1 — This paper presents design and characterization of a MEMS comb accelerometer designated for integration into surgical probe to detect tissue hardness during cataract removal surgery. It helps the surgeon to avoid rupturing posterior lens capsule which if occurs leads to severe complications such as glaucoma, infection, or even blindness. The microsensor having overall dimensions of 480 µm × 395 µm consisted of 41 pairs of comb fingers on each side plus suspension springs, inertial mass and support anchors. Its ability to deliver significant capacitance variations during encountered vibration situations makes it capable to distinguish between different types of tissue. Integration of electronic components on chip ensures high level of reliability and noise immunity while minimizes space and power requirements. Physical characteristics and results on performance testing, proves integration of microsensor as an effective tool to aid the surgeon during the surgery.  —Accelerometer, MEMS, Phacoemulsification I. INTRODUCTION ATARACT removal, involving an ultrasonic cutting technique called phacoemulsification, is one of the most common minimally invasive surgical procedures practiced around the world. In this technique the hard, opaque human lens is fragmented by a sharp, ultrasonically driven cutting needle. Because the surgeon cannot see directly under the hollow titanium or stainless steel cutting needle as the lens is fragmented and aspirated, the underlying and much softer posterior capsule is sometimes unintentionally ruptured. The very fragile posterior capsule can be easily cut in comparison with the hard protein molecules composing the lens. A tear usually requires considerable time to repair and invariably leads to complications such as glaucoma, infection, and sometimes blindness [1]. The complication rate of this procedure is highly dependent on the skill of the surgeon. Manuscript received June 22, 2008. H. B. G. Corresponding author is faculty member of Electrical Engineering Department, Sahand University of Technology (phone: 00984 41243459375; fax: 0098441243444322; e4mail: badri@sut.ac.ir). F. G. Author is faculty member of Mechanical Engineering Department, Sahand University of Technology (e4mail: fghalichi@sut.ac.ir). M. M. Author is M.Sc. student in Mechanical Engineering Department, Sahand University of Technology, and studying biomechanics (e4mail: m_motaghi@sut.ac.ir). To address this problem a microsensor utilizing MEMS technology is designed to help the surgeon in identifying tissue hardness during this procedure that requires delicate cutting. The method to identify tissue hardness is by monitoring amplitude and/or frequency of the ultrasonic vibrating system on the surgical cutting tool. The system can warn the surgeon when a hard4to4soft material transition which is characteristic of the lens4to4posterior capsule transition, is taking place. During the sensor design process, there has been an emphasis on its ability to detect hardness of tissue the surgeon is cutting, rather than exact measurement of vibration parameters. To the best of our knowledge, there has been only one case of microsensor integration into phaco (phacoemulsification) handpiece in order to detect tissue hardness. This is done by biomedical engineering department, university of Minnesota, USA. In their approach, a piezoelectric sensor (force transducer) is designed and inserted directly behind the cutting needle. Their physical sensing method relies on direct detection of the impressed loading on the needle presented by the lens with the help of piezoelectric sensor. It is successfully tested on 252 patients [2]. In previous work, sensor blocks irrigation flow since it is placed exactly behind cutting needle. In order to compensate this negative effect, it is necessary to modify the whole handpiece case with adding another fluid input after force transducer. In our approach on the other hand, the miniature sensor is designed such that it can be easily integrated into phaco probe without any modification in probe case which proves to be more practical and cost effective. Since the proposed sensor fits perfectly into vibrating part of the probe, it dose not make any blockage in pathway of irrigation flow, thus eliminating the need for additional fluid input. II. MECHANICAL DESIGN OF SENSOR Every phaco handpiece utilizes a piezoelectric crystal as source of vibration. Operating frequency of this crystal for studied phaco machine was 40 kHz with 100 Bm total phaco tip displacement [3]. Many other phaco machines share the same or have similar specifications [4]. For every single degree of freedom vibratory system formed of a body of mass Design of a MEMS Sensor for Surgical Handpiece Mehrdad Mottaghi Biomechanics Division Faculty of Mechanical Engineering Sahand University of Technology Sahand New Town, Tabriz, Iran 5133541996 Email: m_motaghi@sut.ac.ir Farzan Ghalichi Biomechanics Division Faculty of Mechanical Engineering Sahand University of Technology Sahand New Town, Tabriz, Iran 5133541996 Email: fghalichi@sut.ac.ir Habib Badri Ghavifekr Faculty of Electrical Engineering, Sahand University of Technology Sahand New Town, Tabriz, Iran 5133541996 Email: badri@sut.ac.ir C 2008 International Conference on Microelectronics 1-4244-2370-5/08/$20.00 ©2008 IEEE 216