Electrical and Acoustical Characterization of the Bessel Transducers

Ultrasonic Bessel transducers produce limited diffraction beams which make them optimal for medical images applications. They satisfy the condition of improved lateral resolution and large depth penetration of the generated ultrasonic field. In this work Bessel transducers using conventional ceramic disks were constructed following a direct poling method, with a center frequency of 2 MHz. The piezoelectric elements contain three concentric electrode rings, which were poled following a Bessel function. Transducers were backed with low impedance and matched to water with a front matching layer for characterizations. The mechanical vibration characteristics of these transducers were investigated through the analysis of electric impedance measurements of their radial and thickness vibration modes. The experimental results were compared with the simulations made by the finite element method (FEM). The experimental resonance frequencies of the Bessel transducer are in agreement with the FEM simulated results in the low and high frequency range. For Bessel transducers, results show that some mechanical resonant modes (i.e. radial fundamental and several harmonics modes) are suppressed when an in phased excitation of the rings is applied. That is not the case for uniformly poled disk.

Keywords:

• Ultrasonic Bessel transducers
• limited diffraction beam
• vibration modes

Acknowledgments

The authors would like to thank to RITUL/CYTED Magias Project network, CNPq and FAPESP (Brazilian agencies), CLAF (Latin-American agency) and PEDECIBA (Uruguayan agency) for financial support.

Paper originally presented at IMF-11, Iguassu Falls, Brazil, September 5–9, 2005;