Steven R. Anton

A review of power harvesting using piezoelectric materials (2003-2006)

The field of power harvesting has experienced significant growth over the past few years due to the ever-increasing desire to produce portable and wireless electronics with extended lifespans. Current portable and wireless devices must be designed to include electrochemical batteries as the power source. The use of batteries can be troublesome due to their limited lifespan, thus necessitating their periodic replacement. In the case of wireless sensors that are to be placed in remote locations, the sensor must be easily accessible or of a disposable nature to allow the device to function over extended periods of time. Energy scavenging devices are designed to capture the ambient energy surrounding the electronics and convert it into usable electrical energy. The concept of power harvesting works towards developing self-powered devices that do not require replaceable power supplies. A number of sources of harvestable ambient energy exist, including waste heat, vibration, electromagnetic waves, wind, flowing water, and solar energy. While each of these sources of energy can be effectively used to power remote sensors, the structural and biological communities have placed an emphasis on scavenging vibrational energy with piezoelectric materials. This article will review recent literature in the field of power harvesting and present the current state of power harvesting in its drive to create completely self-powered devices.

Frequency Self-tuning Scheme for Broadband Vibration Energy Harvesting

The recent proliferation of microscale devices has raised the issue of energy harvesting for replacing batteries that present maintenance and recycling problems. Particularly, piezoelectric seismic microgenerators offer the advantages of easy maintenance and high power output, but are very sensitive to frequency drifts that can dramatically decrease their performance. The purpose of the present article is to expose a technique to ensure that the harvester resonance frequency matches the base motion frequency, without any external intervention. The principles of the proposed method rely on ultralow-cost frequency sensing combined with an energy-efficient stiffness tuning, through the use of an additional actuator. Experimental results carried out to validate the model show that such an approach permits increasing the effective bandwidth of the structure by a factor of 4 in terms of mechanical vibrations and having a 100% frequency band gain in terms of total power output of the device (i.e., taking into account the energy spent by the actuation). The total energy produced by the harvesting device, taking into account the actuation cost, is discussed as well.

Multifunctional self-charging structures using piezoceramics and thin-film batteries

Multifunctional material systems combine multiple functionalities in a single device in order to increase performance while limiting mass and volume. Conventional energy harvesting systems are designed to be added to a host structure in order to harvest ambient energy surrounding the system, but often cause undesirable mass loading effects and consume valuable space. Energy harvesting systems can benefit from the introduction of multifunctionality as a means of improving overall system efficiency. This paper presents the investigation of a novel multifunctional piezoelectric energy harvesting system consisting of energy generation, energy storage, and load bearing ability in a single device. The proposed self-charging structures contain piezoelectric layers for power generation, thin-film battery layers for energy storage, and a central metallic substrate layer, arranged in a bimorph configuration. Several aspects of the development and evaluation of the self-charging structure concept are reviewed. Details are provided on the fabrication of a piezoelectric self-charging structure. An electromechanical model is employed to predict the response of the harvester under harmonic base excitation. Experimentation is performed to confirm the ability of the device to simultaneously harvest and store electrical energy. Finally, both static and dynamic strength analyses are performed to determine the load bearing ability of the structure.

Reference-free damage detection using instantaneous baseline measurements

A novel method of guided wave-based structural health monitoring is developed in which no direct baseline data are required to identify structural damage. Conventional wave propagation structural health monitoring techniques involve the comparison of structural response data to a prerecorded baseline or reference measurement taken while the structure is in pristine condition. The need to compare new data to a prerecorded baseline can present several complications, including data management issues and difficulty in accommodating the effects of varying environmental and operational conditions on the data. To address the complications associated with baseline comparison, this new method accomplishes reference-free damage detection by acquiring what is referred to as an instantaneous baseline measurement for analysis. The instantaneous baseline technique is validated through both analytical and experimental testing. Analytical tests show that the instantaneous baseline method is able to correctly identify simulated damage. It is found experimentally that nonpermanent damage in the form of removable putty as well as permanent damage in the form of corrosion and cuts are all identifiable in thin aluminum plate test structures without direct comparison to baseline data when implementing the instantaneous baseline method.

