The resonant behavior of landmines has been exploited by an acoustic detection technique to find buried mines. The resonance of the buried mine is induced by broadcasting an acoustic wave, which couples into the ground. The resonating mine causes the soil above it to vibrate and this vibration is measured with either a laser Doppler vibrometer (LDV) or a geophone. A set of resonance frequencies, which can be attributed to the design, material, and dimensions of the mine, is exhibited when the mine, sitting on a rigid surface above the ground, is excited by an acoustic wave. These resonance frequencies shift when the mine is buried. Acoustic models have been developed to predict these burial effects on mine resonant frequency behavior. This paper will discuss measurements made of several mines of the same type buried at various depths and will compare these measurements to predictions made by a lumped element model.

The detection of land mines using acoustic and seismic excitation is problematic due to the small amplitude of vibration that can be induced in the soil. Increasing this level reduces the requirement on a sensor's noise floor and may be useful for nonlinear detection. For these experiments, an array of loudspeakers broadcast orthogonal noise signals to excite ground vibrations. A contacting geophone measures the system's vibration response to all signals. We then correlate an excitation signal with the measured vibration response to approximate the system impulse response between a loudspeaker and the geophone. Time reversing the impulse response generates a pre-filter for each loudspeaker. Subsequent signals transmitted through the pre-filter and loudspeaker tend to be temporally focused at the receive location as well as greater in amplitude. Results compare vibration amplitude with and without the time reversal process for spatial locations near the mine.