Detection and Analysis of Mechanical Stress Waves in IGBTs Using a Fiber-Optic Ring Acoustic Emission Sensor

Acoustic emission (AE) detection has been widely used for power semiconductor device (PSD) condition monitoring recently. However, conventional piezoelectric AE (PZT-AE) sensors are easily affected by electromagnetic interference (EMI) generated by the PSD switching transients, making it difficult to extract full mechanical stress waves (MSW) signals. Therefore, this article proposes a novel measurement method for insulated gate bipolar transistor (IGBT) MSW signals using a fiber-optic ring AE (FOR-AE) sensor. The time-domain signals and noise components measured by PZT-AE and FOR-AE sensors are compared first. The FOR-AE sensor shows much lower switching-synchronized EMI than PZT-AE sensors and achieves a higher signal-to-noise ratio. Then, experiments under different current, voltage, and temperature conditions were conducted to further analyze the applicability of FOR-AE sensors in different operating conditions. The results indicate that the FOR-AE sensor exhibits a more sensitive response to changes in the IGBT's conduction current and bus voltage. Furthermore, as the temperature rises, the peak-to-peak variation in the IGBT's MSW signal reaches an inflection point, showing a trend of first increasing and then decreasing. The frequency centroid increases with junction temperature, while the normalized energy ratios shift from the 10-25 kHz band toward the 25-40 kHz band. These results indicate that the FOR-AE sensor has promising application potential under strong EMI and complex operating conditions.