Time delay spectrometry (TDS) measurements on civil engineering materials

The Time Delay Spectrometry (TDS) method was invented by R. C. Heyser (1967) for characterizing an acoustical system in a reverberant environment. The method offers a new method to isolate and extract a signal from noise based on the signal's time delay. The characteristics of the TDS method are: (a) It utilizes a swept frequency signal. (b) At the receiver, a tracking filter selects the signal based on its delay time. The filter consists of a narrow bandpass filter that is swept linearly with the same rate as the transmitted signal.; Civil engineering (denoted as CE) materials, such as soils and concrete, attenuate amplitudes of the elastic waves propagating through them. This attenuation limits the range of frequencies that can be used to obtain the minimum time resolution for time measurements on CE materials.; Attenuating media are dispersive which means that different frequency components of an elastic wave travel with different velocities. The dispersion of the body waves violates the basic assumption of the TDS method that every frequency component travels with the same velocity. This research measured the dispersion of the body waves in major CE materials, i.e. sand and concrete and showed that the dispersion can be neglected.; An integrated time domain program which combines the TDS time domain program, a peak-tracker program and elastic modulus computation program was developed. The program incorporates the zero-filling method and the stacking method to improve the time resolution and the signal to noise ratio of the time response measurements. Using the developed TDS system, some time response measurements on sand and concrete were performed. The results of the sand tests showed reasonable results whereas for the concrete cylinder tests, some difficulties were encountered in the interpretation of later arrival peaks of the time response results. These difficulties may be due to the fact that the applied wavelength was much longer than the dimension of the concrete cylinder.