SBIR Phase II: Microminiature, High Resolution, Passive Peak Strain Detector for Smart Structures and Materials

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This Small Business Innovation Research (SBIR) Phase II project combines hermetically packaged, differential variable reluctance transducers (DVRT) capable of peak strain detection (PD) with shape memory alloy (SMA) actuators to produce improved passive PDs. These detectors can withstand harsh environmental conditions, e.g., moisture, salt, vibration, and can be reset for repeated uses. Sensors in smart structures generally require system power in order to operate, but power outages may result in loss of key data. Therefore, sensors that can record peak information without power, i.e., passively, are needed in smart structures. Earlier passive PDs have relied on measuring the magnetic properties of transformation induced plasticity (TRIP) steels. However, these devices suffer from bulky size, low resolution, high nonlinearity, and a one time use limitation due to material yielding. This technology addresses these problems by using modified, microminiature DVRT-PDs. Phase I successfully designed, built, and tested hermetic packages, and SMAs were successfully employed for resetting of the devices. Techniques for remote interrogation using radio frequency identity tags were investigated, micropower prototypes were designed and built, and methods for wireless delivery of power to the SMA actuator were demonstrated. In Phase II, highly integrated microelectronics will be combined with the hermetic DVRT-PD packages to produce self-contained, remotely queried and remotely resettable PDs. Novel micropower sensor excitation circuits, capable of long range interrogation, will be built, tested, and packaged for independent laboratory evaluation and eventual field deployment. Field tests will include health monitoring of structural joints, repairs, and supporting members of civil structures, including bridges. The physical attachment of the DVRT-PDs to these structures will be designed for reliability, low cost, and ease of use. Applications include health monitoring of composite structures, aircraft, trains, bridges, dams, and buildings. Military and commercial markets for these systems are significant. Health monitoring has the potential to enhance the safety and life of military, aerospace, and civil structures. Sensate structures equipped with passive networks of peak displacement or strain measurement devices could be interrogated for their response to test loads or potentially damaging events, and either replaced or their embedded sensors reset for future interrogation. Critical civil and military structures require 'smart' sensors in order to report their strain histories; this can help to insure safe operation after exposure to potentially damaging loads, e.g., earthquakes, hurricanes, military combat, etc.