Micromotor of Less Than 1 mm^3 Volume for In Vivo Medical Procedures

The body's stress response to surgery has been cited as a primary cause of post-operative morbidity and has prompted growth in minimally invasive surgical techniques. The future of such techniques lies in the use of in vivo procedures, but is currently limited by the availability of motors with a volume of less than 1 mm
³
. In response to this we present a piezoelectric ultrasonic resonant micromotor with a volume of approximately 0.75 mm
³
. The motor has a novel helically cut stator that couples axial and torsional resonant frequencies, excited by a lead zirconate titanate element 0.03 mm
³
in volume. The motor performance reaches a start-up torque of 47 nNm and no load angular velocity of 830 rad/s. This gives the motor a power density of 18.4 kW/m
³
. This performance is on the order necessary to propel a swimming microbot in small human arteries.