BULLETIN OF DEFENCE RESEARCH ANDDEVELOPMENT ORGANISATION

ISSN : 0971-4413

TechnologyVol. 18 No. 4 August 2010

Sonar systems have undergone evolutionary changes from

unitary systems to composite systems where fusion of data from

multiple sensors makes sonar displays highly user-friendly.

Over the last three decades, DRDO has designed, developed and

inducted several sonar systems for the warships and

submarines of the Indian Navy to enhance its capabilities.

Functional Layout of a typical Sonar System

Signal Processingand Post Processing

Sub-systems

Raw Data

FE Front-endHardware

Processed Data

Data Recorder

Gigabit Ethernet Gigabit Ethernet

Raw Data Bus Display Data Bus

Real-time Information andControl Data

Transducers

Display

High Bandwidth Real-timeSensor Data

Sonar is basically a remote sensing technique that uses sound waves to detect, locate and identify objects in water. Theterm sonar is an acronym for Sound Navigation and Ranging. Sonars are the eyes and ears of ships or submarines in waterand are mainly used for underwater navigation and surveillance. Civilian uses of sonar include determination of water

depth, mapping the ocean floor, locating various objects in the ocean, determining the characteristics of ocean bottom, andeven fish finding. Sonar system consists of underwater transducers, front-end signal conditioning units, signal processors, anddisplays. Sonar transducers transmit acoustic power and pick up the echo returns or merely listen to the underwater sounds,process the signal and provide information about targets on the display units.

TECHNOLOGIES FOR SONAR SYSTEMSTECHNOLOGIES FOR SONAR SYSTEMSTECHNOLOGIES FOR SONAR SYSTEMSTECHNOLOGIES FOR SONAR SYSTEMS

SONAR systems still remain the primary surveillance technique for ships and

submarines in naval warfare In the case of submarines, SONARs are the eyes and ears

underwater. Ocean going platforms being relatively slow moving, airborne

surveillance SONARs play a key role in early warning. Naval Physical and

Oceanographic Laboratory has been the pioneering R&D establishment in the country

responsible for near-total self-reliance in airborne surface ship mounted as well as

submarine borne SONAR systems of the Indian Navy The technologies associated

with SONAR systems, viz., signal processing, power amplifiers, transducers, handling gears,

hydrodynamics, oceanographic etc are complex and multidisciplinary. This issue of

lucidly brings out the cutting-edge accomplishments of DRDO, in various enabling technologies that

makeup the three-dimensional world class SONARs I am sure this effort would go a long way in

providing the readers, a quick awareness in this specialised area

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Technology Focus

Dr J Narayana DasOS & Chief Controller R&D (NS, M & HR)

MESSAGE

The SONAR systems being the only sensor system that has the capability to overcome thelimitations of the underwater environment it provides the capability for surveillance of underseasituation by naval platforms and ultimately provides inputs for launch of weapons to neutraliseopposing forces It also enables safe navigation obstacle avoidance and underwatercommunication Considering its strategic utility for the underwater vessels availability ofindigenously developed technology in SONAR systems is critical to our Navy

It is a matter of great pride that various SONAR systems developed by DRDO have been inducted into Navalplatforms and their operational utility has provided impetus for further improvement upgradation anddevelopment of new configurations of underwater systems in tune with global standards. Some of the recentdevelopments of DRDO pertaining to this technology have been summarised in this Special Issue of

. These will augur excellence in indigenous developments in this area and further optimise the configurationof the systems

Commodore PK MishraDirector Naval R D and

Member Editorial Board

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Technology

Focus

Technology Focus

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MESSAGEMESSAGE

For an emerging economic power like India with 7600 km long coastline, 12 major and

184 minor ports, and 90 per cent of its international trade through sea routes, the

importance of defending its coastline against threats through superior underwater

surveillance capability needs no emphasis. Over the last three decades, DRDO has

designed, developed and inducted several sonar systems for the warships and

submarines of the Indian Navy to enhance this capability. Surface ship sonars like APSOH,

HUMSA, and HUMSA NG, submarine sonars like PANCHENDRIYA and USHUS, TADPOLE

sonobuoys for airborne applications are some of the major systems delivered by DRDO

and exploited by Navy. Several technologies for the towed array sonar and airborne

dunking sonar have also been developed by DRDO during this period.

DRDO has been working very closely with PSUs, private sector industries, and academic institutions for the

design, development, production, and induction of sonar systems. With the increasing requirement for sonar

systems for the new platforms being acquired by the Indian Navy, the industry has evinced keen interest in

absorbing the complex sonar technologies. Moreover, the sonar systems have undergone evolutionary changes

from unitary systems to composite systems where fusion of data from multiple sensors makes sonar displays

highly user-friendly. Riding on the revolutionary changes offered by the computation and communication

technologies, and the indigenously developed models for prediction and interpretation of sonar performance in

Indian waters, user has gained more confidence in exploitation of these sonar systems. The large number of

unique testing facilities established under DRDO for evaluation of sonars have been gainfully utilised by both Navy

and industry alike.

This issue of gives a summary of various technologies that are at work in the development

and induction of sonar systems. New sonar technologies are under development in DRDO in consonance with the

advances in commercial technologies and increasing demands on performance and reliability of sonar systems.

We are confident that these will further strengthen the surveillance capability of our naval forces through

induction of advanced sonar systems.

S Anantha Narayanan

OS & Director

Naval Physical & Oceanographic Laboratory (NPOL), Kochi

Technology Focus

From the Desk of Special Editor

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Sonar for naval applications

broadly falls into two categories:

active and passive. Active sonar

emits pulses of sound waves that

travel through the water and

processes the received target echo to

estimate the range, bearing, and

Doppler of the target. Passive sonar

involves processing the sound signal

generated by the target for

estimating the bearing and target

characteristics through spectrum

analysis. The information gathered

by the sonar is fed to the Fire Control

Systems to compute other target

parameters like speed, course, and

range.

Intercept sonars are early warning

systems aiding classification of

t a r g e t s b y p r o c e s s i n g t h e

transmitted signals of other

platforms. Obstacle-avoidance

sonars are high frequency active

sonars for submarines to aid safe

surfacing operations. Underwater

communication systems permit

communication between platforms

through acoustic means in different

modes including voice, telegraph,

and data. For submarines, the sonar

is also the navigation equipment.

Sonar systems can also be used to

realign inertial navigation systems by

identifying known ocean floor

features.

The performance of a sonar

system is strongly influenced by the

ocean environment, which is highly

unpredictable, thereby making the

development of a sonar system a

challenging task. Continued ocean

studies for better understanding of

the ocean are being pursued and

better acoustic propagation models

are being developed for accurate

estimation of predicted ranges.

