NASA’s Langley Research Center has developed a Floating Ultrasonic System for improved nondestructive testing. Most ultrasonic scanners require an external liquid coupling agent (e.g., water, gel, oil) to make a good contact between the probe and the surface being scanned. However, some surfaces are sensitive to moisture and/or contamination created by these agents. NASA created the Floating Ultrasonic System to address this issue. NASA’s technology is based on a momentary-touching scheme where a vibrating probe comes in contact with the structure for fractions of a second while performing measurements, giving the probe the appearance of floating across a surface. The design allows for the easy movement of the probe over surfaces being inspected without the use of a liquid couplant between the probe and the surface. Initial test results have also shown NASA’s system to have comparable performance to liquid-couplant-based, ultrasonic scanners.
NASA’s Floating Ultrasonic System includes a transducer assembly with a flexible membrane tip made of nitrile rubber. A small amount of gel couplant is layered between the transducer and the inside of the membrane—the gel is fully contained inside the probe and does not come into contact with surfaces being inspected. The transducer assembly is mounted to a voice-coil motor that acts as an actuator. Electrical current sent to motor moves the transducer up and down over the surface being inspected. The vibrating, or “floating,” transducer design provides two critical functions. First, it applies a small force that enables coupling of the ultrasonic energy from the transducer to the surface being inspected. Second, it facilitates movement of the transducer across the surface. A diagram of NASA’s Floating Ultrasonic System is presented in Figure 1(a). NASA has constructed a bench-top unit that has undergone successful testing. Figure 1(b) shows ultrasonic C-scan images of a composite plate using both NASA’s Floating Ultrasonic System and a traditional watertank-based scanning system. NASA’s system provides comparable results, but unlike the water-tank system, it allows for inspection without the use of an external liquid couplant. NASA researchers are working on additional refinements to the technology, including improving resolution, and plan to develop it into a handheld device. The technology will be used for the in-situ inspection of composite aerospace parts that are undergoing fatigue testing. However, it also has an array of other applications, including medical, as it could be used for imaging soft tissues such as internal organ and msucles.