Acoustical characterization of ultrasonic surgical devices

Ultrasonic surgical instruments operating from 20 to 60 kHz have typically been characterized only by their operating frequency, cutting tip excursion, and input electrical power. This paper presents acoustical measurement methodologies which more completely characterize device output. The methods are divided into two frequency regimes: frequencies below 100 kHz which correspond to the tip driving frequency, and frequencies above 1 MHz which corresponds to the cavitation developed at the tip. Low frequency radiation is modelled as an acoustic dipole; high frequency acoustic radiation is caused by cavitation bubble collapse at the tip, generating spherically diverging shock waves. This measurement method incorporates the energy in a single shock wave event, the number of events per unit time, and the spherical divergence of the wave. Combining the two measurement techniques shows the growth of the total radiated energy as a function of excursion, and a commensurate shift from low frequency energy to cavitational energy