CALCULATION OF ACOUSTIC NEAR-FIELD FROM BESSEL BEAM TRANSDUCERS WITH ANNULAR TRANSDUCER ARRAY

This paper describes acoustic fields radiated from Bessel beam transducers with an annular ring array. We calculate the fields without the para-axial approximation such as the Fresnel one, in order to elucidate the near fields from the transducers. We find that field intensities from some transducers abruptly increase and decrease in the near region. This makes the transducers inappropriate for imaging applications. Annular transducer elements of width less than 1 wavelength prove to be effective in avoiding the abrupt changes.