AN ELECTRONIC OSCILLATOR WITH AUTOMATIC GAIN-CONTROL - EQCM APPLICATIONS

An electronic oscillator for use with thickness-shear-mode acoustic wa ve sensors is described. The oscillator monitors not only the resonanc e frequency of the sensor, but also provides an automatic gain control signal that monitors the energy dissipated by the sensor. Electrochem ical quartz-crystal microbalance (EQCM) experiments have been performe d in which one of the sensor's electrodes serves as the working electr ode in an electrochemical cell. Electrochemical deposition of Tl+ on t he sensor's surface results in a frequency shift that is attributed to mass loading, while a negligible amount of energy loss from the senso r is observed. Results from the cyclic voltammetry of the K3Fe(CN)(6)/ K4Fe(CN)(6) couple, which does not alter the mass on the sensor, indic ate that the energy loss from the sensor can be directly monitored by the automatic gain control voltage and is related to the microviscosit y of the solution adjacent to the sensor. The addition of automatic ga in control to an oscillator circuit provides energy-loss information t hat is usually only given by impedance analyzers. The circuit is appli cable to situations where remote sensing or cost are important factors .