Frequency selective surfaces for terahertz applications

This thesis presents Terahertz (THz) Frequency selective surfaces (FSS) that can be realized using standard microfabrication techniques. These FSS structures are designed for frequencies around 0.8 THz, which is a crucial operating frequency in security and medical imaging. Using THz waves for such applications, multilayer frequency selective surfaces are preferred due to their wide band response, lower dependency to angle of incidence, and low loss. The implementation of such structures requires very thin layers of substrates and membranes in order to improve the performance in THz regime. In order to alleviate the difficulty in the implementation of multilayer structures, a fabrication process is proposed where a 100 u m-thick glass membrane is formed through HF etching of a 500 um-thick glass wafer. Using this fabrication process, three separate designs consisting of single-layer FSS are investigated using high frequency structural simulator (HFSS). The fi rst design, consists of a circular ring slot in a square metallic structure on top of a 100 um-thick Pyrex glass membrane with 95% transmission bandwidth of approximately 0.042 THz , which remains nearly constant till 30 (degrees) angle of incidence. The second design consists of a tripole structure on top of a 100 m-thick Pyrex glass membrane with nearly 95% transmission bandwidth of 0.015 THz, which remains nearly constant till 30 (degrees) angle of incidence. The third structure consists of a triangular ring slot in a square metal on top of a 100 u m-thick Pyrex glass membrane with 95% transmission bandwidth of 0.015 THz, which remains nearly constant upto 20 (degrees) angle of incidence. These designs show that the reflections from samples can be reduced compared to the conventional sample holders used in THz spectroscopy applications; by using single layer FSS structures manufactured through a relatively simple fabrication process.