Micro Ultrasonic Motors for Medical Diagnostic Instruments

(Faculty mentor: Kenji Uchino)

This research project is geared to develop world-smallest rotary-type ultrasonic motors (USMs) to apply for medical diagnostic instruments such as catheters and endoscopes. The target is to develop USMs with a size of 1.5 mm in diameter and 4 mm in length, but with 0.1 mNm in torque.

Regarding conventional electromagnetic motors, tiny motors smaller than 1cm long are theoretically difficult to produce with sufficient energy efficiency. Thus, a new class of motors using high power ultrasonic energy, i.e., ultrasonic motor, is gaining wide spread attention. Ultrasonic motors made with piezoceramics whose efficiency is insensitive to size are superior in the micro-motor area.

A “Metal Tube” type motor, as shown in Fig. 1 (Patented at Penn State) will be adopted. It utilizes a metal hollow cylinder, bonded with two PZT rectangular plates uniformly poled. When one of the PZT plates, Plate X, is driven by E-field, a bending vibration is excited basically along x axis. However, because of an asymmetrical mass (Plate Y), another hybridized bending mode is excited with some phase lag along y axis, leading to an elliptical locus in a clockwise direction. On the other hand, when Plate Y is driven, counterclockwise wobble motion is excited. Also note that only a single-phase power supply is required. Figure 2 is a picture of a prototype motor with a center hole of a rotor rod, through which an optical fiber can pass.

The REU student will learn the principle and design flow of the USMs, and participate in both micro motor fabrication and design of a compact and highly efficient drive/control circuit for the newly developed motors, alongside with a postdoctoral personnel. In parallel, the instructing postdoctoral personnel will design medical catheters or endoscopes coupled with the developed ultrasonic motors, in collaboration with the medical instrument companies such as Aloka, Japan. The REU student may also have the opportunity in collaboration with the company. This project may take longer than 10 weeks to complete and continuing interest of a student would be beneficial.