Improving tactile feedback with an impedance adapter

Vibration motors are often used to generate tactile effects by exciting a mass at a given frequency and amplitude. The characteristic impedance of this vibrotactile device is not always in harmony with the impedance of the human skin. This impedance mismatch can result in poor energy transfer, necessitating larger motors and greater power consumption than otherwise required. Herein, we investigate the feasibility of improving the energy transfer by placing a medium between the skin and the motor, which we dub an impedance adapter. We simulate the effects of this impedance adapter using a mathematical model, and evaluate its effect on skin displacement and a parameter we call skin stimulus. Skin stimulus is introduced as a measure of the perceptive effects of a haptic system, and is used to compare results between systems with an impedance adapter and those without. Our findings suggest a factor of four improvement in skin displacement and a two-fold increase in skin stimulus are possible by introducing an optimized impedance adapter.