Odanaka I., Mizutani K., Mizutani K., Wakatsuki N.

Sound probe used for measurement of a time of flight (TOF) consists of a pair of a loud speaker and a microphone. TOF is obtained by cross correlation between transmitted and received signals. TOF measurement error exists over all frequency, and the value is not constant. The improvement of the measurement accuracy is difficult, because the definition of the error factor is not sufficiently clarified. We measured the difference in actual phase against ideal value of the received signal. Measurement error according to the phase characteristics of the sound probe is added to the TOF. TOF calculated from the phase difference has the measurement error and this error has the similar characteristic to the measurement error of TOF that is calculated by cross correlation of transmitted and received signal. Either characteristic suggests that measurement error is larger in the low frequencies and measurement error becomes smaller as frequency increases. This result suggests that the phase difference of received signal from ideal phase generated according to phase characteristic of the sound probe is one of the error factors of TOF. Therefore, all there is some relationship between measurement error of TOF and phase characteristic of sound probe. This relationship may apply to analysis of the measurement error factor of TOF and more accurate measurement of TOF.