Echo Signal from Rough Planar Interfaces

The received electrical signal from a pulse-echo system insoni'ing a planar acoustical interface was measured for varying degrees of rms roughness (0 0.16 mm), angle of incidence (typically +/-7'/ and range to the transducer. A planar and a focused 5 MHz transducer was used. When insonifying a smooth interface, the normalized spectrum of the received signals for a planar transducer exhibits an increasing number of nulls with increased angle of insonification, as predicted from numerical modeling while the dependence on insonification angle for the focused transducer was smaller and the null pattern was much less distinct. ducer with the interface located at the geometrical point For the planar transducer and for the focused transof focus, the energy of the received signal as a function of incident angle was appraximately Gaussian with maximum at 09 For the smooth interface, the -3 dB width was -0.5and -3for the planar and the focused transducer, respectively. 1 . Introduction research for several decades. The progress has, however, Tissue characterization has been an active area of been limited by the fac t that the ID electrical signal from the receiving transducer is the result of not only the 3D distribution of scatterers, the geometry and acoustic properties of interfaces and scatterers, but also to a large extent the field pattern and frequency response of the given transducer and constructiveldesmctive interference in the backscattered field at the surface of the receiving transducer. pulse-echo system insonifying a planar acoustical interAs an example, the received electrical signal from a face depends mainly on surface characteristics, orientation of the interface and on transducer geometry. When the surface characteristics is limited to smooth, the given measurement configuration can be simulated with computer models[" even when the interface is non-planar'". When a rough planar surface is considered, the modeling becomes stochastic in nature'", and computer modeling tools are not yet available to readily predict the received electrical signal. 0-7803-4095-7/98/$10.00