Amen Agbossou

On thermoelectric and pyroelectric energy harvesting

This paper deals with small-power energy harvesting from heat. It can be achieved using both thermoelectric and pyroelectric effects. In the first case, temperature gradients are necessary. The main difficulty of thermoelectric energy harvesting is imposing a large temperature gradient. This requires huge heat flows because of the limited surface heat exchanges and the large heat conductivity of thermoelectric materials. This results in a drastic decrease of power and the efficiency of conversion. In case of pyroelectric energy harvesting, a time varying temperature is necessary. Although such a temperature time profile is hard to find, the overall optimization is easier than the thermoelectric strategy. Indeed, it depends much less on heat exchange between the sample and the outer medium, than on heat capacity that dimensions optimization may easily compensate. As a consequence, it is shown that the efficiency and output power may be much larger using pyroelectric energy harvesting than thermoelectric methods. For instance, using a limited temperature gradient due to the limited heat exchange, a maximum efficiency of 1.7% of Carnot efficiency can be expected using a thermoelectric module. On the contrary, a pyroelectric device may reach an efficiency up to 50% of Carnot efficiency. Finally, an illustration shows an estimation of the output power that could be expected from natural time variations of temperature of a wearable device. Power peaks up to 0. 2m W cm −3 were found and a mean power of 1 μ Wc m −3 on average was determined within 24 h testing.

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.

Segmented piezoelectric fiber composite for vibration control: fabricating and modeling of electromechanical properties

Abstract This work presents an available prototyping technique and numerical model for development and optimization of piezoelectric fiber composites (PFC). The proposed technique, named “segmented piezoelectric fiber composite” (S-PFC) technique, consists of forming and polarizing PFC directly in the structure. To do this, we make molds directly in the structure, stack PZT fiber layers in the molds and develop specific segmentation techniques used to achieve connections, which allow reversed electric fields in consecutive segments during poling. The developed S-PFC technique yields long PFCs. To illustrate the vibration control concept, we present experimental results in passive vibration controls. The performances of the active beam depend on the electromechanical properties of S-PFCs. Then we propose periodic homogenization model to forecast electromechanical properties of the S-PFCs and to recommend a fiber aspect ratio ( l f 2r f ) to achieve optimal electromechanical properties of S-PFC with a fixed fiber volume fraction.

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 5.46 cm3, and it reaches a power density of 0.48 mW/cm3. The wideband and high-power energy harvesting properties are first validated using chirp excitations with an obtained bandwidth of 11 Hz (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.

Dynamic analysis of piezoelectric fiber composite in an active beam using homogenization and finite element methods

The purpose of this work is to point out the improvement, which could be achieved through use of piezoelectric fiber composite elements in place of piezoelectric patch elements, in structural vibration systems. Therefore, we review the homogenization method for prediction of the overall properties of piezoelectric fiber composite and we propose the Periodic Medium Homogenization model. The results indicated a good correlation between our proposed model and the MoriTanaka approach. Then we considered the cases of incorporated bulk piezoelectric and piezoelectric fiber composite in two epoxy cantilevered beams loaded by static and dynamic forces. The numerical results show that, with the piezoelectric fiber composite, one can adapt the electromechanical coupling coefficient for a specific task by simply changing the fiber content. The results also suggest that increasing fiber content above 35% for the analyzed beam, will effectively result in reduced performance of the active structure.

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.