MR sensors offer a significant increase in sensitivity for inspection of subsurface features and flaws in metallic aircraft structure. This is especially true for deeper inspections with depths between 10 and 20 mm below the accessible surface. I show C-scan images of deep flaws, with dimensions down to one-tenth of the thickness of the covering metal. Issues involved in developing and operating an imaging scanner using these sensors are discussed.
A fiber optic magnetic gradiometer has been successfully configured to detect the cardiac magnetic field. The gradiometer is comprised of a Mach Zehnder interferometer, with extremely thin transducers to allow placement of the sensor very near to the chest of a human subject. The sensor detects the cardiac magnetic field in real time, and demonstrates good fidelity in both the time and frequency domains, with only a low pass filter used for signal processing. To our knowledge, this is the first detection of a biomagnetic signal with an optical sensor.
This work investigates the development of Shape Memory Alloy (SMA) actuators and a fiber-optic
Mach- Zehnder interferometric dynamic motion sensor as components of an active vibration control
system. The test set-up consisted of a graphite-epoxy flexible cantilever beam with distributed SMA
wires and optical fibers attached along both sides. A constant amplitude dead-band control algorithm
was used to provide a rate feedback force to actively control transient vibrations. The SMA actuators
were also used to demonstrate static shape control. The settling time of the beam was reduced by more
than a factor of 24 through the use of the SMA actuators and fiber optic dynamic motion sensor.
Analytical models were developed for the integrated structure/actuator/sensor system which helped
understand the dynamic effects and the results correlated well with the experimental results. This
investigation demonstrated the feasibility ofusing SMA actuators and fiber optic dynamic motion sensor
for control of flexible structures. The work described in this paper was sponsored by the Astronautics
Laboratory AL(AFSC) as a part of the "Advanced Composites with Embedded Sensors and Actuators
(ACESA)" program.
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