Moving‐Coil Pressure‐Gradient Hydrophone

A pressure‐gradient hydrophone exhibiting uniform response and precise polar pattern has been developed based on the moving‐coil principle. The coil, under mass control, closely matches the impedance of the medium contributing to high sensitivity. Equivalent‐circuit analysis demonstrates how to select the electrical‐termination resistance for any desired degree of damping and for proper phase‐shift control. Theoretical performance is compared with measurements using a CBS Laboratories gradient hydrophone calibrator, and in free field. [Work supported by U. S. Naval Air Development Center, Johnsville, Pennsylvania, under subcontract from Sanders Associates, Nashua, New Hampshire.]