Measurement of Dynamic Stiffness of Subcutaneous Tissues Using Self-Excited Vibration Generated by Positive Feedback of Velocity

This paper describes the measurement method of dynamic stiffness of subcutaneous tissues. After the ball indenter which is attached to the Voice Coil Motor (VCM) is pressed against body surface with any preload, the mass-spring-damper system is constructed between the subcutaneous tissues and the VCM. When the VCM is controlled with positive feedback of velocity, self-excited vibration is occurred. Spring constant of the subcutaneous tissues is identified with this resonance frequency of the system. Further, the VCM is controlled to realize the constant amplitude of velocity using a variable velocity feedback gain. Damping coefficient of the subcutaneous tissues is identified with velocity feedback gain. This method can be realized as a real time system, and accordingly measures time-varying dynamic stiffness of subcutaneous tissures.