Acoustic Characterization of Integrated Circuits During Operation¹

Power electronics are widely serving as core components of propulsion systems in electric vertical takeoff and landing (eVTOL) aircraft. Nevertheless, affected by the Paschen effect, the breakdown voltage of these electronics during flight is significantly lower than that on the ground, which could deteriorate system stability, or even cause aircraft faults or crashes, increasing safety risks for the public. As such, condition monitoring of power electronics has become critical for the safe operation of eVTOL. To achieve nonintrusive monitoring, acoustic emission (AE) sensors have gained traction with their prominent resistance to electromagnetic interference and high temperatures. However, existing studies yield conflicting results regarding whether an increase in loading voltage impacts the internal mechanical stress of electronics. To address this issue, we present this work to probe the existence and the pattern of a relationship between load voltage and stress wave, since the change of mechanical stress could generate acoustic waves that can be acquired by AE sensors. In this study, an AE sensor was applied onto an oscillator placed upon an epoxy substrate to characterize the acoustic waves emitted from the device under various input loads. In the experiment, we observed a unique AE signal pattern characterized by two distinct components that consistently intersect at a specific frequency. The time required to establish such intersections progressively lengthens as the load voltage increases. Through time-domain and frequency-domain analyses of the unique AE signals under different load voltages, it was discovered that certain features of the unique AE signals have an approximately linear relationship with the load voltage.