## 2 Application of Particle Dampers  
Particle damping technology is conceptual simple, robust, low-maintenance, and cost-effective, which make this technique extremely attractive for industrial application. The ability of particle dampers to sustain under harsh environments and its damping characteristics over a wide range of frequency and temperature makes its application more favorable in comparison to conventional passive dampers and active damping techniques. Moreover, particle dampers are easily recyclable or can be reused depending on the granular materials. In the ongoing project, it has been shown that the waste of automobile tires can be used in particle dampers for a wind turbine blade vibration attenuation [18]. [PERSON] et al. [19] have attached a particle damper capsule on a printed circuit board (PCB), which is used in a spacecraft. Authors have used tungsten carbide, stainless steel, and aluminium alloy as granular materials. In their investigation, it has been observed that materials with higher densities are more efficient for vibration attenuation. Authors have found the packing ratio of 60% effective for vibration suppression for all the materials they have investigated. Furthermore, they have observed that irrespective of granular materials, the packing ratio of 100% is not effective for reducing the vibration amplitude. A very similar effect of filling ratio on vibration reduction has been also observed in our previous study [17]. The effectiveness of particle dampers to reduce the vibration amplitude from a spacecraft cantilever beam type appendages was investigated experimentally by [PERSON] [20]. A small cavity box containing 30 g lead shot, which was attached to the main structure at the position with the highest deflection during flight, reduces the vibration amplitude significantly under random vibration. He has concluded that in comparison to conventional damping materials, such as viscoelastic materials or viscous fluids, particle dampers are more suitable for spacecraft applications due to their immense damping performance for higher vibration amplitude and also for their insensitive nature towards extreme temperature. [PERSON] et al. [16] have filled the tip of a honeycomb beam with acrylic balls (1.25 mm radius) to investigate the efficiency of particle damping technique on vibration attenuation. The reason for choosing only the tip of the beam for the granular material filling was to keep the additional mass as low as possible. Apart from this, the tip of the beam experiences significant motion for all the bending modes, which makes this area suitable for placing the particle damper. In their investigation, they have found a significant reduction in vibration of the primary structure. The experimental investigation of [PERSON] et al. [21] has shown that using hollow soft viscoelastic particles can reduce the vibration amplitude of a honeycomb beam. Implementation of soft hollow particles can also be useful in reducing the additional mass coming from granular materials. The authors have investigated three filling ratios, namely: 50%, 80%, and 100%. They found that the filling ratio of 80% has more influence on the damping ratio. In an experimental study, [PERSON] [22] has shown that the steel ball-bearing can reduce the vibration amplitude significantly when attached to the tip of a rotating cantilever beam. [PERSON] et al. [23] have shown the usefulness of hollow glass microspheres in reducing the vibration amplitude of a composite honeycomb beam. They have studied the influence of the packing ratios of 50%, 70%, and 90% on vibration attenuation and found that the frequency response of the main structure decreases as the packing ratio increases. [PERSON] et al. [24] have used tungsten carbide and lead sphere to reduce the vibration amplitude from a precision instrument in spacecraft. In their investigation, it has been shown that the filling ratio of 70% is more efficient for reducing the vibration amplitude of the primary structure in comparison to the filling ratio of 50% and 90%.