To offset the adverse effects on

detection by the bathymetric profile

of the ocean and self-noise of the

p l a t f o r m , t h e d e p l o y m e n t

mechanisms of sonar transducers

have undergone changes to

maximise the detection range.

Though the hull-mounted and bow-

mounted transducers are the most

common approaches, the variable-

depth towed array sonars also help in

detection of targets and torpedoes

below the surface-sound channel.

Dunk bodies housing transducers

and associated electronics are

dipped from hel icopters for

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Advanced Sonar Systems Technologies

Signal Processing

Signal Conditioning Sensor Structures/Handling Systems

OceanographyASWAlgorithm

Transducers

DesignModelling & Simulation

MaterialsMMI/Display

detection of sub-surface targets.

These requirements have posed new

challenges in sonar technology

development related to winches and

towed bodies. Development and

characterisation of exotic materials

for sonar systems in various areas like

composite materials, nanomaterials,

baffles, encapsulants, etc., are

important for improved reliability

and enhanced life of transducers and

interconnect materials.

DRDO has been striving to meet

the aspirations of the Indian Navy

on sonar systems through the

technologies and systems devel-

oped by the Naval Physical and

Oceanographic Laboratory (NPOL) at

Kochi. During the last four decades

DRDO has delivered various types of

sonar systems for ships, submarines,

and airborne platforms of Indian

Navy, and thereby NPOL has matured

as a System Laboratory of DRDO.

Keeping in view the growing

strategic requirements of the Indian

Navy, the Laboratory is focusing on

developing advanced sonar systems

technologies.

Over the years, Advanced Sonar

S y s t e m s t e c h n o l o g i e s b e i n g

developed by NPOL have made an

impressive growth in the research

and development in all the above

a r e a s . T h i s s p e c i a l i s s u e o f

highlights the

technologies developed and

implemented into various sub-

systems and the technologies

transferred to production agencies

for realising the sonar systems

inducted in various Naval platforms.

Technology Focus

Sonar systems rely on acoustics

and a suitable transduction of the

acoustic energy to electrical energy.

NPOL has pioneered the designing of

transducer using finite element

analysis. The designs have been

prototyped and engineered for use

in ship, submarine, and helicopter-

borne sonar systems. Their detailed

acceptance tests and characteri-

sation have also been done using the

unique test facilities available at

NPOL. Usually these acoustic

transducers are made of piezo-

electric materials; their working

principle is based on piezoelectric

effect.

Acoustic transducers are mainly

o f t w o t y p e s — p r o j e c t o r f o r

underwater transmission and

hydrophone reception. The

piezoelectric ceramics used in these

transducers are indigenously

manufactured at a cost that is

comparable to that of imported

for

components but meet tighter

tolerances. The technology for

manufacturing the transducers has

been transferred to production

agencies. There are mainly four

different types of designs for

underwater projectors.

Tonpilz (German for “singing

mushroom”) transducers are used in

active sonar systems to radiate high

levels of directional acoustic

pressure. The echo is received

through a hydrophone array and

processed to detect, track, and

classify targets. Members of this

family of transducers have been used

in active submarine sonar, active ship

sonar, underwater communication,

and obstacle-avoidance systems.

Several Tonpilz transducers have

been designed and developed with a

high transmitting voltage response,

a 3 dB bandwidth of more than one

octave, and a power-to-weight ratio

much higher than that achieved

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Circular ArraySingle Stave

earlier. Transducers, in this family,

with resonance frequencies ranging

from 1.5 kHz to 25 kHz are

individually encapsulated, are

capable of operating at a depth of

300 m for more than 10 years, and

have been extensively tested and

characterised. Tests with specially

tuned transducers and indigenous

power amplifiers have demonstrated

very high source leve l over

reasonably large bandwidth.

Most of these transducers are also

used as hydrophones to receive the

echo. In addition, these are also used

in passive sonar operations where

the usable bandwidth is much higher

as the receiving sensitivity has a roll-

off below resonance and, therefore,

reduces the high and low frequency

ambient noise.

The flextensional transducer has a

shell that is driven by piezoelectric

ceramic stacks. The extensional

vibration of the electrically-excited

stack causes the shell to flex, giving

the transducer its name. These

transducers are well suited for low

frequency sonar applicat ions

because these are omni-directional.

These have better power handling

capacity, and power-to-weight and

power-to-size ratios much higher

than those of Tonpilz transducers.

The shape of the shell determines

the class of the transducer. A family of

class IV transducers has been

designed using finite element

analysis. These transducers have

elliptical cylindrical shells, made of

aluminium, that are excited by stacks

of piezoelectric ceramics.

Flextensional transducers with

low resonant frequencies have been

designed and developed for use in

helicopter-borne dunking sonar

systems and ship-borne towed sonar

systems. The arrays have been

pressure tested to operate at depths

up to 300 m. Efforts are on to further

a c h i e v e l o w e r f r e q u e n c i e s .

Piezoceramics used in these

transducers have been indigenously

developed. The technology for

manufacturing these transducers has

been transferred to industrial

partners.

Hydrophones are broadband

r e c e i v e r s u s e d i n p a s s i v e

surveillance, intercept, and towed

array sonars with very good free-field

receiving sensitivity and effective

acceleration compensation. These

devices are designed for deep water

applications with long operational

life for submarine sonar systems.

H y d r o p h o n e s h a v e o m n i -

directional response in the radial

direction in desired frequency range.

Mainly there are three different

kinds of acceleration-balanced

hydrophones: Passive Surveillance

Array (PSA) hydrophones; Medium

F r e q u e n c y ( M F ) i n t e r c e p t

hydrophones; and towed array

hydrophones.

The PSA hydrophone is one of the

broadband hydrophones operating

in the frequency range up to 10 kHz

without any baffles. The hydrophone

is capable of operating up to a depth

of 600 m and has an operational life

of more than 7 years. It has omni-

directional response in radial

direction up to 10 kHz within 1dB. Its

specially designed mounts at the

ends, with central spacer design,

provide low acceleration sensitivity.

The MF intercept hydrophone is a

wideband hydrophone used in the

Flextensional Transducer

Low Frequency Flextensional Transducer Array

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frequency above 10 kHz. This is

capable of operating up to a depth of

450 m. Two piezoelectric ceramic

tubes have been assembled with

passive components and encapsu-

lated using PV bonding technology.

DRDO has excelled in developing

different types of towed array

h y d r o p h o n e s w i t h a w i d e

operational frequency range. These

hydrophones are small in size and

moulded with oil-compatible rubber

encapsulant. The technology has

been transferred to production

agency for the bulk fabrication of the

hydrophones.

E lectro-acoust ic reference

transducers of two different types

have been designed for underwater

a c o u s t i c m e a s u r e m e n t s a n d

calibration to work over different

operating bands. These transducers

work as a projector as well as a

hydrophone. As a projector, it

operates over a wide frequency band

and is capable of providing high

acoustic source level. As hydro-

phones, these provide flat frequency

response. The transducer technology

has been transferred to production

agency.

