ASA 124th Meeting New Orleans 1992 October

5aPAb9. Generation of nondiffracting X waves using annular-array transducers.

Mostafa Fatemi

K. Ghaseminejad

Iran Res. Org. for Sci. & Tech., and Elec. Eng. Dept., Tehran Univ., N. Kargar Ave., Tehran 14399, Iran

Nondiffracting beams have been suggested for ultrasonic imaging and tissue characterization applications because of their long depth of field. Recently, a new class of nondiffracting beams, termed the X waves, has been discovered. An advantage of these beams over the J[sub 0] Bessel beam is that the X waves are nondispersive. An ideal zero-order X wave has infinite time duration and requires infinitely large aperture area, excited by a spatially nonuniform, circular-symmetric, input, h(r,t), where r and t are the radial distance and time, respectively. In practice, X waves can be generated employing a finite size annular-array transducer. In this paper, annular-array implementation of the X waves is investigated and the errors introduced in the field due to such implementation are analyzed. Each ring in the array is excited by a different time-limited waveform. Quantitative comparisons between the field of the array and the ideal X wave is made possible by computer simulations. Results indicate that, in the range of parameters usually encountered in medical diagnosis, the errors introduced due to array implementation of the X wave can be made negligible, if a reasonable number of rings is used. The relative error is presented in terms of the ratio of element width to spacing, number of elements, and radius of the transducer. Simulation results at various observation points will be presented.