Practical calibration method of airborne ultrasound measurement system by using acoustic calibrators

Airborne ultrasonic apparatus, such as haptic devices and parametric speakers, have been actively developed and are becoming increasingly popular. In order to evaluate the performance of these apparatuses and to assess their safety against exposure to airborne ultrasound, quantitative sound pressure measurement of the emitted airborne ultrasound is required. Currently, various instruments are used to measure airborne ultrasound. However, since there is no instrument like a sound level meter that integrates the measurement and the display of the measured value, we need to set up a measurement system and then calibrate the system. For the feasibility of calibration, a system comprising a measurement microphone as specified in IEC 61094-4 and general measuring instruments is more realistic. There are a few possible calibration methods for this system. Considering the calibration effort and the required accuracy in actual measurement, it is practical to calibrate one specific frequency by an acoustic calibrator and the other frequencies by adopting the relative sensitivity curve of the microphone given by a manufacturer or the specification of the instruments. The paper discusses the uncertainty when the measurement system is calibrated as described above.