Helicopters suffer from a number of problems raised from the high vibratory loads, noise generation, load capacity limitations, forward speed limitation etc. Especially unsteady aerodynamic conditions due to the different aerodynamic environment between advised and retreating side of the rotor cause most of these problems. Researchers study on passive and active methods to eliminate negative effects of aerodynamic loads. Nowadays, active methods such as Higher Harmonic Control (HHC), Individual Blade Control (IBC), Active Control of Structural Response (ACSR), Active Twist Blade (ATB), and Active Trailing-edge Flap (ATF) gain importance to vibration and noise reduction. In this paper, strain-induced blade twist control is studied integrated by Macro Fiber Composite (MFC) actuator. 3D model is presented to analyze the twisting of a morph and bimorph helicopter rotor blade comprising MFC actuator which is generally applied vibration suppression, shape control and health monitoring. The helicopter rotor blade is modeling with NACA23012 airfoil type and consists of D-spar made of unidirectional fiberglass, ±45° Glass Fiber Reinforced Polymer (GFRP) and foam core. Two-way fluid-structure interaction (FSI) method is used to simulate loop between fluid flow and physical structure to enable the behavior of the complex system. To develop piezoelectric effects, thermal strain analogy based on the similarities between thermal and piezo strains. The optimization results are obtained to show the influence of different design parameters such as web length, spar circular fitting, MFC chord length on active twist control. Also, skin thickness, spar thickness, web thickness are used to optimization parameters to illustrate effects on torsion angle by applying response surface methodology. Selection of correct design parameters can then be determined based on this system results.

This article illustrates an approach to develop innovative smart materials based on carbon fiber composites. The proposed approach relies on the use of ultra-light strain sensors that are embedded into the composite and are adopted to monitor in real-time the actual material configuration. Such sensors are composed of electrospun PVDF fibers that exploit piezoelectricity to identify strain and thanks to their extreme lightweight can easily be embedded within the composite layers without affecting the structural integrity. On the other hand, the composite is equipped with a system of internal distributed heaters that can locally and globally vary the composite temperature. Since the adopted epoxy has a considerable temperature-dependent behaviour, it is possible to control its stiffness and thus to control the structural frequencies and damping. By coupling the sensing system with the control system, the structural properties are tuned to match prescribed working conditions, thus optimizing the performance of the proposed smart system. The proposed approach is investigated experimentally by manufacturing prototypes of the smart composite and by performing multiple tests to study the material response and evaluate the obtained performance.

A piezoelectric-coupled finite element model for a THUNDER harvester (THin layer UNimorph DrivER) is developed and studied in this work. THUNDER is a curved piezoelectric energy generator developed by NASA Langley Research Center, which has better vibration absorption and higher energy recovery efficiency at low-frequency vibration compared to a flat PZT harvester. To apprehend the piezoelectric effect of the THUNDER harvester, finite element method was used to perform the piezoelectric coupled field analysis. Piezoelectric THUNDER harvester was studied under cantilever boundary condition. In the model, the excitation forces are distribution force allied on the top of the dome line. An electric circuit element was used to create load resistance across the electrodes to obtain the generated voltage and power. The effect of the geometric parameter was investigated via the varying radius of curvature, which affects the resonance frequency, voltage, and power output of the THUNDER. Good agreement between finite element analysis and experimental results were also observed. In finite element analysis: Modal analysis was carried out to find the resonance frequency at which maximum performance characteristics of the THUNDER can be achieved. Then, the harmonic analysis was performed to distinguish the voltage and power output variation as the load resistance changes. The effects of the varying radius of curvature on the power efficiency of the THUNDER were summarized.

