Free Damping Test Method For Vibration Characteristics Of Microstructures

Micro-cantilevers and micro-membranes are typical microstructures, which have been widely applied in micro- and nanometer science and technology. The mechanical characteristics of microstructures are highlighted in the process of design, research and application. In atomic force microscope (AFM), the mechanical characteristics of micro-cantilevers are important to improve the quality of imaging and the precision of testing. Meanwhile, micro-membranes are also taking on a wider foreground in micro-electronics, micro-electronics machine system and surface protection techniques. So it is very significant to research and develop the experiment techniques of testing the dynamic characteristics of microstructures for Microsystems design, simulation and evaluation.After a lot of investigation, the free damping test method,microstructures excited by one pulse signal,is introduced into micro field and a test system for transient motion of microstructures is built on the base of a laser Doppler vibrometer and virtual instruments techniques. This new system has a success to efficiently test the velocity, nature frequency, damping ratio, quality factor and Young's module. The major works in the paper are following:1. The measurement principle of micro Laser Doppler technology is carefully analyzed. Connection and debugging of the system's hardware and software are accomplished, including a mechanical exciting device to make micro-structures produce free damping motion.2. The Laser Doppler vibrometer and signal generator are controlled by computer through GPIB bus, in order to make the system more automatic and compatible. A synchronous method for exciting signal and data acquisition is advanced and put into practice in the process of microstructures'free damping vibration.3. The free damping test method is researched on three aspects, the measurement principle, experiment technique, data acquisition and analysis. The characteristic parameters of a micro-cantilever and a micro-membrane, including nature frequency, damping ratio, quality factor and Young's module, are measured accurately by using this testing system,4. The testing error and the reason of error are analyzed, compared with the results received by the sweep-frequency measurement method.