Device for focussing particles suspended in a gas stream
A device for controlling the motion of particles suspended in a gas stream is provided, including a pipe, through which at least a fraction of the gas stream flows, a source of AC voltage, a source of DC voltage, and a plurality of electrode sets positioned within the pipe in series, generating an inhomogeneous electric field to cause the particles suspended in the gas stream to concentrate into a narrow axial region in the center of the pipe. Each electrode set includes a first pair of opposed hyperboloidally shaped electrodes connected to the AC voltage source and a second pair of opposed hyperboloidally shaped electrodes connected to the DC voltage. The first and second pairs of opposed electrodes are positioned at spaced apart intervals around the circumference of the pipe to define an opening through which at least a fraction of the gas stream flows. The electrode sets are positioned within the pipe in series such that the gas stream flows through the openings defined by each successive electrode set. The spaced apart distance between the electrodes of each successive electrode set is decreased to reduce the size of the openings, causing the particles suspended in the gas stream to focus or concentrate along successively narrower axial regions in the center of the pipe.