Electro-dynamic soil-plate-oscillator transducer for monitoring the buried vibration response to airborne sound excitation

A plastic drum-like anti-personal mine simulant (2 inch diam, by 1 inch tall, by ¼ inch thick aluminum tube, capped by a ¼ Al bottom circular plate and an elastic acrylic 1/16 inch thick circular top plate) was constructed. It was then modified to generate an electrical response to top-plate vibration. The mine simulant was converted to a transducer by fastened a sewing machine size bobbin wound with fine enamel copper wire onto the inside face on the bottom plate of the simulant. Next, a rare earth magnet was fastened to the inside surface of the elastic top plate (using a tacky wax). Leads were connected using insulated feed through connectors to complete the transducer design. In testing out the electro-dynamic transducer landmine simulant, results showed that the design was adequate to detect the vibration resonant response using a 2 inch burial depth in a concrete soil box filled with dry masonry sand. Two 12 inch diameter subwoofers were located a meter above the soil box and radiated sound levels on the order of 80-90 dB re 20 micro Pa, were measured near the soil surface. The swept sinusoidal transducer/microphone response exhibited a fundamental resonance near 190 Hz.