US Patent 10420579 Surgical instruments

An ultrasonic surgical instrument is disclosed including a transducer, an ultrasonic blade operably coupled to the transducer, and a control circuit. The control circuit is configured to provide a drive signal to the transducer to cause the transducer to transmit ultrasonic vibrations to the ultrasonic blade, detect a change in a vibration frequency of the ultrasonic blade based at least in part on a change in a frequency of the drive signal, wherein the change in the vibration frequency of the ultrasonic blade corresponds to a tissue condition of tissue treated with the ultrasonic blade, and modify the drive signal in response to the tissue condition.