Performance improvement of ultrasonic therapy equipment by modifying the classical transducer design

In ultrasonic therapy equipment, the construction of the transducer is base d on a piezoelectric ceramic glued to a metallic protection layer. The prot ection layer thickness is commonly chosen to be a multiple of the acoustic half-wavelength. This classical transducer design criterion is focused on m aximising the energy transfer through this layer. However, it is demonstrat ed that the optimum thickness protection layer depends not only on the ener gy transfer through the layer, but also on the complete ultrasonic therapy system. Other factors such as the finite dimensions of the piezoelectric ce ramic, the electrical excitation circuitry, and the propagation medium must be taken into account. By using an electrical model to simulate the piezoe lectric material, the protective layer, the propagating medium and the exci tation generator, and with the aid of electrical simulation programs, it ca n be concluded that a different layer thickness would be preferable. The pe rformance improvement in ultrasonic therapy equipment is based on the fact that the variation of the protective layer thickness permits modification o f the relative values of the electrical impedance of both the generator and the ultrasonic transducer, i.e., is their electrical matching. Theoretical results, obtained by means of simulations based on the electrical models, are in accordance with the experimental measurements of the transducer made with the proposed design.