Acoustic emission

The video added to this post shows a part of the Philae spacecraft that descended onto a comet earlier this week. At around 2:30 into the video, it shows us the important part for this post: the SESAME research part.

Sesame is a great example of the practical applications for acoustic emission as a non destructive test method.

Each landing foot of Philae has acoustic emitters and receivers. Each of the legs will take turns transmitting acoustic waves (100 Hertz to KiloHertz range) into the comet which the sensors of the other legs will measure. How that wave is attenuated, that is, weakened and transformed, by the cometary material it passes through, can be used along with other cometary properties gained from Philae instruments, to determine daily and seasonal variations in the comet’s structure to a depth of about 2 meters.
source

To clarify this and explain acoustic emission: an emitter produces sound waves which get reflected or absorbed by the object we’re testing. The reflected waves are captured by the receivers and based on these patterns, it’s possible to reconstruct the object, determine the material and properties of the object or even detect small cracks and other imperfections in the object.

This last application, detection of imperfections, is often used for rods or ball bearings to trace fatigue before the component fails and could cause damage to other components of the machine.

Do you see other useful applications for this technique? Leave it in the comments.

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2 thoughts on “Acoustic emission

  1. I don’t know if it already exist, but it would be useful when they make this kind of devices on a small scale. You could use it for example to check if there are cracks inside a concrete wall by placing/sliding this devise over it. You could also use it to test metal constructions.
    Another example is the detection of cavities in casted pieces of machinery, which can cause a lot of problems.

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    1. If I understand you correctly, you are talking about this type of device
      http://www.bosch-do-it.com/gb/en/diy/tools/pdo-6-3165140435543-199930.jsp
      I’m not entirely sure this uses sound waves though.

      Using it to hunt down cracks in concrete is used regularly, though not very often in consumer applications. It can be used in labs or on large scale for instance to detect cracks when 2 different types of concrete are mixed and are drying/shrinking at a different speed.

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