Why is degassed water used in ultrasound wattmeters instead of regular clean water?
Most ultrasound standards specify water as the test media, since water approximates soft body tissues and fluids in propagation velocity and can be readily distilled, filtered, or degassed. Removal of some of the oxygenpreferably around 5 ppmis necessary for accurate measurements. Small air bubbles cause secondary reflections and attenuation of beam radiation force, which causes lower power readings.