This paper proposes a novel idea of a combined piezoelectric energy harvesting and torsional vibration absorber for rotating system. In particular, among possible alternative solutions for durable power sources useable in mechanical components, vibration represents a suitable method for the amount of power required to feed a wireless sensor network. For this purpose energy harvesting from structural vibration has received much attention in the past few years. Suitable vibration can be found in numerous mechanical environments including automotive moving structures, household applications, but also buildings and bridges. Similarly, a dynamic vibration absorber (DVA) is one of the most used devices to mitigate the vibration structures. This device is used to transfer the primary structural vibration to the auxiliary system. Thus, vibration energy is effectively localized in the secondary less sensitive structure and it can be harvested. This paper describes the design process of an energy harvesting tuned vibration absorber for rotating system using piezoelectricity components. Instead of being dissipated as heat, the energy of vibration is converted into electricity. The device proposed is designed to mitigate torsional vibrations as a rotational vibration absorber and to harvest energy as a power source for immediate use. The initial rotational multi degree of freedom system is initially reduced in equivalent single degree of freedom (SDOF) systems. An optimization method is used for evaluating the optimal mechanical parameters of the initial absorber for the SDOF systems defined. The design is modified for the integration of the active patches without detuning the absorber. In order to estimate the real power generated, a complex storage circuit is implemented. A fixed voltage is obtained as output. Through the introduction of a big capacitor, the energy stored is measured at different frequencies. Finally, the simultaneously achievement of the vibration reduction function and the energy harvesting function is evaluated.

This manuscript investigates energy harvesting from arterial blood pressure via the piezoelectric effect for the purpose of powering embedded micro-sensors in the human brain. One of the major hurdles in recording and measuring electrical data in the human nervous system is the lack of implantable and long term interfaces that record neural activity for extended periods of time. Recently, some authors have proposed micro sensors implanted deep in the brain that measure local electrical and physiological data which is then communicated to an external interrogator. This paper proposes a way of powering such interfaces. The geometry of the proposed harvester consists of a piezoelectric, circular, curved bimorph that fits into the blood vessel (specifically, the Carotid artery) and undergoes bending motion because of blood pressure variation. In addition, the harvester thickness is constrained such that it does not modify arterial wall dynamics. This transforms the problem into a known strain problem and the integral form of Gauss’s law is used to obtain an equation relating arterial wall motion to the induced voltage. The theoretical model is validated by means of a Multiphysics 3D-FEA simulation comparing the harvested power at different load resistances. The peak harvested power achieved for the Carotid artery (proximal to Brain), with PZT-5H, was 11.7 μ W. The peak power for the Aorta was 203.4 μ W. Further, the variation of harvested power with variation in harvester width and thickness, arterial contractility and the pulse rate is investigated. Moreover, potential application of the harvester as a chronic, implantable and real-time Blood pressure sensor is considered. Energy harvested via this mechanism will also have applications in long-term, implantable Brain Micro-stimulation.

We explore the modeling and analysis of nonlinear non-conservative dynamics of macro-fiber composite (MFC) piezo-electric structures, guided by rigorous experiments, for resonant vibration-based energy harvesting, as well as other applications leveraging the direct piezoelectric effect, such as resonant sensing. The MFCs employ piezoelectric fibers of rectangular cross section embedded in kapton with interdigitated electrodes to exploit the 33-mode of piezoelectricity. Existing frameworks for resonant nonlinearities have so far considered conventional piezoceramics that use the 31-mode of piezoelectricity. In the present work, we develop a framework to represent and predict nonlinear electroelastic dynamics of MFC bimorph cantilevers under resonant base excitation. The interdigitated electrodes are shunted to a set of resistive electrical loads to quantify the electrical power output. Experiments are conducted on a set of MFC bimorphs over a broad range of mechanical excitation levels to identify the types of nonlinearities present and to compare the model predictions and experiments. The experimentally observed interaction of material softening and geometric hardening effects, as well as dissipative effects, is captured and demonstrated by the model.

The Maximum Entropy (ME) method is shown to provide a new approach for quantifying model uncertainty in the presence of complex, heterogeneous data. This is important in model validation of a variety of multifunctional constitutive relations. For example, multifunctional materials contain field-coupled material parameters that should be self-consistent regardless of the measurement. A classical example is piezoelectricity which may be quantified from charge induced by stress or strain induced by an electric field. The proposed tools provide new statistical information to address measurement discrepancies, guide model development, and catalyze materials discovery for data fusion problems. The error between the model outputs and heterogeneous data is quantified and used to formulate a second moment constraint within the entropy functional. This leads to an augmented likelihood function that weights each individual set of data by its respective variance and covariance between each data set. As a first step, the method is evaluated on a piezoelectric ceramic to illustrate how the covariance matrix influences piezoelectric parameter estimation from heterogeneous electric displacement and strain data.

