Meaning
Dimensionless ratios measure the energy conversion efficiency of piezoelectric materials. In sensor design for mould cavity monitoring, the electromechanical coupling factor k11 defines the efficiency of conversion between electrical energy and longitudinal mechanical deformation. Higher values of this factor yield stronger acoustic signals for tracking polymer solidification.
Energy Transfer
High efficiency in the longitudinal direction ensures that the transducer converts electrical pulses into clean acoustic waves. A low electromechanical coupling factor k11 results in weak ultrasonic pulses that are easily lost in the dense structure of the steel mould plates. This loss of signal makes it difficult to detect the moment the polymer changes from a liquid to a solid state.
Sensor Design
Selecting materials with a high coupling factor improves the signal to noise ratio of the cavity pressure sensor. Piezoelectric ceramics like lead zirconate titanate or specialized polymers are optimized to maximize this factor along the main axis of compression. This optimization ensures that even small pressure changes in the cavity during the packing phase are recorded with high fidelity.
When the acoustic wave propagates through the moulding resin, the resulting signal provides an accurate profile of the internal density and temperature distribution of the cooling part.
Performance Limit
Thermal degradation of the ceramic crystal reduces the coupling factor when the mould temperatures exceed the curie point. If the operating temperature rises too high, the transducer loses its piezoelectric properties permanently. This thermal limit dictates the cooling layout of the sensor pocket in hot runner tools.
