Physical parameter measuring apparatus and method thereof

摘要

A method and system (22) are provided to measure a physical parameter of a layer (30) of a multi layer article in which first and second pulse of electromagnetic energy are directed to the surface of the article, the first pulse causing ultrasonic motion of a first spot on the surface and the second pulse directed to a second spot which substantially overlaps the first spot being reflected and modulated by Doppler shifting due to the ultrasonic motion of the surface. The reflected pulse is detected to obtain a corresponding ultrasonic electric signal which is processed to obtain a physical parameter of the at least one layer at the overlapping spots.