Liquid metal (LM) alloys such as eutectic gallium indium (EGaIn) and gallium-indium-tin (Galinstan) have been used in the fabrication of soft and stretchable electronics during the past several years. The liquid-phase and high electrical conductivity of these materials make them one of the best candidates for fabrication of deformable electronics and multifunctional material systems. While liquid metals are highly reliable for fabrication of simple circuits and stretchable microfluidic devices, their application for producing complex circuits faces fabrication challenges due to their high surface tension and surface oxidization. In this study, we propose a scalable, cost-effective, and versatile technique to print complex circuits using silver nanoparticles and transform them into stretchable electronics by incorporating eutectic gallium indium alloys to the circuit. As a result, the deposited liquid metal considerably increases the electrical conductivity and stretchability of the fabricated electronics. The reliability and performance of these stretchable conductors are demonstrated by studying their electromechanical behavior and integrating them into skin-like electronics, termed electronic tattoos.

Computational modeling, instrumented linkages, optical technologies, MRI, and radiographic techniques have been widely used to study knee motion after total knee replacement (TKR) surgery. Information provided by these methods has helped designers to develop implants with better clinical performance and surgeons to obtain an improved understanding of the stability and mobility of the joint. Correspondingly, overall patient satisfaction with respect to the reduction in pain and recovery of normal functioning of the joint has been improving. However, about 20% of patients are still not fully satisfied with their surgical outcomes. The main obstacle in the current state-of-the-art is that a comprehensive post-operative understanding of knee balance is still unavailable, mostly due to a lack of in vivo data collected from the joint after surgery. This work presents an attempt to develop a self-powered instrumented knee implant for in vivo data acquisition. The knee sensory system in this study utilizes several embedded piezoelectric transducers in the tibial bearing of the knee replacement in order to provide sensing and energy harvesting capabilities. Through a series of analytical modeling, finite element simulation, and experimental testing, the performance of the suggested system is evaluated and a dimensionally optimized design of an instrumented TKR is achieved. More specifically, a comprehensive platform is established in order to combine the knowledge of embedded piezoelectric sensors and energy harvesters, musculoskeletal modeling of the knee joint, multiphysics finite element modeling, additive manufacturing techniques, image processing, and experimental knee loading simulation in order to achieve the experimentally validated and optimized instrumented knee implant design. The cumulative work presented in this article encompasses three main studies performed on the sensing performance of the proposed design: first, preliminary parametric studies of the effect of local dimensional and material parameters on the electromechanical behavior of the embedded sensory system; second, investigation of the ability to sense total force and center of pressure location; and third, evaluation of an enhanced system with the ability to sense compartmental forces and contact locations. Additionally, the energy harvesting capacity of the system is investigated to ensure the achievement of a fully self-powered sensory system. Results obtained from the experimental analysis of the system demonstrate the successful sensing and energy harvesting performance of the designs achieved in this study.

Ferroelectric materials exhibit strong electromechanical behavior which has led to the production of a wide variety of adaptive structures and intelligent systems, ranging from structural health monitoring sensors, energy harvesting circuits, and flow control actuators. Given the large number of applications, accurate prediction of ferroelectric materials constitutive behavior is critical. This presents many challenges, including the need to predict behavior from electronic structures up to macroscropic continuum. Many of the structure-property relations in these materials can be accurately calculated using density functional theory (DFT). However, DFT is not necessarily conducive to the large scale computations required to solve these problems on a continuum scale. Introducing a phase field polarization order parameter is an alternative approach, which provides a means to simulate the length scale gap between nano- and microscale domain structure evolution. The introduction of the phase field approximation results in uncertainty. Bayesian statistical analysis is an ideal tool for quantifying the uncertainty associated with the continuum phase field model parameters. Analyses of monodomain structures allows for identification of Landau energy and electrostrictive stress parameters. Identifying the exchange parameters, which are proportional to the polarization gradients, requires consideration of polydomain structures. This is a nontrivial problem as domain wall structures are fully coupled between the Landau energy, electrostrictive, and exchange parameters. Accurately quantifying the uncertainty in the phase field parameters will provide insight into the nonlinear constitutive behavior.

