Approximation of Bessel beams with annular arrays

It is shown that the limited-diffraction Bessel beam of order zero can be generated by a transducer with equal-area division of elements and with a fixed prefocus, i.e. conventional transducers used in medical imaging equipment. The element division implies that the scaling parameter must be chosen to contain the first lobe of the Bessel function in the first element. In addition the prefocus must be such that the array is steerable to infinite depth. Examples of low- (3.5 MHz) and high-frequency (20 MHz) arrays are shown where the approximate Bessel beam compares favorably with a spherically focused beam with a fixed focus. The main advantages are a sharper nearfield and a more uniform beamwidth.