The effect of a linear phase taper on the near field of an ultrasonic multi-element array

Electronic beam deflection of the near field of a 10-element ultrasonic array in water has been studied as a preliminary step towards using the principle in solids. The change in the field pattern arising from the change in the path length from each element is discussed for steady state conditions as the beam is caused to be deflected by a linear phase taper. It was shown that the `beam¿ can be deflected a significant amount within the Fresnel region and single discontinuities in the medium lying at an angle to the normal of the array can therefore be examined. Multiple discontinuities, each of different impedance, may give rise to ambiguous results of a more serious nature than those experienced in the far field.