Vibration energy harvesting for unmanned aerial vehicles

Unmanned aerial vehicles (UAVs) are a critical component of many military operations. Over the last few decades, the evolution of UAVs has given rise to increasingly smaller aircraft. Along with the development of smaller UAVs, termed mini UAVs, has come issues involving the endurance of the aircraft. Endurance in mini UAVs is problematic because of the limited size of the fuel systems that can be incorporated into the aircraft. A large portion of the total mass of many electric powered mini UAVs, for example, is the rechargeable battery power source. Energy harvesting is an attractive technology for mini UAVs because it offers the potential to increase their endurance without adding significant mass or the need to increase the size of the fuel system. This paper investigates the possibility of harvesting vibration and solar energy in a mini UAV. Experimentation has been carried out on a remote controlled (RC) glider aircraft with a 1.8 m wing span. This aircraft was chosen to replicate the current electric mini UAVs used by the military today. The RC glider was modified to include two piezoelectric patches placed at the roots of the wings and a cantilevered piezoelectric beam installed in the fuselage to harvest energy from wing vibrations and rigid body motions of the aircraft, as well as two thin film photovoltaic panels attached to the top of the wings to harvest energy from sunlight. Flight testing has been performed and the power output of the piezoelectric and photovoltaic devices has been examined.

Piezoelectret foam–based vibration energy harvesting:

The use of energy harvesting to provide power to low-power electronic devices has the potential to create autonomous, self-powered electronics. This article presents the investigation of a novel material for vibration-based energy harvesting. Piezoelectret foam, a lead-free, polymer-based electret material exhibiting piezoelectric-like properties, is investigated for low-power energy generation. An overview of the fabrication and operation of piezoelectret foams is first given. Mechanical testing is then performed, where anisotropy in the principal length directions is found along with Young’s moduli between 0.5 and 1 GPa and tensile strengths from 35 to 70 MPa. Dynamic electromechanical characterization is performed in order to measure the piezoelectric d 33 coefficient of the foam over a wide frequency range. The d 33 coefficient is found to be relatively constant at around 175 pC/N from 10 Hz to 1 kHz. Finally, the foam is evaluated as an energy harvesting material by first developing an electromechanical model to predict the voltage response during excitation, then performing dynamic experimentation to measure the voltage frequency response with comparisons to modeling predictions for a set of electrical loads, and finally conducting energy harvesting experimentation in which the foam is used to charge a capacitor. Harmonic excitation of a pre-tensioned 15.2 cm × 15.2 cm sample at 60 Hz and displacement of ± 73 µm yields an average power of 6.0 µW delivered to a 1 mF storage capacitor. The capacitor is charged to 4.67 V in 30 min, proving the ability of piezoelectret foam to supply power to small electronic components.

Piezoelectric, solar and thermal energy harvesting for hybrid low-power generator systems with thin-film batteries

The harvesting of ambient energy to power small electronic components has received tremendous attention over the last decade. The research goal in this field is to enable self-powered electronic components for use particularly in wireless sensing and measurement applications. Thermal energy due to temperature gradients, solar energy and ambient vibrations constitute some of the major sources of energy that can be harvested. Researchers have presented several papers focusing on each of these topics separately. This paper aims to develop a hybrid power generator and storage system using these three sources of energy in order to improve both structural multifunctionality and system-level robustness in energy harvesting. A multilayer structure with flexible solar, piezoceramic, thin-film battery and metallic substructure layers is developed (with the overhang dimensions of 93 mm × 25 mm × 1.5 mm in cantilevered configuration). Thermal energy is also used for charging the thin-film battery layers using a 30.5 mm × 33 mm × 4.1 mm generator. Performance results are presented for charging and discharging of the thin-film battery layers using each one of the harvesting methods. It is shown based on the extrapolation of a set of measurements that 1 mA h of a thin-film battery can be charged in 20 min using solar energy (for a solar irradiance level of 223 W m −2 ), in 40 min using thermal energy (for a temperature difference of 31 ◦ C) and in 8hu sing vibrational energy (for a harmonic base acceleration input of 0.5g at 56.4 Hz).

