Self-Energized Acoustic Wireless Sensor for Pressure-Temperature Measurement in Injection Molding Cavity

This paper presents a self-energized acoustic wireless sensing method for simultaneous measurement of pressure and temperature within the cavity of an injection mold and wireless transmission of the measured parameters out of such a metallically shielded environment through ultrasound pulse trains. Two attributes of the ultrasound pulses have been explored to enable dual-parameter sensing: the number of pulses serves as a direct measure for the magnitude of the pressure, and the carrier frequency of the pulses accounts for the polymer melt temperature. A piezoceramic stack serves as an energy harvester that scavenges energy from the pressure differential of the molding process itself to power the sensor electronics. Systematic comparative experiments on a real-world injection molding machine with commercial wired sensors as the reference verified the accuracy and robustness of the new sensor. Small in size, requiring no battery and no holes to be drilled through the mold, the new sensor is suited for embedded monitoring in a wide range of industrial applications characterized by low accessibility and harsh environmental conditions.