Berlin 2024 – wissenschaftliches Programm

Bereiche | Tage | Auswahl | Suche | Aktualisierungen | Downloads | Hilfe

ST: Fachverband Strahlen- und Medizinphysik

ST 6: Medical Imaging Technologies

ST 6.2: Vortrag

Mittwoch, 20. März 2024, 15:15–15:30, PC 203

Seeing Sound: Real-Time Schlieren Imaging of Ultrasound Wavefields — Milan Fritsche, Adrian Dittmaier, Maximilian Jahrsdörfer, and •Florian Steinmeyer — Technische Hochschule Nürnberg Georg Simon Ohm

In 1864 August Toepler visualised acoustic waves by Schlieren imaging. Modern components as aspherical lenses, LEDs, CMOS-sensors expand the method to short timescales and a broad range of amplitudes. We demonstrate a number of novel applications.

The piezo-optic effect is the sensitivity of the refractive index to pressure. Our in-line Schlieren setup consists of a LED illuminating the acoustic wavefield of a transducer in water through a collimating lens. Light is refracted proportional to the pressure gradient integrated along the light path. Downstream, a "Schlieren lens" condenses light onto a knife-edge at the lens focus (blocking unrefracted light, yielding a dark field image of the waves). Eventually, a digital camera reconstructs a real image.

By illuminating stroboscopically (frequency 0.5-8 MHz, acoustic power 50mW-150W) a propagating wave appears frozen, images are very sharp. It is shown that the projection of a radially-symmetric ultrasound field is converted into a tomogram of a central symmetry plane. While wave intensity is hard to quantify, field geometry can be evaluated, e.g. wavelength, phase, focal position, distortion by shocks, propagating or standing waves, reflection, cavitation. As a means of quality assurance beam steering in array transducers and/or manufacturing errors can be detected - down to sub-millisecond shutter speed.

Keywords: Schlieren Imaging; ultrasound; piezo-optic effect; wavefield characterization; therapeutic transducers