Particle position and velocity detectors based on particle transit time across uneven inter-gap electrodes

Abstract

This thesis presents a novel particle position and velocity detector based on the electrical measurement of particle transit time across uneven inter-gap electrodes. Compared to the conventional optical methods, the present electrical method offers high integrability with simple structure. Compared to the previous electrical method, the present method using particle size independent transit time achieves high measurement stability insensitive to particle size variation. The present detector consists of a fluidic channel, two bias electrodes, and three sensing electrodes forming two sensing zones divided by a common electrode between two outer electrodes. Electrical signals are generated during a particle transits through the consecutive sensing zones. The present detector obtains the particle position based on the width ratio of two signals, while measuring the particle velocity by the total signal width. We design and fabricate two types of the devices in order to demonstrate and characterize the detection performance. In the experiment, we use particles having the average diameter of 6.59μm and 5.47μm in order to evaluate the performance of the fabricated devices, including ranges, sensitivities, nonlinearities, and measurement uncertainties of the particle position and velocity detection. The particle position and velocity measurement uncertainties are 25.0% and 2.45%, each normalized by the average particle diameter and velocity, respectively, thus comparable to the PIV method. For the particles having different diameters, the present detector shows uniform performance independent on the particle size. We also verify the particle velocity profile detection capability based on the measured position and velocity of particles. In conclusion, the present particle position and velocity detector shows high measurement stability insensitive to particle size variation, and high integrability applicable to integrated system.