| Vibration energy harvesting has become a viable source of electric power for lowpower and low-voltage wireless terminals and hard-to-reach electronic devices.Of many harvesters through which kinetic energy can be converted to electric energy for powering electronic devices,piezoelectric energy harvesting devices(PEHDs)are often favored for their simple structure,high power density,and ease of self-starting.However,for a common high-Q resonant PEHD,its harvested power drops off dramatically when ambient vibration frequency deviates from its resonance frequency;only at the resonance frequency can the PEHD output maximum power.This is problematic for applications in which the ambient vibration frequency is not known accurately or time varying,and/or in which the resonance frequency of the PEHD is not perfect due to manufacturing tolerances.In addition,low-power and low-voltage electronics to where PEHDs can be implemented with raise an extra requirement that PEHDs should have low output voltages to maintain compatibility with their loads.In such cases it is desirable to increase the energy harvesting bandwidth and reduce the output voltage of the PEHD,thereby enhancing the adaptability of autonomous micro electronic systems working in the environment with a wide vibration spectrum.Revolving around vibration energy harvesting techniques,this thesis conducts researches on the modeling and structure optimization of cantilevered PEHDs along with the design of their power conditioning interface circuits.From the perspective of achieving a low-voltage wideband energy harvesting system,this thesis presents an indepth study on the co-design of both PEHDs and their interface circuits.Detailed innovations include:1.Device modeling: a model parameter extraction method based on the measurement of electrical signals is proposed to characterize the PEHD.The method is more accurate and requires simple measurement equipments.In addition,a nonlinear circuit model is proposed to characterize the nonlinear behavior of the PEHD,based on which the influence of device nonlinear behavior on the wideband energy harvesting is explored.Finally,an impedance modeling method based on artificial neural network is proposed to model the impedance of PEHDs over a large frequency range.The modeling accuracy of the device impedance is improved,which helps to estimate the harvested energy of a PEH system correctly in the early design period.2.Device optimization: the influence of the interaction between device parameters and different electrical loads or interface circuits on the energy harvesting voltage and bandwidth is explored.Based on the above study,a design guidance for the mechanical optimization of PEHDs is proposed to realize a low-voltage and wideband energy harvesting.With the proposed design guidance,by collaborating with MIDE Corporation,a commercial MIDE PPA2014 PEHD is redesigned and fabricated with increased by 1.85 X and the optimal output voltage scaled down by 18%.3.Interface circuit design: to overcome the bandwidth limitation of the traditional Bias-Flip technique,an improved Bias-Flip technique with optimum universal phase is proposed to realize the optimal harvested power away from resonances.In addition,a smart Bias-Flip interface circuit with active rectifier is proposed for zero rectification voltage,which greatly reduces the power dissipation in passive diodes when the output voltage of the PEHD is optimized to be low.The co-optimized system presents a 3d B bandwidth of 81 Hz(13.3% of),which is beyond the bandwidth of the state-of-theart PEH system.In addition,the rectification voltage is scaled down by 30%.4.Application of the PEH system: a vibration sensor with energy harvesting capability for real-time measurement of vibration frequency is proposed to show a practical application of the Bias-Flip technique in industry.Experiments indicate that it can measure the frequency from 80 Hz to 130 Hz with 0.041% error,and harvested sufficient power from 96 Hz to 116 Hz under 2-g acceleration. |
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