Macro-fiber composite (MFC) piezoelectric materials are used in a variety of applications employing the converse piezo-electric effect, ranging from bioinspired actuation to vibration control. Most of the existing literature to date considered linear material behavior for geometrically linear oscillations. However, in many applications, such as bioinspired locomotion using MFCs, material and geometric nonlinearities are pronounced and linear models fail to represent and predict the governing dynamics. The predominant types of nonlinearities manifested in resonant actuation of MFC cantilevers are piezoelectric softening, geometric hardening, inertial softening, as well as internal and external dissipative effects. In the present work, we explore nonlinear actuation of MFC cantilevers and develop a mathematical framework for modeling and analysis. An in vacuo actuation scenario is considered for a broad range of voltage actuation levels to accurately identify the sources of dissipation. Several experiments are conducted for an MFC bimorph cantilever, and model simulations are compared with nonlinear experimental frequency response functions under resonant actuation. The resulting experimentally validated framework can be used for simulating the dynamics of MFCs under resonant actuation, as well as parameter identification and structural optimization for nonlinear operation regime.

We present a distributed-parameter electromechanical model and its modal analysis for flexoelectric energy harvesting using centrosymmetric dielectrics by accounting for both the direct and converse effects as well as size dependence of the coupling coefficient. Flexoelectricity is the generation of electric polarization in elastic dielectrics by the application of a non-uniform mechanical strain field, i.e. a strain gradient. In order to accompany atomistic simulations and experimental efforts at small scales, there is a growing need for high-fidelity device models that can also provide an analytical insight into size-dependent electro-elastodynamics of small structures that exhibit and exploit flexoelectricity. Particularly, although the conversion of mechanical energy into electrical energy (i.e. energy harvesting) is more related to the direct effect, it is necessary to accurately model the converse effect for thermodynamic consistency and completeness. To this end, we present a flexoelectric monolayer centrosymmetric energy harvester model (that yields no piezoelectric effect) for converting ambient vibration into electricity. The flexoelectric energy harvester model based on the Euler-Bernoulli beam theory is focused on strain gradient-induced polarization resulting from the bending (transverse) vibration modes in response to mechanical base excitation. Following recent efforts on the converse flexoelectric effect in finite samples, the proposed model accounts for two-way coupling, i.e. the direct and converse effects, and it also captures the effect of geometric scaling on the coupling coefficient. In addition to closed-form solutions of the electromechanical frequency response functions, various case studies are presented for a broad range of material and geometric parameters. Thickness dependence of the electromechanical coupling is analytically shown and is observed in simulations of the electromechanical frequency response functions as well.

This paper uses the method of Quadratures in conjunction with the Maximum Entropy principle to investigate the effect of parametric uncertainties on the mean power output and root mean square deflection of piezoelectric vibrational energy harvesting systems. Uncertainty in parameters of harvesters could arise from insufficient manufacturing controls or change in material properties over time. We investigate bimorph based harvesters that transduce ambient vibrations to electricity via the piezoelectric effect. Three varieties of energy harvesters — Linear, Nonlinear monostable and Nonlinear bistable are considered in this research. This analysis quantitatively shows the probability density function for the mean power and root mean square deflection as a function of the probability densities of the excitation frequency, excitation amplitude, initial deflection of the bimorph and magnet gap of the energy harvester. The method of Quadratures is used for numerically integrating functions by propagating weighted points from the domain and evaluating the integral as a weighted sum of the function values. In this paper, the method of Quadratures is used for evaluating central moments of the distributions of rms deflection and mean harvested power and, then, in conjunction with the principle of Maximum Entropy (MaxEnt) an optimal density function is obtained which maximizes the entropy and satisfies the moment constraints. The The computed nonlinear density functions are validated against Monte Carlo simulations thereby demonstrating the efficiency of the approach. Further, the Maximum Entropy principle is widely applicable to uncertainty quantification of a wide range of dynamic systems.

