Kenneth R. Erikson

High power, motor driven underwater acoustic transducer

A high intensity, low frequency underwater transducer for non-lethal deterrence of terrorist swimmers or divers in a body of water. The invention consists of a motor driven flextensional underwater transducer. In one embodiment, the phase of a transducer is sensed, enabling multiple projectors to achieve high acoustic sound pressure levels by beamforming and/or modal constructive interference (e.g. taking advantage of harbor bottom topography and boundaries.).

Low‐Noise Condenser Microphone

The limiting self‐noise level of a conventional condenser microphone is determined by the Nyquist noise of the backplate air film resistance. This acoustic resistance is used to damp the microphone diaphragm for flat frequency response near the resonance frequency. This paper discusses condenser microphones constructed with backplates of very low acoustic resistance. Reductions in self‐noise on the order of 40 dB can be achieved. Electronic compensation for flat frequency response can then be introduced at a point in the circuitry that does not add noise. With this noise source eliminated, the Nyquist noise of the acoustic radiation resistance and the internal mechanical resistance of the diaphragm become the limiting noise levels. Measurements of these noise levels are discussed.