Performance improvement of ultrasonic therapy equipment by modifying the classical transducer design
In ultrasonic therapy equipment, the construction of the transducer is based on a piezoelectric ceramic glued to a metallic protection layer. The protection layer thickness is commonly chosen to be a multiple of the acoustic half-wavelength. This classical transducer design criterion is focused on maximising the energy transfer through this layer. However, it is demonstrated that the optimum thickness protection layer depends not only on the energy transfer through the layer, but also on the complete ultrasonic therapy system. Other factors such as the finite dimensions of the piezoelectric ceramic, the electrical excitation circuitry, and the propagation medium must be taken into account. By using an electrical model to simulate the piezoelectric material, the protective layer, the propagating medium and the excitation generator, and with the aid of electrical simulation programs, it can be concluded that a different layer thickness would be preferable. The performance improvement in ultrasonic therapy equipment is based on the fact that the variation of the protective layer thickness permits modification of 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.