D R D O h a s d e s i g n e d a n d

developed high frequency trans-

ducers using 1-3 piezocomposites.Reference Transducers: NP 20 and NP 30 (top)

PSA Hydrophone Intercept Hydrophone for MF Band Towed Array Hydrophone

Specifications: Reference Transducers

Operating depth 0-300 m with 1.5 dB 0-300 m with 1.5 dBvariation variation

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Resonance frequency 30 1 kHz 21 1 kHz+ +

Usable frequency range 3-60 kHz 1-50 kHz

Input power 400 W 400 W

Usable frequency range 3-60 kHz 1-50 kHz

Beam pattern Omni (horizontal) Omni (horizontal)Toroid (vertical @ 12 kHz) Toroid (vertical @ 10 kHz)

Cable length 30 m 30 m

Parameters NP 30 NP 20

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The design is basically different from

that of conventional low frequency

transducer arrays. An array of 1-3

piezocomposite was first fabricated

and the individual transducer

elements were defined later by

applying patterned electrodes on

the major surfaces.

A few prototypes of 150 kHz

transducer arrays have been

evaluated underwater . These

transducers are useful for high

resolution underwater imaging

applications such as Mine Hunting

Sonar and Diver Detection Sonar.

Transducers with Micro-Electro-

M e c h a n i c a l S y s t e m s ( M E M S )

technology are being developed at

NPOL for miniature sensor array

system especially for thin-line towed

arrays (TLTA). MEMS are miniature

devices or systems that combine

electrical and mechanical compo-

nents fabricated using IC batch

processing technology. In MEMS,

sensors and actuators are mono-

lithically integrated with signal

conditioning, interface circuits and

Silicon MOSFET was fabricated

using MOS process technology.

MOSFET hydrophone has been

mounted on a PCB (21mm x 14 mm)

with a pre-amplifier. These hydro-

p h o n e s a r e e n c a p s u l a t e d i n

acoustically transparent potting

material. Dimension of individual

hydrophone after encapsulation is

35 mm x 25 mm x 5 mm.

These miniature sensors find

applications in TLTA for submarines,

surface ships, and Unmanned

Surface Vessels (USV).

electronics to generate intelligent

microsystems that perform superbly

at a reduced cost.

MEMS hydrophone is one of the

devices developed by DRDO. It

comprises an extended gate MOSFET

(Metal-Oxide-Semiconductor Field-

Effect Transistor) and a piezoelectric

sensor. The piezoelectric material

senses the acoustic pressure

fluctuation and an on-chip N–type

depletion mode MOSFET amplifies

the signal. It also acts as an

impedance matching device.

1-3 Piezocomposite Transducer Arrays Receiver. Inset: Projector

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Five-element TLTA using MEMS Hydrophone

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Power Amplifier (PA) is an integralpart of active sonar systems, andamplifies the sonar signal to the

levels required by the transducerelement. NPOL has developedcompact and energy-efficient poweramplif ier plug-in modules ofdifferent power handling capacities

in both linear and switched modesfor use in several sonar systems.Major types of power amplifiersdesigned by the Laboratory are:

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Type Technology Application

(b) Wideband high power Power BJT-based PA for broadband active sonar andamplifier linear class AB broadband underwater communication

systems and wideband ac source andaudio power amplifier

linear

(d) IGBT-based Power IGBT- Low frequency active sonarclass D high power based class Damplifier

Sw

itch

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Mo

de

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we

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Am

pli

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(a) Quad wideband MOSFET-based Mine hunting sonar, obstacle avoidancelinear power linear class AB sonar, echo sounder and side-scan sonar

multichannel wideband ac source andfishing sonar

amplifier

(c ) Energy efficient Power MOSFET- Diver deterrence sonar and lowclass S digital power based class S echo sounderamplifier

frequency

(e) MOSFET-based Power MOSFET- Low frequency active sonarclass D high power based class Damplifier

Quad Wideband Linear Power Amplifier (NP-LAQ-HF-0050)

Wideband High Power Linear Amplifier NP-LAS-WB-1000)

Specifications

Specifications

Configuration : Quad, linear class ABPower output/Amplifier : 50 W rmsDuty cycle : 10 %Distortion at full load : < 0.5 %Frequency band : 10 kHz to 100 kHzLoad impedance : 500 Cane tailored to any loadDimensions (W x H x D) : 21TE x 3U x 235mmWeight : < 4 kg

Configuration : Linear class AB, bridgePower output : 1000 W rms

Ω;

Duty cycle : 10 %Distortion at full load : < 2 %Frequency band : 1 kHz to 12 kHzLoad impedance : 125 can be tailored to any loadDimensions (W x H x D) : 21TE x 3 x 235 mmWeight : < 5 kg

Type Plug in Blind mate typeConfiguration Full bridge class S switchingPower output W rmsDuty cyclePower control to dB in stepsOperating frequency kHz to kHzLoad impedanceDimensions (W x H x D) TE x 3U x 220 mmEfficiency

Configuration : IGBT full bridgeSwitching technique PWM class DInput Pulse width modulated signalPower output W rms (max.)Duty cyclePower control to dB in two stepsOperating frequency kHz to kHzLoad impedanceEfficiencyDimensions (W x H x D) mm x U x 230 m

Configuration Power MOSFET full bridgeSwitching technique Uni polar PWM, class DInput Pulse width modulated signalPower output W rms (max.)Duty cycle duty cyclePower control to dB linearDistortion at full loadOperating frequency kHz to kHz

Load impedance 0EfficiencyDimensions W x H x D TE x 3U x mm

Ω;

Ω

Ω

Specifications

Specifications

Specifications

: ,:: 3000: 10 %: 0 -9 3: 1 10: 100 - 400 10 %: 21: > 90 %

: ,:: 5000: 10 %: 0 -6: 2.5 6.5: 200 10 %: >80 %: 135 6

:: -:: 2000: 10 %: 0 -42 ( ): < 0.5 %: 2.5 6.0

: 20 10 %: > 90 %

( ) : 21 220

+

Ω +

Energy Efficient Class S Digital Power Amplifier NP SAS LF

IGBT-based Class D High Power Amplifier (NP-SAS-LF-5000)

MOSFET-based Class D High Power Amplifier (NP-SAD-LF-2000)

( - - -3000)

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Towed arrays are one of the wellsought out technologies meant forgetting better immunity from ownship noise because of towing thearray far behind the towing ship.Also, the large aperture possible withlarge number of sensors assembledat relatively larger /2, promisesbetter range. Towed array combinesa host of technologies , v iz . ,packaging large number of sensorsinto a proper deployable casing,deployment from a moving platform,and digitisation and telemetry ofacoustic and non-acoustic sensordata.

