Measurement of Silicone Rubber Using Impedance Change of a Quartz-Crystal Tuning-Fork Tactile Sensor

Abstract

Silicone rubber has been investigated experimentally using the impedance change (ΔR) of a quartz-crystal tuning-fork tactile sensor when its base is in contact with the surface of many kinds of rectangular silicone rubber plates in order to discover how viscosity and elasticity of silicone rubber may be separately determined. Eleven silicone rubber plates (the values of the rubber hardness are JIS85, 80, 70, 65, 60, 50, 45, 40, 35, 30, and 20) are investigated in this experiment. ΔR increases linearly according to acoustic impedance ρC (ρ: density of silicone rubber, C: sound velocity of a longitudinal acoustic wave in silicone rubber). We compare ΔR with ρC when C is calculated in three cases: in first, C is calculated using Young's modulus of silicone rubber measured by a tensiometer; in second, using Young's modulus which is converted by the shear modulus measured by a rotating viscometer using the Poisson ratio of silicone rubber, 0.49; in third, using a complex Young's modulus which is converted by the complex shear modulus measured by a rotating viscometer. We investigated which case in the three described showed good linearity between ΔR and ρC. In order to clarify how the longitudinal plane wave generated in the sensor's base travels into the silicone rubber plate, ΔR is measured when the tactile sensor is in contact with the surface of the rectangular silicone rubber plates of varying thickness and a size.