Measurement of Micro-Strain in Nail Caused by Pulse Wave

The micro-strains of a fingernail and toenail caused by pulse wave were measured by a conventional strain measuring method using a biaxial strain gauge. The strain fluctuations of nails were larger in the lateral direction than in the longitudinal direction. In a previous study, pulse wave measurement by a polyvinylidene difluoride (PVDF) film, which is a piezo film, attached to the nail surface was proposed as a new pulse wave measuring method with lower electrical power consumption. The piezo film can transform a nail surface micro-strain caused by pulse wave into an electrical signal. However, the optimal orientation of the piezo film on nails remains unclear. The experimental results of the present study showed that a larger displacement was generated from the nails to the piezo films by aligning the longitudinal direction of the piezo film with the lateral direction of the nails.