Fibre-optic data telemetry systemhas been developed for use in towedarray sonar. The towed arrayelectronics is a distributed multi-channel real-time digital dataacquisition system. The majorchallenges involved in it are:simultaneous acquisition of datafrom multiple channels, transmissionof the data over tow cable of over1 km length, and synchronisation oftransmitter with the onboardreceiver for accurate reconstruction.

The acoustic and environmentalsensors operate at di f ferentamplitude levels and frequencybands with analog and digitaloutputs in serial/parallel format.Acquisition of information fromthese varying sources distributed inan elongated towed body (which canbe up to 1 km long) and combiningthese into a common interface for

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transmission through a serial fibre-optic link is a challenging task.

The realisation of the multi-channel signal conditioning and datatelemetry function has beenachieved in a compact hardwareform (housed in a polyurethane tube)for operations in high pressure andharsh dynamic conditions. Therealisation of data in digital form hasdistinct advantages over analogsystems. The entire hardware hasbeen realised in multiple modulesinterfaced with water-blockedelectromechanical connectors toenable easy repair and maintenance.This technology has been success-fully demonstrated and used intowed array sonars.

Coastal Surveillance Systems areessential to counter the asymmetricthreats posed by hostile submarines,boats, and divers.

DRDO has developed two coretechnologies Seabed ArraysTechnology and Diver DeterrenceSystem—as part of a coastalsurveillance system.

Seabed arrays are off-boardpass ive sonars , which can bedeployed on the seabed for moni-toring strategic locations at sea ona continuous basis to assess thethreats from submarines and sub-mersibles A seabed system withcapability to detect multiple targetsaround 360 without any left/rightambiguity and end-fire anomaly, hasbeen developed and proven for per-formance. Multiple-arrays deployedwith appropriate spatial separationwill facilitate the passive rangeestimation of the target too. Thesystem consists of multiple linearhydrophone arrays with a dataacquisition system The data can betransferred to a processing station atthe coast.

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Specifications: Towed Array Data Acquisition System

Output : 2 x 160 channel/12 bitAcoustic sensors : 96 + 128Serial data rate : 24 Mbps + 24 MbpsPower : 1 A at 300 V dcDimension

Length : 200 mOuter diameter : 80 mm

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Towed Array Electronics

Solid Linear Acoustic Sensor

Solid Linear Acoustic Sensor(SOLASE) array is the latest additionto the family of underwater acousticsurveillance arrays for seabedapplications. It is designed anddeveloped to alleviate the inherentproblems of puncture damages andoil leakages associated with themanufacture and operation of theoi l - f i l led vers ion. SOLASE is apolymer based monolithic flexiblesolid structure that embeds thesensors and allied electronics. It is amulti-channel linear passive acousticreceiver array and offers improvedunderwater surveillance capabilitythrough a new design of pre-m o u l d e d h y d r o p h o n e s , p r e -amplifier PCB, and power supplyu n i t w h i c h a r e a s s e m b l e d o na Kevlar strength member that runsthrough the entire length of thearray in a closed loop.

DRDO has developed a DiverDeterrence system, which can bedeployed around high value assetsand at harbor mouths. On activationunder Command Control, the systememits high decibel acoustic pulses todeter the divers from executing theirmission

Several technologies have beendeveloped to handle low levelsignals picked up by multichannelsonar arrays, and to condition thesesignals in amplitude and signalbandwidth to digitise the signals fordata telemetry, either throughcopper or fibre-optic medium. VHFreceivers have been developed toreceive the data transmitted from

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sonobuoys. RF communicationdevices using commercial-of-the-shelf (COTS) components withduplex communication have beendeveloped and used in sonarsystems.

A 32-channel data acquisitionsystem with a facility to programmev a r i o u s f u n c t i o n s h a s b e e ndeveloped. It incorporates a digitally

programmable gain amplifier, and adigitally programmable anti-aliasingfilter. The system can accept eithersingle-ended or differential inputs.The PCB accommodating the designalso supports two RS-422/485 serialports. The time division multiplexeddata is sent through a 100 Base T-Ethernet. In addition, there is aprovision to send this TDM data overa fibre-optic link.

Notable features of the design arethe excellent phase matching andcommendable high isolat ionbetween the channels. The dataacquisition system is housed in awatertight unit making it readilyd e p l o y a b l e f o r u n d e r w a t e rapplications. A long-range single-mode fibre-optic communicationover 100 km distance for the transferof serial data has been designed anddeveloped with COTS components.Alternately, RF communication of10 km with COTS components withDuplex communication has been

32-channel Data Acquisition Module

Specifications: 32-channel Data Acquisition System

Number of analog input channels : 32 max.PGA : Digitally programmable

1 per channelAnti-aliasing filter : Digitally programmable

up to 10 kHzADC : SAR type, 12 bits resolutionSampling frequency : ProgrammableOutput : Ethernet 100 baseT and fibre

optic Ethernet link

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designed and developed. Thewireless channel utilises IEEE 802.11gstandard at a frequency of 2.4 GHz,capable of providing a data rate up to54 Mbps. The transmitter uses 1 W(30 dBm) power through a 3-sectorantenna with gain of 14 dB. Thesystems are extensively used fortransferring both acoustic andtelemetry data.

The recorder unit is used forrecording the acoustic data directlyfrom sensors for monitoring andstoring for further analysis. This unitreceives 32-channel sensor data,conditions it in both amplitude andfrequency, digitises it and converts itto Ethernet format. It incorporatespre-amplifiers, programmable gainamplifiers, and different types offilters and data converters.

This system is designed foroperation in helicopters for homingon to sonobuoys. The left/rightposition of the sonobuoy, withrespect to the aircraft, is derived froma phase comparison of the signalsreceived from two-directional aerialsdesigned to operate in the VHFfrequency range.

The fore/aft position of the buoywith respect to the aircraft is derived

from an inline aerial array bycomparing the outputs from a phase-sensitive detector alternativelydriven by each element. The signalsfrom the left/right and fore/aft aerialsare sampled to provide a continuousindication of the buoy's position.

The VHF receiver, onboard ASWaircraft, is the communication linkbetween the sonobuoy and theprocessor. The sonobuoy picks upthe acoustic noises in the desiredfrequency band and modulates thecarrier frequency (FM) of a VHFtransmitter in any one of the 99 VHFchannels. The receiver is capable ofreceiving eight sonobuoy channelssimultaneously. The processed datago to the Signal Processor for LOFARa n d D E M O N p r o c e s s i n g a n ddisplaying.

