Direct measurement of index finger mechanical impedance at low force

Non-contact, direct mechanical impedance measurements of the human index finger were performed under sinusoidal force inputs. The force amplitudes from the transducer were from 0.05 N to 0.5 N over the frequency range 50 Hz to 500 Hz, which covers the region of interest for vibrotactile feedback for handheld applications. We found that the vibrational mode of the finger was strongly frequency dependent. Our results indicate that a single degree-of-freedom of mass-damper-spring model, used previously in impedance models at high finger forces, may not be appropriate at these lower force levels.