Thomas R. Howarth
Sam Petrie
Larry E. Ivey
Naval Res. Lab., Underwater Sound Reference Detachment, P.O. Box 568337, Orlando, FL 32856-8337
A prototype hydrophone with planar-omnidirectional radiation
characteristics has been developed for broadband, high-frequency, underwater
acoustic applications. A 9-(mu)m sheet of KYNAR-type polyvinylidene fluoride
(PVDF) was wrapped about a 2.5-mm solid Rho-c rod with a height of 86 mm such
that the resulting cylindrical shape had an omnidirectional radiation behavior
in the X-Y plane. The PVDF was oriented with the 3-1 direction radially wrapped
and the 3-2 axis positioned along the mounting rod for improved vibration strum
rejection from the mounting rod with improved radial sensitivity because of the
orthotropic nature of the KYNAR material. Further discussions will detail the
selection of an impedance matching mounting rod and waterproofing elastomer and
a cable with the low capacitance of 0.018 pF/m (8.5 pF/ft). Measured data to be
shown includes the free-field voltage sensitivity (FFVS) and X-Y plane
receiving radiation patterns from 100 kHz to over 1.5 MHz. The presentation
will conclude with a conceptual discussion on an advanced version of this same
sensor design for a broadband and high-frequency, three-dimensional
omnidirectional sensor.