Research On Modal Test Method Of MEMS Microstructure Based On Air-coupled Ultrasonic Excitation

As MEMS devices are widely used in various fields,modal testing of microstructures to obtain their dynamic characteristic parameters is of great significance to the design,simulation,manufacturing,quality control and evaluation of microstructures.Considering that the microstructure has the characteristics of small size,high natural frequency,small amplitude,etc.,and is used in different environments.Therefore,this article proposes an air-coupled ultrasonic excitation method based on the modal test of single-crystal silicon and 304 stainless steel rectangular micro-cantilever under high temperature environment of20?300?,from theory,simulation and experimental test.In the aspect,the variation law of the natural frequency of the micro cantilever beam with temperature is studied.Aiming at a typical rectangular micro-cantilever with constant cross-section,this paper establishes a temperature coefficient model of its natural frequency.It can be seen from the model that the fundamental reason affecting the change of the natural frequency of the microcantilever is the change of the microcantilever's size and elastic modulus as the ambient temperature changes.For non-contact,non-destructive and ideal excitation methods with large excitation bandwidth,this paper proposes an air-coupled ultrasonic excitation method,studies the principle of the excitation method,and uses a laser Doppler vibrometer to detect vibration signals.The resistance heating method is used to realize the excitation of the microstructure in a high temperature environment of 20?300?,and an experimental device based on air-coupled ultrasonic excitation is built.Solid Works software is used to model single crystal silicon and 304 stainless steel microcantilevers,and ANSYS software is used to simulate and test the microcantilever beams of these two materials.The first three natural frequencies at 20?300? are obtained.It can be seen that the natural frequency of the microcantilever decreases with the increase of temperature,and presents an approximately linear relationship.The dynamic characteristics of monocrystalline silicon and 304 stainless steel microcantilever beams were tested at a temperature of 20?300? using the built-up MEMS microstructure modal test system based on air-coupled ultrasonic excitation,and the first three natural frequencies of the microcantilever were obtained.The reason for the error between the simulated value and the experimental value is analyzed.The experimental results show that the natural frequency of the microcantilever decreases with the increase of temperature,and the relative natural frequency temperature coefficient is close to the theoretical value,which confirms that the fundamental reason for the change of the natural frequency of the micro cantilever with temperature is the thermal expansion coefficient and the temperature coefficient of elastic modulus of the material.