Development of the fuel-powered compact SMA actuator: second-generation actuator

This paper discusses the design and experimental results of the improved fuel-powered compact SMA actuator system and its comparison with the first-generation design. The K-alloy SMA strip (12 mm × 0.9 mm), actuated by a forced convection heat transfer mechanism, is embedded in a rectangular channel. In this channel, a rectangular piston, with a slot to accommodate the SMA strip, runs along the strip and prevents mixing between the hot and cold fluid in order to increase the efficiency of the system. The main energy source is fuel, such as propane, in order to achieve high energy and power densities of the system. Numerical analysis was performed to determine optimal channel geometry and to estimate maximum available force, strain and actuation frequency of the SMA actuator. The combustor/heat exchanger was designed to achieve higher heat transfer rates to the hot fluid from the energy source. The SMA actuator system is composed of pumps, valves, bellows, radiator, combustor/heat exchanger and control unit. The experimental testing of the SMA actuator system resulted in 735 N force with 2.5% strain and 0.25 Hz actuation frequency in closed-loop operation.