A high-efficiency low-frequency power source for vibration excitation

The production of continuous sinusoidal vibrations of low frequency or transients of a comparably long period is beyond the scope of existing electro-dynamic force generators in which displacement is relatively limited. Moreover, the transformer-coupled amplifiers employed to drive the units have a limited low-frequency bandwidth unable to cater for the pulse shapes required. This paper describes the power source of a system which has been devised to overcome these disadvantages and to demonstrate a means of highefficiency amplification which can also be employed with the existing types of vibration generators. The power amplifier employs a pulse-width modulated signal and output transistors operating as saturated switches, with a frequency bandwidth from d.c. to about 350 c/s. The efficiency of the output stage is high (85¿90 %), and considerable economy of design is possible at high powers.