2017 Volume 30 Issue 9 Pages 339-346
The distance to a target is fundamental information in many engineering applications. Recently,an acoustic distance measurement (ADM) method has been proposed based on the interference between transmitted and reflected waves, but it requires two applications of the Fourier transform. The ADM method in which a linear chirp whose frequency changes linearly with lapse of time is adopted as a transmitted sound has been also proposed. However, due to the influence of the measuring system from the loudspeaker to the microphone, the ADM would often estimate the spurious short distance different from true distance. This paper describes a fundamental study on the ADM method by applying the cross-spectral method to observed signals of the adjacent two-channel (2ch) microphones, adopting a linear chirp as transmitted wave and removing the influence of the measuring system. More concretely, since the component of the interference of the transmitted wave and reflected wave is included in the observed signal and the interference is a function of the distance from the microphone to the target, the distance can be estimated by utilizing the interference. We confirmed the validity of the chirp-based ADM method by performing a computer simulation and by applying it to an actual sound field.