The air filters in ordinary vacuum cleaners clog with dust and fluff and need frequent cleaning. Now Bosch and Siemens in Munich, Germany, are automating this dirty and annoying job (WO 2004/100750 and 753).
Their new filter is made from a sheet of porous ceramic with an electric heating coil attached to one side and a small loudspeaker clamped to the other. From time to time the coil warms the filter to break down large particles of dirt, while the speaker blasts it with ultrasound to shake the particles out.
