The failure, e.g. fatigue crack, weld crack, and bolt loosening, of infra-structure is one of the causes of serious accidents. To prevent these accidents, structural health monitoring systems have been proposed. Among them, the evaluation methods by measurement of natural vibrations are useful for various structures because of ease in introducing a monitoring system. Currently, the natural vibrations at low-frequency range are usually used because of the difficulty of exciting natural vibrations at high-frequency range. In this paper, the excitation method of natural vibrations by multi excitation using decentralized control is developed. Firstly, the difficulty of excitation of ultrasonic natural vibrations is confirmed. Secondly, the basic performance of the multi-excitation using decentralized control is investigated by the experiment using a simple beam structure. The excitation of an ultrasonic natural vibration in the case of multi-excitation using decentralized control with the self-excitation automatically is examined. From the phase differences between each measurement signal, it is clarified that mutual synchronization is realized. Thus, it is confirmed by the measurement of vibration mode shape that an ultrasonic natural vibration is excited. Finally, it is tried to excite another natural vibration by forced entrainment.

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