Piezoelectric power generators have immense potential for applications such as self-powered nanoelectronic devices and systems. Piezoelectric power generators based on aligned zinc oxide (ZnO) nanowires have been previously reported with an output voltage of 10 mV under the driving of ultrasonic wave. Among the aqueous-grown methods, the hydrothermal method has emerged as a powerful method for the fabrication of 1-D ZnO nanostructures, offering significant advantages such as controllable structures and a cost-effective low-temperature process technique. In this project, we propose a low-frequency-vibration-based power generator using ZnO cylindrical nanowires grown by hydrothermal method for process integration and low cost. This device can scavenge vibration energy under normal and shear modes for improving its output power.

Selected Publications:

1. Bin Yang, Chengkuo Lee, Ghim Wei Ho, Wei Li Ong, Jingquan Liu and Chunsheng Yang, Modeling and experimental study of a low frequency vibration based power generator using ZnO nanowires arrays, IEEE/ASME J. Microelectromech. Syst. Letters, vol. 21, no. 4, pp. 776-778, 2012. [PDF] [DOI]

 

A key challenge for vibration-based EH device is that it obtains the optimal power within a narrow frequency bandwidth near its resonant frequency. Away from the resonant frequency, the power generation drops dramatically and is too low to be utilized. Energy harvesting mechanisms which can respond to low-frequency vibrations with wideband operation range or tunable resonant frequency are considered to be promising solutions.

In this research area, we demonstrated the design, fabrication, and characterization of a MEMS-based piezoelectric energy harvester device operating at a relatively low resonant frequency with a wideband operation range. A Si proof mass integrated with piezoelectric beam has been designed to realize a resonant frequency as low as 36 Hz. By adjusting the spacer thickness, the vibration behavior of the cantilever can be limited in amplitude domain but extended in frequency domain. For input acceleration of 1.0 g, a 17 Hz operation frequency bandwidth is, which is as large as 0.47 in terms of NFB. By integrating ten PZT elements in parallel, the power generated at 1.0 g with respect to load resistance of 330 kΩ is able to achieve a wideband output ranging from 32.3 nW to 85.5 nW within the operation bandwidth from 30 Hz to 47 Hz. Theoretical calculation shows that the maximum power and power density at an acceleration of 1.0 g would be around 0.53 μW and 33 μW/cm³, respectively.

In another design, a piezoelectric energy harvester system with a wide operating bandwidth introduced by mechanical stoppers is proposed. The wideband frequency responses of the piezoelectric energy harvester system with stoppers on one side and two sides are investigated thoroughly. The experimental results show that the operating bandwidth is broadened to 18 Hz (30–48 Hz) and the corresponding optimal power ranges from 34 to 100 nW at the base acceleration of 0.6g and under top- and bottom-stopper distances of 0.75 mm and 1.1 mm, respectively. By adjusting the mechanical stopper distance, the output power and frequency bandwidth can be optimized accordingly.

In the third design, two MEMS-based piezoelectric energy harvesting (EH) systems with wideband operation frequency range and capability of converting random and low-frequency vibrations to high-frequency self oscillations have been proposed. In the first EH system (EH-I), by incorporating a high-resonant-frequency (HRF) cantilever as a frequency-up-conversion (FUC) stopper, the vibration amplitude of a low-resonantfrequency (LRF) cantilever with a resonant frequency of 36 Hz is suppressed and the operation bandwidth is increased to 22 Hz at 0.8 g. The HRF cantilever is then triggered to vibrate at 618 Hz. In the second EH system (EH-II), by employing a straight cantilever as the FUC stopper, the operation frequency range of a meandered cantilever which responds to lower frequency vibration is further moved downward from 12 Hz to 26 Hz, and the voltage and power generation are significantly improved. The peak-power densities of the EH-II system are 61.5 μW/cm3 and 159.4 μW/cm3 operating at relatively lower operation frequencies of 20 Hz and 25 Hz at 0.8 g, respectively.

Selected Publications:

1. Huicong Liu, Chengkuo Lee, Takeshi Kobayashi, Cho Jui Tay and Chenggen Quan, Piezoelectric MEMS-based wideband energy harvesting systems using a frequency-up-conversion cantilever stopper, Sens. & Actuators A: Phys., vol.186, pp. 242-248, 2012. [PDF] [DOI]
2. Huicong Liu, Chengkuo Lee, Takeshi Kobayashi, Cho Jui Tay and Chenggen Quan, Investigation of MEMS piezoelectric energy harvester system with frequency-widen-bandwidth mechanism introduced by mechanical stopper, Smart Mater. Struct., vol. 21, no. 3, 035005, 2012. [PDF] [DOI]
3. Huicong Liu, Cho Jui Tay, Chenggen Quan, Takeshi Kobayashi and Chengkuo Lee, Piezoelectric MEMS energy harvester for low-frequency vibrations with wideband operation range and steadily increased output power, IEEE/ASME J. Microelectromech. Syst., vol. 20, no. 5, 1131-1142, 2011. [PDF] [DOI]

