• 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.
    • Real-world evaluation of a self-startup SSHI rectifier for piezoelectric vibration energy harvesting

      Du, Sijun; Jia, Yu; Zhao, Chun; Chen, Shao-Tuan; Seshia, Ashwin A.; University of Cambridge; University of Chester (Elsevier, 2017-08-02)
      This paper presents an enhanced SSHI (synchronized switch harvesting on inductor) rectifier with startup circuit and representative environment validation using real world vibration data collected from a tram. Compared to a conventional SSHI rectifier, the proposed rectifier dynamically monitors the working status of the circuit and restarts it when necessary. The proposed rectifier is designed in a 0.35 μm HV CMOS process and its performance is experimentally evaluated. With a 500-second real-world collected vibration data, the conventional and the proposed SSHI rectifiers record average power performance improvements by 9.2× and 22× respectively, compared to a passive full-bridge rectifier. As the startup circuit helps restart the SSHI rectifier several times, it is able to extract energy in an increased excitation range and its average power output performance is 2.4× higher than a conventional SSHI rectifier.