In recent years, active material driven actuators have been widely researched for potential applications in the fields of aerospace, automotive and civil engineering. While most of these active materials, such as piezoelectric, magnetostrictive and electrostrictive materials, have high force and bandwidth capabilities, they are limited in stroke. In combination with hydraulic systems, the field dependent motion of these materials can be amplified to produce high force, high stroke actuators. In a hybrid hydraulic pump, the motion of an active material is used to pressurize a hydraulic fluid. Since the properties of active materials vary greatly in terms of free strain and block force, there is a need to identify the optimum active material for a particular application. This study compares four active materials, Lead-Zirconate-Titanate (PZT), Lead-Magnesium-Niobate (PMN) and Terfenol-D, as the drivers of a hybrid hydraulic actuation system. The performance of each of these active materials was evaluated in the same hydraulic actuator through systematic testing of the actuator while maintaining the same length and volume for each active material. In each case, the active material had a length of around 54 mm and a cross-sectional area of 25 mm2. Commonly used metrics such as output power and electromechanical efficiency are used for comparison. Of the four materials tested in this study, PMN presented the largest free strain (2000με), while Terfenol presented the least (1000με). The highest no-load velocity was also exhibited by the PMN based actuator (270mm/s). The maximum output power obtained was 2.5W for both PMN and Terfenol-D based actuators while the highest electromechanical efficiency obtained was 7% for the PMN based actuator.

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