Monday 18 July 2016


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 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. 

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