Meaning
Dimensionless parameters measure the efficiency of mechanical energy storage and dissipation in acoustic resonators. For ultrasonic transducers used in polymer thickness or flow monitoring, the mechanical quality factor qm indicates how cleanly the crystal vibrates without wasting energy as heat. A high factor ensures that the sensor can generate sharp, well-defined acoustic pulses for precise measurement.
Energy Retention
Low mechanical dampening within the crystal structure produces a high mechanical quality factor qm, which results in a narrow frequency bandwidth. This sharp resonance peak provides high sensitivity to changes in the acoustic impedance of the polymer melt. When the resin starts to cool, the transducer can resolve minute changes in density because of this high signal resolution.
It allows the monitoring system to detect the precise moment of gate freeze-off, which represents the point where no more plastic can be packed into the cavity.
Sensor Output
Strong acoustic waves generated by high quality factors can penetrate through the steel mold plates into the flow channel. If the transducer has a low coupling or low mechanical quality factor qm, the signal loses strength before reaching the polymer melt. This reduction in amplitude makes it difficult to track the solidification rate in real time.
Thermal Hazard
High mechanical loss within the transducer generates internal heat during continuous ultrasonic operation. If the mechanical quality factor qm is too low, the crystal’s temperature can rise, causing the piezoelectric properties to drift. This thermal rise disrupts the accuracy of the measurements and shortens the operational life of the sensor.
