The vibrating motion of our eardrum by which we hear, proves that sound is able to induce movement to structures. It is also possible to move suspended particles in water in the direction of propagation by means of sound. In order to fix the particle, we need a sound wave from the opposite direction with the same magnitude and frequency, thus creating a fixed wave pattern, which is called a standing wave. Standing waves can lead to high acoustic pressure and are thus able to hold the particles in place, even when the water is flowing. In this way we can construct a filter using sound.
The aim of this PhD study was to design an efficient acoustic water filter. The design was made with advanced computer models, while each design step was verified with experiments. The final design is a small rectangular glass container of just 7 cm length, 2 cm width and 3 cm height. Testing proved that the system was able to separate suspended starch from water with an efficiency of 54% using 1 kWh of electrical energy per cubic meter of water. This efficiency needs to increase further for feasible industrial applications. Direct market opportunities are related to the possibility to separate to particle size in water or air. Clearly one would need an array of these systems in order to treat large water flows, but this is common practice in water treatment.