 ¸ 15000) pF, Cf varies in the range of (4678.62 ¸ 7478.99)pF, and Ccel varies in the range of (2808.31 ¸ 3000) pF. This indicated that the double layer capacitance decreased with the increase in the solution conductivity, as well as at the same time the ferroelectric protective layer capacitance increased and Ccel decreased with the increase in the solution conductivity. The theoretically calculated parameters of equivalent circuits are compared with the experimental results and obtained good agreement.
