Objects within a flow generate pressure variations around them that are unique and characteristic to the objects' shape and size. A vehicle approaching a three-dimensional object or a wall-like obstacle is subject to sharp pressure gradients. Sensing these pressure variations allows the unique detection and identification of the obstacles for vehicle navigation. Pressure sensing, then, is the equivalent of "touching at a distance" underwater.

In cluttered environments or when navigating under poor visibility conditions, this capability is essential. While active acoustic means can be used, the process is power-intensive and complex, and depends strongly on the acoustic environment, while the required equipment may occupy much of the payload space of the vehicle. A far simpler alternative is to use a passive system which can resolve the pressure signature of obstacles in the near field. Similarly, unsteady flow contains vortical patterns with associated unique pressure signatures, which can be used for flow mapping so as to implement optimal vehicle actuator control. In fact, for operation within an unsteady stream, a vehicle must have knowledge of the flow environment. A passive pressure sensor as described above can detect unsteady flow features, including the intermediate field wake of objects. With proper design, it can be used to sample acoustic signals as well. Figure 1 illustrates some of these applications, as well as related tasks that would be enabled by the array of high-sensitivity pressure transducers we are developing. This work will focus in applying the sensors to navigation and flow control in AUVs and biomimetic vehicles. These sensing capabilities have become possible today by developing arrays containing hundreds or even thousands of pressure sensors fabricated using MEMS technology, with diameters around 1 mm, arranged over a °at or curved surface in various configurations, such as a single line, a patch consisting of several parallel lines, or specialized forms to fit the hull shape of a vehicle or its fins. The sensors will be packaged close together at distances of a few millimeters apart, to be able to resolve pressure and flow features near the array spacing, which in turn can be used to identify the overall flow features. Hence, the pressure transducer array serves as a bio-inspired \lateral line" sensor array: Fish have such a sensory lateral line which they use to monitor their hydrodynamic environment, including their own motions, but primarily the external disturbances. The lateral line is a spatially distributed set of sensors, extended over a spatial domain so as to become directionally sensitive. Through the ability to resolve the pressure signature of objects, fish can obtain \hydrodynamic pictures," the lateral line acting like a \touch-at-a-distance" device. The lateral line helps animals to: (a) detect, localize and track prey; (b) orient themselves to currents and hold station in strong currents; and (c) match their own swimming speed and direction to that of their neighbors while performing tight and rapid schooling maneuvers.