A high frequency ultrasonic bistoury designed to reduce friction trauma in cystectomy operations

Typical bistouries used in cystectomy operations are designed to work in second harmonic; they are able to produce displacements of more than 60 microns at a working frequency of about 40 kHz. The needle of the bistoury is inserted in the eye for about 9 mm. Due to the relatively high wavelength, a relevant vibration velocity is present also at the insertion point. The friction between needle and eye produces a trauma due to hyperthermia. In this work a bistoury able to minimize this trauma is proposed, designed and realized. The proposed bistoury is composed of a Langevin transducer and of two displacement amplifiers. It is designed to work in third harmonic at about 130 kHz and presents a node of the longitudinal displacement at the second concentrator, which is 9 mm from the end of the needle. In the final prototype the second concentrator was realized at 11 mm from the end of the needle, in order to permit the surgeon little movements during operations. Measurements of the displacement distributions along the needle were carried out in air and in water for both the prototypes, showing that the proposed solution is satisfactory for the intended application.