Measuring phase characteristics of ultrasonic microphones for accurate ultrasonic localization Systems

We have so far developed and evaluated a 3D ultrasonic localization system using the Extended Phase Accordance Method (EPAM) [3]. The method allows us to measure a 3D position of a transmitter by using a single compact receiver unit whose baseline is 76.2 mm and shows the satisfactory level of accuracy (13mm standard deviation in a static situation) for indoor positioning. However, we found that ultrasonic microphones showed different phase characteristics to different wave incident angles. Since EPAM uses the phase information of received signals for 3D localization, these phase characteristics induce a ranging error and therefore a transmitter is not correctly localized. To compensate these localization errors, we have conducted experiments and clarified phase characteristics of microphones.