This paper presents the self-powered active control of elastic and aeroelastic oscillations. A plate-like wing with two piezoelectric layers on the bottom surface and one piezoelectric layer on the top surface is modeled along with an electrical circuit. The direct piezoelectric effect of the bottom layer is used for mechanical to electrical energy conversion. The electrical circuit calculates the control voltage to be applied into the top piezoelectric layer that works as an actuator. The required actuation energy is fully supplied by the harvested energy. The control voltage is obtained from a Linear Quadratic Regulator (LQR) control law. Three cases are investigated. In the first one the harmonic base excitation of the cantilevered wing is considered, the suppression of flutter oscillations is investigated in the second case and the atmospheric turbulence induced vibrations problem is presented in the third case. The performance of the self-powered controller is similar to the performance of a conventional active controller with limited control voltage.

A novel cement-sand based piezoelectric smart composite was developed for structural health monitoring (SHM) in civil infrastructures. Most researches have focused on cement-based piezoelectric composites that are unrealistic in their applications due to their incompatibility with reinforced concrete with cement and sand. In this study, sand was applied to fabricate the composite to address the important issue. Two sets of specimens containing 30 vol% and 50 vol% lead zirconate titanate (PZT) were manufactured and their piezoelectric coefficient and dielectric constant were determined. The results showed that the piezoelectric effect and dielectric constant were enhanced with increasing PZT content. In addition, the sensing effect was conducted under compressive tests. The invesitigation demonstrated the feasibility of the new composite in its application to the SHM system.

The development of self-powered wireless microelectromechanical (MEMS) sensors hinges on the ability to harvest adequate energy from the environment. When solar energy is not available, mechanical energy from ambient vibrations, which are typically low frequency, is of particular interest. Here, higher power levels were approached by better coupling mechanical energy into the harvester, using improved piezoelectric layers, and efficiently extracting energy through the use of low voltage rectifiers. Most of the available research on piezoelectric energy harvesters reports Pb(Zr,Ti)O 3 (PZT) or AlN thin films on Si substrates, which are well-utilized for microfabrication. However, to be highly reliable under large vibrations and impacts, flexible passive layers such as metal foil with high fracture strength would be more desirable than brittle Si substrates for MEMS energy harvesting. In addition, metallic substrates readily enable tuning the resonant frequency down by adding proof masses. In order to extract the maximum power from such a device, a high level of (001) film orientation enables an increase in the energy harvesting figures of merit due to the coupling of strong piezoelectricity and low dielectric permittivity. Strongly {001} oriented PZT could be deposited by chemical solution deposition or RF magnetron sputtering and ex situ annealing on (100) oriented LaNiO 3 / HfO 2 / Ni foils. The comparatively high thermal expansion coefficient of the Ni facilitates development of a strong out-of-plane polarization. 31 mode cantilever beam energy harvesters were fabricated using strongly {001} textured 1∼3 μm thick PZT films on Ni foils with dielectric permittivity of ∼ 350 and low loss tangent (<2%) at 100 Hz. The resonance frequency of the cantilevers (50∼75 Hz) was tuned by changing the beam size and proof mass. A cantilever beam with 3 μm thickness of PZT film and 0.4 g proof mass exhibited a maximum output power of 64.5 μW under 1 g acceleration vibration with a 100 kΩ load resistance after poling at 50 V (E C ∼ 16 V) for 10 min at room temperature. Under 0.3g acceleration, the average power of the device is 9 μW at a resonance frequency of ∼70 Hz. Excellent agreement between the measured and modeled data was obtained using a linear analytical model for an energy harvesting system, using an Euler-Bernoulli beam model. It was also demonstrated that up to an order of magnitude more power could be harvested by more efficiently utilizing the available strain using a parabolic mode shape for the vibrating structure. Additionally, voltage rectifying electronics in the form of ZnO thin film transistors are deposited directly on the cantilever. This relieves the role of voltage rectification from the interfacing circuitry and provides a technique improved harvesting relative to solid state diode rectification because the turn-on bias can be reduced to zero.

