Planar RF Antenna Reconfiguration With Ni-Ti Shape Memory Alloys

Nickel-titanium shape memory alloys (SMA) are utilized to achieve a multi-band RF (radio frequency) antenna through reconfiguration. Switches made from shape memory alloys electronically connect together a planar antenna arrangement, creating several electrical signal pathways and reconfiguration to be realized. The changes in geometry induced by the switching create different working frequencies of the antenna leading to multiple bands. The switches open and close due to an induced phase change from martensite to austenite via resistive heating from a separate electric circuit. Switch design is based on a previously successful switch geometry with the goal of miniaturizing the reconfigurable antenna system. Simulations were performed to determine an optimal geometry for reconfiguration with the switches to generate measurable changes in working frequency in a planar antenna. Based on these simulations, a planar antenna consisting of a dielectric material between conductive copper layers was designed and constructed for use with the SMA switches. The antenna design is based on a patch antenna that is reconfigured to new geometries as the SMA switches are activated. The working frequency of the planar antenna arrangement can be tuned to between 2.25 GHz and 2.43 GHz depending on geometry as measured with S₁₁ signal reflection.