Periodic Surface Lattices for Novel mm-Wave and THz Sources
by Dr. Amy MacLachlan et al.
Department of Physics, SUPA, University of Strathclyde, Glasgow, G4 0NG, Scotland, UK
(host F. Capolino)
The ability to exploit and control electromagnetic (EM) fields on the surface of periodic lattices is relevant to the realization of high-power, high-frequency coherent radiation sources. Such sources are suited to various applications including imaging and security, communications, the quality control of pharmaceutical products and monitoring atmospheric pollution and space debris. To avoid multi-mode excitation, which is detrimental to the efficiency of the source, cavity dimensions are typically scaled according to the intended operating wavelength. This reduction in cavity size with wavelength limits the power output of high-frequency sources. Periodic surface lattice (PSL) structures provide a novel solution to this challenge, enhancing the mode selectivity of oversized cavities and thereby maintaining high power output capabilities at mm-wave and THz frequencies. When the necessary conditions are met, PSLs facilitate coupling of volume and surface fields, resulting in the formation of a single cavity eigenmode.
Planar PSL structures are studied to demonstrate the fundamental “proof of principle” coupling of volume and surface fields. Conformal mapping allows these planar PSLs to be fabricated into cylindrical PSLs compatible with the construction of high power electron-beam-driven sources.
Planar PSL structures have been designed, fabricated and measured at 140-220 GHz and 325-500 GHz in order to demonstrate the coupling of volume and surface fields resulting in the formation of a coherent cavity eigenmode. Numerical modelling carried out using CST Microwave Studio (MWS) predicts the location of possible coupled eigenmodes, demonstrating good agreement with the experimental measurements. The planar PSLs’ numerical dispersion diagrams, obtained using CST MWS, resemble analytical dispersion diagrams obtained by solving a coupled dispersion equation, applicable to both planar and cylindrical geometries, when similar parameter values are chosen.
Progress on the experiment underway at the University of Strathclyde, involving a cylindrical PSL incorporated in a W-band (75-110 GHz) Cherenkov source, is presented in this work. The intricate design of cylindrical PSLs required for high-frequency sources can be manufactured using high-resolution 3D printing. Cylindrical PSLs designed to operate at 0.1 THz, 0.4 THz and 1 THz are realised using additive manufacturing techniques and measured using a Vector Network Analyzer, demonstrating their potential for use in high frequency sources.
Short Bio of Dr. Amy MacLachlan
Amy MacLachlan was born in the Scottish Highlands. She graduated with an MSci in Physics in 2011 and received her PhD in 2016, both from the University of Strathclyde in Glasgow, Scotland. She currently works with the Atoms, Beams and Plasmas group at Strathclyde, continuing the research presented in her PhD thesis titled “Control, Manipulation and Exploitation of Complex Electrodynamic Structures”. Her current areas of research interest include metamaterials and the study of novel periodic surface lattice structures for the realization of high-power electron-beam driven sources at GHz-THz frequencies.