Millimeter-Wave Multi-Static Scattering for Sub-Wavelength Particle Characterization

The concept and formulations for characterization of an isolated spherical particle based on multistatic measurements of electromagnetic scattering are demonstrated in the V -band (50-75 GHz). Both diameter and relative dielectric permittivity, along with an estimate of dielectric loss tangent, are extracted simultaneously through rigorous postprocessing of the measured scattering attributes. For the case of an alumina sphere with a dielectric constant of around 10, the classical Mie theory is explored. For comparatively lower permittivity quartz spheres of the dielectric constant of around 4, the electrostatic modeling of induced dipole moment and its associated electric polarizability is employed. Spheres of diameter as small as 1/12-th of the operating wavelength are characterized with small uncertainty for extracted diameters, and the extracted dielectric properties for the spheres agree well with the literature. The advantages and challenges of the proposed multistatic scattering measurement scheme are critically addressed. Finally, the potential of characterization of particle-in-flow in a futuristic integrated subterahertz lab-on-chip module is outlined.