This paper presents a Bond graph approach to analyzing the energy efficiency of a self-powered wireless pressure sensor for pressure measurement in an injection mold. The sensor is located within the mold cavity and consists of an energy converter, an energy modulator, and a signal transmitter. Pressure variation in the mold cavity is extracted by the energy converter and transmitted through the mold steel in the form of ultrasound pulses to a signal receiver located outside of the mold. Through Bond graph models, the energy efficiency of the sensing system is characterized as a function of the configuration of the piezoceramic stack within the energy converter, and the pulsing cycle of the energy modulator. The obtained energy model is then used to identify the minimum level of signal intensity required to ensure successful detection of the ultrasound signals by the signal receiver. The Bond graph models established can be further used to optimize the design of the sensing system and its constituent components.
This paper presents the design, analysis, and experimental verification of a piezoelectric device that extracts energy from low-level vibrations. Such a device may be configured as a new source of power supply to operate wireless sensor networks. A millimeter-sized, non-uniformly shaped beam consisting of two piezoelectric layers is proposed as the key component of the device. An analytical model of the beam is established and used to predict the dynamic response of the beam and subsequently, its power output, when it is subject to vibration inputs. Through a coupled-field analysis, the coupling between the mechanical and electrical domains of the energy extraction device is analyzed. Simulations and experiments on a vibration shaker have shown that, compared with the rectangular beam design that has been traditionally used, the new design has increased the energy extraction capability of the beam by as much as 70%. In addition to beam design, issues related to device packaging are also addressed in the paper.
A self-powered wireless sensing module for the condition monitoring of mechanical systems and high energy manufacturing processes is described, with injection molding as a special application. The design and analysis of three constituent components in such a sensing module: an energy converter consisting of a piezoceramic stack, an energy regulator based on a pair of bipolar transistors, and a piezoelectric transmitter that transmits ultrasound signals proportional to the pressure within the injection mold, are presented in this paper. The energy extraction mechanism is investigated based on the interactions between the mechanical strain and the electric field developed within the piezoceramic stack. Analytical models for the energy modulator and signal transmitter are also established. Quantitative results are obtained that describe the energy flow among the three components and guide the parametric design of the three constituent components. Simulations and experimental studies have validated the functionality of each component. The models established can be used to subsequently optimize the design of the entire sensor module in terms of minimizing the energy requirement for the sensor and identifying the minimum level of signal intensity required to ensure successful detection of the signal by the signal receiver on the outside of the injection mold. The proposed self-powered sensing technique enables a new generation of sensors that can be employed for the condition monitoring and health diagnosis of a wide range of mechanical and civil systems that are characterized by high energy contents.