This article describes the active vibration control of a plate using a self-sensing actuator (SSA) and an adaptive control method. In a self-sensing actuator, the same piezoelectric element functions as both a sensor and an actuator so that the total number of piezoelectric elements required can be reduced. A method to balance the bridge circuit of the SSA was proposed and its effectiveness was confirmed by using an extra piezoelectric sensor, which is not necessary for balancing bridge circuits of SSA in future applications. A control system including the SSA and an adaptive controller using a finite impulse response (FIR) filter and the filtered-X LMS algorithm was established. The experimental results show that the bridge circuit was well balanced and the vibration of the plate was successfully reduced at multiple resonance frequencies below 1.2 kHz.

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This article presents a study of active noise isolation using an advanced composite board with built-in piezoelectric elements, which are used as both sensors and actuators. An identification system, which estimates the radiated sound from the voltage signals of the built-in piezoelectric elements in the smart board, was constructed based on Rayleigh's integral formula so that no external microphone is needed for noise control. A FIR (Finite Impulse Response) filter was used as the controller and its coefficients were updated adaptively using the Filtered-X LMS algorithm to minimize the estimated value of the sound pressure. The technique of self-sensing actuators was also used to reduce the number of needed piezoelectric elements in the control. Experiments were performed and the results showed that the transmitted noise level was successfully reduced at several resonant peaks.

Time delays in the feedback control often deteriorate the control performance or even cause the instability of a dynamic system. This paper presents a control strategy for the dynamic system with a constant or a slowly timevarying input delay based on a transformation, which simplifies the time-delay system into a delay-free one. Firstly, the relation is discussed for two existing reduction-based linear quadratic controls. One is continuous and the other is discrete. By extending the relation, a new reduction-based control is then developed with a numerical algorithm presented for practical control implementation. The controller suggested by the proposed method has such a promising property that it can be used for the cases of different values of an input time delay without redesign of controller. This property provides the potential for stabilizing the dynamic system with a time-varying input delay. Consequently, the application of the proposed method to the dynamic system with a slowly time-varying delay is discussed. Finally, numerical simulations are given to show the efficacy and the applicability of the method.

The paper deals with the criteria for the closedloop stability of a noise control system in a duct. To study the stability of the system, the model of delay differential equation is derived from the propagation of acoustic wave governed by a partial differential equation of hyperbolic type. Then, a simple feedback controller is designed, and its closedloop stability is analyzed on the basis of the derived model of delay differential equation. The obtained criteria reveal the influence of the controller gain and the positions of a sensor and an actuator on the closed-loop stability. Finally, numerical simulations are presented to support the theoretical results.