Special Mention:

1. Our team member Dr. Huicong Liu was honored with the Silver Award at the International Union of Materials Research Societies - International Conference on Electronics Materials (IUMRS-ICEM) 2012 for her research on "MEMS Based Piezoelectric Energy Harvesters Using PZT Cantilevers". [LINK]

 

Most of the reported vibration based harvesters provide a maximum output power when they operate at their mechanical resonances. However, the vibration frequency of environment excitation sources often vary for different cases in real-life situations. Therefore, it is necessary that the energy under different vibration frequencies with respect to a given MEMS harvester can be collected.

We first proposed a novel multi-frequency electromagnetic energy harvester, which offers major advantages such as low cost and capability of harvesting more energy from vibrations with multiple frequencies. This device consists of three permanent magnets, three sets of two-layer copper coils and a supported acrylic beam. The energy under the first, second and third resonant modes, corresponding to the resonant frequencies of 369 Hz, 938 Hz and 1184 Hz, respectively, can be harvested. The maximum output voltage and power of the first and second vibration modes are 1.38 mV, 0.6 μW and 3.2 mV, 3.2 μW for 14 μm exciting vibration amplitude and a 0.4 mm gap between the magnet and coils, respectively. The major advantages of our first design are low cost and capable of harvesting more energy from vibrations of multi-frequency.

In another design, a electromagnetic energy harvester with multiple vibration modes has been developed and characterized using three dimensional (3D) excitation at different frequencies. The device consists of a movable circular-mass patterned with three sets of double-layer aluminum coils, a circular-ring system incorporating a magnet and a supporting beam. The 3-D dynamic behavior and performance analysis of the device shows that the first vibration mode of 1285 Hz is an out-of-plane motion, while the second and third modes of 1470 and 1550 Hz, respectively, are in-plane at angles of 60° (240°) and 150°(330°) to the horizontal x- axis. For an excitation acceleration of 1g, the maximum power density achieved are 0.444, 0.242 and 0.125μWcm^-3 at vibration modes of I, II and III, respectively. The experimental results are in good agreement with the simulation and indicate a good potential in the development of a 3-D EH device.

1. Huicong Liu, Bo Woon Soon, Nan Wang, Cho Jui Tay, Chenggen Quan, and Chengkuo Lee, Feasibility study of a 3-D vibration-driven electromagnetic MEMS energy harvester with multiple vibration modes, J. Micromech. Microeng., vol. 22, no. 12, 125020, 2012. [PDF] [DOI]
2. Bin Yang, Chengkuo Lee, Wenfeng Xiang, Jin Xie, Johnny Han He, Rama Krishna Kotlanka, Siew Ping Low, and Hanhua Feng, Electromagnetic energy harvesting from vibrations of multiple frequencies, J. Micromech. Microeng., vol. 19, no. 3, 035001, 2009. [PDF] [DOI]

 

It is pointed out that piezoelectric energy harvesters present high power density and are more suitable for microsystem applications, while electromagnetic energy harvesters are good at applications of relatively large size. In order to overcome drawbacks of each individual type of the three energy harvesting mechanisms, a creative hybrid energy harvester is proposed to harness energy from electromagnetic and piezoelectric mechanisms. The device contains a piezoelectric cantilever of multilayer piezoelectric transducer ceramics, permanent magnets, and substrate of two-layer coils. The output power of the PZT cantilever and coils is measured as high as 176 μW and 0.19 μW for a type III device with six magnets under the vibrations of 2.5 g acceleration at 310 Hz. The major advantages of this device are low cost and capability of harvesting energy by both piezoelectric and electromagnetic mechanisms.

Selected Publications:

1. Bin Yang, Chengkuo Lee, Wei Loon Kee and Siak Piang Lim, A hybrid energy harvester based on piezoelectric and electromagnetic mechanisms, SPIE J. of Micro/Nanolithography, MEMS, and MOEMS (JM3), vol. 9 (2), 023002 (Apr-Jun, 2010). [PDF] [DOI]

Special Mention:

1. Our novel hybrid energy harvester design was highlighted by SPIE newsroom in an article titled "Hybrid energy harvesters could power handheld electronics," 18th Oct. 2010. [LINK]

 

