This Small Business Innovation Research (SBIR) Phase I project investigates high-temperature wirelessly interrogated acoustic sensors for monitoring insulated structures such as piping and storage vessels that are in difficult to access locations and operate at elevated temperatures. Current 2-D acoustic imaging systems are wiring and data processing intensive, as well as difficult to embed in a permanently installed structural health monitoring system. The proposed innovation addresses this challenge through taking advantage of the advanced capabilities of the frequency-steered acoustic transducer (FSAT). The unique FSAT architecture allows 2-D imaging with a simple interface that can be controlled by a low-power wireless system. This proposed effort will simulate, design, and, demonstrate MEMS-based fabrication processes and material sets that allow FSAT operation in elevated temperature applications. The effort will also demonstrate low-power wireless embeddable interface electronics for simple integration of multiple FSAT devices into a distributed structural health monitoring system. If successful, this research will enable new in situ health monitoring capabilities at high-temperature. This technology is highly scalable and will provide these benefits at low capital cost and low ongoing cost.
The broader impact/commercial potential of this project is in the cost savings and energy savings that can be gained through increased structural health monitoring of critical components and processes in manufacturing facilities. Because the target market is high temperature industrial process control and structural monitoring, these sensors would permit savings in terms of production time, and reduced plant downtime, as well as the energy required to maintain the process temperature. Within certain situations, this sensor technology would enable wireless point measurements of structural health that are currently not feasible or affordable. Relevant and affordable monitoring solutions for low- to medium-cost industrial equipment will be beneficial to rural facilities and small-scale manufacturers who tend to use older technology, maintain small capital budgets, and operate under tight cash-flow restrictions. Broader impacts of this technology to science and education include a novel advance in existing structural health monitoring technology and funding for continued research and education in wireless sensors, acoustic imaging, and damage detection using acoustic methods.
This technical effort investigated the use of the frequency steered acoustic transducer (FSAT) in wireless structural health monitoring systems. Demonstrating this capability is important to increasing the capability of wireless structural health monitoring, especially in difficult to access locations, as well locations requiring wave scanning abilities. In addition, achieving these capabilities at elevated temperatures opens up a large number of structural health monitoring and embedded non-destructive evaluation applications. The effort demonstrated the feasibility of wireless frequency-steered acoustic transducers as an alternative to electronically scanned phased arrays. The geometry of the transducer provides wave phasing, thereby allowing the transducer to be driven by a single channel. This makes these devices amenable to small wireless readout. Feasibility was investigated by investigations into four objectives. The first objective of the effort was to increase the temperature range of embedded ultrasonic transducers, such as the FSAT. Two problems arose, high-temperature material availability and robust transducer-to-structure interfaces. In working towards this first objective, we evaluated material and interface options and fabricated test articles. This first objective was met through fabricating FSAT devices from high temperature materials, and operating devices attached to structures. The fourth objective of the effort was intimately related to the first. The fourth objective defined fabrication approaches for the transducers. The fabrication processes required to realize high-temperature devices had to be affordable and scalable to batch-level fabrication approaches. This objective was met through the development of batch scalable approaches to FSAT fabrication. The second objective of the effort was to demonstrate the scanning area and imaging capabilities of embedded ultrasonic transducers, and apply the FSAT steering capability to the monitoring of plate-like structures. This objective was met by simulating FSAT derived wavefields in structures, and through attaching transducers to structures and characterizing their ability to detect phenomena. In addition, a new FSAT design was realized that could steer bulk waves through structures. The third objective of the effort was to demonstrate that a wireless interrogation system for the FSAT is feasible and beneficial structural health monitoring applications. This objective was met through defining the components, volume, power requirements, and cost of a transducer drive system and wireless data link. In summary, the wireless FSAT is feasible with respect to the key technical challenges that were investigated.
