Shadow Doppler technique for sizing particles of arbitrary shape

Area of Science:

• Fluid dynamics
• Optical metrology
• Particle characterization

Background:

• Accurate measurement of irregular particle size and shape is crucial in various scientific and industrial applications.
• Existing techniques often face limitations in accuracy, robustness, or cost-effectiveness.

Purpose of the Study:

• To develop and validate a modified laser Doppler velocimeter (LDV) for measuring the size and shape of irregular particles.
• To evaluate the accuracy and limitations of the proposed shadow Doppler technique.

Main Methods:

• Utilizing the output from a linear diode array within a modified laser Doppler velocimeter.
• Employing the shadow Doppler technique to analyze particle trajectories and dimensions.

Main Results:

• Achieved sizing accuracy better than 10% for transparent and opaque particles (30–140 µm).
• Inaccuracy due to particle trajectory angles (< 24°) was < +5%.
• Inaccuracy due to defocusing (±500 µm) was < +5%.

Conclusions:

• The shadow Doppler technique provides accurate size and shape measurements for irregular particles.
• This method offers superior robustness, lower alignment sensitivity, and cost-effectiveness compared to amplitude systems.
• The technique is suitable for analyzing particles within a specific size range and under defined optical conditions.