Richard D. Patton
Raspet Flight Res. Lab., Dept. of Mech. Eng., Drawer ME, Miss. State Univ., Mississippi State, MS 39759
Patrick C. Marks
Mississippi State Univ.
Since individual layers in a composite material return their own reflections, it is necessary for ultrasonic NDE to separate a received signal into a series of reflections. This becomes more complicated when the layers are thinner than the wavelength of the ultrasonic signal used for testing, resulting in overlapping reflections. The Gauss linearization minimization method was used to separate overlapping reflections [J. V. Beck and K. J. Arnold, Parameter Estimation in Engineering and Science (Wiley, New York, 1977)]. This algorithm fits a pulse obtained from the pulser receiver to the measured data. Amplitude and time delay estimates are made for each reflection. Multilayer Plexiglas samples with subwavelength thicknesses at 1 but not at 5 MHz were fabricated to verify the performance of the algorithm. Each sample was tested at 1 and at 5 MHz. The algorithm provided curve fits for the 1-MHz data that were almost identical to the theoretical results. The maximum error was 8% and the average error was 2%. Each of the reflections predicted by the curve fits were identified and verified in the 5-MHz data. [Work supported by the Mississippi NSF EPSCoR grant.]