Design of a self-energized wireless sensor for simultaneous pressure and temperature measurement

On-line monitoring of polymer melt state is critical to ensuring part quality in injection molding. This paper presents the design of a dual-parameter acoustic wireless sensor for simultaneous measurement of pressure and temperature variations within the mold cavity. The sensor consists of three major functional components: a piezoceramic energy harvester, a modulator circuit, and an electric-acoustic signal converter. It discretizes pressure and temperature variations during the molding cycle into a number of acoustic pulses with varying carrier frequencies, and transmits them to an remote receiver for data retrieval. To minimize sensor dimension and optimize functionality, the mechanical and electronic portions of the sensor are concurrently designed as a mechatronic system. The sensor is prototyped and evaluated on a production grade injection molding machine. Good agreement is found between the new, wireless sensor and traditional wired sensors.