Ring vibrations in an acoustic medium as a source of ultrasonic radiation

In this paper, the vibrational characteristics of ultrasonic transducers consisting of a ceramic ring filled with a plastic disk are considered. For axially symmetric resonances, the vibrational amplitude on the surface of the plastic core is approximately described by a truncated Bessel function of zero order and first kind J(0), leading to an ultrasonic beam which is nondiffracting near the transducer. The near- and far-field pressure distributions of such transducers are measured and compared with model predictions. In the near zone, the width of the measured main lobe is narrow, which is in accordance with the theoretical results for circular transducers with a truncated Bessel function amplitude distribution. By changing the inner diameter of the ring, it is possible to control the resonance frequency of the plastic core. On the other hand, the resonance frequency of the ring may be regulated by varying its width. The existing coupling of resonant vibrations of the ceramic ring and plastic core enables variations of the bandwidths of the considered circular transducers.