Smart Switch Metamaterials for Multiband Radio Frequency Antennas

We investigate metal-matrix composite metamaterials with embedded electrical switches made of shape memory nickel-titanium (Ni-Ti) for use in broadband radio frequency (RF) antennas. Experiments show that a Ni-Ti ribbon can form an electrical contact that opens and closes depending on the Ni-Ti phase being austenite or martensite. Finite element modeling of thermal gradients illustrates the phase change within the ribbon. Ultrasonic additive manufacturing (UAM), a solid-state additive manufacturing process, was utilized for embedding a Ni-Ti switch in an aluminum matrix. The aluminum matrix must have structural-grade strength for use in load-carrying antennas; thus, mechanical testing was conducted to quantify the longitudinal tensile, transverse tensile, and shear strength of the UAM matrix. Reconfiguration using a Ni-Ti switch was proven using a shape memory switch on a monopole RF antenna producing an operating frequency shift from 270 to 185 MHz when the switch is connected. A planar microstrip line was used to demonstrate signal transmission and reflection efficiency in a smaller, second switch. Transmission tests yielded less than -10 dB signal reflection proving the feasibility of reconfigurable planar antenna arrays using smart switches.