Fig. 2.

A reconfigurable directional coupler based on liquid metal actuation. The directional coupler consists of two vertically stacked PPWGs with a gap in the shared metal slab between them. In this gap, a glass capillary contains an electrolyte solution and a liquid metal plug (shown in gold). By applying a small voltage, the liquid metal plug can be electrically repositioned so that it is out of the beam path (as in a, c) or in the beam path (as in b, d), thereby changing the electromagnetic coupling between the two waveguides. a, b Diagrams of the geometry where the input excites the top waveguide. c, d Finite-element simulations of the dual waveguide, showing the vertical component of the electric field. The upper waveguide is excited by at Port 1 in the TEM mode, at a frequency of 123 GHz. a, c When the liquid metal is out of the beam path (so that the capillary is backfilled with electrolyte), most of the THz signal remains in the upper waveguide and exits from Port 2. b, d When the liquid metal is in the beam path, nearly all of the THz wave couples to the lower waveguide and exits from Port 3