Design of Bessel transducers based on circular piezoelectric composites for cranial Doppler detection

A Bessel transducer is constructed based on a ceramic with two external electrodes and an internal structure of alternated active and inactive annular piezoelectric zones. This type of transducers allows obtaining a good relationship between the depth of field and the lateral resolution of the acoustic field. This behavior of the acoustic field becomes the Bessel transducers in appropriate devices for applications in intra-cranial Doppler detection. In this report, a study of lateral contact between the rings of several Bessel transducers is presented. Four Bessel transducers were constructed and grouped in two sets. The first set contains annular composites combining PZT-5 and epoxy. The second set includes non-homogeneously polarized PZT-5 discs. The influence of the structure in the radiation pattern and the vibration modes is obtained through measurements of the input electric impedance in transducers.