Vibration transmitting unit and ultrasonic treatment instrument

A vibration transmitting unit comprising:

• an extending portion which extends along a longitudinal axis, and which is capable of transmitting ultrasonic vibration from a proximal side to a distal side;
• a first component which is provided in the extending portion, and which has a first cross-sectional area in a cross-section perpendicular to the longitudinal axis;
• a second component which is provided on the distal side with respect to the first component in the extending portion, and which has a second cross-sectional area, which is larger than the first cross-sectional area, in a cross-section perpendicular to the longitudinal axis;
• a third component which is provided between the first component and the second component in the extending portion, and which has a third cross-sectional area, which is larger than the first cross-sectional area and is smaller than the second cross-sectional area, in a cross-section perpendicular to the longitudinal axis, a standard vibration anti-node, which is one of vibration anti-nodes, being positioned at the third component by the ultrasonic vibration causing the extending portion to vibrate at a frequency in a predetermined frequency range, the third cross-sectional area being constant in an entirety of the third component in a direction parallel to the longitudinal axis;
• a first cross-sectional increasing portion which is provided at a boundary between the first component and the third component, and an entirety of the first cross-sectional increasing portion being perpendicular to the longitudinal axis;
• and
• a second cross-sectional increasing portion which is provided at a boundary between the second component and the third component, and an entirety of the second cross-sectional increasing portion being perpendicular to the longitudinal axis, wherein
• the third component, in which a cross-sectional area perpendicular to the longitudinal axis is kept constant at the third cross-sectional area in an entire length in the direction parallel to the longitudinal axis, continuously extends from the first cross-sectional increasing portion to the second cross-sectional increasing portion,
• the extending portion includes a first cross-sectional reduction portion which is provided on the proximal side with respect to the first component, and which reduces a cross-sectional area perpendicular to the longitudinal axis towards the distal side to the first cross-sectional area of the first component, and
• in a state where the extending portion vibrates at a frequency in the predetermined frequency range, all of the vibration anti-nodes are positioned away from the first cross-sectional reduction portion in the direction parallel to the longitudinal axis.