Electret based energy scavenging devices utilize electro-static induction to convert mechanical energy into electrical energy. Uses for these devices include harvesting ambient energy in the environment and acting as sensors for a range of applications. These types of devices have been used in MEMS applications for over a decade. However, recently there is an interest in triboelectric generators/harvesters, i.e., electret based harvesters that utilize triboelectrification as well as electrostatic induction. The literature is filled with a variety of designs for the latter devices, constructed from materials ranging from paper and thin films; rendering the generators lightweight, flexible and inexpensive. However, most of the design of these devices is ad-hoc and not based on exploiting the underlying physics that govern their behavior; the few models that exist neglect the coupled electromechanical behavior of the devices. Motivated by the lack of a comprehensive dynamic model of these devices this manuscript presents a generalized framework based on a Lagrangian formulation to derive electromechanical equation for a lumped parameter dynamic model of an electret-based harvester. The framework is robust, capturing the effects of traditional MEMS devices as well as triboelectric generators. Exploiting numerical simulations the predictions are used to examine the behavior of electret based devices for a variety of loading conditions simulating real-world applications such as power scavengers under simple harmonic forcing and in pedestrian walking.

The unique micro/nano-structure of an intrinsically conducting polymer can be tuned to get higher gauge factors (GF) and reliability, which make them better materials for piezo-resistive applications than conducting carbon based composites and metallic composites. This work reports a highly sensitive conducting polyaniline (PANI)-based composite film that showed a GF ∼66. This high GF was achieved by forming a particular microstructure of conducting PANI particles in a free standing film of PANI-DBSA/EVA. The paper also attempts to explain the mechanism for the observed high sensitivity using the electronic percolation theory, shape and size of the conducting particles and the changes in the microstructure, due to strain. The high sensitivity, high stability during cyclic loading and low electrical hysteresis together with high mechanical strength make PANI-DBSA/EVA conducting composite film a promising material for piezo-resistive strain sensing applications.

EAP based actuator technologies are extensively studied to design smart/intelligent systems ranging from deployable space structures, morphing wings, to medical devices and artificial muscles. Despite the extensive research on electroactive polymers (EAP), practical implementation of this technology is slow because of low induced forces and defect-driven premature electrical breakdown. Multilayered or stacked configuration can address the low induced force issue. However, construction procedure of multilayered sample is susceptible to more defects, which can further aggravate defect-driven premature breakdown of EAP actuators. Reducing the number of defects using self-clearing concept can improve the EAP actuators’ ability to withstand high electric fields. Self-clearing refers to the partial local breakdown of dielectric medium due to the presence of impurities, which in turn results in the evaporation of some of the metalized electrodes. After this evaporation, the impurity is cleared and any current path would be safely cut off, which means the actuator continues to perform, albeit with a reduced actuation area due to electrode evaporation. In this paper we study the impact of self-clearing metalized silver electrodes on the electrical and electromechanical behavior of EAPs, more specifically P(VDF-TrFE-CTFE) terpolymer. First, we use Weibull statistics to systematically estimate the self-clearing/preconditioning field needed to clear the defects. Then electrical breakdown experiments are conducted with and without preconditioning the samples to investigate their effects on the breakdown strength of the EAP. Finally, we implement this self-clearing/preconditioning field on single and multilayered P (VDF-TrFE-CTFE) unimorph actuators and investigate the resulting electromechanical performance. Due to preconditioning of the actuators using self-clearing concept, the actuators endure higher electric fields compared to a control sample. Loss of capacitance occurs during self-clearing, which in turn affects the electromechanical performance of the actuator. For that reason, we also report on the blocked force of preconditioned and controlled actuators to evaluate and compare their electromechanical performance.

