Pattanaphong Janphuang

The realization and performance of vibration energy harvesting MEMS devices based on an epitaxial piezoelectric thin film

This paper focuses on the fabrication and evaluation of vibration energy harvesting devices by utilizing an epitaxial Pb(Zr0.2Ti0.8)O3 (PZT) thin film. The high quality of the c-axis oriented PZT layer results in a high piezoelectric coefficient and a low dielectric constant, which are key parameters for realizing high performance piezoelectric energy harvesters. Different cantilever structures, with and without a Si proof mass, are realized using micro-patterning techniques optimized for the epitaxial oxide layers, to maintain the piezoelectric properties throughout the process. The characteristics and the energy harvesting performances of the fabricated devices are experimentally investigated and compared against analytical calculations. The optimized device based on a 0.5 µm thick epitaxial PZT film, a cantilever beam of 1 mm × 2.5 mm × 0.015 mm, with a Si proof mass of 1 mm × 0.5 mm × 0.23 mm, generates an output power, current and voltage of, respectively, 13 µW g − 2, 48 µA g − 1 and 0.27 V g − 1 (g = 9.81 m s − 2) at the resonant frequency of 2.3 kHz for an optimal resistive load of 5.6 kΩ. The epitaxial PZT harvester exhibits higher power and current with usable voltage, while maintaining lower optimal resistive load as compared with other examples present in the literature. These results indicate the potential of epitaxial PZT thin films for the improvement of the performances of energy harvesting devices.

Epitaxial piezoelectric MEMS on silicon

This paper reports on the microfabrication and characterization of piezoelectric MEMS structures based on epitaxial Pb(Zr0.2Ti0.8)O3 (PZT) thin films grown on silicon wafers. Membranes and cantilevers are realized using a sequence of microfabrication processes optimized for epitaxial oxide layers. Different issues related to the choice of materials and to the influence of the fabrication processes on the properties of the piezoelectric films are addressed. These epitaxial PZT transducers can generate relatively large deflections at low bias voltages in the static mode. Estimations of the piezoelectric coefficient d31 of the epitaxial PZT thin film (100 nm) yield 130 pm V−1. In the dynamic mode, the performance of the epitaxial PZT transducers in terms of the resonant frequency, modal shape and quality factor are examined. An epitaxial PZT/Si cantilever (1000 × 2500 × 40 µm3) resonating in air and in vacuum exhibits a deflection of several microns with quality factors of 169 and 284, respectively. For a 1500 µm diameter membrane, the quality factor is 50 at atmospheric pressure, and this rises to 323 at a pressure of 0.1 mbar. These results indicate the high potential of epitaxial piezoelectric MEMS, which can impact a variety of technological applications.

Design optimization of vibration energy harvesters fabricated by lamination of thinned bulk-PZT on polymeric substrates

The design optimization through modeling of a thinned bulk-PZT-based vibration energy harvester on a flexible polymeric substrate is presented. We also propose a simple foil-level fabrication process for their realization, by thinning the PZT down to 50 mu m and laminating it via dry film photoresist onto a PET substrate at low temperature (<85 degrees C). Two models, based on analytical and finite element modeling (FEM) methods, were developed and experimentally validated. The first, referred to as the hybrid model, is based mainly on analytical equations with the introduction of a correction factor derived from FEM simulations. The second, referred to as the numerical model, is fully based on COMSOL simulations. Both models have exhibited a very good agreement with the measured output power and resonance frequency. After their validation, a geometrical optimization through a parametric study was performed for the length, width, and thicknesses of the different layers comprising the device. As a result, an output power of 6.7 mu W at 49.8 Hz and 0.1 g, a normalized power density (NPD) of 11 683 mu W g(-2) cm(-3), and a figure of merit (FOM) of 227 mu W g(-2) cm(-3) were obtained for the optimized harvester.

Harvesting Energy From a Rotating Gear Using an AFM-Like MEMS Piezoelectric Frequency Up-Converting Energy Harvester

This paper presents an analytical and experimental study of a compact configuration to harvest energy from a rotating gear using piezoelectric microelectromechanical system harvesters. The reported configuration realizes a contact-type frequency up-conversion mechanism in order to generate useful electrical energy. The up-conversion mechanism was achieved using an atomic force microscope (AFM)-like piezoelectric cantilever plucked by the teeth of the rotating gear that could be eventually driven by an oscillating mass. This paper describes relevant design guidelines for harvesting energy from the low-frequency mechanical movement of a rotating gear through analytical modeling and finite element method (FEM) simulation followed by experimental validation. Different harvester configurations are investigated to identify the optimal configuration in terms of the output energy and energy conversion efficiency. The latter results are reported for the first time because of the implementation of an original concept based on the coupling of the harvester with a rotational flywheel. The experimental results reveal that free vibrations of the harvester after plucking contribute significantly to the output energy and efficiency. By adding a proof mass, the efficiency of the system can be greatly improved. For plucking speeds between 3 and 19 r/s, average output powers in the order of tens of microwatts were obtained for continuous plucking. By combining interaction energy, friction, and energy absorption, between the harvester and inertial mass, the maximum efficiency of the impact piezoelectric harvesters was found to be 1.4%. The efficiency results obtained were compared with the noncontact magnetic plucking approach further demonstrating the potential of our concept. Finally, different tip-gear materials combinations were evaluated showing the importance of their nature on the reliability of the presented configuration.

