Passive low pass filtering effect of mechanical vibrations by a granular bed composed of microglass beads

Passive low pass filtering characteristics of a granular bed composed of microglass beads (MGBs) are investigated for military applications to a shock isolator. The granular bed attenuates the transmission of vibrations over a given frequency range sensitive to electronic devices through kinetic energy absorption like low pass filters in electric system. The experimental studies on five kinds of MGB with different diameters demonstrate that the cutoff frequency and the steepness of rolloff of the granular bed are inversely proportional to the diameter of MGB, and the vibration absorptivity is proportional to the diameter of MGB. The granular bed composed of 68μm diameter MGB absorbs incident mechanical vibrations with the cutoff frequency of 16.0±1.5kHz, the vibration absorptivity of 0.22, and the stopband transmittance of 1%–10%.