### 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.