Vibration Damping using a Semi-passive Piezoelectric Technique Daniel Guyomar, Claude Richard, Lionel Petit Laboratoire de Génie Electrique et Ferroélectricité, INSA Lyon 8 rue de la physique, 69621 Villeurbanne Cedex France. Daniel.guyomar@insa-lyon.fr Abstract The damping of resonance vibration is a crucial problem for light and elongated structures. Different kinds of solutions have been developped in order to address the problem of volume or mass, or temperature dependence which are common to the passive approach. In the semi- passive technique proposed here, dampening is obtained through the use of piezoelectric (ceramic or composite) patches bonded on the structure. These piezoelements are controlled with a very simple approach only requiring switches which are continuously driven synchronously with the structure motion. The control circuit requires very few energy and can be made completely self powered if associated with an energy harvesting device using the same piezoelements. Results obtained on a plate demonstrate that the technique which is self-adaptive is able to control simultaneously different modes on a broad frequency range. Moreover using a proper positionning, various patches can be dedicated to specific frequencies, thus broadening even more the vibration control. 1. Introduction Reduction of noise and vibration becomes a top priority research topic in various industrial activities such as automobile, aerospace, sport equipment, measurement devices, etc. With such a potential application variety, various damping methods were designed using piezoelectrics since these “solid-state actuators” are well suited for controlling stiff structures. The piezoelectric elements (patch, piezo-fiber composite, thick or thin layer…) are bonded on or embedded in the structure and are used as a sensors and/or actuators. Most of the work is devoted to active control in which the actuator is driven by a feedback voltage computed from the sensor through complex algorithms [1]. Although very powerfull, this technique requires complex signal processing and power amplifier. Therefore it is not suited for small remote structures. The passive technique is interesting for its simplicity. In this case, the piezoelements are simply connected on a dissipative electrical network (usually a resistor and an inductor) which degrades the mechanical energy converted by the piezoelectric elements [2]. Its major drawback is the need for tuning the resonance frequency of the dissipative network on the vibration frequency, thus resulting in a norrow band action and a strong sensitivity to any resonance frequency shift. More recently, switching shunt techniques were developped allowing to address the main weaknesses of the passive techniques an to optimize the degradation or the conversion of the vibration mechanical energy. The state switching method proposed by W W Clark [3] is a variable stiffness technique in which piezoelements are periodically held in open circuit, then switched and held in short circuit, synchronously with the structure motion , thus dissipating energy and synchronizing itself on the piezovoltage and therefore on the resonance frequency. The SSD technique (Synchronized Switch Damping) developped at INSA-LGEF [4,5] and that will be used in this paper, presents some similarities with Clark’s work, but differs in the fact that piezoelements are held in open circuit and switched to short-circuit only for a very brief period, each time the voltage reaches an extremum. Moreover at each extremum instead of being short circuited, the piezovoltage can be inversed using a half oscillation through an inductor (SSDI). This process naturally synchronized with the vibration leads to optimized energy conversion and to resonance damping performance close to active techniques without the need for complex electronics. In a first part the passive and SSD techniques will be presented more in detail. Then they will be applied using the same piezoelectric inserts configuration to the damping of a plate. This is a pure multimodal case with several modes in a 100Hz wide frequency band. Results are compared and discussed showing the naturally large bandwith capability of the SSDI technique. 2. The passive technique Passive piezoelectric damping is an energy dissipation mechanism. A resistor R s is connected across the electrodes of the piezoelement. When the piezoelement is stressed, a current flows through the shunted circuit and energy is degraded in the resistor. Because the capacitance C o of the piezoelement limits the drawn current and then reduces the energy dissipation, an inductor L s is added in series to cancel its reactive effect. This resonant (R s -C o -L s ) circuit can be tuned on the frequency of a structural mode and thereby greatly increase the dissipation mechanism on this mode. The optimal values of R s and L s are well known and given in the litterature [2] : Mo.P2.17 I - 767