ULTRASOUND CRYSTAL ARRAYS

Ultrasound arrays are the soul part of an ultrasound transducer. They are created by slicing piezoelectrical crystal into many smaller active elaments. each elements are unique and they slit in different compartments that are shielded fro each other.

TYPES OF ARRAYS

1. Linear array
2. Phased array
3. Curved array

Linear array

• Elements are arranged in linear line that is in a sequence order
• Crystals are arranged side by side
• Each crystal creates a single scan line
• Up to 512 crystals
• Used for vascular ultrasound applications
• Eg:- GE 8L probe

Linear array

Phased array

• Crystals are arranged in a linear line
• Each crystals creates multiple scan images
• They are fixed in phases
• Up to 128 elements
• Small footprints
• Used for cardiac ultrasound applications
• Eg:- GE 3S probe

Phased array

Curved array

• Crystals are arranged in side by side. but transducer shape is curved.
• Naturally creates an image with arc.
• Used for Gynaecology applications
• Eg:- GE 4C probe

Curved array

ULTRASOUND COUPLING FLUIDS

The transmission of the ultrasound wave between the transducer and test piece through air gap is very inefficient because of the large acoustic impedance mismatch. This situation can be avoided by introducing coupling fluids  between the transducer and the test piece.

Generally there are two types of coupling fluids.

• The fluids used inside the ultrasound probe (For volume probe only) 

Coupling fluid inside a volume probe

• The fluids used on the surface of the test piece (ultrasound gels)

ultrasound gels

• The main function of the coupling fluid is to avoid the acoustic impedance mismatching. But in the case of volume probes it also act as lubricant for mechanical systems.in such probes the motor is floated in the fluid chamber.Generally a special kinds of the mineral oils are used as this type of coupling fluid
• The ultrasound gels are formulated to act as a coupling agent and reduce static. They are usually composed of propylene glycol and water.