ArraysWaite AD. 2002. SONAR for Practising Engineers 3rd Ed. Sussex (GB): Wiley.

Angga DwinovantyoC552150141

Program Studi Teknologi KelautanSekolah PascasarjanaInstitut Pertanian Bogor

2015

ARRAY

SONAR

1. Alat: SL, DI, DT, NL2. Medium: TL, NL, RL3. Target: TS, SL

EL = SL – 2TL + TS – NL + DI

• Projector Array (Transmit) Purpose: increase source level of transmited

pulse The directivity concentrates in direction. Typical array is designed to make vertical

beamwidth between 3⁰ - 30⁰ to the 3 dB points.

• Hydrophone Array (Receive) Purpose: increase the response from array (dalam

arah yang diinginkan. Sehingga meningkatkan SNR dan menunjukkan arah dari sumber sinyal)

• Beam PatternsResponse against angle, describing the relative responses

of a beam formed from an array to signals and noise from all directions.

Tipe-Tipe Array

• Linear sequential array (switched array)• Linear phased array (vector, sector)• Curved sequential array (convex array, curvilinear sequential array).• Curved phased array (convex array, curvilinear phased array).• Annular array

• A linear transducer is something that most of us are familiar with for imaging small parts and shallow structures. The image is rectangular.

• Each crystal is fired and creates a single scan line. So the image corresponds to the width of the actual transducer.

• A simple linear array will not have steering. As the beams are fired they run parallel to each other and straight from the face of the transducer. These beams stay parallel to each other no matter the depth. The space between the beam stays constant because they run parallel to each other.

Linear phased array

• A phased array works by exciting all the crystals in the transducer at the same time. This creates many individual waves which constructively interfere with each other to create a single pulse. Since the crystals are able to be fired at different times with a small delay between each pulse the beam that is formed is able to be steered as well as focused

Curved sequential array

A curved or convex sequential (switched) array is aligned the same as a linear array. Crystals side by side with each crystal creating a single line on the screen but the transducer shape is curved so you get a classic fan shaped image.

Beam steering is not necessary on this transducer because it naturally creates an image with an arc.

You don’t need beam steering on this transducer because it naturally creates an arc shaped image.A drawback to the curved array versus a linear array is that the beam at depth separates from the beam running parallel so you end up with gaps that the machine has to account for. So the deeper the image the greater the decrease in lateral resolution. A structure could sit in the gap between the beams and the machine would never know it exist

Annular Array

Annular arrays are unique in their composition. They are created by taking a single crystal and cutting it into rings. Think of the cross section of an onion. Smaller and smaller rings.

Because an annular transducer is steered mechanically it will have an image with a sector shape.

ARRAY

• Cylindrical Array• Planar Array• Line Array• Spherical Array• Square Array

• Array Gain: improvement in SNR due to array factor

• Directivity Index: Signal is coherent and noise is incoherent

DI

• Cylindrical Array

DI

• Line Array: kumpulan elemen kecil yang dikumpulkan membentuk seperti garis

n = number of element

DI

• Directivity of a Plannar Array

Kesimpulan

1. Beam pattern dipengaruhi oleh jumlah array, disamping durasi pulsa, freq, panjang gelombang

2. Setiap bentuk array memengaruhi pembentukan beam

3. Array (komponen dalam alat) berperan dalam perhitungan nilai Echo Level DI

• Sonar arrays are used both actively and passively in 1-, 2-, and 3-dimensional arrays.

• 1-dimensional "line" arrays are usually in multi-element passive systems towed behind ships and in single or multi-element side scan sonar.

• 2-dimensional "planar" arrays are common in active/passive ship hull mounted sonars and some side-scan sonar.

• 3-dimensional spherical and cylindrical arrays are used in 'sonar domes' in the modern submarine and ships.