Interview

Abstract

Mikko Kokkonen Mikko Kokkonen, from the University of Oulu, Finland, talks to us about his group's submission “Focal length of a low permittivity plano-convex lens at frequencies 30–600 GHz” page 223 One of the exciting research focuses in the microelectronics department at the University of Oulu is research into lenses for sub-terahertz (0.1 THz–1 THz) band applications, which is part of the 6G flagship program (https://www.oulu.fi/6gflagship/). Lenses can be used for focusing the radiation patterns toward a desired direction, which can improve communication between units and reduce the need for higher signal power. Additionally, from the materials side, low-loss and low-permittivity lens materials are an attractive choice for research, as they can be made from novel, sustainable materials. The Letter examines a hemi-spherical lens with geometric optics coupled with a finite element method and compares the results. Geometric optics is a form of optical theory where the wave is assumed to be a line, so it has no information about the waveform. However, the finite element method takes the waveform into account. In this Letter, we have presented simulated results for a hemi-spherical lens and show how different frequencies propagate through and beyond the lens. When using the lens on the front of the receiver to collect radio-waves, it is important to have at least some idea of ​​where to place the lens. As can be seen from the results, different distances mean different electrified intensities that affect antenna performance, so proper placement is important. The biggest challenge we faced is the lack of information relating to lens behaviour for different radio frequencies. There are plenty of research papers out there that are within the realms of the topic, but there is little to no coherent information about how frequency changes should be taken into account with regards to lens dimensions when designing lenses. I'm still fairly new to this field, but I have seen the frequency band increasing from tens of gigahertz to hundreds of gigahertz, and I'm convinced that it will rise even higher! The sixth generation of mobile wireless networks (6G) is tentatively envisioned to launch in the next ten years, so I guess that there will be a lot of different kind of devices utilising the 0.1 THz–1 THz frequency band. Also, I think we can expect to see lots of information on how lenses should and should not be utilised at the sub-terahertz band.