Cross-comparison of the optical and acoustical calibration methods for microphones based on microelectromechanical system technologies

Calibration methods and associated international standards in airborne acoustics have enabled national metrology institutes to establish and maintain a fully defined traceability chain for designated laboratories and end users of microphones. However, such microphones need to be reciprocal, of condenser type and of specific dimensions; this, in effect, does not allow for the calibration of alternative existing sensor technologies and creates a further obstacle for the calibration of emerging technologies. An example relates to microphones based on microelectromechanical systems which are an integral part of a wide range of electronic devices; yet, there is no established calibration traceability chain other than methods employed by manufacturers. From a metrological perspective, new calibration methods that can accommodate microphones regardless of their size, reciprocal nature and utilised technology must be developed and subsequently standardised and adopted. This paper discusses the optical calibration method based on free field photon correlation and the acoustical calibration methods based on pressure comparison and free field substitution. These approaches can provide traceability to the international measurement standard system for novel types of microphones, and the measurement results showed themselves to be consistent. Based on this study, the possibility of expanding the new standard system was investigated.