• Cantilevers-on-membrane design for broadband MEMS piezoelectric vibration energy harvesting

      Jia, Yu; Du, Sijun; Seshia, Ashwin A.; University of Chester; University of Cambridge (IOP Publishing, 2015-12-01)
      Most MEMS piezoelectric vibration energy harvesters involve either cantilever-based topologies, doubly-clamped beams or membrane structures. While these traditional designs offer simplicity, their frequency response for broadband excitation are typically inadequate. This paper presents a new integrated cantilever-on-membrane design that attempts to both optimise the strain distribution on a piezoelectric membrane resonator and improve the power responsiveness of the harvester for broadband excitation. While a classic membrane-based resonator has the potential to theoretically offer wider operational frequency bandwidth than its cantilever counterpart, the addition of a centred proof mass neutralises its otherwise high strain energy regions. The proposed topology addresses this issue by relocating the proof mass onto subsidiary cantilevers and integrates the merits of both the membrane and the cantilever designs. When experimentally subjected to a band-limited white noise excitation, up to approximately two folds of power enhancement was observed for the new membrane harvester compared to a classic plain membrane device.
    • Experimental and theoretical study of a piezoelectric vibration energy harvester under high temperature

      Arroyo, Emmanuelle; Jia, Yu; Du, Sijun; Chen, Shao-Tuan; Seshia, Ashwin A.; University of Cambridge; University of Chester (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.
    • Micromachined cantilevers-on-membrane topology for broadband vibration energy harvesting

      Jia, Yu; Du, Sijun; Seshia, Ashwin A.; University of Cambridge; University of Chester (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.
    • A New Electrode Design Method in Piezoelectric Vibration Energy Harvesters to Maximize Output Power

      Du, Sijun; Jia, Yu; Chen, Shao-Tuan; Zhao, Chun; Sun, Boqian; Arroyo, Emmanuelle; Seshia, Ashwin A.; University of Cambridge; University of Chester (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.
    • Shock Reliability Enhancement for MEMS Vibration Energy Harvesters with Nonlinear Air Damping as Soft Stopper

      Chen, Shao-Tuan; Du, Sijun; Arroyo, Emmanuelle; Jia, Yu; Seshia, Ashwin A.; University of Cambridge; University of Chester (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.