Open Access Planar Plasmonic Terahertz Waveguide Based Upon One Dimensional Array of Pyramidal Corrugations and Refractive Index Sensing Volume 12, Number 6, December 2020 KM Dhriti Maurya, Member, IEEE Amir Ahmad Gagan Kumar, Senior Member, IEEE DOI: 10.1109/JPHOT.2020.3034549