AbstractThe electrostatic charge and size distribution of aerosol particles play a very important role in many industrial applications. Due to the complexity and the probabilistic nature of the different charging mechanisms often acting simultaneously, it is difficult to theoretically predict the charge distribution of aerosol particles or even estimate the relative effect of the different mechanisms. Therefore, it is necessary to measure the size and also the bipolar charge distribution on aerosol particles.
The main aim of this research project was to design, implement and simulate a signal processing system for novel, fully functional measurement instrument capable of simultaneously measuring in real time the bipolar charge and size distribution of medical
aerosols. The Particle Size and Charge Analyser (PSCA), investigated in this thesis, uses Phase Doppler Anemometry (PDA) technique. The PDA system was used to track the motion of charged particles in the presence of an electric field. By solving the equation of particle motion in a viscous medium combined with the simultaneous measurement of its size and velocity, the magnitude as well as the polarity of the particle charge can be
obtained. Different signal processing systems in different excitation fields have been designed and implemented. These systems include: velocity estimation system using spectral analysis in DC excitation field, velocity estimation system based on Phase Locked Loop (PLL) technique working in DC as well as sine-wave excitation fields, velocity estimation system based on Quadrature Demodulation (QD) technique under sine-wave
excitation method, velocity estimation system using spectral analysis in square-wave excitation field and phase shift estimation based on Hilbert transformation and correlation
technique in both sine-wave and square-wave excitation fields. The performances of these systems were evaluated using Monte Carlo (MC) simulations obtained from the synthesized Doppler burst signals generated from the mathematical models implemented in MATLAB. The synthesized Doppler Burst Signal (DBS) was subsequently corrupted with the added Gaussian noise. Cross validation of the results was performed using hardware signal processing system employing Arbitrary Waveform Generator and also NASA simulator to further confirm the validity of the estimation.
It was concluded that the velocity estimation system based on spectral analysis in square-wave excitation field offers the best overall performance in terms of the working range, noise sensitivity and particle capture efficiency. The main reasons for the superiority of the square-wave excitation over the sine-wave excitation system are as follows: Firstly, in the square-wave field particles attain higher velocities and greater amplitudes of displacement, which increases their probability of crossing the measurement volume from various injection points. Secondly, the sine-wave excitation requires that the particle residence time in the measurement volume is at least equal to one period of the
excitation, which effectively eliminates shorter and discontinuous burst. Thirdly, the signal processing based on FFT is less demanding in terms of the quality of DBS, which increases the likelihood of the detected particles to be successfully processed.
|Date of Award
|5 Oct 2010
|Janusz Kulon (Supervisor)