Abstract
A non-destructive inspection system using 50MHz ultrasound has been developed. The system has been designed to provide magnified visual images of the interior of solid materials. An ultrasonic transducer is scanned across the specimen to produce these images and consequently the system has become known as the Scanning Acoustic Microscope (SAM). The principles of operation of the SAM have been described in terms of wave theory and the electronic and computer sub-systems of which it is comprised. Images are presented on a computer monitor in eight colours. The colour of each picture point, or pixel, is determined by the amplitude of a reflection from the specimen. As the transducer scans in a raster pattern over the specimen a video cursor scans over the video memory in the computer and each pixel is coloured in turn. Thus the image is built up in real time as the transducer is scanned. The maximum range of scan is 300 x 300iran in the horizontal plane and 200mm vertically. The spatial resolution in all three axes is 7.5 microns. Applications in several areas of engineering and one medical area have been developed. The underlying principles of each inspection situation are described and results reported. These areas include inspection and evaluation of various forms of bond, volumetric inspection, particularly of engineering ceramic materials and the skin, and a measurement problem in the gas turbine industry. All the work reported has been undertaken on behalf of customers of Fulmer Research Institute Limited and it therefore represents a series of practical problems and solutions across a wide spectrum of industry.