Sonar uses sound waves to detect, locate, and identify objects in water. The term Sonar is an acronym for sound navigation and ranging. Ships and submarines primarily use Sonars for underwater navigation and surveillance. The design of Sonar requires expertise in sensor technology, signal conditioning and processing, electronic packaging, materials technology, ocean acoustics, and mechanical engineering.

Naval Physical and Oceanographic Laboratory (NPOL), a premier system laboratory of DRDO in Kochi, has proven the expertise required to develop various Sonar requirements for the Indian Navy. NPOL has been engaged in cutting-edge research in the area of underwater surveillance and communication systems for the past 70 years.

We look a few of the core technologies developed by NPOL/DRDO for the Indian Navy:

Technologies For Compact Hull Mounted Sonar For Shallow Water Crafts

Technologies were developed for a state-of-the-art compact SONAR system suitable for installation onboard Anti-Submarine Warfare (ASW) ships. The hardware comprises a compact staggered transducer array, a sleek and rugged display cum processing console, modular front-end signal conditioning hardware, and high-efficiency switched-mode power amplifiers.

Features

♦ Compact dimensions to suit space-constrained platforms
♦ Optimized for shallow-water operations
♦ Automatic target designation and tracking of multiple targets
♦ Reverberation suppression capability
♦ Provision for self-noise cancellation
♦ Beam stabilization to overcome own-ship platform dynamics
♦ Automatic LRU-level fault detection and fault localization
♦ Integrated SONAR performance prediction

Transducer Array

♦ Staggered Cylindrical Transducer Array
♦ More staves in less space
♦ Higher source levels
♦ Better radiation characteristics Front-end Electronics
♦ Modular design
♦ Conforms to the VME form factor
♦ Wide dynamic range
♦ Programmable Gain Control
♦ Supports remote configuration via Ethernet interface

Power Amplifier

♦ Class D switched-mode power amplifier
♦ IGBT full bridge configuration
♦ Employs pulse width modulation
♦ High efficiency (> 85 %)
♦ Low distortion (< 5 %)
♦ 3U form factor ♦ Power level control in steps of 1 dB

Multi-Function Console

♦ High-resolution (1600 x 1200) display monitors, Touch Input Display (TID)
♦ COTS General Purpose Processor (Intel Core i7/XXeon)
♦ A software framework based on the Qt4 toolkit for HMI software
♦ Seamless cursor and support for streaming audio/video
♦ Rugged servers for signal processing
♦ Software developed in MATLAB, C++, and Qt in a Linux environment

Subsequent to the development of these technologies, they were integrated, installed onboard, and successfully demonstrated to the User. The production version of the demonstrated equipment technology is being considered for installation on shallow water crafts. To facilitate this, NPOL transferred equipment technology to Bharat Electronics Limited (BEL).

Sonar Transducer Technology - Free-Flooded Ring Transducer

The Free-Flooded Ring (FFR) transducer is one of the main stay underwater transmitters developed in NPOL for ASW Sonars.

The high power-to-weight ratio and depth-independent acoustic characteristics make the FFR transducer more popular among other designs.

FFR transducers are highly efficient compared to conventional Tonpilz transducers, which operate at the same frequency.

The resonance frequency, or frequency band, of FFRs is governed by the dimensions of the FFR and the type of piezoelectric material used. 

The frequencies can be tuned by adding appropriate inactive materials between active piezoelectric segments that form the ring. FFR also uses multi-mode resonance to enhance its operating frequency band.

Features

♦ High power-to-weight ratio
♦ Depth-independent characteristics
♦ Unlimited depth of operation
♦ High source level and band width
♦ Omnidirectional in the azimuth plane

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