Macro-fiber composite (MFC) actuators offer simple and scalable design, robustness, noiseless performance, strong electromechanical coupling, and particularly a balance between the actuation force and deformation capabilities, which is essential to effective and agile biomimetic locomotion. Recent efforts in our lab have shown that MFC bimorphs with polyester electrode sheets can successfully be employed for fish-like aquatic locomotion in both tethered and untethered operation. MFC swimmers can outperform other smart material-based counterparts, such as the compliant ionic polymer-metal composite based swimmers, in terms of swimming speed per body length. Cantilevered flaps made of MFC bimorphs with different aspect ratios can be employed for underwater actuation, sensing, and power generation, among other aquatic applications of direct and converse piezoelectric effects. In an effort to develop linearized electrohydroelastic models for such cantilevers, the present work investigates MFC bimorphs with three different aspect ratios. The MFCs used in this study use the 33-mode of piezoelectricity with interdigitated electrodes. Underwater dynamic actuation frequency response functions (FRFs) of the MFCs are defined as the tip velocity per actuation voltage (tip velocity FRF) and current consumption per actuation voltage (admittance FRF). The tip velocity and admittance FRFs are modeled analytically for in-air actuation and validated experimentally for all aspect ratios. Underwater tip velocity and admittance FRFs are then derived by combining their in-air counterparts with corrected hydrodynamic functions. The corrected hydrodynamic functions are also identified from aluminum cantilevers of similar aspect ratios. Both tip vibration and current consumption per voltage input are explored. The failure of Sader’s hydrodynamic function for low length-to-width aspect ratios is shown. Very good correlation is observed between model simulations and experimental measurements using aspect ratio-dependent, corrected hydrodynamic function.

In this paper, we demonstrate a novel miniature three-axis piezoelectric energy harvester. The energy harvester consists of four piezoelectric lead zirconate titanate cantilever beams, connector, proof mass, and mechanic frame. Through the connector, a special configuration with a well-constrained mechanism of the energy harvester is achieved. Due to the configuration/mechanism of the energy harvester, the Newton’s law of inertia and piezoelectric effect are utilized to convert the in-plane (either x-axis or y-axis) and out-of-plane (z-axis) environmental vibrations into voltage responses. This achieves energy harnessing from 3-axial environmental vibration.

In this paper, we demonstrate a magnetic/mechanical approach for optimizing a miniature self-powered current sensor. The sensor consists of a piezoelectric PZT sheet, CuBe cantilever beam, NdFeB magnet, and mechanical clamp. When the sensor is placed nearby an AC-current carrying wire from a breaker, the magnet fixed on the beam of the sensor experiences an alternative magnetic attractive and repulsive force produced by an AC magnetic field generated by the wire. Due to the alternative magnetic attractive and repulsive force, the magnet fixed on the beam is oscillated. The oscillating beam deforms the PZT sheet and subsequently produces strain in the PZT sheet. Due to the piezoelectric effect, the strain is converted to a voltage response. Through the optimized approach, the voltage output of the sensor is increased from 1.27 volts to 4.01 volts when the sensor is used to detect an AC current-carrying wire of 8 ampere at 60 Hz.

Lead zirconate titanate (PZT) and Shape memory alloys (SMA) smart composites have been previously investigated for use as actuators. SMAs exhibit a high actuating strain but responds slowly, while PZTs supply small actuation with a fast response. The composite can be tailored to control its shape when subjected to different loads, thus leading to multiple functions actuators. In this study, the concept is applied in the design of energy harvesting devices for self-tuning and control of the output response. The material type and the composite fractions properties can be optimized to tune the system’s response in order to achieve maximum output and to compensate for the external environmental effects such as temperature. In this paper, the energy harvesting capabilities of a cantilevered composite beam, containing piezoelectric ceramic and shape memory alloy cylindrical inclusions, are studied. The system is subject to base excitation input load. Only non-prestrained SMA inclusions are considered. A model based on the mean field theory, linear piezoelectricity, and one dimensional constitutive behavior of shape memory alloys is developed to describe the effect of SMA inclusions on the time and the frequency response of the composite. The PZT and the matrix behaviors are considered linear. The overall response of the composite is highly non-linear due to the phase transformation within the SMA inclusions. A preliminary analysis of the variations of the frequency response, the time response, the power output, and the efficiency of the device with respect to the materials fractions is presented. The temperature effects are also investigated.