Metamaterials made from flexible structures with piezoelectric laminates connected to resonant shunt circuits can exhibit vibration attenuation properties similar to those of their purely mechanical locally resonant counterparts. Thus, in analogy to purely mechanical metamaterials, electroelastic metamaterials with piezoelectric resonators can exhibit vibration attenuation bandgaps. To enable the effective design of these locally resonant electroelastic metamaterials, the electromechanical behavior of the piezoelectric patches must be reconciled with the modal behavior of the electroelastic structure. To this end, we develop a novel argument for the formation of bandgaps in bimorph piezoelectric beams, relying on modal analysis and the assumption of infinitely many segmented shunted electrodes (unit cells) on continuous piezoelectric laminates bracketing a substrate. As a case study, the frequency limits of the locally resonant bandgap that forms from resonant shunting is derived, and a design guideline is presented to place the bandgap in a desired frequency range. This method can be easily extended to more general circuit impedances, and can be used to design shunt circuits to obtain a desired frequency response in the main structure.

Growing demands for Total Knee Arthroplasty (TKA) and also total knee revision surgery combined with the cost, risk, and complication of the surgery have led to numerus attempts to improve surgical techniques, implant design, and postoperative orthopedic therapies. Although abundant information about knee function and reaction forces and moments have been provided by researchers through biomechanical models, cadaver testing, in-vitro testing, and limited in-vivo measurements, rigorous real-time in-vivo data from knee implants is still required to improve the performance of TKAs. Instrumented knee implants using piezoelectric (PZT) transducers have promising potential to satisfy clinical needs in terms of continuous in-vivo data acquisition, self-powered operation, and retention of prevalent implant design, which can ultimately lead to improved patient satisfaction. In this study, a simplified Ultra High Molecular Weight (UHMW) Polyethylene TKA bearing geometry with an embedded PZT on the bottom surface is proposed and investigated to analyze sensing and power harvesting, and longevity of the conceptual design. As a result, this work is separated into two distinct sections. The first part provides an evaluation study on the performance of the design in terms of output voltage and power using both simulations and experimental tests. Finite element analysis (FEA) is employed to model the stress-strain behavior of the system and to develop effective force reaction on the PZT transducer. An analytical model is used to describe the electromechanical behavior of the PZT transducer under the effective force predicted by FEA, and the output voltage and power of the system are simulated. Furthermore, results obtained from modeling are validated through experimental compression testing using simulated gait conditions. Embedding a PZT element in the knee bearing may cause changes in stress distribution in UHMW and as a result the variation in the fatigue life of the bearings with encapsulated PZTs is considered as a remarkable factor to investigate. Therefore, in the second part of the work, a parametric study on the effect of dimensional parameters on the longevity and electromechanical performance of the design is performed. High cycle stress life of the polyethylene component with embedded PZT transducer as well as transferred force to the PZT and generated voltage under periodic knee load are studied. . The diameter and depth of the pocket machined in the UHMW bearing, the thickness ratio of the PZT element to the UHMW component, and modification of the contact edges inside the PZT pocket and PZT are considered as effective geometrical parameters on the fatigue life of the UHMW bearing and are studied individually. Two designs are investigated; the initial design with sharp corners and a revised design with filleted corners. The results show a significant fatigue life improvement by adding a fillet radius modification on the sharp corners of the UHMW and PZT components accompanied by a slight reduction in output voltage. The effect of pocket diameter is dependent on the geometry and for the initial design the fatigue life and output voltage increase when diameter increases. For the revised design, fatigue life decreases for large fillet radii and increases for small fillet radii and converge as diameter is increased, whereas the output voltage slightly increases with large pocket diameters. Pocket depth has a significant reverse effect on fatigue life and output voltage of the PZT, such that a 0.05 mm deeper pocket results in no force transfer and no voltage but improved fatigue life.

