Design of Sonic Amplitude Transformers for High Magnification

Using the design method described by Eisner and Seager, in which a suitable wavefunction is chosen and the corresponding profile is deduced, a new class of amplitude transformers is designed. The wavefunction used is a fourth-order Fourier series. The resulting transformers give a useful compromise between the properties of the “stepped” and the “exponential” transformers. The output amplitude produced for a given maximum strain is somewhat lower than the amplitude given by the exponential transformer of the same magnification, but is much higher than that given by the corresponding stepped transformer. While the “Fourier” transformer is slightly less stiff in bending than the stepped, it is very much stiffer than the exponential.