Re: medical ultrasonic probe : I'm looking for some works on influence of the thickness of a backing on the response of transducers". : Could you help me to find it ? : The backing material consists normally of an resin and filler materials for damping sound and for increasing the acoustical impedance of the backing. Increasing acoustic impedance means increasing density (weight) (e.g. by putting tungsten into the backing) and increasing the speed of sound (e.g. by putting aluminia oxide into the backing). Of further interest there is the diameter of the grain of these filler materials, which should be in a certain dimension to the wavelength of the sound. If the acoustic impedance does not match as close as possible to the acoustic impedance of the piezoceramic, only few sound energy can travel into the backing for beeing damped/destructed into the backing. The most of the sound energy would be reflected several times between backing and piezoceramic and would produce additional resonances. In this case an increasing of the thickness of the backing would not increase much the damping of sound. If the backing is matched sufficiently to the piezoceramic, you can increase the damping by increasing the backing thickness in a certain range. Increasing the damping of the sound means decreasing the quality of this "oscillator" and thus increasing bandwidth. In the analysis of materials you sended it seems not so as some tungsten or aluminia oxide would be in this backing. I think they use Pb for increasing the density / weight and thus increasing the acoustic impedance of their backing, because tungsten is much more expensive than Pb.
Re: medical ultrasonic probe : I'm looking for some works on influence of the thickness of a backing on the response of transducers". : Could you help me to find it ? : I found a manufaturer's web site with a lot of information which is attached below. Maybe it can be of some use to you or they may be able to answer more specific questions.
your question : I'm looking for some works on influence of the thickness of a backing on the response of transducers". : Could you help me to find it ? : it would be depending on the accuracy of the application as well as the range. ie the lower the range of the transducer the more sensitive it would be for atm flactuations (it would be sensitive to noise), but even though the influence can be checked by using both transducer (equivalent) and isolate the "backing" of only one of them, and than try to measure for the same input.... hope it helps