Swept-frequency diffraction of ultrasound by cylinders and arrays

Abstract

Diffraction of ultrasound in water by single cylinders and arrays of equally spaced cylinders is studied experimentally using a swept-frequency technique and the results are compared with theoretical predictions. Scattering by single metallic cylinders is computed from a model which includes the effect of reverberations within the cylinder. A one-dimensional, single-scattering approximation is used for data reduction in the case of the regular array where Fourier inversion of the data is used to determine the scatterer spacing of the array. Swept-frequency measurements were made in a fixed geometry using long pulses of a sinusoidal signal whose center frequency was essentially constant during the pulse interval but was varied over the total sequence of pulses. The observed scattering spectrum of a single metallic cylinder agrees closely with the calculated prediction. The Fourier transformation spectra of the array scattering data shows good agreement with the known scatterer spacing even when the data were taken in the nearfield and the data are reduced using a plane wave, farfield assumption. This investigation provides a foundation for additional studies of factors involved in the use of ultrasound diffraction in tissue characterization.