Novel Sound Imaging Method for the Localization of Leakages in Automotive Components and Structures

This contribution describes a novel method for visualizing leakages in automotive structures using a rotating linear array of a few digital ultrasound microphones in combination with a multi-frequency ultrasound transmitter. The rotating array scans the incident sound field generated by the ultrasound transmitter on a circular area. In a typical measurement setup, the ultrasound transmitter is placed in a cavity (e.g. car interior, trunk or similar) and operates at distinct harmonic frequencies at around 40kHz in an omnidirectional fashion. The rotating linear array is operated on the outside of the cavity and captures the sound field escaping through small leakages. While the reduced hardware complexity allows for the design of a lightweight, handheld sound imaging device, the algorithmic portion of the measurement system requires special attention. In fact, established methods of sound imaging like beamforming and nearfield holography cannot be applied to signals stemming from moving sensors. The proposed method of computing an acoustic image using the described measurement setup is based on compensating the moving microphone signals for Doppler distortions and evaluating the coherence of the resulting signals with a non-moving reference microphone for each point in the acoustic image. The setup and methodology is evaluated for leakage and tightness testing of actual automotive components and structures for production cars in a quality control context. The corresponding troubleshooting process from assessment and quantification of the situation to resolution of the root cause is described from a user perspective.