Particle image velocimetry using Bragg cell as optical shutter

To better understand the human pulmonary, flows within lung bifurcations have been experimentally investigated with a new Particle Image Velocimetry (PIV) technique. Instationarities in the flow can be studied with this technique where both spatial and temporal information of the entire flow field can be obtained, in providing the simultaneous visualisation of two dimensional streamline pattern in unsteady flow. This new technique of PIV was developed using a continuous laser and a Bragg cell as optical shutter. A Bragg cell is used to switch the laser beam, with an acousto-optic modulation, creating single and periodic laser pulses by the use of an electrical input signal. To record the images of the flow field, a CCD video sensor that uses a frame memory buffer, is used. A synchronisation device ensures that each laser pulse generated by the modulator really occurs in a different field of the image. To process the two fields, a cross-correlation program was developed using Fast Fourier Transform algorithms. The images are processed with Gaussian scheme for sub-pixel interpolation.