Videos

Macroscopic analogy of a microbubble UCAs "Model 1"

Microbubbles, either in the form of free gas bubbles surrounded by a fluid or encapsulated bubbles used currently as contrast agents for medical echography, exhibit complex dynamics under specific acoustic excitations. Nonetheless, considering their micron size and the complexity of their interaction phenomenon with ultrasound waves, expensive and complex experiments and/or simulations are required for their analysis. The behavior of a microbubble along its equator can be linked to a system of coupled oscillators. In this study, the oscillatory behavior of a microbubble has been investigated through an acousto-mechanical analogy based on a ring-shaped chain of coupled pendula. Observation of parametric vibration modes of the pendula ring excited at frequencies between 1 and 5 Hz is presented. Simulations have been carried out and show mode mixing phenomena. The relevance of the analogybetween a microbubble and the macroscopic acousto-mechanical setup is discussed and suggested as an alternative way to investigate the complexity of microbubble dynamics.

Note: Microbubble experimente by Versluis et al, you will find his video attached to his paper Link

(Up) By Ahmed Mehrem(Down) By Versluis

High-intensity focused ultrasound

High-Intensity Focused Ultrasound (HIFU) is a non-invasive cancer treatment method that focuses ultrasound generated outside the body on target tissue, which is heated and coagulated. Thus higher energy levels can be increased and delivered accurately to a small size, without affecting the surrounding tissue. This technique is widely used in the treatment of early-stage cancer in which the affected cells are concentrated in a small area.

Bubble Trap

Also in the video, you can see the bubbles are trapped inside the flow.

By Ahmed Mehrem

Nonlinear waves in repulsive lattices "Model 2"

The propagation of nonlinear waves in a lattice of repelling particles is studied theoretically and experimentally. A simple experimental setup is proposed, consisting of an array of coupled magnetic dipoles. By driving harmonically the lattice at one boundary, we excite propagating waves and demonstrate different regimes of mode conversion into higher harmonics, strongly influenced by dispersion and discreteness. The phenomenon of acoustic dilatation of the chain is also predicted and discussed. The results are compared with the theoretical predictions of the α-Fermi-Pasta-Ulam equation, describing a chain of masses connected by nonlinear quadratic springs and numerical simulations. The results can be extrapolated to other systems described by this equation.

Simplified model for chain of atoms (How the air molecules vibrate?)Experimental Setup. By Ahmed Mehrem

Particle tracking

Regading Model 2

We used Matlab 2015a-MathWorks in all numerical process especially the calibration toolbox cameraCalibrator. This toolbox is used to detect and locate the checkerboard calibration pattern including corner detection with subpixel accuracy. We Estimate all intrinsic and extrinsic parameters including axis skew, calculate radial and tangential lens distortion coefficients, correct the optical distortion. This toolbox also support single camera and stereo calibration.To start the calibrationwe have to prepare checkerboardwith specific dimensions. We recorded 50 videos 100fps in different positions for the checkerboard with resolution 1920x1080. This resolution is enough to track all pendulums (which are very small) without loosing any information.From cameraCalibrator one can load all the calibration images. Notice that at some point in the process are asked about the width of one square of the board and you can choose it in mm. After processing each image, it will show the overlapping detected corners on the concrete image. If all went well, you should observe all corners; otherwise, it may happen that you have not indicated the end corners with sufficient precision or because there is too much distortion in the image or the number of image is not enough to cover all the areaof interest. Once you extract all corners, now Matlab is ready to calibrate the camera. After a series of calculations, the result of the calibration parameters should appear with value of Focal Length, Distortion, Errors in pixel....etc.