Dielectric Elastomers (DEs) are deformable dielectrics, which are currently used as active materials in mechatronic transducers, such as actuators, sensors and generators. Nonetheless, at the present state of the art, the industrial exploitation of DE-based devices is still hampered by the irregular electro-mechanical behavior of the employed materials, also due to the unpredictable effects of environmental changes in real world applications. In many cases, DE transducers are still developed via trial-and-error procedures rather than through a well-structured design practice, one reason being the lack of experimental data along with reliable constitutive parameters of many potential DE materials. Therefore, in order to provide the practicing engineer with some essential information, an open-access database for DE materials has been recently created and presented in [1]. Following the same direction, this paper addresses the temperature effect on the visco-hyperelastic behavior of two DE candidates, namely a natural rubber (ZRUNEK A1040) and a well-known acrylic elastomer (3M VHB 4905). Measurements are performed on pure shear specimens placed in a climactic chamber. Experimental stress-strain curves are then provided, which makes it possible to predict hyperelasticity, plasticity, viscosity, and Mullins effect as function of the environmental temperature. Properties of these commercial elastomeric membranes are finally entered in the database and made available to the research community.

Polyaniline (PANI) an electronically conducting polymer, and its charge transfer complexes are interesting engineering materials due to their unique electronic conductivity, electrochemical behavior, low raw material cost, ease of synthesis and environmental stability in comparison with other conjugated polymers. The main disadvantage of PANI is its limited processability. Blending of conducting polymers with insulating polymers is a good choice to overcome the processability problem. In this study a solution-blend method is adopted to prepare conductive polyaniline/polyvinyl alcohol (PANI/PVA) blend films at various blend ratios. Interest in applications for polyaniline (PANI) has motivated investigators to study its electro mechanical properties, and its use in polymer composites or blends with common polymers. The work described here looks at the uniaxial deformation behavior of the conducting polymer films and the anisotropic dependency of electrical conductivity of the blend films exposed to static and dynamic loading conditions. The relation between mechanical strain, electrical conductivity and film microstructure is investigated on PANI/PVA blend films.

Converting aeroelastic vibrations into electricity for low-power generation has received growing attention over the past few years. Helicopter blades with embedded piezoelectric elements can provide electrical energy to power small electronic components. In this paper, the non-linear modeling and analysis of an electromechanically coupled cantilevered helicopter blade is presented for piezoelectric energy harvesting. A resistive load is considered in the electrical domain of the problem in order to quantify the electrical power output. The non-linear electromechanical model is derived based on the Variational-Asymptotic Method (VAM). The coupled non-linear rotary system is solved in the time-domain. A generalized-α integration method is used to guarantee numerical stability, adding numerical damping at high frequencies. The electromechanical behavior of the coupled rotating blade is investigated for increasing rotating speeds (stiffening effect).

The trend towards higher reliance on fiber-reinforced composites for structural components has led to the need to rethink current nondestructive evaluation (NDE) strategies. In principle, embeddable sensor schemes are desired for green-light/red-light structural health monitoring systems that do not negatively affect the properties and performance of the host structure. However, there are still numerous challenges that need to be overcome before these embedded sensing technologies can be realized for real-world structural systems. For example, some of these issues and challenges include the damage detection sensitivity/threshold, reliability of the system, transportability of the system to multiple configurations and different types of structural components, and signal processing/interpretation. The objective of this study is to develop a novel, embedded sensing system that can accurately quantify damage to composites without interfering with structural performance and functionality. In particular, this study will utilize multi-walled carbon nanotube (MWNT)-polyelectrolyte (PE) thin films deposited on a glass fiber substrate for in situ composite structural monitoring. A layer-by-layer (LbL) film fabrication methodology is employed for depositing piezoresistive nanocomposites directly onto glass fiber fabrics, and the resulting film exhibits excellent strain sensing performance, homogeneity, and exhibits no phase segregation. Specifically, the LbL fabrication process will employ polycationic poly(vinyl alcohol) (PVA) and polyanionic poly(sodium 4-styrene sulfonate) (PSS) doped with MWNTs for fabricating the electrically-conductive and piezoresistive thin films. Upon film deposition, the glass fiber substrates are infused with an epoxy matrix via wet-layup to fabricate self-sensing glass fiber-reinforced polymer (GFRP) composite specimens for testing. A frequency-domain approach, based on electrical impedance spectroscopy, is used to characterize the electromechanical response of the GFRP-MWNT-based thin film samples when subjected to complex uni-axial tensile load patterns. A resistor connected to a parallel resistor-capacitor circuit model is proposed for fitting experimental impedance spectroscopic measurements. It has been found that the series resistor models the bulk thin film piezoresistive performance accurately. In addition, these impedance measurements shed light on the glass fiber-thin film interaction electromechanical behavior. Bi-functional strain sensitivity is observed for all GFRP specimens, and the transition point of bilinear strain sensitivity is utilized as a possible metric for GFRP damage detection.

