Adrien Badel

Novel piezoelectric bistable oscillator architecture for wideband vibration energy harvesting

Bistable vibration energy harvesters are attracting more and more interest because of their capability to scavenge energy over a large frequency band. The bistable effect is usually based on magnetic interaction or buckled beams. This paper presents a novel architecture based on amplified piezoelectric structures. This buckled spring‐mass architecture allows the energy of the dynamic mass to be converted into electrical energy in the piezoelectric materials as efficiently as possible. Modeling and design are performed and a normalized expression of the harvester behavior is given. Chirp and band-limited noise excitations are used to evaluate the proposed harvester’s performances. Simulation and experimental results are in good agreement. A method of using a spectrum plot for investigating the interwell motion is presented. The effect of the electric load impedance matching strategy is also studied. Results and comparisons with the literature show that the proposed device combines a large bandwidth and a high power density. (Some figures may appear in colour only in the online journal)

Piezoelectric vibration energy harvesting by optimized synchronous electric charge extraction

This article presents a novel nonlinear energy extraction technique for piezoelectric vibration energy harvesting. The proposed approach is an improvement of the previous technique, “synchronous electric charge extraction,” which is the first that optimizes the harvested power whatever the connected load. The new approach is then named as “optimized synchronous electric charge extraction.” Compared with synchronous electric charge extraction, the conversion effectiveness is enhanced while simplifying the electronic circuitry and the switch control strategy. The analytical expression of the harvested powers is derived for a classical electromechanical structure. Finally, theoretical predictions confirmed by experimental results show that optimized synchronous electric charge extraction increases the harvested power for a very large range of load resistance, which is a favorable characteristic for wideband vibration energy harvesting.

Nonlinear vibration energy harvesting device integrating mechanical stoppers used as synchronous mechanical switches

Nonlinear energy extraction techniques for piezoelectric vibration energy harvesting usually require synchronized electronic switches in their electronic interface circuits. But the difficulty to self-power their complex switching control strategies limits their performances, especially in the presence of wideband ambient excitations. This technical note presents a nonlinear energy extraction interface achieved by synchronous mechanical switches. The complex switching control strategy is dodged by taking advantage of mechanical stoppers and the moving part of the piezoelectric oscillator, which is driven by the vibration itself. As a result, the added mechanical stoppers and the self-synchronized nonlinear energy extraction circuit also make the energy harvesting device system be particularly suited to wideband ambient vibrations.

Wideband energy harvesting using a combination of an optimized synchronous electric charge extraction circuit and a bistable harvester

The challenge of variable vibration frequencies for energy harvesting calls for the development of wideband energy harvesters. Bistability has been proven to be a potential solution. Optimization of the energy extraction is another important objective for energy harvesting. Nonlinear synchronized switching techniques have demonstrated some of the best performances. This paper presents a novel energy harvesting solution which combines these two techniques: the OSECE (optimized synchronous electric charge extraction) technique is used along with a BSM (buckled-spring–mass) bistable generator to achieve wideband energy harvesting. The effect of the electromechanical coupling coefficient on the harvested power for the bistable harvester with the nonlinear energy extraction technique is discussed for the first time. The performances of the proposed solution for different levels of electromechanical coupling coefficients in the cases of chirp and noise excitations are compared against the performances of the bistable harvester with the standard technique. It is shown that the OSECE technique is a much better option for wideband energy harvesting than the standard circuit. Moreover, the harvested energy is drastically increased for all excitations in the case of low electromechanical coupling coefficients. When the electromechanical coupling coefficient is high, the performance of the OSECE technique is not as good as the standard circuit for forward sweeps, but superior for the reverse sweep and band-limited noise cases. However, considering that real excitation signals are more similar to noise signals, the OSECE technique enhances the performance.

Self-powered optimized synchronous electric charge extraction circuit for piezoelectric energy harvesting:

This article presents a self-powered interface circuit for the optimized synchronous electric charge extraction technique applied to piezoelectric vibration energy harvesting. A peak detector circuit is developed to detect the maximum and minimum vibration displacements and drive the electronic switches synchronously. This approach does not require additional piezoelectric elements to power the electronic interface itself for which a detailed analysis and a simple model are proposed to give a better understanding on the working principle. Finally, the influence of the switching phase lag and the peak detector power consumption on the harvested power is studied. Experimental studies are conducted and successfully compared with the theoretical approach.

