Application of the finite-element method for modeling backed transducers

To model backed transducers by the finite-element method, the main drawback is generally the large size of the numerical problem. Thus, the aim of this paper is to show how the backing mesh can be quite limited. For this purpose, the backing is considered as a lossy transmission line. Then, the equivalent acoustic impedance of the backing is expressed in terms of its thickness T-B and the tangent of the phase angle (tan delta). It will be shown that the characteristics of a backed transducer (electrical impedance, acoustic radiated power, etc.,...) can stay unchanged if the thickness T-B is scaled down and tan delta is scaled up, keeping the product T-B tan delta constant. Finally, finite-element results are successfully compared with measurements results using lithium niobate backed transducer. (C) 1996 Acoustical Society of America.