Journal of Pure and Applied Ultrasonics

Pradeep Kumar Garu ¹, Dipak Khastgir ², Tapan Kumar Chaki ²

Affiliations
1 Rubber Technology Division, Naval Science & Technological Laboratory, DRDO, Visakhapatnam-530027, IN
2 Rubber Technology Centre, Indian Institute of Technology, Kharagpur-721502, IN

Abstract

Electro-acoustic transducers capable of converting electric energy to acoustic energy and vice versa are critical elements in Sonar systems. Among different types of electro-acoustic transducers Tonpilz transducer is widely used due to their ability to operate in both transmitting and receiving mode and generation of directional high acoustic power. Typically tonpilz transducers are encapsulated by a visco-elastic material when used in underwater applications. The primary function of encapsulation material is to protect the transducer from water ingression and physical damage without affecting significantly the acoustic transmission and reception properties, thereby influencing efficiency and reliability of transducers. In view of these, epoxy elastomers are widely used for encapsulation of tonpilz transducers. The term epoxy, epoxy resin or epoxide refers to a broad group of reactive compounds that are characterized by the presence of an oxirane or epoxy ring. For applicability and suitability of epoxy for a particular underwater application, its compositions and encapsulation thickness are the crucial parameters. In this paper the effect of the variation of encapsulation thickness of epoxy on the transmitting voltage response (TVR) and free field sensitivity (FFS) of a tonpilz transducer designed for underwater applications are presented.

Keywords

Electro-Acoustic Transducer, Acoustic Impedance, Epoxy, TVR and FFS.

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Pradeep Kumar Garu ¹, Tapan Kumar Chaki ²

Affiliations
1 Rubber Technology Division, Naval Science and Technological Laboratory, DRDO, Visakhapatnam-530027, IN
2 Rubber Technology Centre, Indian Institute of Technology, Kharagpur-721502, IN

Abstract

Epoxy materials exhibit a great range of properties (from soft to hard) which leads to a great versatility in application. Epoxy is the material of choice for underwater acoustic window applications as its acoustic impedance can be made to match the acoustic impedance of sea water. Acoustic impedance can be modified over a broad range for epoxy material by changing the resin (prepolymer) to curing agent ratio in the composition. Acoustical and mechanical properties of these epoxy composition have been investigated. Sound velocity and density of materials were measured. Acoustic impedance of the materials were evaluated and compared with the acoustic impedance of sea water. Insertion loss and echo reduction of the materials were measured in the frequency range 15 kHz to 100 kHz. Insertion loss was less than 2 dB and echo reduction was more than 10 dB throughout the frequency range which is suitable for underwater transducer encapsulation material. Mechanical properties like tensile strength, elongation at break and hardness etc. were investigated, which are important for encapsulation materials to withstand hydrostatic or hydrodynamic pressure. Ageing resistance to hot air was also conducted in the present study.

Keywords

Acoustically Transparent, Acoustic Impedance, Encapsulation, Sound Speed, Insertion Loss, Echo Reduction and Epoxy.

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