Calibration of 800 MEMS Microphones for Array Measurement

Kurzfassung

This study presents the calibration of a large array of 800 MEMS microphones integrated into the DLR-developed SUPREMA architecture. It focuses on assessing sensor sensitivity, amplitude, and phase response through both pressure-field and free-field calibration methods, specifically designed for this unique setup. Each MEMS sensor is mounted individually on printed circuit boards, necessitating a self-developed calibration procedure due to the absence of standardised tools for such configurations. The free-field calibration method yields very good results up to approximately 1 kHz. At higher frequencies, the MEMS sensor’s frequency response is limited by the complex influence of the setup geometry, particularly the support structure of the PCBs and reference microphones. Despite these constraints, the method effectively characterises the sensor under conditions similar to its real-world free-field application. The pressure-field calibration method proved highly reproducible up to 20 kHz but is sensitive to precise test execution and primarily characterizes the sensor in its cavity rather than in its mounted configuration. In general, the results demonstrate that all MEMS microphones show a very high degree of similarity, particularly in phase and group delay, leading to an almost identical overall phase response up to high frequencies. This makes the sensors ideally suited for array measurements such as beamforming and acoustic imaging, with a phase consistency even surpassing that of Class 1 microphones. These findings underscore the high potential of the MEMS array for precise acoustic applications and provide valuable insights into the comparative strengths and limitations of both calibration approaches.