The use of Polyalkylene Glycol in Sonar Transducers.

摘要

Polyalkylene Glycol (PAG) has been proposed as a sonar-transducer fill fluid with nearly ideal properties, but PAG is far from being a universal fill fluid. Its speed of sound and acoustic impedance are both about 13% lower than those of seawater at 20 C, causing internal reflections (sensitivity loss) and refraction (directivity loss). Low thermal expansion and moderate compressibility make PAG a good choice in a nonpressure-relieved design. The electrical resistivity of PAG is 1000 to 10,000,000 times lower than that of other common fill fluids, partly from high water solubility. Also, some of the large amount of water in PAG at equilibrium will precipitate if the temperature drops and may cause catastrophic failure. Another concern with PAG is low resistivity if exposed to tin salts or perhaps tin, which may cause electrical failure. PAG is in general compatible with fewer acoustic-grade elastomers than caster oil. An advantage of PAG is low viscosity. It is much easier than caster oil to degas; hence air bubbles are less likely. The toxicity of PAG is low, and poisoning by vapors from overheating is easily avoided. PAG is readily available and not costly. If the vendor ceased production, the synthesis and specifications in this report would let additional vendors become qualified. In conclusion, with care in avoiding water exposure and in choosing exposed materials, PAG may find use in several Navy sonar units. (Author)