A high-sensitivity method to measure acoustic
wave speed in soils by analyzing the reflected ultrasonic signal
from a resonating layered interface is proposed here.
Specifically, an ultrasonic transducer which can be used to both
transmit and receive signals is installed on a low-high acousticimpedance layered structure of hard PVC and steel, which in turn
is placed in contact with the soil deposit of interest. The acoustic
impedance of the soil (the product of density and wave velocity)
is deduced from analysis of the waves reflected back to the
transducer. A system configuration design is enabled by
developing an analytical model that correlates the objective
wave speed with the measurable reflection coefficient spectrum.
The physical viability of this testing approach is demonstrated
by means of a one-dimensional compression device that probes
the stress-dependence of compression wave velocity of different
sizes of glass ballotini particles. Provided the ratio of the
wavelength of the generated wave to the soil particle size is
sufficiently large the data generated are in agreement with data
obtained using conventional time-of-flight measurements. In
principle, this high-sensitivity approach avoids the need for the
wave to travel a long distance between multiple transmitterreceiver sensors as is typically the case in geophysical testing
of soil. Therefore it is particularly suited to in-situ observation of
soil properties in a highly compact setup, where only a single transducer is required. Furthermore, high spatial
resolution of local measurements can be achieved, and the data are unaffected by wave attenuation as transmitted in
soil.