Space-periodic capacitance transducer for the measurement of flow velocity

A capacitance transducer with a periodic electrode structure is described for the measurement of particle velocity in particulate flows. The electrodes are in the form of interdigital combs deposited on an alumina substrate, and the expected capacitance variation when particles pass over the transducer is found from numerical field calculations. The effect of substrate thickness and the influence of screening electrodes is examined using the same method. An experimental system is described, and a method of calculating particle velocity from the mean frequency of the power spectrum of the transducer signal is examined theoretically. Examples of waveforms and power spectra from the experimental system are given, and the errors in the velocity estimate, which in practice are less than 5%, are compared with the theoretical results.