Piezoelectric MEMS switch to activate event-driven wireless sensor nodes

We have developed a wireless sensor node for monitoring the health conditions of animals, in particular chickens. Each wireless sensor node measures the body temperature and activity of a chicken. Because chickens are farmed for a maximum of two years, the required lifetime of a wireless sensor node without replacing the battery must be two years. To achieve ultra-low power consumption, the sensor node we use is an event-driven system activated by the movement of chickens. The activation conditions are determined by the threshold voltage of a comparator circuit, and the output voltage of a piezoelectric MEMS switch. Although the piezoelectric MEMS switch is an important element of our system, it poses challenges in generating enough output voltage from chicken movement (4~15 Hz, below 0.5 m/s²). In this paper, we measured the output voltage of the piezoelectric MEMS switch at low frequency, and with low acceleration vibrations. We used an experimental device with a piezoelectric MEMS switch to evaluate the relationship between the threshold voltage of the comparator circuit and acceleration, and determined when the comparator is switched during low-frequency vibrations.