Scanning acoustic microscope
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A Scanning Acoustic Microscope (SAM) is a device which uses focused sound to investigate, measure, or image an object. It is commonly used in the failure analysis and non-destructive evaluation. It also has applications in biological and medical research. The semiconductor industry has found the Scanning Acoustic Microscope useful in detecting voids, cracks, and delaminations within microelectronic packages.
Principles of operation
Scanning Acoustic Microscopy works by directing focused sound from a transducer at a small point on a target object. Sound hitting the object is either scattered, absorbed, reflected (scattered at 90°) or transmitted (scattered at 0°). Typically, either the reflected or transmitted sound is gathered and measured. Based on the measurement, a value is assigned to the location investigated. The transducer (or object) is then moved slightly and then insonified again. This process is repeated in a systematic pattern until the entire region of interest has been investigated. Often the values for each point are assembled into an image of the object. The contrast seen in the image is based either on the object's geometry or material composition. The resolution of the image is limited either by the physical scanning resolution or the width of the sound beam (which in turn is determined by the frequency of the sound).
The SAM is used mostly by engineers. It is used for inspecting metals after alloy tests. For example, a group of engineers may need a bolt installed in a bridge. So they might test an 8 in. copper-iron alloy bolt under a specific weight that the bolt must withstand everyday with out failing. They put that certain weight on it and then use the SAM to look deep into the metal to look for cracks or metal fatigue. IF they find any they increase the bolt size or change the alloy. Basically the SAM works by using something similar to echolocation or sonar. It bounces sound off the specimen and judging by the pitch, volume, and time in between the bounce back it after many small changes in locations and repeating the steps many times manages to create a three dimensional image.
Resources
- Sonix. Manufacturer of SAM systems