Abstract
Objects' surfaces are classified by analyzing the relative spectrum of an ultrasonic echo with respect to the spectrum of an echo from a flat plane, which serves as a reference echo. This new method enhances accuracy of range measurement by using linear phase difference for detecting time delay between transmission pulse and its echo. Range difference between two planes, which are separated along longitudinal direction, is obtained from frequency dips in the spectrum. Echo from an edge of a prism is recognized by a decrease of power in higher frequencies. Frequency dependency of the transducer's directivity is also considered. Theoretical analysis and some experimental data are presented.
