Question

What is the purpose of the coupling medium.

Comment on whether transducer bandwidth can be increased and if it is possible describe the method used to increase it.

Comment on the terminology you would use to describe the ability of a system to detect low-amplitude echoes accurately.

Answer 1

In ultrasonic transducer coupling medium is very necessary because coupling medium provide very smooth transmission of ultrasound energy from one material to another
we know that all the material in the universe has some impedance in it and for the proper transmission of a sound wave from one medium to another medium the impedance between these two medium have to be same
In case of ultrasound transducer the impedance of a ultrasound transducer is a different from the impedance of the tissue of our body. And we know that greater the impedance at the boundary the greater the reflection if that is the case then the sonography will not be possible at any cost because whatever ultrasound will be produced by the transducer will be reflected back by the boundary of ultrasound and the tissue it will not go inside the body as there is a much difference in impedeimp between the boundary of ultrasound and the tissue To minimise this difference in impedance we use coupling medium
Coupling medium reduces the difference in the impedance between the transducer and the tissue or between the two material
the primary job of a coupling medium is to felicitate the transmission of ultrasound energy from machine head to the tissue given an ideal circumstances this transmission would be maximally effect with no absorption of ultrasound energy nor any distortion of its path
Coupling medium can be anything it can be air water oil creams gel

The transducer bandwidth can be increased or decreased by various method one such method is introducing of a backing material and matching layer in a transducer
Baking material is located behind the piezoelectric crystal or element
And matching layer is applied on the skin the matching layer is nothing but coupling material
A backing material is usually highly attentive highly density material that is used to control the vibration of a transducer by observing the energy radiating from the back face of of piezoelectric element when the acoustic impedance of a backing matches the acoustic impedance of the active element the result will be in highly damped transducer that displays good range of resolution
If there is a mismatch in acoustic impedance between the element and the back king more sound energy will be reflected forward into the test material
Backing material is located behind the piezo element to prevent excessive vibration reducing excessive vibration will cause the element to generate ultrasonic wave with the shorter per length improving the axial resolution in image
By controlling the backing material we can increase or decrease the bandwidth of ultra sound wave this is the traditional method of increasing or decreasing the bandwidth of ultrasound wave