Abstract: In this paper, we report the study of complex focusing acoustic field of a convex phased array probe widely used in ultrasonic diagnostic B-scanner, we present the time delay necessary for electronic focusing and equivalent to geometric focusing when complex focusing is going on. Making use of Helmholtz's integral formula,we give the expression of acoustic pressure for the electronic or complex focusing acoustic field. Utilizing Simpson's numerical integral and a great deal of computation on 86/330 computer by means of altering the parameters, we select better focal range and beam width of 4 sequences electronic and complex focusing acoustic field.
By comparing the results of computation, we show that the transverse lens doen't affect the lateral focal range and beam width, but only increases the acoustic pressure amplitude (that means, the energy has been concentrated).
At oprating frequency 3.5MHz, the lateral focal rang reaches 10 cm, but the beam width doesn't exceed 3.5 mm, the transverse focal range reaches 5.5 cm, the beam width is less than 4 mm, and at 7.5 MHz, the lateral focal range reaches 6 cm, the beam width is less than 1.2 mm. The numerical computation also gives the influence of the convex array aperture and column heigh on the lateral focal range and beam width.
Making use of FUB-40 ultrasonic diagnostic B-scanner produced by Hitachi company, we photographed the lateral focusing acoustic field and lateral resolution in anechoic water tank. The experiment result agrees quite well with the theory.