Lionel Petit

Double synchronized switch harvesting (DSSH): a new energy harvesting scheme for efficient energy extraction

This paper presents a new technique for optimized energy harvesting using piezoelectric microgenerators called double synchronized switch harvesting (DSSH). This technique consists of a nonlinear treatment of the output voltage of the piezoelectric element. It also integrates an intermediate switching stage that ensures an optimal harvested power whatever the load connected to the microgenerator. Theoretical developments are presented considering either constant vibration magnitude, constant driving force, or independent extraction. Then experimental measurements are carried out to validate the theoretical predictions. This technique exhibits a constant output power for a wide range of load connected to the microgenerator. In addition, the extracted power obtained using such a technique allows a gain up to 500% in terms of maximal power output compared with the standard energy harvesting method. It is also shown that such a technique allows a fine-tuning of the trade-off between vibration damping and energy harvesting.

Semi-passive piezoelectric structural damping by synchronized switching on voltage sources

Semi-passive damping techniques have been developed recently to address the problem of structural damping. Contrary to the standard passive piezoelectric damping, these new techniques adapt to environmental variations. Moreover, they present interesting multimodal damping performances. However, their efficiency is strongly correlated with their electromechanical coupling. The enhanced semi-passive damping technique presented herein compensates for this drawback. It reinforces the electromechanical coupling by artificially increasing the voltage amplitude delivered by the piezoelectric patches. Theoretical predictions and experimental results show a −24 dB attenuation on the vibration of a resonant cantilever steel beam, while reducing the piezoelectric material volume by 83%.

A broadband semi passive piezoelectric technique for structural damping

The damping of vibration resonance is a crucial problem for light and elongated structures. Different kinds of solutions have been developed 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, damping is obtained through the use of piezoelectric patches bonded on the structure. These piezoelements are controlled with a very simple approach only requiring switches which are driven periodically and synchronously with the structure motion. The overall control circuit requires a very few amount of energy. Results obtained on a beam and on a plate demonstrate that this self-adaptive technique is able to control simultaneously different modes on a broad frequency range.

Nonlinear optimization of acoustic energy harvesting using piezoelectric devices

In the first part of the paper, a single degree-of-freedom model of a vibrating membrane with piezoelectric inserts is introduced and is initially applied to the case when a plane wave is incident with frequency close to one of the resonance frequencies. The model is a prototype of a device which converts ambient acoustical energy to electrical energy with the use of piezoelectric devices. The paper then proposes an enhancement of the energy harvesting process using a nonlinear processing of the output voltage of piezoelectric actuators, and suggests that this improves the energy conversion and reduces the sensitivity to frequency drifts. A theoretical discussion is given for the electrical power that can be expected making use of various models. This and supporting experimental results suggest that a nonlinear optimization approach allows a gain of up to 10 in harvested energy and a doubling of the bandwidth. A model is introduced in the latter part of the paper for predicting the behavior of the energy-harvesting device with changes in acoustic frequency, this model taking into account the damping effect and the frequency changes introduced by the nonlinear processes in the device.

Frequency behaviour and speed control of piezomotors

The rotational speed of a piezomotor is directly linked to the vibration velocity of its stator. Because some drifts of the stator characteristics lead to an unwanted variation of the motor speed, a control is necessary. This paper discusses the origins of drifts in travelling wave ultrasonic motors (TWUM). The typical behaviour of this kind of motor and its consequences on speed control are presented. While control is easily achieved when the applied torque is constant, variations of this quantity make more difficult to obtain an efficient method. Finally, the basic idea of this paper is to derive a general control method by using the absorbed current, which is the only always detectable quantity.

