Backing layer
The backing layer has two functions: on one hand it works as mechanical support for the
active element, on the other hand it has to attenuate the acoustic energy lost from the back
face of the transducer. In this way no energy is radiated back to the active layer hindering
therefore the production of parasitic echoes (Levassort et al., 2004). To optimize the
transmission of the ultrasounds to the back surface of the transducer, the backing and active
layer materials must have similar impedance values. For this reason epoxy resins filled with
tungsten particles are generally used as materials for backing layers.
Matching layer
On the front of the transducer (i.e. between the piezoceramic and the propagation medium)
a matching layer is generally used. This layer must mediate the impedance values of the
ceramic with those of the biologic tissues thus maximizing the acoustic energy amount
transmitted by the transducer and improving consequently its efficiency.
The optimal impedance value for a matching layer is defined as: