Vibration energy harvesting is receiving a considerable amount of interest as a means for powering wireless sensor nodes This paper presents a small (component volume 01 cm3, practical volume 015 cm3) electromagnetic generator utilizing discrete components and optimized for a low ambient vibration level based upon real application data The generator uses four magnets arranged on an etched cantilever with a wound coil located within the moving magnetic field Magnet size and coil properties were optimized, with the final device producing 46 µW in a resistive load of 4 k? from just 059 m s-2 acceleration levels at its resonant frequency of 52 Hz A voltage of 428 mVrms was obtained from the generator with a 2300 turn coil which has proved sufficient for subsequent rectification and voltage step-up circuitry The generator delivers 30% of the power supplied from the environment to useful electrical power in the load This generator compares very favourably with other demonstrated examples in the literature, both in terms of normalized power density and efficiency

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A micro electromagnetic generator for vibration energy harvesting

Vibration energy harvesting is an attractive technique for potential powering of wireless sensors and low power devices. While the technique can be employed to harvest energy from vibrations and vibrating structures, a general requirement independent of the energy transfer mechanism is that the vibration energy harvesting device operate in resonance at the excitation frequency. Most energy harvesting devices developed to date are single resonance frequency based, and while recent efforts have been made to broaden the frequency range of energy harvesting devices, what is lacking is a robust tunable energy harvesting technique. In this paper, the design and testing of a resonance frequency tunable energy harvesting device using a magnetic force technique is presented. This technique enabled resonance tuning to ±20% of the untuned resonant frequency. In particular, this magnetic-based approach enables either an increase or decrease in the tuned resonant frequency. A piezoelectric cantilever beam with a natural frequency of 26 Hz is used as the energy harvesting cantilever, which is successfully tuned over a frequency range of 22‐32 Hz to enable a continuous power output 240‐280 μW over the entire frequency range tested. A theoretical model using variable damping is presented, whose results agree closely with the experimental results. The magnetic force applied for resonance frequency tuning and its effect on damping and load resistance have been experimentally determined. (Some figures in this article are in colour only in the electronic version)

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A vibration energy harvesting device with bidirectional resonance frequency tunability

Power harvesting refers to the practice of acquiring energy from the environment which would be otherwise wasted and converting it into usable electric energy. Much work has been done on studying the optimal AC power output, while little has considered the AC–DC output. This article investigates the optimal AC–DC power generation for a rectified piezoelectric device. In contrast with estimates based on various degrees of approximation in the recent literature, an analytic expression for the AC–DC power output is derived under steady-state operation. It shows that the harvested power depends on the input vibration characteristics (frequency and acceleration), the mass of the generator, the electrical load, the natural frequency, the mechanical damping ratio and the electromechanical coupling coefficient of the system. An effective power normalization scheme is provided to compare the relative performance and efficiency of devices. The theoretical predictions are validated and found to be in good agreement with both experimental observations and numerical simulations. Finally, several design guidelines are suggested for devices with large coupling coefficient and quality factor.

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Analysis of power output for piezoelectric energy harvesting systems

This paper presents an electromagnetic based generator which is suitable for supplying generating power from human body motion and has application in providing energy for body worn sensors or electronics devices. A prototype generator has been built and tested both by a shaker at resonance condition and also by human body motion during walking and slow running. The experimental results will show that the prototype could generate 300 μW to 2.5 mW power from human body motion. The measured results are analyzed and compared with the theoretical model.

Electromagnetic generator for harvesting energy from human motion

This paper reviews the development of energy harvesting for low-power embedded structural health monitoring (SHM) sensing systems. A statistical pattern recognition paradigm for SHM is first presented and the concept of energy harvesting for embedded sensing systems is addressed with respect to the data acquisition portion of this paradigm. Next, various existing and emerging sensing modalities used for SHM and their respective power requirements are summarized followed by a discussion of SHM sensor network paradigms, power requirements for these networks, and power optimization strategies. Various approaches to energy harvesting and energy storage are discussed and limitations associated with the current technology are addressed. The paper concludes by defining some future research directions that are aimed at transitioning the concept of energy harvesting for embedded SHM sensing systems from laboratory research to field-deployed engineering prototypes. Finally, it is noted that many of the technologies discussed herein are applicable to powering any type of low-power embedded sensing system regardless of the application.

