Analytical comparisons of four types of low-frequency, cylindrical hydrophones

Low-frequency, cylindrical hydrophones are compared for an application which required small elements capable of operation to a depth of 4,500 feet. Critical parameters are maximum ceramic diameter of 0.3 inch, minimum acoustic sensitivity of -110 dBV/microbar, and minimum free capacitance of 300 pF. Comparison of performances offered by a wide range of element designs narrows the field to these four candidates: radially-polarized, ceramic cylinders with 1) capped ends, air-filled core; 2) shielded ends,solid core; 3) metal-diaphragm ends, air-filled and kerosene-filled core; and 4) double-ended bilaminar, flexidisk elements filled with kerosene, silicone fluid, and transformer oil. Expressions from the classical literature are used to calculate acoustic sensitivities of the first two types, and new expressions are used for the second two types. Acoustic sensitivity curves are included for outside diameters ranging from 0.2 to 1.5 inches, and for the critical parameters listed above, it is concluded that all four candidate designs could potentially meet the stated requirements.