Volumetric Acoustic Intensity Probe

Abstract : How often have we sat in an automobile or airplane and wondered where an annoying sound source was coming from? In military vehicles and aircraft, or habitation spaces on ships and submarines, annoying sources promote fatigue and may interfere with mission success. Identification of these sources is crucial so that measures may be taken to quiet them. Pressure or vibration sensors are generally not successful in localization and identification of noise sources. Modern metrology has turned to intensity probes for a solution. These probes have had marked success since they measure the direction and magnitude of energy flow at the measurement point. When used to scan over surfaces or in an array configuration, they are also effective at locating noise sources. The ability to locate detrimental noise sources and quantify them has taken a quantum leap forward with the invention at the Naval Research Laboratory (NRL) of a new and radically different type of intensity probe. Called the Volumetric acoustic Intensity Probe (VIP), it works by imaging the acoustic intensity vector in a volume nearly a cubic meter in size using an array of relatively inexpensive microphones. This holographic like imaging capability is remarkable since it tracks the energy flow throughout this volume at points in space where measurements are not made. Furthermore, energy-flow tracks of multiple noise sources are separated by state-of-the-art, front-end signal processing. This new measurement device can be used to diagnose any complex noise source, whether flow-noise or shock induced, for example.