Harmonic

Ans  a

20K to 50 k Hz

The harmonic scalpel transduces high-frequency ultrasonic energy through a metallic jaw to generate mechanical vibration. It has an active and an inactive blade When in contact with tissue, the vibration of a single blade against a static blade results in vaporization and coagulation.

Harmonic scalpel also called ultrasonic scalpel cuts through tissues and causes coagulation by protein denaturation caused by vibrating force. As compared to electro cautrey harmonic scalpel

1. takes longer time 
2. produces less smoke
3. Cause less tissue edema, swelling

Ref : bailey page 49