The sonar signal processing anddisplay system extracts informationfrom the data sensed by the sensors.The information extracted includesdirection of arrival, speed of thecontact, the bearing rate, dominanttonal frequencies, shaft rpm, and thenumber of blades. For this, the datacoming from the various sensors issubjected to a variety of signalp r o c e s s i n g t e c h n i q u e s . T h eprocessing is done using high perfor-mance Digital Signal Processors(DSP) and PowerPC-based boards.The information is subsequentlypresented to the operator throughsuitable human- machine interfaces.

To meet the requirement ofprocessing a large number ofchannels of data simultaneously toprovide all-round surveillance, sonarsystems use a high-speed signalprocessing strategy. Adaptive sonarsignal processing techniques, whichform the core of the processing,require enormous amount of

Homing Receiver System VHF Receiver

Specifications: 32-channel Sensor Data Recorder

Number of analog input : 32 maxSignal bandwidth : 100 Hz to 12 kHzDynamic range : 80 dBGain control : ProgrammableSampling frequency : 31.25 kHzADC resolution : 12 bitsOutput data format : 100 Mbps Ethernet

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computational capability along withthe capacity to handle high inputdata rates. The resulting signalprocessing functions have beenimplemented using high-speeddigital signal processor boards basedon open standards using TigerSHARCprocessors. The processor board isdesigned in 6U form factor pluggingon a VXS back plane.

The TigerSHARC processor-basedDSP board combines 24GFlops ofraw computing power along with avariety of high-speed interfaces forefficient data transfer. The designcombines a cluster of eight such highperformance processors along with aseparate communication enginebased on a dual-core BlackFINprocessor.

The communication engineconnects to two Ethernet ports, eachoperating at 1Gbps, and VME andUSB ports over the PCI bus. Thiscompletely takes care of all datainterfaces and leaves the highperformance core unhindered to doall core signal processing functions.The board also has two audio ports, aPMC site for PCI mezzanine boards aswell as JTAG ports for debugging.The high computational powerprovided by the design makes the

cherished dream of single-boardsonar closer to reality.

The NP-TS201-24 is completewith a user-friendly developmentsupport system, facilitating theu t i l i s a t i o n o f t h e h a r d w a r eresources, most effectively. Thedesign supports software develop-ment in C language, utilising anextensive collection of routinesdeveloped for signal processingapplications and runs on a personalcomputer. Utility software comm-unicates with NP-TS201-24 fordownloading the compiled code,monitoring, and debugging theprogram during execution.

Together with the availablesoftware support, the NP-TS201-24offers significant advantages inhardware reduction and easy systemintegration. The board is being usedin the latest series of sonar systemsand was developed with the help ofreliable industrial partners.

For control, networking, andinformation and display dataprocessing, a high-end Single BoardComputer (SBC) is essent ia l .Adapting open standards, an SBC in

6U VME form factor based onPowerPC MPC7448 processoroperating at 1 GHz has beendesigned and developed in closecol laborat ion with industr ia lpartners. The board combines highprocessing power and IO bandwidth,and low power dissipation.

The PowerPC has become themost widely used new generationReduced Instruction Set Computer(RISC) processor because of itssuperscalar architecture, extendedtemperature options, instruction setcompatibility across the entireproduct line, multiprocessingcapabilities, long-term growth path,a n d t h e w i d e s e l e c t i o n o fdevelopment tools. A 128-bitimplementation of "AltiVec" SIMD(Single Instruction, Multiple Data)engine accelerates typical net-working and information processingfunctions.

The NP-PPC7488 SBC has 512 MBDDRII SDRAM, 256 MB Flash, and twoGigabit Ethernet ports. Real-timeClock (RTC), high resolution timers,and watchdog timer are alsoavailable. The board is ported withU-Boot and Linux kernel. The SBCprovides two PMC expansion slots forextended flexibility and integrationof additional I/Os to the board.

NP-TS 201-24 Board

Configuration of NP-TS 201-24

Processing engine : Eight TigerSHARC processor @ 500 MH z

Internal memory : 24 Mb/processor

Onboard memory : 128 MB SDRAM; 16 MB Flash

External interface : Gigabit Ethernet; VME; Link and

Serial ports

Communication engine : Black FIN processor

Software support : VDSP IDE; TigerSHARC communicator;

Signal processing library

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Hardware

Linux OS

Middleware

ApplicationProgram

Services

Utilities

Communication

Management

MultithreadManagement

TCP UDP

VMEEthernet

SerialThreads

QueuesSDLC

Communication Interface

Common architectural frame-work for applications software forinformation processors of sonarsystems was achieved by developinga middleware in-house. This, alongwith the use of open standardinterfaces between sonar sub-systems, helped in developing highlymaintainable, reusable software in ashort t ime span with lesserm a n p o w e r . T h e m i d d l e w a r efunctions as a layer between theapplication and the Linux operatingsystem. The bottom hardware layercould be the NP-PPC7448 SBC withnecessary communication inter-faces. Linux OS comes on top of thehardware. The middleware layer is

sandwiched between the Linux andthe application program. This layerprovides a set of services, which canbe accessed by the applicationprogram through well-definedinterfaces.

The middleware mainly providesservices for communication andmult i-thread management. Itpresents the application program aprotocol and hardware transparentcommunication interface to handledifferent interfaces like Ethernet,VME, serial port, and SDLC, channel,etc.

For achieving protocol andhardware transparency, a commoncommunication packet structure hasbeen defined and modules forcommunicating data using different

interfaces have been provided in themiddleware. It provides a genericmethod to communicate the datathrough different interfaces. Usingthese services, the applicationprogrammer is insulated from thecomplexities of low-level commu-nication.

As part of the architecturalframework, the middleware providesa set of threads with specificfunctions. These include: receivethread (for receiving data), transmitthread (for transmitting data),process thread (processing ofreceived data), health thread (forperiodic health monitoring), andsimulation thread (for simulatingdata). In addition to the majorservices described above, middle-ware also provides several utilityservices like handling of sub-systemhealth, maintenance of system log,etc.

The middleware was designedusing OOD principles and isorganised as different layers ofproject-independent common,project-specific common, and sub-system-specific common along withcore functional logic required in thecore domain. This also promotesreuse of software to a large extent

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NP-PPC7448 Single Board Computer

Configuration of NP-PPC7448 Single Board Computer

Processor : Power PC 7448 @ 1GHz

Memory : 512 MB DDR II SD RAM; 256 MB Flash;

L2 1 MB Cache

PMC sites : Slot 1(64 bit/66 MHz); Slot 2 (32 bit /33 MH z)

Network : 2 channel Gigabit Ethernet

USB : 2 USB 2.0 ports

Backplane : VME 64 x with 2eSST

Firmware : U-Boot 1.2.0 and Linux 2.6.16 BSP

and reduces time period required forsoftware development .

