Low-Power Low-Error Wireless Sensor Network for Health and Usage Monitoring Systems

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Health and Usage Monitoring Systems (HUMS) consist of a network of sensors to collect data from different parts of a system under actual operating conditions in a variety of applications, including aircrafts, bridges, or systems whose maintenance cost is high, or their failure can have life-threatening consequences. The focus of this dissertation is to develop a HUMS that can wirelessly monitor the dynamic motion and behavior of any system using at least two nodes synchronously with timing error <30 μs. Wireless connectivity poses challenges in terms of time synchronization and extended operational lifetime.

Battery-powered and BLE (Bluetooth Low Energy)-enabled sensor nodes were custom- designed and tested. New low-error and low-power synchronization protocols are developed, including BlueSync, Discrete Adjustments, and AdaptSync. BlueSync is compatible with the BLE standard and reduces synchronization error to <1 μs per 60 s of measurement, the lowest reported error for BLE. Discrete Adjustments increases node operational lifetime by reducing the overhead of synchronization calculations by up to 15x. AdpatSync enables both low-power consumption and low synchronization error for long sessions by eliminating the need for wireless resynchronizations. In a 10-minute recording session, AdaptSync reduces the error by 7x compared with standard synchronization methods. To further increase the node lifetime, a 915 MHz, -61 dBm, 2.8 nW wake-up radio is designed in TSMC 65 nm CMOS technology, to listen for wake-up commands during the sleep state.

A complete system is prepared for collecting inertial data from rotor blades of a helicopter testbed platform. Results validate that the developed wireless system performs similarly to a wired system and an optical measurement reference for this application.