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NUWC XP-1 Polyurethane-Urea: A New, "Acoustically Transparent" Encapsulant for Underwater Transducers and Hydrophones

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Conference paper

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Almost all acoustic projectors and hydrophones are encapsulated in polymeric materials. These coatings protect the underlying sensors and electronics from physical damage and water ingression, while allowing the passage of acoustical energy without significant reflection, loss, or distortion. Critical material parameters for superior acoustical performance include 1 density and sound speeds close to those of seawater 2 low mechanical loss tangent 3 medium to high shear loss tangent 4 low shear storage modulus 5 Poissons ratio near 0.50 and 6 no major polymeric transitions innear the frequency and temperature ranges of interest. Recently, a new polyurethane-urea elastomer was synthesized at Naval Undersea Warfare Center NUWC, Division Newport for use as an encapsulant for transducers and hydrophones. This material, NUWC XP-1, utilizes a toluene diisocyanatepolyether polyol base molecular weight about 1500 and dimethylthiotoluenediamine as the cross-linkingcuring agent. NUWC XP-1 cures overnight at room temperature to 75 Shore A hardness. Its sound speed is very close to that of seawater at room temperature, and at 25 degrees Celsius, its acoustic impedance is 1.71 x 106 metric Rayls. NUWC XP- 1 exhibits a sub-ambient glass transition temperature -31 degrees Celsius and its dynamic mechanical properties are almost ideal for underwater transducerhydrophone encapsulants. Side-by-side comparisons with several commonly used, commercially-manufactured polyurethane encapsulants PRC-DeSotos PR-1547 and PR-1592 Cytecs Conathane EN-7 determined that properties of NUWC XP-1 are equal to, or better in almost every category required for effectively encapsulating acoustic devices and sensors. A distinct benefit to the industry is that the chemical formula of NUWC XP-1 is controlled by the U.S. Navy. The material is made from basic raw materials thus its future availability is more assured than many other commercial products.

Subject Categories:

  • Elastomers and Rubber
  • Submarine Engineering
  • Logistics, Military Facilities and Supplies
  • Acoustic Detection and Detectors
  • Physical and Dynamic Oceanography

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