Two-phase magnetoelectric nanopowder/polyurethane composites

This study deals with the observation of magnetoelectric (ME) effect in nanocomposite films constituted of semicrystalline polyurethane matrix filled with magnetic Fe3O4 (hard) or Ni (soft) nanoparticles. The measurement of the magnetic field-induced ground current of the so-called particulate composites enabled the precise determination of true ME current after extraction of the part corresponding to the inductively coupled (loop) current. Experimental ME current could be successfully simulated considering coexistence of both true linear and quadratic ME effects and by taking into account the nonlinear variation of applied dc bias and ac field magnitude due to the magnetization saturation of the magnetic field generator. Although linear ME coefficients of particulate composites are lower than those of laminate composites, they are of the same order of magnitude than that of reference ME material Cr2O3 (up to 18 mV/cm Oe). Besides, nanocomposites are simple to prepare, flexible, easily integrable, and sen...

Wave reflection and transmission reduction using a piezoelectric semipassive nonlinear technique

This study addresses the problem of noise reduction using piezoelements. The nonlinear technique, synchronized switch damping (SSD), is implemented. The device is a pulse-tube termination equipped with piezoelements, which allows performant damping of the vibration resulting from an incident acoustic wave. Due to this damping, both reflected and transmitted wave are reduced. In the semipassive damping approach proposed in this paper, energy degradation is strongly enhanced when the piezoelements are continuously switched from open to short circuit synchronously to the strain. This technique has been developed following two strategies. The first is SSD on a short circuit in which the piezoelement is always in open circuit, except for a very brief period at each strain extremum where it is short-circuited. The second approach is SSD on an inductor. The process is very similar, except that instead of forcing the voltage to zero, the voltage is exactly reversed using a controlled oscillating discharge of the piezoelement capacitor on an inductor during switch drive. Due to this switching mechanism, a phase shift appears between the strain and the resulting voltage, thus creating energy dissipation. Following SSD on an piezoelement, attenuations of 15 dB in reflection and 7 dB in transmission were obtained.

A piezomotor using longitudinal actuators

A new travelling wave type ultrasonic motor has been developed which uses longitudinal piezoelectric actuators to generate a progressive wave on the surface of a metallic ring. The rotor, which moves through frictional force, is pressed on this elastic plate. This paper deals with the motor construction and its characteristics. Theoretical modelling and experimental performances obtained with the motor prototypes are reported. A maximum of 0.8 Nm and a no-load rotation speed of 120 rpm have been obtained with a double rotor prototype. The results indicate that this piezomotor is proved to operate successfully at a mechanical output power of 4 W.

Electromechanical conversion in an ultrasonic motor using a non-axisymmetric (1,1) mode

An ultrasonic motor using a non-axisymmetric (1,1) mode has been built in our laboratory. Such motors are based on a double energy conversion: the piezoelectric material in the stator converts electrical energy into mechanical vibrations; a rotor pressed on the vibrating stator moves due to the frictional force at the interface. These two conversions have been modelled by using electromechanical circuits derived from the Mason model. The mechanical performance of the whole motor has been experimentally determined. The losses which occur during the electromechanical conversion have been studied. Our work points out that they depend on the ratio between the inner radius and the outer radius of the annular ceramic plate used for the stator and the electromechanical characteristics of the chosen ceramic material. A criterion based on an electrical model is given in order to make a better choice between different PZT materials.

Self-powered Wireless Health Monitoring Supplied by Synchronized Switch Harvesting (SSH) Method

The development of autonomous wireless sensors and actuators in order to design advanced structural health monitoring (SHM) systems is an exciting challenge for both the industrial and the academic communities. Some studies have dealt with the implementation of wireless devices. Almost all the studies about so-called autonomous systems today still require power supply. It means that a fully self-powered system has not been achieved yet. The present study shows the design of self-powered wireless health monitoring system, for which the energy is supplied by the original method called the synchronized switch harvesting (SSH) method. The piezoelectric elements and electrical circuit, located on the vibrating structure, harvest electrical energy from the direct conversion of mechanical energy vibration. Lamb wave transmission is chosen for the SHM of a composite beam of length around 30 cm. Some piezoelectric elements, used for energy harvesting and signal transmission, are located on the beam. The energy required to wake-up the micro-controller and to achieve two complete transmission cycles is only 1.5mJ. This small amount of energy can be harvested in a short time period for reasonable beam displacement levels. The study details the different trade-off concerning such a self-powered health monitoring device.