The transducer that converts the light, rays into electrical energy is called photo electric transducer. When a light energy falls on the surface of a metal, then this energy is converted into kinetic energy of the electron and the electron leaves the metal.
This depends on the work function φ and charge "e" of the material. The electrons that are emitted depend on the intensity of light "I" falling on the surface. This photoelectric transducer was developed to measure diameter and length variations in arterial segments in vitro and in elastic tubes.
Its construction is simple, its nonlinearity small and its sensitivity adequate. The cut-off frequency is 300 Hz and its small phase lag changes linearly with frequency.