The Human Machine Interface(HMI) of the sonar allows theoperator to configure different sonarfunctions and present the processedinformation in an easily compre-h e n s i b l e m a n n e r . F r o m t h econventional approach of usingcustom devices, the new generationsonar HMI uses industry standarddevices such as high resolution LCDdisplays, keyboards, and tracker ballsshared through KVM switches.

T h e d a t a i s p r e s e n t e d i ncomposite pages in a Windows-likeenvironment. The HMI pages have allthe advanced graphics widgets likepop-up menus, combo boxes,command buttons, etc. Unlikeconventional sonar systems display,where controls are selected througha nested series of soft key operations,in the new generation display, therequired controls are available in theinformation page directly throughthe above widgets. In addition, theoperator commands can be giventhrough the touch panels.

The HMI has been developedusing object oriented methodologyusing C++/Qt over Linux operatingsystem on indigenously developedNP-PPC7448 SBC with Graphics PMC.The graphics toolkit Qt, running on Xwindow system, provides a lot offlexibilities in terms of the fonts andc o l o u r s . C o m p a r e d t o t h econventional sonar HMIs, which usedto run on dedicated hardware withlimited graphics support, the client-server architecture of the newgeneration sonar HMIs provide much

more flexibility to meet manyrequirements.

A typical sonar display is broadlydivided into video and annotations/control areas. The video areacontains graphs and cursors, whichpresents information from varioussonar sensors. The information ispresented as the amplitude andwaterfall graphs. The amplitudegraph provides the instantaneoussignal amplitude, whereas thewaterfall graph provides the historyinformation in the form of signalintensities over time to the operator.The annotation area provides allnecessary controls and statusinformation.

DRDO has acquired sufficientexpertise in phased array signalprocessing, which forms core of thesonar signal processing. Spatialprocessing incorporating conven-tional and adaptive techniques arebeing used extensively in all thesonar designs. These include MVDR,MUSIC, ESPIRIT and STAP algorithms,which have been perfected to makethese implementable on the signal

processing hardware. The standardtechniques of detection, tracking,background normalisation, andspectral analysis used in sonar signalp r o c e s s i n g h a v e a l s o b e e nextensively refined to give betterperformance of both active andpassive sonar systems. NPOL hasexpertise to detect transient signals,which are of short duration. Robusttechniques have been developed forproviding automatic transient alertusing both cylindrical and lineararrays. The Laboratory has estab-lished its credibility in resolving theleft/right ambiguity—a bane for atowed array sonar system. Theleft/right ambiguity resolution isachieved using a three-elementlinear sensor assembly, supportedby powerful signal processingalgorithms.

Automatic Target Recognition(ATR) provides early warning so as togive sufficient reaction time fortaking counter-measures. To thisend, ATR extracts features of each ofthe tracked targets. A number ofdiscriminatory features to distin-guish different types of targets withvery low miss-classification errorhave been successfully identified andestablished. All algorithms of signalprocessing have been subjected toelaborate Monte Carlo simulationsfor f inal is ing the parametersinvolved.

The 3-G Underwater WirelessAcoustic Communication System (3GUWACS) is the third generationproduct in underwater communi-

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Triplet Sensor for L/R Array

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cation from NPOL succeeding thestand-alone Underwater Telephone( U W T ) a n d t h e i n t e g r a t e dUnderwater Telephone System usedin submarines. The product has beendeveloped in collaboration with anindustrial partner.

In modern network-centricwarfare enabled operat ionalscenarios, seamless connectivitybetween underwater platforms andsurface vessels is of prime impor-tance. This calls for an advancedwireless communication system withability to cater to a variety ofoperational modes like multibandvoice and robust data transfer. The3-G UWACS has been developedwith such an operational frameworkin view. It is a state-of-the-art systembased on Software Defined Radio(SDR) Architecture.

The 3-G UWACS has several newfeatures in comparison with theearlier underwater communicationproducts. This system incorporatesadvanced modulation and codingtechniques in addition to datarecording and analysis features. Itoffers the user enormous flexibility in

operation, easier maintenance, and ahost of additional features through acomprehensive GUI. Besides, itsupports remote operation andmonitoring through standardnetworking technologies critical forplatform-level integration. Thesystem has been designed with aview to make it backward compatiblewith the earlier versions of UWT tofacilitate operational requirementswith platforms equipped with theearlier product. The system can beutililsed in stand-alone or integratedmode of operation.

The various sub-components in asonar system are sensor arrays, winchand handling systems, systemelectronics, and display units. Thepackaging of system electronics isdone in compact enclosures withefficient thermal management andwith EMI/EMC compatibility. Intowed sonar systems the deploy-ment and retrieval of sensor arrayswith very long cables and separatetransmitter bodies are handled bycomplex winch and handlingsystems.

Winches for airborne applicationsare designed using lightweight

materials without compromisingstrength and safety. The above sub-systems have been designed anddeveloped with the state-of-the-arttechnology in collaboration withindustrial partners and inducted inseveral sonar systems used by theNavy.

Air Transport Rack ATR is aruggedised enclosure used forpackaging of electronics andelectrical items onboard airborneplatforms The ATR is designed as permilitary standards MIL STD F forenvironmental testing MIL STD

E for EMI EMC compliance MILSTD D for qualification of brick

( )

.- -810

, - -461 / , -

-704

Salient Features: Air Transport Rack

Backplane : 12 slots, 6U-VME64xHeat load : 300 WCooling method : Forced convection using ambient airCooling fans : Two ebm-NADI axial fansPower supply unit : 115 V ; 400 Hz- brick type, integratedI/O connection : MIL-C-38999 connector on

frontal panel

Display Processor ATR Card Cage Assembly

3-G Underwater Communication System

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type power supply unit, and IEEEstandard 6U VME card cages. The rackdeveloped is a display processor cardcage assembly of standard one ATRlong dimensions and fabricatedusing airworthy aluminium alloy

The unit is fully integrated andhas successfully completed all theenvironmental tests as per thespecifications Heat generated byP C B s i s r e m o v e d b y f o r c e dconvection of air. The cooling designis such that it maintains a positivepressure in the enclosure to keepdust ingression to minimal The unitis mounted on an ARINC tray for easymaintenance and installation, andprovided with shock mounts Barrycontrols for isolating the ATR fromthe shock and vibration of theplatform

Display-cum-Processor cabinet isintended to integrate displayprocessing and signal processingfunctions of a sonar system. Thecabinet comprises five levels whereeach level is a standard subrackstacked one over the other. IEEEstandard 6U form factor subracksalong with VME backplane havebeen incorporated in this cabinet. In

.

.

.

()

.

addition, VME standard plug-in unitssuch as PCB and power supplyincluding injector and extractorhandles have also been used. Thecooling design of the cabinet is acombination of series and parallelflow types. Cooling is achieved bylateral entry of fresh air at each levelthrough a double-walled duct at the

side panels. The temperaturethroughout the cabinet is main-tained to be within limits.