Most electrostatic mechanisms are designed to harvest kinetic energy from linear motion. However, the vibrations from the natural resources may not always be along one direction. An electrostatic energy harvester converting 2-D in-plane vibration energy into electrical energy is proposed and successfully fabricated using a CMOS compatible process. This energy harvester comprises of novel rotary comb electrodes. Upon planar vibrations, the variable capacitor of the rotary comb under bias is characterized with respect to ambient vibrations of various accelerations. A maximum measured output power in air for vibrations of 0.5 g, 1 g, 1.5 g, 2 g and 2.5 g is 0.11 μW, 0.17 μW, 0.24 μW, 0.3 μW and 0.35 μW, respectively. This is obtained when the loading resistance matches the parasitic resistance of 80 MΩ at the resonant frequency of 110 Hz. The testing results in vacuum level of 3 Torr show that the resonant frequency decreases from 110 Hz in air to 63 Hz, and the maximum electrical output power at 0.25 g is 0.39 μW. The preliminary results show that this new device provides an intriguing alternative for harvesting energy from planar vibrations.

Selected Publications:

1. Bin Yang, Chengkuo Lee, Rama Krishna Kotlanka, Jin Xie and Siak Piang Lim, MEMS rotary comb mechanism for harvesting kinetic energy of planar vibrations, J Micromech. Microeng., vol. 20, 065017, 2010. [PDF] [DOI]

 

Wind-flow is present everywhere in open environments and has also been regarded as a renewable energy source. Only a few wind-driven MEMS energy harvesters have been reported so far. Hence, we develop a piezoelectric (PZT) microcantilever as an air flow sensor and a wind-driven energy harvester for a self-sustained flow-sensing microsystem. A bent cantilever design is employed to receive the maximum amount of momentum from the fluid or wind flow and hence the maximum transduction between the wind energy and mechanical vibration and eventually the electrical energy. A flow sensing sensitivity of 0.9mV/(m/s) is obtained. The output voltage and optimized power regarding to the load resistance of 100 kX are measured as 18.1mV and 3.3 nW at flow velocity of 15.6 m/s, respectively. The corresponding power density is as large as 0.36mW/cm³. The experimental results have elucidated the smart function of using PZT microcantilevers as flow-sensors and wind-driven energy harvesters

Selected Publications:

1. Huicong Liu, Songsong Zhang, Ramprakash Kathiresan, Takeshi Kobayashi and Chengkuo Lee, Development of piezoelectric microcantilever flow sensor with wind-driven energy harvesting capability, Appl. Phys. Lett., vol. 100, no. 22, 223905, 2012. [PDF] [DOI]

 

As a kind of energy harvesting device, thermoelectric power generators have been proposed to generate electricity from body heat or any environment where there is a temperature gradient. Currently, most commercial thermoelectric power generators use Bi₂Te₃ as thermoelectric material due to its large thermoelectric figure of merit. Researchers at IMEC presented the first prototype of wireless sensor nodes on human beings powered by thermoelectric generators using Bi₂Te₃ material. However, it is not a CMOS-compatible material, which means that Bi₂Te₃ material-based approaches cannot be monolithically integrated on microelectronics in normal CMOS manufacturing lines. Large Seebeck effects are found in doped poly-Si, which make it a promising choice for thermoelectric devices based on CMOS technology. We developed a CMOS MEMS-based thermoelectric power generators to convert waste heat into a few microwatts of electrical power. For a device in the size of 1 cm² and with a 5-K temperature difference across the two sides, the open-circuit voltage is 16.7 V and the output power is 1.3 μW under matched load resistance. The generated energy can be efficiently accumulated as useful electricity over time such that it can prolong the battery life.

Selected Publications:

1. Jin Xie, Chengkuo Lee, Ming-Fang Wang, and Hanhua Fang, Seal and encapsulate cavities for CMOS MEMS thermoelectric power generators, J. Vacuum Sci. & Technol. B, vol. 29, no. 2, pp. 021401, Mar 2011. [PDF] [DOI]
2. Jin Xie, Chengkuo Lee, and Hanhua Feng, Design, Fabrication and characterization of CMOS MEMS-Based Thermoelectric Power Generators, IEEE/ASME J. Microelectromech. Syst., vol. 19, no. 2, 317-324, Apr. 2010. [PDF] [DOI]
3. Jin Xie, Chengkuo Lee, Ming-FangWang, Youhe Liu and Hanhua Feng, Characterization of heavily doped polysilicon films for CMOS-MEMS thermoelectric power generators, J. Micromech. Microeng., vol.19, no. 12, 125029, 2009. [PDF] [DOI]
4. Chengkuo Lee and Jin Xie, Design and optimization of wafer bonding packaged microelectromechanical systems thermoelectric power generators with heat dissipation path, J. Vac. Sci. & Technol. B, vol.27, no. 3, pp. 1267-1271, 2009. [PDF] [DOI]

Special Mention:

1. Our novel CMOS compatible Thermoelectric Power Generator (TPG) was highlighted by Nanowerk News in an article titled "Microfabrication: The power of heat," in 15th Sep. 2010. [LINK]

 

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