Abstract
A new method for measuring a delay time is proposed. If an observed signal is regardedas an output signal of a minimum phase system with delay, its delay time can be estimated by use of the Hilbert transform relationship between the log magnitude and phase of the transfer function of the minimum phase system. Discussions are mainly focused on practical cases where the observed signal is band limited. A procedure for extrapolating the frequency characteristics of the signal is also presented to minimize the estimation error due to the bandwidth limitation. The method is applied to measure the boundary location of acoustic materials whose reflection characteristics are minimum phase. The estimation error less than ±0.7 mm in distance is achieved when the test signal of 5 kHz bandwidth is used. As an example, the location of the reflecting surface of a gravel layer is estimated. Using this result, the acoustic impedance of gravel is computed.
