8. New Technology Roots
Transversal filters based on the charge-coupled device (CCD) technology may be applied to processing received signals in an ultrasonic NDE system. Filters having a fixed response (fixed tap weightings) could be used to compensate for the characteristics of a given ultrasonic transducer. A more flexible arrangement allowing programmability employs a CCD delay line whose tap electrodes are accessible externally for weighting. The response of this device can be altered by changing a set of resistors mounted on a printed circuit board which can be plugged into a socket connected to the CCD. Proper response for a given ultrasonic transducer is obtained by plugging in the proper circuit board. Because present commercial CCD's allowing programmability have clock frequencies too low for direct processing of ultrasonic NDE signals, the filter is preceded by a CCD video delay line which quickly stores the return signal and then outputs it more slowly for processing during the time between successive excitations of the ultrasonic transducer.
White, Richard M., "Programmable Filter for Ultrasonic NDE Systems" (1978). Proceedings of the ARPA/AFML Review of Progress in Quantitative NDE, September 1976–June 1977. 55.