Du, Sijun; Jia, Yu; Seshia, Ashwin A. (SAGE, 2016-12-12)
For a conventional monolithic piezoelectric transducer (PT) using a full-bridge rectifier, there is a threshold voltage that the open-circuit voltage measured across the PT must attain prior to any transfer of energy to the storage capacitor at the output of the rectifier. This threshold voltage usually depends on the voltage of the storage capacitor and the forward voltage drop of diodes. This article presents a scheme of splitting the electrode of a monolithic piezoelectric vibration energy harvester into multiple (n) equal regions connected in series in order to provide a wider operating voltage range and higher output power while using a full-bridge rectifier as the interface circuit. The performance of different series stage numbers has been theoretically studied and experimentally validated. The number of series stages (n≥1n≥1) can be predefined for a particular implementation, which depends on the specified operating conditions, to achieve optimal performance. This enables the system to attain comparable performance compared to active interface circuits under an increased input range while no additional active circuits are required and the system is comparatively less affected by synchronized switching damping effect.
Du, Sijun; Jia, Yu; Chen, Shao-Tuan; Zhao, Chun; Sun, Boqian; Arroyo, Emmanuelle; Seshia, Ashwin A. (Elsevier, 2017-07-19)
A resonant vibration energy harvester typically comprises of a clamped anchor and a vibrating shuttle with a proof mass. Piezoelectric materials are embedded in locations of high strain in order to transduce mechanical deformation into electrical charge. Conventional design for piezoelectric vibration energy harvesters (PVEH) usually utilizes piezoelectric materials and metal electrode layers covering the entire surface area of the cantilever with no consideration provided to examine the trade-off involved with respect to maximize output power. This paper reports on the theory and experimental verification underpinning optimization of the active electrode area in order to maximize output power. The calculations show that, in order to maximize the output power of a PVEH, the electrode should cover the piezoelectric layer from the peak strain area to a position, where the strain is a half of the average strain in all the previously covered area. With the proposed electrode design, the output power can be improved by 145% and 126% for a cantilever and a clamped-clamped beam, respectively. MEMS piezoelectric harvesters are fabricated to experimentally validate the theory.
Jia, Yu; Du, Sijun; Seshia, Ashwin A. (IOP Publishing, 2016-10-17)
The overwhelming majority of microelectromechanical piezoelectric vibration energy harvesting topologies have been based on cantilevers, doubly-clamped beams or basic membranes. While these conventional designs offer simplicity, their broadband responses have been limited thus far. This paper investigates the feasibility of a new integrated cantilevers-on-membrane design that explores the optimisation of piezoelectric strain distribution and improvement of the broadband power output. While a classic membrane has the potential to offer a broader resonant peak than its cantilever counterpart, the inclusion of a centred proof mass compromises its otherwise high strain energy regions. The proposed topology addresses this issue by relocating the proof mass onto subsidiary cantilevers and combines the merits of both the membrane and the cantilever designs. Numerical simulations, constructed using fitted values based on finite element models, were used to investigate the broadband response of the proposed design in contrast to a classic plain membrane. Experimentally, when subjected to a band-limited white noise excitation, the new cantilevers-on-membrane harvester exhibited nearly two fold power output enhancement when compared to a classic plain membrane harvester of a comparable size.
Arroyo, Emmanuelle; Jia, Yu; Du, Sijun; Chen, Shao-Tuan; Seshia, Ashwin A. (IOP Publishing, 2016-12-06)
Energy harvesters withstanding high temperatures could provide potentially unlimited energy to sensor nodes placed in harsh environments, where manual maintenance is difficult and costly. Experimental results on a classical microcantilever show a 67% drop of the maximum power when the temperature is increased up to 160 °C. This decrease is investigated using a lumped-parameters model which takes into account variations in material parameters with temperature, damping increase and thermal stresses induced by mismatched thermal coefficients in a composite cantilever. The model allows a description of the maximum power evolution as a function of temperature and input acceleration. Simulation results further show that an increase in damping and the apparition of thermal stresses are contributing to the power drop at 59% and 13% respectively.
Chen, Shao-Tuan; Du, Sijun; Arroyo, Emmanuelle; Jia, Yu; Seshia, Ashwin A. (IOP Publishing, 2016-12-06)
This paper reports on the theory and experimental verification of utilising air damping as a soft stopper mechanism for piezoelectric vibration energy harvesting to enhance shock resistance. Experiments to characterise device responsiveness under various vibration conditions were performed at different air pressure levels, and a dimensionless model was constructed with nonlinear damping terms included to model PVEH response. The relationship between the quadratic damping coefficient ζ n and air pressure is empirically established, and an optimal pressure level is calculated to trade off harvestable energy and device robustness for specific environmental conditions.
