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Laser-ultrasound and imaging

We are developing laser ultrasonic and ultrasonic imaging methods in collaboration with several industry partners. Applications range from ultrasonic quality control in food or steel to laser ultrasonic tomography.

For more information, please contact: Joona Eskelinen

 


LASER ULTRASONICS

Laser-ultrasonics provides a non-contact probing method for versatile applications. Ultrasound is generated with a pulsed laser and detected with an interferometer. We are developing several different techniques employing laser-ultrasonics. Couple of example cases are presented below.

 

Laser-ultrasonic layer thickness estimation with Rayleigh wave dispersion

Illustration of the surface wave dispersion method principle for coating thickness estimation. Higher frequencies propagate mainly in the coating and are less affected by the bulk properties of the material.

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Thin zirconium oxide layer thickness estimation from Rayleigh wave dispersion curves. Theoretical dispersion curves for different oxide layer thickness (left).  An automated fit for a measured curve gives an estimate of the layer thickness (6.5±0.3µm) (right).

 

Non-contact laser-ultrasonic and  photo-acoustic tomography

Laser ultrasound transmission tomography image of a cylindrical aluminium sample (left) with two drilled holes. Illustration of the sample on right.

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Non-contact photo-acoustic tomography image of an epoxy bar with embedded pencil graphites.

 

Thickness measurement of layered polymers

 

Laser ultrasonic point-by-point B-scan of a layered polymer structure. Image shows both two layers and the wedge shaped structure of the lower layer.

 

Laser induced air breakdown as a sound source

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Laser sparks can be used as a point-like, broadband and massless sound source. The source can be arbitrarily positioned and enables versatile applications.

 


IMMERSION ULTRASONICS

Defect detection and sizing in rolled steel samples

We have been developing methods to improve steel quality control by characterising inclusions and pores in rolled steel samples.

A 10 MHz amplitude C-scan showing inclusions/pores inside a bearing steel 100Cr6 sample.  Three inclusions/pores were identified by the method.

 

 Defect detection in polymers

We have been employing immersion ultrasonic methods for defect detection in polymer samples.

A 30MHz ultrasonic transducer is scanned in immersion over ~1 mm thick polymer structure, which contains a defect. Resulting B-scan shows polymer containing an air bubble defect (marked with an arrow).

 

 


PHASED ARRAY ULTRASONICS

We are also developing phased array methods to allow dynamic focusing and faster scanning speeds for industrial purposes.

 

Characterization of structural defects in cheese blocks.

A 128 element 2 MHz ultrasound phased array is used to produce images of cheese blocks for automated defect classification.

 

Top view of an 85kg cheese block scanned and analyzed with a structure characterization algorithm. Red area represent identified cheese eyes and green identified cracks defects.