Self-energized wireless pressure sensor using energy extraction from injection mold pressure differential

With the prolific use of sensors for manufacturing process monitoring and the growing demand for system integration, the issue of packaging and installation has assumed an increasingly central role. This paper presents the design of a self-energized pressure sensor that extracts energy from the pressure differential of the polymer melt during the injection molding process. A piezoelectric element is used as the energy converter to convert the high melt pressure into proportional electrical charges, which in turn, actuate an ultrasound signal through a miniature energy switch. Based on predetermined energy threshold values, the actuator generates a train of ultrasound pulses, which represent the continuous melt pressure in a digitized form. The ultrasound pulses propagate wirelessly through the mold steel and are detected by a remotely located signal receiver. Through multiplication of the number of pulses with the energy threshold values, the polymer melt pressure profile is reconstructed. To enable a self-energized sensor design, an analytical study has been conducted to establish a quantitative relationship between the polymer melt pressure and the energy that can be extracted through the use of a piezoelectric converter.