In this paper, the influence of disbonds on Lamb wave propagation in GLARE composites is described. Guided Lamb
waves were launched and detected with Polyvinylidene Fluoride (PVDF) comb transducers. Disbond defects were
introduced with ball drop test to study their influence on the Lamb wave signals. The amplitudes of the detected Lamb
wave signals show distinct differences with and without disbonds, which can be used to monitor the disbond growth. In
addition, a thermal imaging technique was applied to inspect the disbond region so as to cross-correlate the disbond size
with its influence on the Lamb wave signals measured by the PVDF sensors. It is demonstrated that the amplitudes of the A<sub>o</sub> mode Lamb wave decrease exponentially with increasing disbond size.
A photoacoustic imaging system that incorporates a commercial ultrasonic camera for real-time imaging of two-dimensional (2-D) projection planes in tissue at video rate (30 Hz) is presented. The system uses a Q-switched frequency-doubled Nd:YAG pulsed laser for photoacoustic generation. The ultrasonic camera consists of a 2-D 12×12 mm CCD chip with 120×120 piezoelectric sensing elements used for detecting the photoacoustic pressure distribution radiated from the target. An ultrasonic lens system is placed in front of the chip to collect the incoming photoacoustic waves, providing the ability for focusing and imaging at different depths. Compared with other existing photoacoustic imaging techniques, the camera-based system is attractive because it is relatively inexpensive and compact, and it can be tailored for real-time clinical imaging applications. Experimental results detailing the real-time photoacoustic imaging of rubber strings and buried absorbing targets in chicken breast tissue are presented, and the spatial resolution of the system is quantified.
Two modifications to an ultrasonic camera system have been performed in an effort to reduce setup time and post
inspection image processing. Current production ultrasonic cameras have image gates that are adjusted manually. The
process to adjust them prior to each inspection consumes large amounts of time and requires a skilled operator. The
authors have overcome this by integrating the A-Scan and image together such that the image gating is automatically
adjusted using the A-Scan data. The system monitors the A-scan signal which is in the center of the camera's field of
view (FOV) and adjusts the image gating accordingly. This integration will allow for defect detection at any depth of the
inspected area. Ultrasonic camera operation requires the inspector to scan the surface manually while observing the
cameras FOV in the monitor. If the monitor image indicates a defect the operator then stores that image manually and
marks an index on the surface as to where the image has been acquired. The second modification automates this effort
by employing a digital encoder and image capture card. The encoder is used to track movement of the camera on the
structures surface, record positions, and trigger the image capture device. The images are stored real time in the buffer
memory rather than on the hard drive. The storing of images in the buffer enables for a more rapid acquisition time
compared to storing the images individually to the hard drive. Once the images are stored, an algorithm tracks the
movement of the camera through the encoder and accordingly displays the image to the inspector. Upon completion of
the scan, an algorithm digitally stitches all the images to create a single full field image. The modifications were tested
on a aerospace composite laminate with known defects and the results are discussed.