A wideband integrated piezoelectric bistable generator: Experimental performance evaluation and potential for real environmental vibrations

Bistable generators have been proposed as potential solutions to the challenge of variable vibration frequencies. This article presents a novel mono-block design of bistable generator based on mechanical buckling effect. A bistable structure composed of four thin beams as flexible hinges, two amplified piezoelectric stacks as electromechanical springs, and a dynamic mass is fabricated. Its volume is 5.46u2009cm3, and it reaches a power density of 0.48u2009mW/cm3. The wideband and high-power energy harvesting properties are first validated using chirp excitations with an obtained bandwidth of 11u2009Hz (812% improvement compared with the linear equivalent case). The generator’s good performance is then further confirmed for bandlimited noise excitations and a real vibration signal from a driving car wheel.

Sub-nanometer active seismic isolator control

Ambitious projects such as the design of the future Compact Linear Collider require challenging parameters and technologies. Stabilization of the Compact Linear Collider particle beam is one of these challenges. Ground motion is the main source of beam misalignment. Beam dynamics controls are, however, efficient only at low frequency (<4 Hz), due to the sampling of the beam at 50 Hz. Hence, ground motion mitigation techniques such as active stabilization are required. This article shows a dedicated prototype able to manage vibration at a sub-nanometer scale. The use of cutting edge sensor technology is, however, very challenging for control applications as they are usually used for measurement purposes. Limiting factors such as sensor dynamics and noise lead to a performance optimization problem. The current state of the art in ground motion measurement and ground motion mitigation techniques is pointed out and shows limits of the technologies. The proposed active device is then described, and a realistic model of the process has been established. A dedicated controller design combining feedforward and feedback techniques is presented, and theoretical results in terms of power spectral density of displacement are compared to real-time experimental results obtained with a rapid control prototyping tool.

A new figure of merit for wideband vibration energy harvesters

The performance evaluation method is a very important part in the field of vibration energy harvesting. It provides the ability to compare and rate different vibration energy harvesters (VEHs). Considering the lack of a well-recognized tool, this article proposed a new systematic figure of merit for the appraisement of wideband VEHs. Extensive investigations are first performed for some classic figures for linear VEHs. With the common fundamental information obtained, the proposed figure integrates four essential factors: the revised energy harvester effectiveness, the mechanical quality factor, the normalized bandwidth and the effective mass density. Special considerations are devoted to the properties of wideband VEHs about the operation range and the average power in this domain which are related to the performance target of stable power output. Afterward, this new figure is applied to some literature VEHs and demonstrated to present good evaluations of wideband VEHs. Moreover, it exhibits the ability to point out the improvement information of the concerned VEHs further developments.

Investigation of a buckled beam generator with elastic clamp boundary

A compact nonlinear bistable oscillator (NLBO) based on a double buckled beams and a concentrated mass is proposed and studied considering elastic boundary conditions. A unified analytical model including different elastic conditions is derived. Comparative modal analysis studies of the model and a finite element approach present consistent results. Good agreements with experiments results further validate the effectiveness of the model. It is shown that the proposed NLBO overcomes the band limitation of the regular linear oscillators and possesses a good capability of wide bandwidth for different applications. The proposed investigations suggest that the elastic clamp boundary can enhance the NLBOs performance with proper arrangements. A feasible solution of modifying the axial stiffness to tune the desired energy potential shape and keeping the beam parameter unvaried simultaneously is then available. It provides additional options of design and optimization to break the restriction of fabrication or other issues.

Development of low frequency, insulating thick diaphragms for power MEMS applications

Major challenges of micro thermal machines are the thermal insulation and mechanical tolerance in the case of sliding piston. Replacing piston by membrane in microengines can alleviate the latter and lead to planar architectures. However, the thermal isolation would call for very thick structures which are associated to too high resonant frequencies which are detrimental to the engine performances. A thermal and mechanical compromise is to be made. On the contrary, based on fluid structure interaction, using an incompressible fluid contained in a cavity sealed by deformable diaphragm it would be possible to design a thick, low frequency insulating diaphragm. The design involves a simple planar geometry that is easy to manufacture with standard microelectronics methods. An analytical fluid-structure model is proposed and theoretically validated. Experimental structures are realized and tested. The model is in agreement with the experimental results. A dimensionless model is proposed to design hybrid fluid structures for micromachines.