An Automatic Test Bench for Complete Characterization of Vibration-Energy Harvesters

This paper presents an automated test bench, based on a rigorous measurement procedure, used to fully characterize vibration energy harvesters including determination of the resonance frequency, impedance, optimal load, and output power as a function of both frequency and acceleration. The potential of this method and the performance of the automated test bench allows systematic data acquisition which is essential for a good comparison of all harvesters. A dedicated automation circuit was designed and fabricated. It uses stepper motors to mechanically control trimmers to vary the resistive load and reed relays to switch between the measurement sequences. With this, the setup is able to determine the optimal load of the device-under-test at its resonant frequency for a given acceleration. The test bench was used to fully characterize several types of vibration harvesters fabricated on both silicon and polymeric substrates. A comparison of the characterized devices is discussed using a figure of merit proposed here. A survey and compilation of current practices used to benchmark vibration harvesters is also reported.

Energy harvesting from a rotating gear using an impact type piezoelectric MEMS scavenger

This paper reports on energy harvesting from an impact by using a piezoelectric MEMS scavenger. Useful electrical power is generated by the impact of the rotating gear on the MEMS piezoelectric transducer. The design of the device structure was based on both analytical and FEM models for the estimation of induced voltage generated from piezoelectric transducer. A prototyping of piezoelectric MEMS based impact harvester consisting of a piezoelectric unimorph transducer was operated on a gearbox with a speed of 25 rpm. For the cantilever type harvester occupying approximately 4.2 mm3, an average output power of 1.26 µW was measured across a resistive load of 2.7 MΩ.

A sub 100µW UWB sensor-node powered by a piezoelectric vibration harvester

Piezoelectric harvesters are considered an alternative power source for applications that can support low to medium data rate transmissions in wireless sensor networks where ambient vibrations can provide microwatts to milliwatts of power. In this paper, we report the design and performance of a proof-of-concept (POC) autonomous sensor-node prototype including: an in-house piezoelectric harvester; a power management unit (PMU) made of discrete components; and an in-house ultra-wide band impulse radio (UWB-IR) transmitter. The piezoelectric harvester provides 54μW at 3.3Vrms at 450 milli-g and resonant frequency of 160 Hz. In these conditions, it was observed that the sensor node is capable of sending 1 burst of 100 pulses every 110 seconds consuming an average of 8.2μW, which is much less than the generated energy. The POC sensor node using kinetics energy harvester shows energy autonomy, thus opening range of possibilities for sub 100μW energy harvesting wireless sensor nodes.

On the experimental determination of the efficiency of piezoelectric impact-type energy harvesters using a rotational flywheel

This paper demonstrates a novel methodology using a rotational flywheel to determine the energy conversion efficiency of the impact based piezoelectric energy harvesters. The influence of the impact speed and additional proof mass on the efficiency is presented here. In order to convert low frequency mechanical oscillations into usable electrical energy, a piezoelectric harvester is coupled to a rotating gear wheel driven by flywheel. The efficiency is determined from the ratio of the electrical energy generated by the harvester to the mechanical energy dissipated by the flywheel. The experimental results reveal that free vibrations of the harvester after plucking contribute significantly to the efficiency. The efficiency and output energy can be greatly improved by adding a proof mass to the harvester. Under certain conditions, the piezoelectric harvesters have an impact energy conversion efficiency of 1.2%.

Epitaxial Piezoelectric Pb(Zr0.2Ti0.8)O3 Thin Films on Silicon for Energy Harvesting Devices

We report on the properties of ferroelectric Pb(Zr0.2Ti0.8)O3 (PZT) thin films grown epitaxially on (001) silicon and on the performance of such heterostructures for microfabricated piezoelectric energy harvesters. In the first part of the paper, we investigate the epitaxial stacks through transmission electron microscopy and piezoelectric force microscopy studies to characterize in detail their crystalline structure. In the second part of the paper, we present the electrical characteristics of piezoelectric cantilevers based on these epitaxial PZT films. The performance of such cantilevers as vibration energy transducers is compared with other piezoelectric harvesters and indicates the potential of the epitaxial approach in the field of energy harvesting devices.

Vibration energy harvesters on plastic foil by lamination of PZT thick sheets

This paper presents a low-complexity and low temperature (85°C) fabrication process for vibration energy harvesters. The process employs lamination steps to transfer thinned PZT thick sheets onto flexible polymeric substrates, using dry film photoresist. The influence of geometrical parameters on the device performance were assessed by FEM simulations (using COMSOL) and supported by experiments. Optimization of the output power was performed by modifying the neutral plane within the device and by using a localized seismic mass at the tip, which has resulted in an output power of 30 μW at 52 Hz and an acceleration of 1g. Finally, a low-complexity and fully polymeric package is proposed, which together with the harvester process are compatible with large area fabrication methods.