Effect of impedance mismatching and time delays in ultrasonic measurements

In many applications ultrasonic waves are required to travel in different propagation mediums, hence, are subjected to diffraction, diffusion, reflection, scattering, absorption etc. The shapes of the mediums are arbitrary and complex, thus introducing further distortions and nonlinearity. In this paper the effect of the arbitrary shape of propagation medium on the ultrasonic wavefront has been discussed with particular reference to solid level measurements in containers. The scattering and break-up of the wavefront has been illustrated. The effect of acoustic impedance mismatching, with reference to flow measurements in closed pipes, has been detailed and some statistical data has been presented. The data is derived from assumptions that arbitrary magnitude acoustic mismatching is introduced by the operational conditions and imperfect structure of the medium travelled e.g. unintended air gaps between transducers and pipe. Time delays are shown to limit the applications and affect the accuracy seriously as in the case of liquid flow measurements. However, it is possible to teach the instruments to eliminate some of the shortfalls