This paper presents a new technique of electrical energy generation using mechanically excited piezoelectric materials and a nonlinear process. This technique, called synchronized switch harvesting (SSH), is derived from the synchronized switch damping (SSD), which is a nonlinear technique previously developed to address the problem of vibration damping on mechanical structures. This technique results in a significant increase of the electromechanical conversion capability of piezoelectric materials. Comparatively with standard technique, the electrical harvested power may be increased above 900%. The performance of the nonlinear processing is demonstrated on structures excited at their resonance frequency as well as out of resonance.

Toward energy harvesting using active materials and conversion improvement by nonlinear processing

This paper presents a comparison between four vibration-powered generators designed to power standalone systems, such as wireless transducers. Ambient vibrations are converted into electrical energy using piezoelectric materials. The originality of the proposed approaches is based on a particular processing of the voltage delivered by the piezoelectric material, which enhances the electromechanical conversion. The principle of each processing circuit is detailed. Experimental results confirm the predictions given by an electromechanical model: compared to usual generators, the proposed approaches dramatically increase the power of the generators.

A comparison between several vibration-powered piezoelectric generators for standalone systems

This review covers energy harvesting technologies associated with pyroelectric materials and systems. Such materials have the potential to generate electrical power from thermal fluctuations and is a less well explored form of thermal energy harvesting than thermoelectric systems. The pyroelectric effect and potential thermal and electric field cycles for energy harvesting are explored. Materials of interest are discussed and pyroelectric architectures and systems that can be employed to improve device performance, such as frequency and power level, are described. In addition to the solid materials employed, the appropriate pyroelectric harvesting circuits to condition and store the electrical power are discussed.

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Pyroelectric materials and devices for energy harvesting applications

This article presents a nonlinear approach to optimize the power flow of vibration-based piezoelectric energy-harvesting devices. This self-adaptive principle is based on a particular synchronization between extraction of the electric charge produced by the piezoelectric element and the system vibrations, which maximizes the mechanical to electrical energy conversion. An analytical expression of the optimal power flow is derived from a simple electromechanical model. An electronic circuit designed to perform the synchronous charge extraction is proposed. Theoretical predictions confirmed by experimental results show that the new principle increases the harvested power by 400% as compared with a quasilinear impedance adaptation optimization method.

Piezoelectric Energy Harvesting Device Optimization by Synchronous Electric Charge Extraction

The SSD technique proposed here addresses the problem of resonance damping on a mechanical structure. SSD stands for Synchronized Switch Damping. Apart from active techniques, passive ones consist in connecting a piezoelectric insert attached to the structure to a passive electric network in which the energy generated by the piezoelectric inserts is degraded. In the semi passive approach, the piezoelectric inserts are continuously switched from open circuit to short circuit synchronously to the structure motion. Due to this switching mechanism, a phase shift appears between the piezoelectric strain and the resulting voltage, thus creating energy dissipation. For the new technique proposed here, instead of discharging the piezoelectric inserts during a brief short circuit, they are connected on a small inductor, allowing the inversion of the voltage and then released to open circuit. In this case the voltage amplitude is optimized and is 90 degrees out of phase with the motion then enhancing the damping mechanism. The technique is applicable at any frequency without the need for a large tuned inductor, especially for low frequency applications. There is no need for external power supply unless for the low power circuitry of the switch device. The implementation of the switch drive with a very cheap micro-controller is described. Experimental results measured on cantilever beams made with different materials are proposed. Damping ability ranges from 6 dB on a very viscoelastic epoxy beam to nearly 20 dB on a steel beam. Harmonic excitation and transient results are both proposed and compared. Finally, an electromechanical model is proposed, giving an interpretation of the damping mechanism. Theoretical predictions are in good agreement with the experiments.

Enhanced semi-passive damping using continuous switching of a piezoelectric device on an inductor

Passive damping using a piezoelectric device is a well-known technique. Both resistor and inductor loads connected to the piezoceramic are commonly used to attenuate a given resonance mode on a structure equipped with piezo dampers. The main drawback of this technique is its narrow band behavior and especially in the case of an inductor tuned passive piezo damper. The proposed technique is inherently wide band and does not rely on any tuned electric load. The piezoelectric device is simply continuously switched from open-circuit to short-circuit synchronously to the mechanical strain. It is called semi-passive because of the need of a sensor giving the strain of the piezo device. There is no need for external power supply unless for the low-level circuitry of the switch device. The damping efficiency appears to be twice what is obtained with pure resistive damping and is equivalent to what is achievable with a tuned inductor damper. It can work at any frequency without the need for large inductor especially for low frequency applications. A qualitative model gives an understanding of the damping mechanism.

Semi-passive damping using continuous switching of a piezoelectric device

A liquid spraying device including an elongate first vessel closed at one of its ends by a first free face of a piezoelectric transducer capable of emitting waves into a liquid filling the vessel, and open at its end remote from the piezoelectric transducer. The piezoelectric transducer includes a second free face opposite its first free face, and wherein an elongate second vessel is disposed symmetrically to the first vessel relative to the piezoelectric transducer, the second vessel being closed at one of its ends by said second free face of the piezoelectric transducer, which is thus also capable of emitting waves into a liquid filling the second vessel, said second vessel being open at its end remote from the piezoelectric transducer.

High efficiency spraying device, in particular for spraying water in the form of micro-droplets

The invention relates to a spraying device including a tank which is open at its upper part, capable of containing a liquid to be sprayed, such as water, while being filled up to its opening, a piozoelectric element capable of emitting waves into the liquid and fan means for creating a circulation of air in the vicinity of the surface of the liquid. The waves are focused in the vicinity of the opening of the tank, and the cross-section of the tank (1) has a progressive constriction towards the opening (2) of the tank (1).

Device for spraying, in particular water in the form of microdroplets, capable of functioning in a nonstationary environment

The water is contained in a tank (1) which has a cylindrical base (1a) but tapers (1b) towards a top opening (2) from which micro-droplets are ejected into a circulation (16) of air drawn through vents in the top cover (4a) by a fan (6). The micro-droplets are generated by a cylindrical piezoceramic vibrator (3) on the floor of the tank, and deflected by a cap (19) fitted over the opening with a seal (20). The tank is replenished from a reservoir (12) by means of a pump (5) driven by the fan motor (7). The moistened air escapes through a port (18).

Spraying device, in particular for spraying water in the form of microdroplets, for a non-stationary environment

The water micro-drop spray has a first water filled vat (1a) and second water filled vat (1b) separated by a central transducer (5). The transducer has two faces flush with the water one for each vat section. The piezoelectric transducer transmits waves in both water sections, and each water vat has an open section (4a,4b) opposite the transducer faces.

Gil Ching

Papers

Semi-passive damping using continuous switching of a piezoelectric device

High efficiency spraying device, in particular for spraying water in the form of micro-droplets

Device for spraying, in particular water in the form of microdroplets, capable of functioning in a nonstationary environment

Spraying device, in particular for spraying water in the form of microdroplets, for a non-stationary environment

High efficiency spray device particularly for producing water microdroplets