Abstract: A detector of acoustic emissions from a structure includes a piezoelectric element responsive to both compressional wave energy and to shear wave energy from any direction so that the source of the acoustic emission may be determined.

Abstract: An energy imaging system providing high resolution at the center of the field of view and reduced resolution as a function of the distance away from the center.

Abstract: The invention provides a transducer for use with a conical reflector in which the transducer comprises a frusto-conical radiating member that is coaxially positioned with respect to the reflector member. The half angles of the radiating member and reflectors are related such that every ray from a selected point of interest on the axis that is reflected from the reflector cone to the active surface of the radiating member intersects substantially normally to the active surface.Where the energy is directed to a point of interest distant from the reflector, the half angles are related in accordance with the formula ##EQU1## ; AND, WHERE THE POINT OF INTEREST IS ON THE AXIS, THE HALF ANGLES ARE RELATED IN ACCORDANCE WITH THE FORMULA ##EQU2## where .phi. = CONICAL REFLECTOR HALF ANGLE;.theta.

Abstract: A large depth-of-field arc-transducer for use in sonar systems is provided in which at least one transducer element is positioned to lie along the arc of a circle of radius R. The active faces of the transducer elements are directed to a point that lies on a line normal to the plane of the arc and passes through the center thereof. The radius R is equal to between 0.3 to 0.6 Rs and, preferably about 0.5 Rs, where Rs is the distance from said point to the midpoint of the arc-transducer.An improved depth-of-field sonar system is provided where at least two arc-transducers are used having different radii, and preferably, where each radius R is equal to between 0.3 to 0.6 Rs.