  A new concept is presented for mechanical acoustic transmitters and matched
resonant receivers. The lightweight, compact, and low-cost transmitters produce
high-power acoustic pulses at one or more discrete frequencies with very little
input power. The transducer systems are well suited for coupling acoustic pulse
energy into dense media, such as walls and water. Applications of the impact
transducers are discussed, including detection and tracking of humans through
walls and long-duration underwater surveillance by a low-cost network of
autonomous, self-recharging, battery-operated sonobuoys. A conceptual design of
a sonobuoy surveillance network for harbors and littoral waters is presented.
An impact-transmitter and matched-receiver system that detected human motion
through thick walls with only rudimentary signal processing is described, and
results are presented. Signal processing methods for increasing the
signal-to-noise ratio by several tens of dB are discussed.
