Navigation and Seamanship

3.1.8.2. Transducer

               

                 Transducer is very important part of the echosounder , which is fixed in the hull region, below the waterline of the vessel. The main function of the transducer is to convert electrical energy into sound energy when sound is to be sent and conversely, to convert the sound energy into electrical energy when echoes are received. The transducer is also responsible for concentrating the sound pulse in a directional beam, similar to the beam of light produced by search light. The width of the sound beam is inversely proportional to the frequency of the sound. The transmitted pulse of sound propagates through the water away from transducer. The sound pulse travelling through water may face various targets such as fish, seaweed, sea bed etc.. These targets reflect or scatter the sound pulse, and some energy returns towards the transducer. This bounced sound (the echo) is detected by the transducer and converted to electrical energy as the received signal. The time at which the echo is received is calculated by the echosounder and the distance of the target from the transducer is calculated. This sound beam sent out from the transducer will be in the form of a cone, or of a main beam with some irregularities called secondary beams or side lobes. The angle between the two points on the main beam where the sound intensity is one half the intensity along the acoustic axis is known as beam width.

                  There are two main types of transducers for sounding equipment used in fisheries - Nickel transducers and ceramic transducers. Their function is based upon the principles of magneto-striction and electro-striction respectively.The quality of transducers may vary considerably, and is measured by their efficiency to transform electrical energy into sound waves and vice versa.