Relationship between acoustic properties and structure of polyurethanes

Abstract

Commercial polyurethanes, although convenient, do not provide close sound-speed or density matches with seawater. Several series ofdiblock copolymer polyurethanes were prepared in order to study the compositional parameters that determine the acoustic properties of this class of compounds. Compositional changes that principally affect the hardblock part of the structure were shown to exert little influence on sound speed or density. Conversely, an increase in the size or quantity of the softblock causes large decreases in the properties, allowing production of polyurethanes with very closely matched properties. Correlation equations for sound speed, density, and specific acoustic impedance are given as a function of calculated number-average molecular weights of the polyurethane softblock. The essential independence of the sound speed from the Shore hardness suggests that the hardblock composition controls the hardness property whereas acoustic properties are determined by the softblock parameters. PACS numbers: 43.85.Bh, 62.65. d-k, 43.85.Dj, 43.30.Jx BACKGROUND

Fabrication and characterization of novel polyurethane Encapsulant with excellent underwater acoustic transparency and hydrophobicity

“…At present, reports about underwater acoustically transparent polyurethane mainly concentrate on polyether-based polyurethane. [9,10,12,22,23] There are few studies concentrating on the use of polybutadiene-based polyurethane in underwater acoustic systems. The application of fluorosiloxane in the modification of polybutadiene-based polyurethane is also rarely reported.…”

Acoustic properties of nitrile butadiene rubber for underwater applications

“…In early research, acoustic properties were investigated for commercially available polymers such as poly(methyl methacrylate),4 rubber,5 and polyurethane 6. Recently, structural variations of polymer were also investigated to prepare appropriate polymer compositions for underwater applications 7–10. Thompson et al7 reported intensive investigation of the effect of polyurethane structure on acoustic properties.…”

“…Recently, structural variations of polymer were also investigated to prepare appropriate polymer compositions for underwater applications 7–10. Thompson et al7 reported intensive investigation of the effect of polyurethane structure on acoustic properties. Soft‐segment polyurethane was shown as a major factor to determine sound speed.…”

An Omnidirectional FM Monitor Hydrophone for Low-Frequency Towed Projectors

“…At low frequencies, the characteristic impedance (pc, the product of material density and sound speed) of the encapsulant is near that of water, making it acoustically near-transparent. 2 The encapsulant is tough and under normal conditions will not break, tear, or stretch. It provides excellent abrasive protection.…”

“…The demodulated signal is filtered, amplified, and made available· at a front-panel connector. Status lamps on the front panel indicate (1) when the system is powered and locked onto the FM carrier, (2) if the FM signal is excessive, and (3) whether the hydrophone wire pair is open or shorted.…”