S.E. Kvashnin

Ultrasonic surgical instruments of longitudinal vibrations are used for cutting, coagulation, destruction, tissues separation, to destroy pathogenic microflora in infected wounds and cavities. However, the electro-acoustic transducers (EAT), used in these tools get heated significantly in the process. Mathematical modeling of EAT heating at different load impedance and different amplitudes was carried out for three EATs of longitudinal vibrations, based on the Langevin scheme and being double half-wave transducers with similar geometric characteristics and the same materials of all EAT parts. Working resonance frequencies of all EATs matched. The internal dissipation of mechanical energy was described in the ultrasonic vibration system materials as the elastic-viscous friction model. Steady-state forced vibrations with frequency  were considered. The electrical active output resistance of the ultrasonic generator was assumed to be equal to 10 Ohms, and reactive resistance was assumed to be equal to zero. The longitudinal vibrations calculations were carried out for different values of load impedance at the EAT working tip. They resulted in dependences of the longitudinal displacement amplitude of the EAT working end, the EAT electrical impedance, EAT efficiency as a function of the mechanical load impedance ZE real part at the EAT working end. It is that The EAT work in the mean values of load impedance (15 to 40 NS / m) per transducer is shown to be the most efficient due to high (70 to 92%) values of efficiency, EAT low heating, and the system low sensitivity to the load. It was noted that the modes of the EAT weak loading lead to the EAT significant heating. The two control algorithms of ultrasonic vibration system heating were compared: A) the resonance frequency maintenance, B) the maintenance of resonance frequency and a constant amplitude of mechanical vibrations of the EAT working end. The use of the control algorithm B proved reduction of the heat losses in the transducer and in the vibration system many times compared to the control algorithm A. Assuming that during the surgical manipulation the system is in the idle mode for K% of time, and is at rated load for (1-K)% of time, the ratio of average power dissipation to the power dissipation at nominal load for K = 20% is 3  27, for K = 40% is 5  27 for algorithm A. While using the control algorithm B, the average power dissipation to the power dissipation at nominal load is equal to 1.