Piezoelectric systems and structures have been used for decades in a variety of applications ranging from vibration control and sensing to morphing and energy harvesting. Conventional piezoelectric ceramics with uniform electrodes typically employ the 31-mode of piezoelectricity in bending, where the 3- and 1-directions are the directions of poling and strain, respectively. In order to employ the more effective 33-mode of piezoelectricity, Interdigitated Electrodes (IDEs) have been used recently in the design of the Macro-Fiber Composite (MFC). In this paper, an investigation into the two-way electroelastic coupling in bimorph cantilevers (in the sense of direct and converse piezoelectric effects) that employ IDEs for 33-mode operation is conducted. To this end, distributed-parameter electroelastic models are developed for the dynamic scenarios that involve two-way coupling, namely piezoelectric power generation and shunt damping as well as the problem of dynamic actuation. Various interdigitated MFC bimorph cantilevers are tested against the model under dynamic actuation, power generation, and shunt damping to identify their modal electromechanical coupling terms. Detailed investigations are conducted by decoupling the system dynamics to keep the direct and converse effects separately pronounced for parameter identification. Additionally, this work sheds light on the literature comparing the electrical power generation performances of 33-mode (interdigitated electrodes) and 31-mode (uniform electrodes) piezoelectric bimorphs of the same volume based on extensive experiments and distributed-parameter electroelastic modeling.

The prorogation of electro-magneto-elastic coupled shear-horizontal waves in one dimensional infinite periodic piezoelectric waveguides is considered within a full system of the Maxwell’s equations. Such setting of the problem allows to investigate the Bloch-Floquet waves in a wide range of frequencies. Two different conditions along the guide walls and three kinds of transmission conditions at the interfaces between the laminae of waveguides have been studied. Stop band structures have been identified for Bloch-Floquet waves both at acoustic and optical frequencies. The results demonstrate the significant effect of piezoelectricity on the widths of band gaps at acoustic frequencies and confirm that it does not affect the band structure at optical frequencies. The results show that under electrically shorted transmission conditions Bloch-Floquet waves exist only at acoustic frequencies. For electrically open interfaces the dynamic setting provides solutions only for photonic crystals. In this case the piezoelectricity has no effect on band gaps.

Piezoelectric energy harvesters have recently captured a lot of attention in research and technology. They employ the piezoelectric effect, which is the separation of charge within a material as a result of an applied strain, to turn what would otherwise be wasted energy into usable energy. This energy can then be used to support remote sensing systems, batteries, and other types of wireless MEMS devices. Such self powered systems are particularly attractive where hardwiring may not be feasible or numerous battery sources unreasonable. The source of excitation for these systems can include direct actuation, natural or mechanical vibrations, or fluid energy (aerodynamic or hydrodynamic). Fluid based energy harvesting is increasingly pursued due to the ubiquitous nature of the excitation source as well as the strong correlation with other types of excitation. Vortex-induced vibrations as well as vibrations induced by bluff bodies have been investigated to determine potential gains. The shape and size of these bluff bodies has been modeled in order to achieve the maxim power potential of the system. Other studies have focused on aeroelastic fluttering which relies on the natural frequency of two structural modes being achieved through aerodynamic forces. Rather than a single degree of freedom, as seen in the VIV approach, aeroelastic flutter requires two degrees of freedom to induce its vibrational state. This has been modeled through a wing section attached to a cantilevered beam via a revolute joint. To accurately model the behavior of these systems several types of dampening must be considered. Fluid flow excitation introduces the component of dampening via fluid dynamics in addition to structural dampening and electrical dampening from the piezoelectrics themselves. Air flow speed modifies the aerodynamic dampening and it has been shown that at the flutterer boundary the aerodynamic dampening dissipates while the oscillations remain. However, such a system state exhibits a decaying power output due to the shunt dampening effect of the power generation itself. Research in energy harvesting is quickly progressing but much has yet to be discovered. The focus of this paper will be fluid as a source of excitation and the development that has followed thus far. Configurations and applications of previous works will be examined followed by suggestions of new research works to move forward in the field.