Envelope analysis is a widely used tool for fault detection in rotating machines. In envelope analysis, impulsive noise contaminates the measured signal, making it difficult to extract the features of defects. This paper proposes a time–frequency envelope analysis that overcomes the effects of impulsive noises. Envelope analysis is performed by dividing the signal into several sections through a time window. The effect of impulsive noises is eliminated by using the frequency characteristics of the short time rectangular wave. The proposed method was verified through simulation and experimental data. The simulation was conducted by mathematically modeling a cyclo-stationary process that characterizes rotating machinery signals. In addition, the effectiveness of the method was verified by the measured data of normal and defective air-conditioners produced on the actual assembly line. This simple proposed method is effective enough to detect the faults. In the future, the approaches of big data and deep learning will be required for the development of the prognostic health-management framework.

Cylindrical transducer arrays are used in many applications such as SONAR, depth sounding, ultrasound imaging, etc. This study developed the equivalent circuit (EC)-based-model of a cylindrical array with theoretical acoustic coupling. The electro-mechanical-acoustic coupling impedance matrix was first constructed to determine the response of the array. The electrical and mechanical impedances of the individual transducers were obtained by the EC model. The acoustic radiation impedances were obtained by the theoretical model. The cylindrical array is modeled by coupling the EC model and acoustic radiation impedances. The acoustic transfer matrix was then constructed using the theoretical method to determine both the far-field and near-field acoustic responses. The characteristics of the transducer array were represented with the electrical admittance, velocity response as a function of the voltage, transmit voltage response, beam pattern, and normalized pressure curve. To verify the proposed model, the analysis results were successfully compared to those of the fully coupled finite element model. Due to its high accuracy and computational efficiency, the proposed EC-based-model is expected to be useful for the conceptual design stage, which requires frequent design changes.

Transducer arrays are commonly analyzed by the finite element method (FEM) with high accuracy, but it is costly, particularly when having flexible surrounding structures. In this study, we developed an equivalent circuit (EC)-based model of an array of transducers with flexible surrounding structures for effective analysis. The impedance matrix was first constructed by coupling the electrical, mechanical impedance, and the acoustic radiation impedance obtained by the EC method and finite element-boundary element (FE-BE) coupling method. The transfer matrix of far-field pressure to the transducer response was then constructed by the FE-BE coupling method, and finally the sound pressure of the external acoustic field was obtained. To verify the accuracy, the results of the proposed method were compared with those of the conventional FEM. To evaluate the efficiency of the proposed method, the reduction in the degrees of freedom (DOFs) of the proposed method from the conventional FEM analysis was investigated. The simulation results of the proposed method are highly accurate and efficient. The proposed method is expected to be useful for conceptual design.