Active Shape Control of Parabolic Antenna Systems Using Shape Memory Alloy (SMA)

Abstract

Active shape control of flexible antenna structures has become highly demanding in the antenna community. This is due to multiple advantages of control of thermal fluttering and reconfigurability of the antenna. It also enables the antenna to get uniquely shaped against any complicated / irregular footprint. In this work, an effort was made to understand and implement active shape control of various sizes of antenna using Shape Memory Alloy (SMA) wire as actuators. It has been demonstrated that a polycarbonate parabolic antenna surface fitted with curved acrylic stiffeners at the back could be actively deformed by a network of SMA wires. The phase transformation of SMA wires results in the generation of end moment and force at the control points. This can deform the stiffener and thereby the antenna structure. This procedure can generate a maximum deflection greater than 3mm (3000 μm) at the pre-defined control points and can be used for macro shape control. By controlling the current in the SMA wires selectively one can achieve both inward and outward deflection. For numerical study, experiments were conducted to understand the physical properties of these SMA wires and an Equivalent Coefficient of Thermal Expansion (ECTE) model was built for use in numerical simulations. Temperature of the SMA wire was measured during experiments by J-type thermocouple. Later, these temperatures were used to apply necessary boundary conditions in numerical study using ABAQUS. Antenna deflections at a couple of control points were studied experimentally and numerically. Both results were compared and inferences were drawn on the discrepancies. A closed loop system was proposed using a proportional-integral-derivative (PID) control system applicable in real-time with the aid of dSPACE unit. With the help of Ziegler-Nichols method, gains were predicated and the response of the system was captured. This work is envisaged to enable us to design deformable antenna which can be reconfigured for various control point deflections.