Ultrasonic transducers with Bessel function distribution of vibrational amplitude on their surfaces

In this paper the far field and near field of an ultrasonic circular transducer with a Bessel distribution of vibrational amplitude on its surface are calculated. The practical realizations of approximate Bessel-like amplitude distribution on the transducer surface are known. In this paper the vibrational characteristics of ultrasonic transducers consisting of a ceramic ring filled with a plastic disk were considered. Assuming that the amplitude on the surface of the plastic disk inside the ring is described by the Bessel function of zero order, the directivity characteristics of those transducers measured experimentally were presented. 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 truncated Bessel function amplitude distribution. Changing the inner diameter of the ring, it is possible to control the resonance frequency of the filling plastic material. 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 material enables variations of the bandwidth of the considered circular transducers. The Bessel transducers generate nondiffracting beams with a large depth of field. This is why the potential applications of Bessel transducers in robotics for object identification are worth noting.<
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