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Energy Harvesting for Structural Health Monitoring Sensor Networks

Advances in low power design open the possibility to harvest energy from the environment to power electronic circuits. Electrical energy can be harvested from various transducers including piezoelectric materials. Piezoelectric materials can be used as mechanisms to transfer mechanical energy usually ambient vibration into electrical energy that can be stored and used to power other devices. It has been found that a piezoelectric device attached to a beam with cantilever boundary conditions provides an effective configuration for capturing transverse vibrations and converting them into useful electrical power. Piezoelectric thin films attached to a silicon beam also have attracted attention for energy harvesting applications. In this paper, we present the results of a preliminary study of the effect of vibration amplitude on the performance of a PMN-PT single crystal beam with interdigitated electrodes pattern. The structure is used to demonstrate that feasibility of a novel piezoelectric monomorph cantilever beam for producing high AC voltage. The energy harvesting capability of a PMN-PT cantilever beam is tested on a 10mm-long and 1.2mm-wide rectangular prototype made out of 0.1mm-thick PMN-PT film with interdigitated electrodes. The experiments are performed to test the level of AC voltage and current generated from the PMN-PT cantilever beam device when subjected to transverse vibration of varying amplitude at the first mode of the resonant frequency. The frequency response of the monomorph prototype shows that the first mode resonance frequency of the excitation model is approximately 190Hz. We found that increasing the poling voltage also causes increased output AC voltage magnitude. These tests show that a significantly high AC voltage of 13V was achieved with 50μm shaker displacement. The measured RMS current was ~20μA.

Single crystal piezoelectric transducers to harvest vibration energy

We report on the use of single-crystal lead zinc niobate-lead titanate films in monomorph actuators. The article responds to the growing interest in solid-solution (1 m x )Pb(Zn 1/3 Nb 2/3 )O 3 - x PbTiO 3 relaxor ferroelectrics based on their large piezoelectric coefficients and their integration into microelectromechanical system. Freestanding films are fabricated by slicing a 7 w m-thick layer off the crystal bulk and assembled into a flexural actuator, thus circumventing polycrystalline deposition techniques. One-micron deflections are observed at 100 V for ∼1 mm-long films. The article discusses the non-uniform electric field distribution profile established in the films and its role in the actuation process.

PZN-PT Single-Crystal Thin Film Monomorph Actuator

We report on the fabrication and performance of (1-x) Pb(Zn/sub 1/3/Nb/sub 2/3/)O/sub 3/-xPbTiO/sub 3/ (PZN-PT) single-crystal relaxor piezoactuators with interdigitated electrodes patterned on a single surface. An electric field gradient across the sample thickness induces a differential contraction between opposite faces, and it is responsible for the actuation. The samples are poled by energizing the electrodes at 100/spl deg/C and cooling in a field. Calculations of the piezoelectric response based on a periodically modulated dipolar field yield good agreement with experiment. Discrepancies with the model are ascribed to multidomain formation in the ferroelectric sample as a result of field reversals in the applied electric field along the sample length.

Single-crystal relaxor ferroelectric piezoactuators with interdigitated electrodes

A smart cantilever structure using single-crystal relaxor ferroelectric material is presented. The smart cantilever possesses both sensing and actuation capabilities, embedded in a monomorph and resulting in a smart structure. Single crystal relaxor ferroelectric materials (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 (PZN-PT) and (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) are ideal for actuator and sensor applications since they exhibit very high piezoelectric coefficients. We separately pattern interdigitated electrodes on the top and bottom surfaces of a single crystal cantilever beam. The interdigitated electrode design results in an electric field- gradient that after poling not only induces flapping actuation but also, simultaneously, allows us to detect internally or externally induced stresses. As a monolithic actuator integrated with a sensor, it has potential applications in various Micro-Electro-Mechanical Systems (MEMS), Scanning Probe Microscopy (SPM) and Near-field Scanning Optical Microscopy (NSOM). We fabricate monomorph prototypes and characterize their performance in terms of actuation displacement and sensing capabilities, respectively. Finally, an active vibration control experiment was successfully conducted by using the smart cantilever structure.

Design and performance of a self-sensing, self-actuating piezoelectric monomorph with interdigitated electrodes

In this paper, the design and the fabrication of novel devices using single crystal lead zinc niobate-lead titanate (1 − x)Pb(Zn 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PZN-PT) and lead magnesium niobate-lead titanate (1 − x)Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PMN-PT) are presented. Piezoelectric biosensors using PZN-PT and PMN-PT are discussed. These single-crystal sensors improve on the existing detection sensitivity of quartz or silicon based devices. The biosensors can be miniaturized through the fabrication of freestanding single crystal films and patterning by ion milling and argon-ion laser etching. A smart cantilever structure using PZN-PT and PMN-PT is also presented. This device possesses both sensing and actuation capabilities, in a single monomorph configuration. Finally, a PMN-PT energy harvester with interdigitated electrodes is demonstrated. The device converts mechanical vibration energy into electrical energy through the piezoelectric effect. A simple PMN-PT energy harvesting beam is integrated into an e...

Yong K. Hong

Papers

Single crystal piezoelectric transducers to harvest vibration energy

PZN-PT Single-Crystal Thin Film Monomorph Actuator

Single-crystal relaxor ferroelectric piezoactuators with interdigitated electrodes

Design and performance of a self-sensing, self-actuating piezoelectric monomorph with interdigitated electrodes

Single-Crystal Film Piezoelectric Sensors, Actuators and Energy Harvesters with Interdigitated Electrodes