James E. Barger
BBN Systems and Technol., 70 Fawcett St., Cambridge, MA 02138
Projectors for the acoustical radiator for tactical search (ARTS) program must be very thin, to minimize drag, while at the same time produce large surface displacements in the 70- to 300-Hz band. To accommodate these requirements, the projectors are flat pads of thickness 0.1 m laminated from 1400 layers of polyurethane film that has deposited, on one side, a 300-(Angstrom) aluminum electrode. The individual projector pads are to be arrayed in a self-propelled vehicle that is 100 m deep, 3 m long, and 0.2 m wide, and that is capable of stable operation to 15 kn. Polyurethane was chosen for the transduction material mostly because of its small modulus (15 MPa) and large displacement coefficient (10 (Angstrom)/V). The low-Q resonance for an individual projector pad, determined by the stiffness of the pad and radiation mass, occurs at about 200 Hz; but this frequency is expected to be lowered to 150 Hz for the array of projectors, owing to a greater radiation mass. Since polyurethane film has not before been used as a transduction material, its electrostrictive and mechanical properties are described. The projectors are fabricated in the manner of polymeric film capacitors, with some modifications.