Multifunctional Unmanned Aerial Vehicle Wing Spar for Low-Power Generation and Storage

DOI: 10.2514/1.C031542 This paper presents the investigation of a multifunctional energy harvesting and energy-storage wing spar for unmanned aerial vehicles. Multifunctional material systems combine several functionalities into a single device in order to increase performance while limiting mass and volume. Multifunctional energy harvesting can be used to provide power to remote low-power sensors on unmanned aerial vehicles, where the added weight or volume of conventional harvesting designs can hinder flight performance. In this paper, a prototype self-charging wing spar containing embedded piezoelectric and battery elements is modeled, fabricated, and tested to evaluate its energy harvesting and storage performance. A coupled electromechanical model based on the assumed modes method is developedtopredictthevibrationresponseandvoltageresponseofacantileveredwingsparexcitedunderharmonic base excitation. Experiments are performed on a representative self-charging wing spar, and the results are used to verify the electromechanical model. The power-generation performance of the self-charging wing spar is investigatedindetailforharmonicexcitationinclamped–freeboundaryconditions.Experimentsarealsoconducted to demonstrate the ability of the wing spar to simultaneously harvest and store electrical energy in a multifunctional manner.Itisshownthat,foraninputbaseaccelerationlevelof0:25 gat28.4Hzatthebaseofthestructure,1.5mW of regulated dc power isdelivered from the piezoelectric layers to the thin-film battery, resulting in a stored capacity of 0.362 mAh in 1 h.

An evaluation on low-level vibration energy harvesting using piezoelectret foam

Energy harvesting technology is critical in the development of self-powered electronic devices. Over the past few decades, several transduction mechanisms have been investigated for harvesting various forms of ambient energy. This paper provides an investigation of a novel transducer material for vibration energy harvesting; piezoelectret foam. Piezoelectrets are cellular ferroelectret foams, which are thin, flexible polymeric materials that exhibit piezoelectric properties. The basic operational principle behind cellular ferroelectrets involves the deformation of internally charged voids in the polymer, which can be represented as macroscopic dipoles, resulting in a potential developed across the material. Both the mechanical and electromechanical properties of this material are investigated in this work. Mechanical testing is performed using traditional tensile testing techniques to obtain experimental measures of the stiffness and strength of the materials. Electromechanical testing is performed in order to establish a relationship between input mechanical energy and output electrical energy by dynamically measuring the piezoelectric constant, d33. Additionally, the properties of ferroelectret foams are compared to those of polyvinylidene fluoride (PVDF), a conventional polymer-based piezoelectric material whose crystalline phase exhibits piezoelectricity through dipole orientation. Finally, the feasibility of vibration energy harvesting using piezoelectret materials is investigated.

Bending strength of piezoelectric ceramics and single crystals for multifunctional load-bearing applications

The topic of multifunctional material systems using active or smart materials has recently gained attention in the research community. Multifunctional piezoelectric systems present the ability to combine multiple functions into a single active piezoelectric element, namely, combining sensing, actuation, or energy conversion ability with load-bearing capacity. Quantification of the bending strength of various piezoelectric materials is, therefore, critical in the development of load-bearing piezoelectric systems. Three-point bend tests are carried out on a variety of piezoelectric ceramics including soft monolithic piezoceramics (PZT-5A and PZT-5H), hard monolithic ceramics (PZT-4 and PZT-8), single-crystal piezoelectrics (PMN-PT and PMN-PZT), and commercially packaged composite devices (which contain active PZT-5A layers). A common 3-point bend test procedure is used throughout the experimental tests. The bending strengths of these materials are found using Euler-Bernoulli beam theory to be 44.9 MPa for PMN-PZT, 60.6 MPa for PMN-PT, 114.8 MPa for PZT- 5H, 123.2 MPa for PZT-4, 127.5 MPa for PZT-8, 140.4 MPa for PZT-5A, and 186.6 MPa for the commercial composite. The high strength of the commercial configuration is a result of the composite structure that allows for shear stresses on the surfaces of the piezoelectric layers, whereas the low strength of the single-crystal materials is due to their unique crystal structure, which allows for rapid propagation of cracks initiating at flaw sites. The experimental bending strength results reported, which are linear estimates without nonlinear ferroelastic considerations, are intended for use in the design of multifunctional piezoelectric systems in which the active device is subjected to bending loads.