||In injection molding, a key polymer processing technique, the requirements of product quality have been significantly increased in the past decade. The product quality highly depends on the processing condition, and this directs to the development of a capacitive transducer (CT) for process monitoring. Cooling time, which takes up most of the injection cycle time, has critical effects on the quality and productivity of products. Insufficient cooling time leads to inconsistent moldings, while excessive one increases the cost of process. A specifically designed capacitive transducer, which can be described by a basic parallel plate capacitor, was embedded into the mold for monitoring the polymer status inside the mold cavity. The CT output shows a specific pattern during the cooling stage, providing a possible mean for solidification rate monitoring. The characteristic signal pattern can be divided into three phases: (i) solidification without shrinkage, (ii) solidification with shrinkage and (iii) core solidification. By applying the process principles to model the solidification process of polymer, the methods for estimating the solidification rate and the degree of product shrinkage are well analyzed. The results quantitatively monitor the rates of solidification and shrinkage. Also, the end of solidification is detected, such that further control schemes to optimize the cooling time can be achieved. The capacitive transducer is novel concept for product quality monitoring, and model calculations to estimate the solidification is simple and robust.