Background <p>The authors consider using the metal particle damper to attenuate vibration in the Gas Generator cycle Air Turbo Ramjet (GG-ATR) engine. Its stiffness and damping characteristics largely depend on the preload on the particles and should be investigated for the particle damper design.</p> Methods <p>The authors conducted vibration tests for the metal particle damper, and its configuration is the same as that employed for the GG-ATR engine. Its metal particles are made of SUS 440C with a 0.6mm diameter. The electrodynamic shaker generates sinusoidal oscillation in the particle damper. The excitation amplitude ranges from 20 to 80 microns peak-to-peak (p-p), and the excitation frequency is from 150 to 350 Hz. The preload pressure on the particle ranges from 41.73N to 153kPa. The experimental data are applied to the Fast Fourier Transformation to evaluate the damping and stiffness coefficients of the particle damper.</p> Results <p>The stiffness coefficient of the particle damper decreases with the increase of the vibration amplitude. However, for frequency characteristics, the stiffness of coefficients is roughly constant for the frequency range from 150 Hz to 300 Hz and reduced for frequencies greater than 300 Hz. Therefore, the stiffness coefficients of the preload pressure from 41.73 to 153.0 kPa converge to a certain level for the vibration amplitude of more than 40 microns p-p. For the damping coefficient of the particle damper, the theoretical friction damping theory can explain its damping behavior. Moreover, the damping coefficients are proportional to the preload for any amplitude and frequency condition.</p> Conclusion <p>A linear relation can be observed between the damping coefficients and the preload pressure. However, the stiffness coefficient has such a linear relation only for the amplitude of 20 micron p-p. and does not for the amplitude of 60 micron p-p.</p>