Direct measurement of moment mobility and a moment excitation system

Over the years, a number of investigators have tried to solve the problems in the direct measurement of moment mobility. However, no one has found a moment excitation system that can produce a pure and sufficiently powerful moment. In the past, most investigators tried to solve the problem of impurity in moment by tackling the problem in unmatched shakers in a moment exciter. Su and Gibbs (Su J, Gibbs BM. Measurement of point moment mobility in the presence of non-zero cross mobility. Applied Acoustics 1998;54(1):9-26) have indicated theoretically that compromise between the purity and the power of a moment generated by the moment exciter is greatly affected by the output force impedance of the moment excitation system. In this paper, experiments have been conducted to investigate the effect of output force impedance on direct measurement of moment mobility from which theory of Su and Gibbs has been verified. Methods of improvements of the moment exciter have been proposed in order that the moment exciter can generate a pure and sufficiently powerful moment.