Non-linear characteristics of transmissibility in the dynamic responses of standing subjects exposed to vertical whole-body vibration
In this paper we studied the action of vibrations with low amplitude and high frequency on the human body, especially on the bone system, because this type of vibration is quite common for some work equipment and the effect on the workers is obvious: predisposition to bones fractures, osteoporosis, etc. For the study of vertical vibrations through the body were used oscillations at amplitudes of 1, 1.5 and 4 mm and at frequencies between 5÷35Hz. Whole-body vibration measurement was carried out with a NetdB multiple acquisition system using Piezotronics 356A16 PCB triaxial accelerators. Data was processed using dBFA Suite – Purchase and post-processing data acquisition software. The transmissibility of vibrations to the body was determined as a ratio of the mean square root of the acceleration signal received by the accelerometers (arms) to the mean square root of the signal acceleration given by the vibrant platform for three regions of the body: the knee, the lumbar region and the forehead. It was found that most arms peaks were obtained for 5÷10Hz frequencies, but there were also other frequencies for which the maximum was reached, which proves that there are more maximum accelerations specific to the position than those imposed by the vibrant platform. On the other hand, it was also found that the acceleration of transmitted vibration highly decreases compared to the acceleration given by the vibrating platform. There are important differences between the transmissibility of different people, in regard to BMI: it was found that for overweight people, transmissibility is lower than that of the normal ones.