The acoustic field around the focused point of an ultrasonic transducer (12-mm diameter with a radius of curvature
of 60 mm) was measured with the fabricated ultrasonic sensor. The transducer had a nominal frequency of 4.0 MHz. To measure the field of the transducer, the fabricated ultrasonic sensor was moved using a 3-axis positioning system, as shown in Fig. 6. A pulser/receiver was used to generate and detect the ultrasonic pulse.
Fig. 8 shows the measured pressure contours of the transducer, as indicated by the measured sound pressure and its position in the field. A profile of the focused pressure field was
Fig. 9. Comparison of sound pressure profiles of the ultrasonic source along the vertical axis around the focal region: (a) calculated and (b) measured pressure profiles.
thus obtained by using the fabricated ultrasonic sensor. Fig. 9 shows the calculated and measured pressure profiles along the vertical axis of the transducer around the focused region. The pressure profile was estimated using the diameter and the radius of curvature. The measured pressure peak was in good agreement with the estimated value. The estimated and measured peak positions were at approximately 44 mm and 48 mm, respectively