Strip excitation of slender beams

Abstract

Strip excitation of beams is studied. A real-valued force distribution function is derived which minimizes the active power input to the beam. It is demonstrated that for this force distribution the part of the strip mobility vanishes, implying that no active power is transmitted. The minimizing force distribution is no-cophase and an associated co-phase distribution is developed which is comparatively simple to establish in practice. For the co-phase force distribution the real part vanishes for certain regions of Helmholtz numbers. The high-frequency asymptotes of the real and imaginary parts of the strip mobilities are the same as those associated with the minimizing force distribution. Experiments are made on both finite and “infinite” beams. The results show that the minimizing force distribution is highly selective in frequency, and that if a broadband suppression of the input power is required, the uniform force distribution is preferable. For real-valued force distributions, the strip mobility can be seen to give an adequate description of the structural acoustic behavior of the beam.