Abstract: It is increasingly recognized that machines and other vibrational sources can impart structure-borne sound power into supporting and connected structures through rotational components of excitation as well as translational components.It is well known that the rotational components are difficult to estimate since moments are not easy to generate and measure.ln this paper a prototype moment actuator is introduced.It consists of two parallel rods of giant magnetostrictive material.The Performance of the actuator has been investigated by means of a transfer function involving magnitude and phase.A quantity, "purity of moment excitation",has been proposed to estimate the ability of the actuator to impart moments.