LINEAR PREDICTION METHOD TO EXTRAPOLATE ULTRASONIC DATA

摘要

The paper discusses use of Linear Prediction method (LP) to retrieve the main echo from a noisy ultrasonic signal. The method extrapolates the data beyond a desired point of time, from where the noise starts to suppress the true signal. The data used for testing is one which is obtained from our previously conducted experiment. The LP method is useful when presence of a number of scattering entities in the medium or that of some other disturbance, makes the 'signal to noise' ratio of transmitted ultrasonic signal low. Due to enormous scattering of acoustic waves in two phase materials like composites and biomedical samples, the wave gets partially absorbed, some scattered and the rest collected by receiver transducer. Echoes obtained in successive reflections are equally spaced and their height reduces to the extent that is a function of amount of absorption (dependent on media) and scattering (dependent on scattering entities). More the scattering entities as is the case with multi phase materials, higher is the attenuation due to scattering. Beside these there could be electrical disturbances. Due to all these, the higher order echoes get merged with the noise. The echoes are therefore hardly visible beyond the initial ones and ultrasonic wave parameters can not be evaluated accurately.