An actuator for the n=2 circumferential mode of a pipe

The axial propagating wave of the n=2 circumferential mode in a pipe can cause large vibration when the wave cuts on and may cause fatigue damage or transmit structure-borne noise along the pipe. For this reason, a control system (passive or active) is desirable. In this paper, a PZT modal actuator for the n=2 mode, which could be used in an active control system, is described. It is constructed from a set of PZT elements bonded to the pipe. By arranging them in form of the n=2 mode, only the motion of that particular mode is generated and is proportional to the applied voltage. With two PZT modal actuators, which are in forms of sine and cosine functions, the orientation of the propagating wave of the n=2 mode can be modified to any angle. In this paper a theoretical model for the actuator is developed and is validated by some experimental work.