Arroyo, Emmanuelle; Jia, Yu; Du, Sijun; Chen, Shao-Tuan; Seshia, Ashwin A. (IEEE, 2017-08-01)
This paper focuses on studying the effect of increasing the ambient temperature up to 160 °C on the power harvested by an MEMS piezoelectric micro-cantilever manufactured using an aluminum nitride-on-silicon fabrication process. An experimental study shows that the peak output power decreases by 60% to 70% depending on the input acceleration. A theoretical study establishes the relationship of all important parameters with temperature and includes them into a temperature-dependent model. This model shows that around 50% of the power drop can be explained by a decreasing quality factor, and that thermal stresses account for around 30% of this decrease.
Chen, Shao-Tuan; Du, Sijun; Arroyo, Emmanuelle; Jia, Yu; Seshia, Ashwin A. (IOP Publishing, 2017-09-20)
This paper presents a novel application of utilising nonlinear air damping as soft mechanical stopper to increase the shock reliability for MEMS vibration energy harvesters. Theoretical framework for nonlinear air damping is constructed for MEMS vibration energy harvesters operating in different air pressure levels, and characterisation experiments are conducted to establish the relationship between air pressure and nonlinear air damping coefficient for rectangular cantilever MEMS micro cantilevers with different proof masses. Design guidelines on choosing the optimal air pressure level for different MEMS vibration energy harvesters based on the trade-off between harvestable energy and the device robustness is presented, and random excitation experiments are performed to verify the robustness of MEMS vibration energy harvesters with nonlinear air damping as soft stoppers to limit the maximum deflection distance and increase the shock reliability of the device.
Du, Sijun; Jia, Yu; Seshia, Ashwin A. (IOP Publishing, 2015-12-01)
A resonant vibration energy harvester typically comprises of a clamped anchor and a vibrating shuttle with a proof mass. Piezoelectric materials are embedded in locations of high strain in order to transduce mechanical deformation into electric charge. Conventional design for piezoelectric vibration energy harvesters (PVEH) usually utilizes piezoelectric material and metal electrode layers covering the entire surface area of the cantilever with no consideration provided to examining the trade-off involved with respect to maximizing output power. This paper reports on the theory and experimental verification underpinning optimization of the active electrode area of a cantilevered PVEH in order to maximize output power. The analytical formulation utilizes Euler-Bernoulli beam theory to model the mechanical response of the cantilever. The expression for output power is reduced to a fifth order polynomial expression as a function of the electrode area. The maximum output power corresponds to the case when 44% area of the cantilever is covered by electrode metal. Experimental results are also provided to verify the theory.
Du, Sijun; Jia, Yu; Do, Cuong D.; Seshia, Ashwin A. (IEEE, 2016-08-10)
Piezoelectric vibration energy harvesters have been widely researched and are increasingly employed for powering wireless sensor nodes. The synchronized switch harvesting on inductor (SSHI) circuit is one of the most efficient interfaces for piezoelectric vibration energy harvesters. However, the traditional incarnation of this circuit suffers from a significant start-up issue that limits operation in low and variable amplitude vibration environments. This paper addresses this start-up issue for the SSHI rectifier by proposing a new architecture with SSHI startup circuitry. The startup circuitry monitors if the SSHI circuit is operating correctly and re-starts the SSHI interface if required. The proposed circuit is comprehensively analyzed and experimentally validated through tests conducted by integrating a commercial piezoelectric vibration energy harvester with the new interface circuit designed in a 0.35-μm HV CMOS process. Compared to conventional SSHI rectifiers, the proposed circuit significantly decreases the required minimum input excitation amplitude before energy can be harvested, making it possible to extract energy over an increased excitation range.
Jia, Yu; Du, Sijun; Seshia, Ashwin A. (Nature Publishing Group, 2016-07-22)
This paper contends to be the first to report the experimental observation of up to 28 orders of parametric resonance, which has thus far only been envisioned in the theoretical realm. While theory has long predicted the onset of n orders of parametric resonance, previously reported experimental observations have been limited up to about the first 5 orders. This is due to the rapid narrowing nature of the frequency bandwidth of the higher instability intervals, making practical accessibility increasingly more difficult. Here, the authors have experimentally confirmed up to 28 orders of parametric resonance in a micromachined membrane resonator when electrically undamped. While the implication of this finding spans across the vibration dynamics and transducer application spectrum, the particular significance of this work is to broaden the accumulative operational frequency bandwidth of vibration energy harvesting for enabling self-powered microsystems. Up to 5 orders were recorded when driven at 1.0g of acceleration across a matched load of 70kΩ. With a natural frequency of 980Hz, the fundamental mode direct resonance had a −3dB bandwidth of 55Hz, in contrast to the 314Hz for the first order parametric resonance; furthermore, the half power bands of all 5 orders accumulated to 478Hz.
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