D R D O h a s d e s i g n e d a n ddeveloped a winch (ASW 4001) forlowering and hoisting the dippingsonar dome into the sea for under-water surveillance operations. Thewinch has been installed onplatforms after obtaining flightclearance certification. It has thefacility to display cable paid outlength, cable angle and hasautomatic speed control withrespect to sonar dome position whilelowering as well as hoisting. Thewinch has been fabricated usingaluminium alloy based on anoptimum design for strength andsafety, and has got a cable spoolingmechanism.

The winch is driven by a mainhydraulic motor capable of deve-loping 10 HP at 4000 rpm. Its speed iscontrolled by an electrical servo valveand a hydraulic circuit. It also has anauxiliary electrical back up motor anda manual cranking device forredundancy, and a

. The winch issoftware-driven in the lines of lateststate-of- the- art technology .

pyrocuttingdevice for emergency

Salient Features: DCP Cabinet

Backplane : 18 slots, 6U-VME64xPackaging capacity : 90 PCBs and 5 power supply unitsHeat load : 1200 WCooling method : Forced convection using ambient airCooling fans : Two centrifugal fansNo. of displays : TwoKeyboard : FoldableEMI/EMC protection : Using EMI fingers and honeycomb

ASW 4001

Display-cum-Processor Cabinet

Low frequency dipping sonar,deployed from a helicopter to detectunderwater targets in the sea hasbeen developed. The dipping sonarutilises a dunk body (NP-DB-214)lowered from the helicopter for ASWoperations. The body consists of anelectronic unit, drive assembly, activeand passive transducer arrayassembly, and non-acoustic sensorsunit. The dunk body is connected tot h e w i n c h b y m e a n s o f a n

electromechanical (EM) connectorusing high strength multi-core EMcable. It has a high-power activetransducer array to transmit soundsignals underwater to detect long-range targets.

The drive assembly comprisesmechanism for the foldable andunfoldable passive transducers arrayfixed in vertical staves and is actuatedby an actuator. The array fold andunfold mechanism can be remotelyoperated from the platform duringsonar deployment. The completecontrol of the dunk body deploy-ment along with winch operationcan be carried out from the operatorconsole unit installed in the platform.The dunk body has been designedkeeping in view the hydrodynamicaspects during the deployment. Allthe mechanical components havebeen manufactured using airbornequality aluminium alloy and GFRP.The components that will beexposed to seawater dur ingdeployment have been anodized towithstand corrosion.

Dunk Body Dome with extended arms

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Salient Features: Airborne Hydraulic Motor

Type Axial pistonDisplacement FixedAxis of rotation Bend axis

Bend angle 30

:::

:Displacement volume : 6 0.1 cc/revFluid : MIL-H-5606 or its equivalentWeight : 2 kg (max.)No. of cylinders : 9 with fixed strokesTheor tical flow rate at max. : 38.5 0.1 lpmcontinuous speedPressure rating : 207 bar (continuous)Maximum pressure : 210 barMax. continuous speed : 6400 100 rpm (at 38.5 lpm)

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Hydraulic Ship-borne Sonar Winches

NPOL has developed ship-bornewinches (SSW 5 H and SSW 7 H) foronboard installation on Navalplatforms. Winches have provenseaworthiness by undergoingseveral sea trials, and are been usedfor deployment, retrieval, spooling,and stowage of the wet-end sonarsystems.

The systems are electrohydraulicwith stand-alone power packs andare controlled by microprocessors.Dedicated sensors and ergonomicdisplays help in online monitoring ofcritical system parameters like cablepaid out length, cable tension, speedof operation, etc. Safety interlocks(software and hardware controlled)have been integrated into the systemfor safeguarding the system as wellas the operator. These winches aredriven by hydraulic motors through

compact planetary gearboxes withprovision for redundant electric driveand manual drive for maintenancepurposes.

SSW 5 H can accommodate 500 m

of tow cable, 30 m passive array, and

is designed for 5 ton. SSW 7 H system

is capable of handling 1300 m of tow

cable and 200 m towed array,

comprises a dedicated handling

system for deployment and retrieval

of underwater towed body and is

designed for survival load of 7 ton.

Electric Ship-borne Sonar Winch(SSW 5 E) is an electric winchdeveloped to deploy, retrieve, and tostore 1500 m of electromechanicaloptical cable and sensor array. Thesystem consists of a drum withflanges on both sides over which thecable is wounded. The drum is drivenby a 3-phase 25 hp induction motor

Electric Ship-borne Sonar Winch

controlled by Variable FrequencyDrive (VFD) through a reductiongearbox. A constant-speed, 3-phase5 hp electrical motor drives the drumat constant speed in redundantmode. Dog clutch mechanism hasbeen provided for change of'operation mode' to 'redundantmode'.

Operational speed of SSW 5 E isbetween 0 and 25 rpm in VFD mode.Operator console has a joystick forspeed control. The control consoleconsists of a variable frequency driveand an overload trip device. Thesystem is built-in with strain gaugeand encoder assembly for onlinecable tension and the cable lengthpay out measurement.

The system is also fitted with fail-safe electrically operated thrusterbrakes. Overall size of the system is2150 mm x 2100 mm x 2000 mm andthe weight is approximately 5 ton.

SSW 5 H SSW 7 H

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A Towed Transmitter Body (TTB)and handling system has beendeveloped by NPOL in collaborationwith an industrial partner. TTB is ahydrodynamically shaped towedunderwater body and has got anelliptical cross-section. The body isused to house f lextens ionaltransducer and serves as an acousticsource for towed array sonar system.The major sub-systems of TTB are:shell assembly, ballast, splitter plates,wing, bridle, and flextensionaltransducer.

The transducer is powered by atuning coil unit, which is also housedinside the TTB. The sub-systems areintegrated with titanium grade fivefasteners. The bridle is connected tothe pivot axis of the body using twofulcrum pins. The TTB fore-end isconnected to the heavy tow cableusing a U-shaped bridle assemblythrough an electrooptic mechanicalinterconnector.

A swivel hub, provided at the rearend of the TTB, connects light tow

cable (LTC) through flexible link. TTBhandling system caters for the safedeployment and recovery of thetowed body from a moving ship. Apair of hydraulically operated roboticarms facilitates the purpose. Themode of operation of the entiresystem is electrohydraulic. Underwater Electromechanical

Connector

The compact and lightweightconnector provides mechanical aswell as electrical connectionsbetween the different functionalmodules of a towed sensor array. Theunique features of the connectorinclude sealing against seawater,high axial load-bearing capacity,automatic polarisation, quicka s s e m b l y / d i s a s s e m b l y , a n dstreamline shape. The connector isdesigned to withstand harsh

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0Salient Features: Strength Member

Material Cross-section (mm) Breaking Strength ( kN)

Kevlar 13 x 2 21

Spectra 1000 13 x 3.5 40

Spectra 1000 dia: 10 13

Towed Transmitter Body and Handling SystemSSW 5 E

operating conditions includingd y n a m i c t o w i n g l o a d s a n dhydrostatic pressure. The connectoris dry-mateable. Mating and de-mating is carried out using a portableassembly fixture.

