A Motion Based Power Management Technique for Wireless Sensor Networks Deployed for SHM

Abstract

Wireless Sensor Networks (WSN) have been deployed to monitor the health of unpowered structures such as bridges, buildings, towers and other infrastructure. Key to proliferation of these systems will be longer battery life enabled by low power components, energy harvesting technologies and creative power management techniques. This paper discusses the features and use of an ultra-low power (ULP) 3- axis accelerometer to monitor structural motion and 'wake up' the primary low noise sensor when excessive vibration is detected. The power management features of the ULP sensor are used to help manage the overall wireless module power budget by maintaining the more sensitive components in a shutdown state until a minimum motion threshold is exceeded in the structure. The ULP sensor allows for autonomous motion switch functionality with minimum intervention from the host processor. The ULP sensor can automatically switch from activity detection to inactivity detection based on external conditions and can be programmed to trigger on single or multiple samples of activity or inactivity. The motion thresholds are user adjustable and can also compensate for the effect of gravity. An embedded FIFO buffer working in conjunction with motion threshold detection further reduces the computational load on the host processor and enables capturing pre-event data. This scheme shifts the measurement cycle of the wireless module from a time based initiation of a measurement to an activity based decision, helping to reduce the duty cycle of both measurement and transmission, hence reducing the average power. The impact on traditional unlicensed band wireless module power budget using an ultra-low power accelerometer to help optimize data acquisition, processing and transmission is discussed. doi: 10.12783/SHM2015/118