Tommaso Delpero

Broadband vibration energy harvesting based on cantilevered piezoelectric bi-stable composites

Bi-stable composites are considered for vibration based energy harvesting, thanks to the broadband nature of their dynamic response. In this letter, a cantilevered piezoelectric bi-stable composite concept is introduced for broadband energy harvesting. The proposed configuration allows for exploiting the large strains developed close to the clamped root, significantly enhancing the harvesting effectiveness in comparison to previous settings. A simple model is used for designing the dynamic response aiming to maximise broadband oscillations. Experimental results reveal wide bands of high power conversion. Additionally, a shunting circuit suitable for broadband conversion is employed, further increasing the effectiveness of the proposed concept.

Passive damping of composite blades using embedded piezoelectric modules or shape memory alloy wires: a comparative study

Emission reduction from civil aviation has been intensively addressed in the scientific community in recent years. The combined use of novel aircraft engine architectures such as open rotor engines and lightweight materials offer the potential for fuel savings, which could contribute significantly in reaching gas emissions targets, but suffer from vibration and noise issues. We investigated the potential improvement of mechanical damping of open rotor composite fan blades by comparing two integrated passive damping systems: shape memory alloy wires and piezoelectric shunt circuits. Passive damping concepts were first validated on carbon fibre reinforced epoxy composite plates and then implemented in a 1:5 model of an open rotor blade manufactured by resin transfer moulding (RTM). A two-step process was proposed for the structural integration of the damping devices into a full composite fan blade. Forced vibration measurements of the plates and blade prototypes quantified the efficiency of both approaches, and their related weight penalty.

Hybrid dispersive media with controllable wave propagation: A new take on smart materials

In this paper, we report on the wave transmission characteristics of a hybrid one dimensional (1D) medium. The hybrid characteristic is the result of the coupling between a 1D mechanical waveguide in the form of an elastic beam, supporting the propagation of transverse waves and a discrete electrical transmission line, consisting of a series of inductors connected to ground through capacitors. The capacitors correspond to a periodic array of piezoelectric patches that are bonded to the beam and that couple the two waveguides. The coupling leads to a hybrid medium that is characterized by a coincidence condition for the frequency/wavenumber value corresponding to the intersection of the branches of the two waveguides. In the frequency range centered at coincidence, the hybrid medium features strong attenuation of wave motion as a result of the energy transfer towards the electrical transmission line. This energy transfer, and the ensuing attenuation of wave motion, is alike the one obtained through internal resonating units of the kind commonly used in metamaterials. However, the distinct shape of the dispersion curves suggests how this energy transfer is not the result of a resonance and is therefore fundamentally different. This paper presents the numerical investigation of the wave propagation in the considered media, it illustrates experimental evidence of wave transmission characteristics and compares the performance of the considered configuration with that of internal resonating metamaterials. In addition, the ability to conveniently tune the dispersion properties of the electrical transmission line is exploited to adapt the periodicity of the domain and to investigate diatomic periodic configurations that are characterized by a richer dispersion spectrum and broader bandwidth of wave attenuation at coincidence. The medium consisting of mechanical, piezoelectric, and analog electronic elements can be easily interfaced to digital devices to offer a novel approach to smart materials.

Identification of electromechanical parameters in piezoelectric shunt damping and loss factor prediction

Shunted piezoelectric elements have been studied for several years as promising devices for vibration damping. Different shunting techniques have been developed to deal with the vibration energy in the appropriate way. The energy dissipated by all these techniques, expressed in terms of loss factor or damping ratio, mainly depends on two different contributions: the electromechanical coupling and the shunt design. Therefore, an accurate prediction of the damping is based on a reliable identification of the generalized coupling coefficient that completely describes the electromechanical coupling. In this study, a robust method for the measurement of this coefficient is proposed, where the influence of the inherent damping of the structure is also considered. This method is based on the analysis of the dynamic response of the structure when the piezoelectric patch is connected to a resonant shunt. The proposed method is applied to different sample structures, and the measured generalized coupling coefficients are used for predicting the values of damping attainable with different shunting techniques (such as the resonant shunt or the synchronized switching damping). Vibration tests are then carried out on the same shunted structures, and the analytical prediction of the damping is compared with the experimental results.

A cantilevered piezoelectric bi-stable composite concept for broadband energy harvesting

Recently, the idea to exploit nonlinearity to achieve broadband energy harvesting has been introduced. Bi-stable systems have been used to realise broadband energy harvesting devices. Amongst these, harvesters constructed with bi-stable composites show great potential due to their rich dynamic behaviour. This paper studies a novel cantilevered configuration for a piezoelectric bi-stable composite device for broadband energy harvesting. The cantilevered configuration allows to exploit high strains developed close to the clamped root, further enhancing the harvesting characteristic of bi-stable composites. Furthermore, the desired broadband dynamics are obtained for lower input amplitudes when compared to previous designs constituting a significant improvement for energy harvesting applications. Several cross-well dynamic behaviours are obtained over a relatively wide range of frequencies with the proposed design. In addition, the performance of the developed concept is investigated using a switching shunt harvesting circuit suitable for conversion of broadband oscillations resulting from the cross-well dynamics exhibited by bi-stable composite laminates showing very good results.

