| In order to realize on-line monitoring of oil film thickness of the mechanical key equipment,the lubrication state of the equipment is always understood.In this paper,the ultrasonic method is used to measure the oil film thickness.It is proposed to adopt the method of depositing the AlN piezoelectric film on the surface of the part and making it into an ultrasonic transducer,so as to achieve no invasion and no damage measurement.Through the two methods of simulation and experiment,some key technologies involved are studied.Two theoretical models for oil film thickness measurement are established.The formulas for calculating the reflection coefficient and film thickness are given at a certain frequency.At the same time,the two models are simulated based on finite element method,the two results are compared and have perfect consistency.The theoretical model of thickness extensional mode piezoelectric vibrator is established and the equivalent electromechanical diagrams under different conditions are drawn in the form of equivalent circuit,and the frequency characteristics and the relationship between the parameters are discussed.For the composite AlN piezoelectric structure,three-dimensional model(electrode-AlN-stainless steel structure)was analyed using finite element method.Based on the three-layer transducer structure,an electro-solid-acoustic coupling analysis model was established to analyze the overall structure of the AlN ultrasonic transducer in frequency and time domain.The method and process for synthesizing AlN piezoelectric thin films using magnetron sputtering have been studied.AlN thin films were deposited on stainless steel substrates.The effects of nitrogen flux,sputtering power and other parameters on the crystallization properties of thin films were analyzed.The synthesized thin films were characterized by XRD,SEM and other advanced equipment to explore their preferred orientation growth mechanism.Based on the oil film thickness measurement theory,two different oil film thickness measurement systems were designed.The static oil film with different thickness was experimentally studied.The experimental results were good and the correctness of the theory of acoustic reflection coefficient was verified. |
