Vibration modes in ultrasonic Bessel transducer

Diagnosis ultrasonic transducers with uniformly poled can not satisfy the condition of improved lateral resolution and a large depth of the generated ultrasonic field. Bessel transducers appear as a good alternative to improve simultaneously both requirements. In this work a 2 MHz circular Bessel transducer was constructed with three concentric electrode rings, which were poled following a Bessel function. The results show a well focused beam and a depth of field as large as ∼20 times the beam width (6 dB). Moreover, it is verified that the fundamental and some harmonic of the radial mode are suppressed, under an in phase excitation of the rings.