NEWS | July 2, 2012

NRL Researchers Win Bowen Patent Invention Award for Hydrophone Transduction Mechanism

By Donna McKinney

Drs. Anthony Dandridge and Alan Tveten of the Naval Research Laboratory's Optical Sciences Division and Dr. Aileen Sansone (Yurek) (former NRLer now working at Naval Undersea Warfare Center) are recipients of the 2011 Vice Admiral Harold G. Bowen Award for Patented Inventions. RADM Matthew Klunder presented the award in a ceremony at the Office of Naval Research on June 5.

The Bowen Award, given by the Office of Naval Research, is named in honor of Vice Admiral Harold Gardiner Bowen, the first Chief of Naval Research. The award recognizes inventions of great benefit to the Navy patented by current or former, civilian or military Navy personnel. Measured by the extent of its use, cost savings, increased military capability or increased quality of life, the invention must have a significant impact upon the operation of the Navy.

The winning NRL invention is a new form of acoustic sensor using optical fibers to both perform the sensing and the telemetry of the hydrophone system. Since being introduced in World War I for Anti-Submarine Warfare (ASW) applications, hydrophones have used piezoelectric elements to detect underwater sound. The hydrophone transduction mechanism invented by the NRL team is based on optical fibers and a simple mechanical structure to form the sensor. This invention initiates a new era in ASW acoustic detection by enabling new Navy systems with increased capability and reliability, and reduced cost.

This NRL-developed hydrophone is designed specifically for use in the Navy's Light Weight Wide Aperture Array (LWWAA), hull mounted submarine sonar array mounted on the VIRGINIA class attack submarines. These lightweight, electrically passive fiber-optic sensors are mounted on the hull of the submarine to perform acoustic detection. All of the electronic/optical components powering and demodulating the system are located inside the hull. This hydrophone differs from the conventional piezoelectric sensor designs, which have numerous electrically powered devices outside the hull in the water, where corrosion and water intrusion can cause sensor failures and make the overall system less reliable. As the active components of this system are positioned inside the hull, they can be easily replaced or upgraded if required.

Dandridge explains that the key point of the patent was a design of a fiber optic hydrophone to meet all the stringent Navy requirements for this application. Other researchers had developed multiple new designs for hydrophones, but these designs have failed to meet the Navy's requirements. Based on their experience with fiber optic communications and acoustic sensing, Dr. Dandridge and his team developed this simple, low cost, elegant design that met all the Navy requirements with a considerable performance margin. This design has also formed the basis of a number of other prototype fiber optic hydrophone systems for Navy applications, ranging from towed arrays (both submarine and surface) and bottom-mounted arrays.

In terms of improvements the NRL-designed hydrophone is projected to lead to approximately a 37% cost savings and is 54% lighter than conventional technology. The dry weight of the NRL design itself is less than a third of the conventional hydrophone system, and in the water it is close to being neutrally buoyant, with approximately 4 tons of electrical wiring being eliminated. As more elements are projected to be on-line at any given time than previous technology, this will result in greater beam gain, increased angular resolution and greater detection range. The hydrophone/telemetry system also provides the huge advantage of immunity to electro-magnetic interference, which means far easier installation and better compatibility with all other ship's systems.

As the LWWAA system goes through its current Tech Refresh cycle, the Navy is already seeing both cost, and performance improvements of the interrogating electro-optic system, while utilizing the same hydrophone elements described in the patent. The low intrinsic noise floor of this patented design of hydrophone, for both current and future systems, has the potential for lower system noise, which will result in greater detection ranges.