Design and implementation of reconfigurable transmitarray unit cells employing the element rotation method by microfluidics

Erdil, Emre
This thesis presents design, fabrication and measurement of a novel, continuously tunable, circularly polarized X-band microfluidic transmitarray unit cell. To the author’s knowledge, this is the first study in the literature where a microfluidics approach is used to tune the phase of the transmitted field through the unit cell by the element rotation method. Furthermore, the generalized transmitarray design conditions necessary to utilize the element rotation method are derived. To implement the novel microfluidic approach, a unit cell comprising a double layer nested ring-split ring is realized as microfluidic channels embedded in Polydimethylsiloxane using soft lithography techniques and bonded to a glass substrate. Conductive regions of the rings are formed by injecting a liquid metal (an alloy of Ga, In, and Sn), whereas the split region is the air gap in the inner ring. Movement of the liquid metal together with the split around the ring realizes the rotation of the unit cell around its axis, which controls the phase of the transmitted field through the unit cell and provides 360 linear phase shift range. A circularly polarized unit cell is designed by using periodic boundary conditions to implement the infinite array approach and satisfies the design conditions at 8.8 GHz. To realize the rotation, unit cell prototypes at different split positions are fabricated in the facilities of METU and the proposed concept is verified by the measurements using the waveguide simulator method, within the frequency range of 810 GHz. The simulation and measurement results show a fair agreement, illustrating the viability of the approach to be used in reconfigurable reflectarrays and transmitarrays.