Amplitude and frequency dependence of magneto-sensitive rubber in a wide frequency range

Two new aspects of the dynamic behaviour in the audible frequency range of magneto-sensitive (MS) rubber are highlighted: the existence of an amplitude dependence of the shear modulus-referred to as the Fletcher-Gent effect-for even small displacements, and the appearance of large MS effects. In order to illustrate these two features, results are presented of measurements performed in the audible frequency range on two different kinds of rubber: silicone and natural rubber with a respective iron particle volume concentration of 33%. The particles used are of irregular shape and randomly distributed within the rubber. An external magnetic field of 0-0.8 T is applied. Both kinds of rubber are found to be strongly amplitude dependent and, furthermore, displaying large responses to externally applied magnetic fields-a maximum of 115%. Also included are graphs of measurements on silicone and natural rubber devoid of iron particles. Those results support the conclusion that introducing iron particles in the rubber gives rise to a strong, non-negligible, amplitude dependence in the entire frequency range.