Cure Control: Strategies for Using Dielectric Sensors

Abstract

Dielectric measurements are becoming increasingly important as a means for feedback control in the area of polymer processing. The changes in dielectric response as a function of changing molecular weight or cross link density have been the subject of much research for the last 50 years [1]. Only now is process control through dielectric feedback becoming a reality due to recent advances in dielectric measurement capability [2]. Microdielectric sensors are now available which function down to frequencies characteristic of mechanical measurements (less than 1Hz) and can be inserted directly into curing composite structures. By monitoring the dielectric properties (permittivity and loss factor) at several frequencies, the ionic conductivity can be extracted [3] with the aid of commercial software packages in real time. This paper investigates the use of first and second derivative information (log ionic conductivity with respect to time) for controlling certain key processin-ing steps during composite curing.