It is a flexible pressure-balancedmodule of towed array system thatperforms the following functions in afield environment with dynamictension:

Electrical, optical and mechanicalinter-connection between HeavyTow Cable (HTC) and LTC.

Mechanical engagement andelectrical powering of TTB.

Transfer of towing loads from LTCto HTC.

Electro-Opto-Mechanical InterConnector (EOMIC) assembly isencapsulated with polyurethane(PU) hose and filled with gel underpressure to block water seepage intothe assembly. It maintains a pressuredifference of zero making it apressure-balanced design. Enoughslackness has been provided for towcable core sheath, electric and fibre-optic lines to compensate relativeelongation. A loop of strengthmember (SS wire rope) takes the

Electro-Opto-Mechanical InterConnector

dynamic load acting on EOMIC. It isdesigned to withstand a pressure of30 bars and can take an axial load of30 kN. The outer diameter of EOMICassembly is 80 mm.

Rubber-based encapsulants areused for protecting the electro-acoustic transducers from the marineenvironment. The need for longshelf-life of rubber encapsulants hasb e e n a d d r e s s e d l e a d i n g t odevelopment of new encapsulants.Adhesives have been used widely fordevelopment of underwater com-ponents meant for sonar systems.Underwater cable junction boxes arenecessary especially for submarinesonar systems to route multichannelsensor array data to the electronichardware kept inside a pressure hullcompartment. Adhesive-free coldmoulded PU underwater junctionbox and cable splicing technologyhave been used for realising thesame.

Encapsulants based on thermo-plastic polyolefine elastomers havebeen developed. The encapsulantshave shelf-life of 25–30 years andpossess better electrical resistivity.

Colourants can be added to theencapsulants for enabling colourcoding and easy traceability ofencapsulated sensors.

A new indigenous adhesive (NP235) has been used for fabrication ofmolded Rubber Junction Boxes( R J B s ) c a b l e s p l i c i n g , a n dtransducers encapsulation Theadhesive is flexible with good peelstrength, seawater compatibility,and insulation resistance. Theadhesive bonds vulcanised rubber toeither vulcanised rubber or primedmetal substrates. It is well-suited forp r o d u c i n g a n d b o n d i n g o ftransducer electrical componentsbecause of its better insulationpropert ies and durabi l i ty inunderwater marine environments.

Underwater cable junction boxesare used to connect multiple single-core neoprene cables to a multi-corecable to be used in deep sea

,

.

Electro-Opto-Mechanical Inter Connector

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Transducers with Long-life Enhancement

environment. Adhesive-free coldmolded PU underwater junction boxand cable splicing technology havebeen developed in collaborationwith industrial partner. To obtainbetter mechanical strength andavoid contamination of solderingslag, connectorisation of the cableshas been achieved by crimping withtinned copper tubes in place ofsoldering. The technology avoids theproblems associated with fabricationat higher temperature, and hencecan be extended to thermally-sensitive cables and sensors.

The sealing material employed isa two-part PU system havingexcellent bonding with varieties ofsubstrates. Higher water imper-meability, stability, and improvedmechanical and electrical propertiesare additional advantages of thematerial employed.

Ocean has a complex environ-ment in which sonar system has toperform to the needs of the Navy, theend user. Since the sonar perfor-mance is largely influenced by theocean behaviour, a proper under-standing of the ocean environment is

most imperative for optimumperformance . Oceanographicstudies are concentrated towardsthis end to know the environmentand the acoustic propagation in abetter way by modelling andvalidation of the model by datacollection.

A sonar performance modellingtool has been developed andimplemented by DRDO. It is a genericmodel catering to the modellingrequirements of a wide range ofactive and passive sonars. This isimplemented as a PC-based menu-driven program with user-friendlyinterface. It is being used extensivelywithin the Laboratory for modellingthe performance of various typesof sonars during the design, develop-ment, and evaluation phases.

Two other software packageshave been developed to understandand visualise the ocean environmentand to support the above modellingtool. Complete with a user-friendlyinterface, one model visualises theenvironment, i.e., temperature,salinity, and velocity up to the watercolumn depth using the best

comprehensive data available tilltoday. The other model is a uniquepackage, to simulate 3-D structure oftemperature, salinity, current fieldsand to estimate the sound velocitystructure off the west coast of Indiafor any desired month, both onclimatologically and daily scales,using a 3-D circulation model.

in situ

Cold Moulded Underwater PU Junction Boxes

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Spliced Cable using NP-235

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cÆ BÉÖEàÉÉ®Editor-in-Chief Assoc. Editor-in-Chief Editors Editorial Assistant Pre-press Coord. Printing DistributionAL Moorthy Shashi Tyagi B Nityanand Dipti Arora SK Tyagi SK Gupta RP Singh

Manoj Kumar Hans Kumar

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ºÉàÉx´ÉªÉBÉE

ºÉnºªÉfuns’kd] MslhMkWd

lh

, esVdkWQ gkml] fnYyh Dr AL Moorthy

Shri R Shankar

Shri Sudhir K Mishra

, Director, DESIDOC, Metcalfe House, Delhi

Director of Materials, DRDO

, Director of CV&E, DRDO New Delhi

Director of Naval Research & Development

DRDO

, Director of Missiles, DRDO

Bhavan,

Coordinator

Members

Dr Sudarshan Kumar

Cmde PK Mishra

, Bhavan

,

Bhavan

Bhavan

, New Delhi

, New Delhi

, New Delhi

Editorial Committee

RNI No. 55787/93

Printed & published by Director, DESIDOC, on behalf of DRDO

MhvkjMhvks dh vksj ls funs’kd] MslhMkWd }kjk eqfnzr ,oa izdkf’kr

Editors thank Letha MM, Scientist D and Local Correspondent offor helping in bringing out this Special Issue.Technology Focus

A large number of technologies asdescribed above have foundapplications in the large number ofsonar systems developed anddelivered by DRDO and fitted onNaval platforms for ship-borne,

airborne, and submarine appli-cations.

The technology roadmap forfuturistic sonar systems envisagedevelopment of high power and lowfrequency transducers, efficientcompact power amplifiers, high-speed high-resolution multichanneldata acquisition systems, high per-formance computing engine forgleaning out sonar information andfusion of data, thin-line towed arrayfor submarine sonar applications,lightweight compact sonar winches,and more accurate sonar range-prediction models.

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