An extended zero-crossing method for ultrasonic velocity measurements.

Abstract

Sound speed that is the response of media to sound propagation provides important information to evaluate elastic characteristics quantitatively. It is desired to develop precise measurement technique of sound speed. Sound speed of media can be determined by measuring travel time of the sound traversing media when the distance between transmitter and receiver is known. The zero-crossing method is popular to measure the travel time using sound pulse. This method is useful in measuring sound speed of homogeneous medium. In homogeneous medium, the wave form of received signal is almost independent of the travel distance of the sound pulse. In inhomogeneous medium, the wave form of received signal is depend on the characteristics of media. The measured sound speed by the zero-crossing method means the speed of early received sound. In this paper, an extended zero-crossing method is proposed. In order to evaluate the time interval, some time range within pulse signal is considered for processing. It increases the reliability of measured sound speed, and is helpful to consider on the physical meaning of measured sound speed of inhomogeneous media.