Sonar – is formed as an abbreviation for Sound Navigation and Ranging.
A systems used aboard Navy ships for sonic and ultrasonic underwater detection, ranging, sounding, and
communications.
Two general types of sonar systems
a) Active type – (sometimes referred to as the echo ranging type), is a target seeking system. It is
capable of transmitting underwater sounds that strike targets and are returned in the form of echoes
indicate the range and bearing of the target.
b) Passive type – (sometimes referred to as the listening type), does not transmit sound. This system
merely listens for sounds produced by the target to obtain range and bearing information.
Active Sonar are divided into two general types
a) Searchlight – transmit the energy pulse at only one bearing at a time, and the transducer is held at
that bearing to listen for a returning echo. Search procedures require the operator to transmit, listen for
returns, and train the transducer (in steps) while searching the area around the ship.
b) Scanning – provides audible and visual indications of all under water objects around the ship. It’s
sound pulse spreads out in all directions simultaneously instead of being limited to a narrow sector as are
searchlight sonars.
Major components of active sonar
1. Transmitter (consisting basically of a high frequency audio oscillator and amplifier)
- Supplies a short, high power, ultrasonic pulse to the transducer for projection into
the water.
2. Transducer
- Convert the electrical pulses from transmitter into sound waves during transmission
and receive sound echoes back to electrical signals during reception.
3. Receiver
- Receives the ultrasonic signals from the transducer.
4. Audio channel
- Detects and amplifies the audio frequencies and feeds them to a loud speaker or
earphones.
5. Video channel
- Detects the video frequencies and feeds them directly to the grid of the CRT in the
control indicator.
Transducer
- function as energy converters, when serving as a transmitter it convert electrical
energy into acoustical energy, and when serving as a receiver it convert acoustical
energy into electrical energy.
Two main types of Transducers
a. Piezoelectric – transducer that are made up of several hundred small crystal blocks of Rochelle salt or
ammonium dehydrogenate phosphate (commonly called ADP). These blocks vibrate at a high frequency
when a high-frequency voltage is impressed across them.
b. Magnetostrictive – transducer that contain a large number of nickel or nickel alloy tubes. Each tube
forms the core of a magnetizing coil, when ac volts supplied across the coil, a magnetizing field is
established, which causes the associated tube to periodically contract with the applied voltage.
Three basic operations of scanning type active sonar system
a. Transmission
b. Reception
c. Presentation
Scanning Identified as : Spiral scan using cathode-ray tube.
Variable Depth Sonar
- a conventional active sonar that is modified to transmit and receive signals through a
transducer contained in a towed vehicle. This sonar designed to overcome the
problems affecting the ability of sonar to detect and maintain contact with a
submarine cause by thermal layer in the ocean. Those layers reflect or bend sonar
signal that cause submarine not to detect.
Passive Sonar
- a systems provide an underwater sound listening system capable of long-range search and tracking
of noise sources.
Two types of Passive Sonar
a. Single line Hydrophone Sonar
b. Array Hydrophone Sonar
Two General Type of Hydrophone
a. Electrostrictive type – utilizes barium titanate and operates on the piezoelectric effect to convert acoustic
energy to electrical energy.
b. Magnetostrictive type – utilizes magnetostrictive alloys and operates on the same principle as the
magnetostrictive transducer.
Single Line Hydrophone Sonar
- a simple passive sonar system which may trained to obtain bearing information.
- a system equipped with an automatic target follower (ATF) circuit. This feature uses right and left
signals which are fed back into the training system, causing the hydrophone to follow the target
automatically.
Array Sonar
- A modern passive sonar systems utilize a hydrophone array. It consists of a number of single line
hydrophones connected together and arranged either in a circle or around the bow of a submarine.
