Author(s): Barrera-Figueroa Salvador
Measurement of sound should also supported by measurement standards that are traceable to relevant units of the International System of units (SI). This is possible for measurements at frequencies around the audio range where standards are available for the pressure and free-field sensitivities of measurement microphones. This traceabiity should be extended to cover measurements at frequencies above the audio range in the ultrasound region.\n\nRecent advances in free-field calibration of microphones have made possible to determine the absolute sensitivity of working standard microphones up to 150 kHz using the reciprocity technique. Microphones calibrated using this technique can be used as references to calibrating other types of microphones by direct comparison.\n\nTraceability is not so clearly established for the pressure sensitivity in the same extent as in the free field. Direct comparison is limited to the frequency range in which references calibrated using primary methods are available, typically up to 30 kHz. In order to extend the frequency range, a quasi-pressure sensitivity is typically determinded using a sound calibrator at a single frequency, and a frequency response determined using an electrostatic actuator. Absolute pressure calibration using the reciprocty technique at high frequencies is challenging because it brings the technique to its limits, hence it has not been tried so far.\n\nThis paper presents an account of the current methods for calibration of microphones at ultrasound frequencies, their potential, and prospects.
Name: Dr Salvador Barrera-Figueroa