This Small Business Innovation Research Phase I project investigates the use of environmental vibrations to increase the interrogation distance between wireless sensors and their readers. The utilization of free vibrations, themselves, for increased performance is a paradigm shift away from existing approaches that use vibrations purely for energy harvesting. Using vibrations to avoid material limitations of semiconductors has broad applicability to sensing, control, data storage, and communications. Currently, wireless sensors achieve usable interrogation ranges through the use of electronics and/or batteries, but this approach adversely impacts operating temperature, cost, and reliability of the sensor node. To address these problems, this project investigates continuous and cycled vibrations to increase interrogation distance in passive wireless sensors. This demonstration will be simulated and then experimentally validated using room-temperature devices. Next, the vibration harvester and sensor will be designed for high-temperature operation. Then, an affordable fabrication process will be developed using electronic packaging techniques. Finally, a prototype sensor will be fabricated to harvests ambient vibrations and operate at temperatures in excess of 300°C. If successful, this will identify usable sensor materials and vibration parameters for high-temperature operation at a broad range of wireless interrogation frequencies.
The broader impact/commercial potential of this project includes fundamental advances in vibration utilization and wireless sensors and applied advances in high-temperature wireless sensing for condition-based maintenance and structural health monitoring. The broader impact to science and education include a novel advance in existing sensor technology, as well as funding for continued research and education in RF sensors, RF power transfer, and high-temperature fabrication. This project includes fundamental analysis and experimentation that will increase scientific and technological understanding of mixed-signal sources for communications and mechanical frequency behavior at high-temperatures. The broader societal impact and commercial potential of this project will be the ability to remotely monitor high-temperature machinery and processes to increase lifetime and efficiency while reducing operating costs. The technology areas of interest for this project include wireless sensors and condition-based maintenance. The wireless sensor market is expected to grow 50-fold between 2008 and 2012, even with existing temperature limitations, because of 20-80% cost savings over traditional monitoring techniques. This project demonstrates a path to increase this growth by enabling monitoring in a wide range of high-temperature industrial and aerospace applications, such as injection molding, gas turbines, oil drilling, and composite manufacturing, among others.
This effort investigated vibration harvesting devices to improve range of wireless sensors. Demonstrating this capability is important to extend interrogation range and signal quality in wireless sensors, especially at high temperatures. The wireless capability improves sensing capabilities and reduces total cost. Compared to wired sensors, wireless sensors add direct measurement capabilities to moving components or within embedded cavities. Wireless sensing also reduce significant installation and lifetime costs compared to wired counterparts. This effort demonstrated the feasibility of utilizing free vibrations for improved sensor range by tacking key issues regarding: proof of concept, system level power requirements, thermal management requirements, and manufacturability. To demonstrate proof of concept, sensor signal was shown to change with both level and frequency of the vibrations. This had an added benefit that the sensor could perform as a dual-sensor, with vibration levels being one sensed phenomenon. The power requirements for the sensor were presented as three sources loss and signal degradation. Thermal management was addressed through material selection. The goal was to maintain reliability while minimizing the resistivity of the conductive traces. Manufacturability and costs were addressed using mature processes similar to those used in the printed circuit board industry. Finally, a prototype sensor and reader were developed and fabricated to conclude the effort. The prototypes demonstrated response to the primary measurement, either pressure or temperature, and to vibration input from a handheld power drill. In summary, the vibration harvesting wireless resonant sensor is feasible with respect to the key technical challenges that were investigated.
