Answer #35

The correct answer is C: the backing material. This is designed to cause dampening which decreases the number of cycles in the pulse that occur naturally from the crystal. This in effect decreases the pulse duration (time of the pulse which is time per cycle x number of cycles in a pulse) and leads to an increase in bandwidth. It also improves axial resolution by decreasing spatial pulse length (length of a pulse which is length of a cycle x number of cycles in a pulse).

The purposes of the other parts, shown in figure below [insert US transducer components figure}are as follows
case insulation - insulates from outside electrical interference
lens - focuses the beam
piezoelectric crystal - converts the electrical energy applied into sound energy to transmit to the patient
matching layer - minimizes the acoustic impedance mismatch between the crystal and the human body to allow more ultrasound waves to be transmitted