acoustic microscope

Acoustic Microscopy

According to the Britannica encyclopedia, a microscope is an instrument that produces enlarged images of small objects, allowing them to be viewed at a scale convenient for examination and analysis. The optical microscope and the electron microscope are, of course, well known. The acoustic microscope is less known to the wide public. An acoustic microscope examines the mechanical properties of a material at a microscopic scale. Because the mechanical properties of a material contain information that is not detectable by means of any other microscope, the acoustic microscope is complementary equipment in the investigation of materials, in materials science as well as for the purpose of nondestructive testing.
Traditionally, acoustic microscopes mainly investigate the surface properties of materials or at the most the near surface regions. Even though this information is very important, it is perhaps not satisfactory for people who would like to investigate the interior regions. In the field of ultrasonics, there are also so called C-scans, that enable inspection of the interior (the bulk) of materials. C-scans are typically formed by means of relatively low frequency ultrasound, in the interval between 0.5 MHZ and 15 MHz. These frequencies allow deep penetration and are generated by transducers of types that are very robust and well known. Nevertheless, for the investigation of thin laminates or for the investigation of thin layers within a layered structure, those C-scan transducers are not satisfactory, because they produce wave lengths well over the characteristic dimensions of the material under investigation. Especially for the study of the microscopic structure of fiber reinforced composites, they are not suitable.

With a microscope, we are able to produce low aperture focused beams at higher frequencies than is used in classical C-scans, and perform acoustic microscopy up to 2 GHz.
The technique can be used to ‘visualize the interior structure of fiber reinforced composites. This is so called ‘bulk imaging of composites. In the future, it is my aim to study this bulk imaging further and to be able to investigate the phenomenon of fatigue damage and impact damage inside composites. This study is very inviting, because fatigue damage and impact damage are two important fields of investigation in our lab and so are heterogeneous structures at micro and nanosclae for optical filtering applicatons. Other studies include investigation of mechanical properties of coatings and new nano-heterostructures.




 

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