SHADOW DOPPLER TECHNIQUE FOR SIZING PARTICLES OF ARBITRARY SHAPE

The output from a linear diode array is used in a modified laser Doppl er velocimeter to measure the size and shape of irregular particles. T he sizing accuracy for transparent and opaque particles between 30 and 140 mu m is better than 10%. The inaccuracy caused by trajectories th at lay at angles of less than 24 degrees to the axis of the array was less than +5%, and a further inaccuracy of +/-5% was caused by defocus ing of the particle from the center of the velocimeter measuring volum e by up to +/- 500 mu m The advantages of the shadow Doppler technique over other techniques for sizing irregular particles, such as amplitu de systems with pointer volumes, are that the shadow Doppler technique records shape, the optical arrangement is more robust, less precise a lignment is required, and the equipment can be constructed at low cost .