Millimeter-Wave Resonant Spectroscopy of Sub-Wavelength Dielectric Particle

A novel technique for dielectric spectroscopy of an isolated, low-loss, homogeneous spherical dielectric particle of moderate permittivity is explored using Mie theory. The superposition of the fundamental electric and magnetic dipole modes in the particle-under-test causes frequency-dependent maximum and minimum of forward scattering, which can straightforwardly be determined by transmission measurements. Then, both the radius and the dielectric constant of the spherical particle-under-test can be uniquely determined. The technique is demonstrated for different Alumina ceramic spheres of about 1mm diameter, measured at W-band frequency (75GHz to 110 GHz). Challenges of the proposed novel millimeter-wave spectroscopy method are discussed.