Review of Techniques for Particle Spectroscopy From DC to Terahertz Frequency

Nondestructive, contactless, and label-free characterization of small particles plays an important role in laboratory research and industrial manufacturing. Also, the analysis of small things, especially particulate biomatter, using electromagnetic waves has a long history in optical microscopy. Light, however, cannot reveal much information about the material property of the particle. Radio waves, on the other hand, apart from being more sensitive and featuring compact instrumentation, interact strongly with a dielectric particle. Thus, in principle, it can provide information about the particle in both shape and material. Therefore, particle spectroscopy using electrical signals plays a vital role in research and development. Although not firmly established as its optical counterpart, it is still reasonable to analyze the nascent stages of its development up until now. In this review article, different state-of-the-art techniques for particle spectroscopy spanning from dc to terahertz frequency regimes are categorized into two board domains: electromagnetic perturbation and electromagnetic scattering-based approaches. A critical analysis of the uniqueness of terahertz frequency in context to particle spectroscopy is outlined. Finally, this article discusses a realistic scaling approach from generic optical sensors to an electronic lab-on-chip design for sensing and characterization of particle-in-flow in microfluidics. It also addresses the feasibility of modern high-frequency circuit design technology for potential electromagnetic scattering-based particle spectroscopy innovations.