Energy harvesting module for the improvement of the damping performance of autonomous synchronized switching on inductance

Shunted piezoelectric transducers can be used to dissipate vibration energy of a host structure. The synchronized switch damping on inductance is a shunting technique characterized by a nearly rectangular shape of the resulting voltage on the transducer being in antiphase with the structure’s velocity. As for these systems, previous studies have reported the strong relationship between the dissipated energy and the slope of the voltage signal occurring during the switch. This implies that any electrical losses have to be minimized in order to increase the slope of the voltage signal and, thus, the damping performance. The rate of change of the voltage represents a critical issue for autonomous shunts, where the switch can be inefficient because the power for switching the circuit is not supplied by an external source but is supplied by the vibrating structure itself. In this study, a new technique for improving the damping performance of autonomous synchronized switch damping on inductance is proposed based on controlling the switch with a square wave signal that reduces its electrical losses. An experimental validation of the proposed shunting technique is carried out in order to assess the performance in both the cases of a single-tone and multimodal responses of the structure.

Extremely Anisotropic Multi-functional Skin for Morphing Applications

Because of their anisotropic properties, corrugated panels are good candidates for morphing skin applications. Their non-smoothness, however, might result in disadvantageous aerodynamic effects. In this work, we suggest the use of electro-bonded laminates (EBL) to realize a smooth corrugated skin. The EBL is applied to a double corrugation (DCo) design, which offers greater structural performance than conventional corrugations. Experimental tests indicate that the electrical adhesion force is sufficient for the intended application. The electrical bonding is also shown to improve the dissipative properties of the skin, which help to counteract vibrations arising from the high axial compliance. The behaviour can be modified by varying the applied voltage, thus resulting in a tunable system.

Analytical Electromechanical Model of Cantilevered Bi-Stable Composites for Broadband Energy Harvesting

Vibration based energy harvesting has received extensive attention in the engineering community for the past decade thanks to its potential for autonomous powering small electronic devices. For this purpose, linear electromechanical devices converting mechanical to useful electrical energy have been extensively investigated. Such systems operate optimally when excited close to or at resonance, however, for these lightly damped structures small variations in the ambient vibration frequency results in a rapid reduction of performance. The idea to use nonlinearity to obtain large amplitude response in a wider frequency range, has shown the potential for achieving so called broadband energy harvesting. An interesting type of nonlinear structures exhibiting the desired broadband response characteristics are bi-stable composites. The bi-stable nature of these composites allows for designing several ranges of wide band large amplitude oscillations, from which high power can be harvested. In this paper, an analytical electromechanical model of cantilevered piezoelectric bi-stable composites for broadband harvesting is presented. The model allows to calculate the modal characteristics, such as natural frequencies and mode shapes, providing a tool for the design of bi-stable composites as harvesting devices. The generalised coupling coefficient is used to select the positioning of piezoelectric elements on the composites for maximising the conversion energy. The modal response of a test specimen is obtained and compared to theoretical results showing good agreement, thus validating the model.Copyright

Piezoelectric vibration damping using autonomous synchronized switching on inductance

Shunted piezoelectric transducers can be used to dissipate vibration energy of a host structure. The Synchronized Switch Damping on Inductance (SSDI) is a shunting technique featured by a nearly rectangular shape of the resulting voltage on the transducer being in anti-phase with the structure’s velocity. As for these systems, previous studies have reported the strong connection of the dissipated energy on the slope of the voltage signal occurring during the switch. This implies that any electrical losses have to be minimized in order to increase the slope of the voltage signal and, thus, the damping performance of the shunt. Moreover, the rate of change of the voltage signal represents a critical issue for autonomous shunts, where the switch can be inefficient because the power for switching the circuit is not supplied by an external source but is supplied by the vibrating structure itself. In this study, a new technique for improving the damping performance of autonomous switching shunt is proposed based on reducing the electrical losses of the switch. Finally, an experimental validation of the novel shunting technique is carried out.Copyright

Low frequency bandgaps in lightweight metamaterial panels using rotation inertia multiplication

Of all possible features of structural metamaterials, the formation of bandgaps is the most studied one due to its direct application for sound and vibration isolation. While achieving low frequency values for the position of the first bandgap is, in general terms, not an unsurmountable challenge, the combination of material properties such as high stiffness, low density, and reduced size of the unit cell, with low (in absolute terms) frequency bandgaps, may well require some careful consideration. In previous work, we designed panels with a 3D network of resonators, clearly improving the vibration isolation compared to a homogeneous panel with the same weight. Recently, we have devised a novel implementation of inertia amplification, based on coupling the energy of longitudinal waves into the rotational oscillation of inertia elements within the unit cell. In this contribution, we present examples of phononic crystals based on this approach, and we discuss the interaction of acoustic waves with the discu...