In this paper, constitutive equations to model the electromechanical behavior of shape memory polymers (SMPs) are introduced for the first time. SMPs are unique material that can be transformed into complicated shapes and recover their original shapes even under large deformations [1]. Above their transition temperature, elastic modulus decreases and they can be easily deformed by mechanical or electrical input. Advantage of this behavior is returning to the deformed shape utilizing a triggering temperature without any applied forces. This can be used to actuate the electroactive polymer to restore the deformed shape without applying an electric field [2]. Therefore in this paper, the equibiaxial extension of two different SMPs (PTBA (poly(tert-butylacrylate)) [2] and Sylgard (Sylgard 184)/PCL (poly(ε-caprolactone)) composite [3]) is simulated numerically to demonstrate the electromechanical behavior with respect to mechanical and electromechanical inputs. For simplification, the response of the SMP above the transition temperature is considered, so that material properties are constant and not a function of temperature. The SMPs are considered a fiber-reinforced membrane with two families of fibers, which enable to tune the material properties of SMPs [3]. To describe the constitutive relation of the SMPs, Mooney-Rivlin and Ogden model for isotropic SMPs, as well as Gasser et al model [4] for anisotropic SMPs, are applied. In the numerical computations, the isotropic and anisotropic electromechanical response of PTBA and Sylgard/PCL composite are presented. PTBA shows larger electromechanical effect in the range of stretch 1.5–2.5. Additionally, the effects of the fiber stiffness, angle, and dispersion on the deformation of the SMPs are observed. According to the result, the fiber stiffness can significantly affect on the electromechanical response and fiber angle and dispersion can influence the anisotropic deformation.

The nonlinear electro-mechanical behavior of 1–3 piezoelectric composites with PZT5A1 fibers embedded in an epoxy matrix are studied under multi-axial mechanical loading. In order to evaluate the orientation effects of the polarization in PZT fibers to the overall performance of the ferroelectric composite system, the direction of the applied compressive loading is oriented by an angle of θ toward to the PZT fiber direction which is also the polarization direction. The non-linear responses in stress-strain and stress-electric displacement were measured at given loading angle θ . A two-level micromechanics theory based on irreversible thermodynamics and physics of domain switch is applied to compare with our experimental data. The theoretical results are found to be in good qualitative and quantitative agreement with our experimental data.

This paper investigated the physical and electromechanical properties of polypyrrole thin films that were prepared using electrochemical synthesis techniques. The morphology, mass, and thickness of the as-made films were examined when the processing parameters were varied in terms of synthesis voltage, deposition time, and polarization time. Upon actuation of the polypyrrole bi-layer, there were similar trends for both morphology and bending displacement with varying deposition and polarization times as well as actuation voltages. A general relationship between morphology and bending displacement was observed when the processing parameters were varied.

Use of ferroelectric materials to improve antenna performance is an area of active research. Applying an electric field across a ferroelectric used as the dielectric in an antenna enables tuning the antenna performance. Ferroelectrics also have coupled electromechanical behavior due to which it is sensitive to mechanical strains and fluctuations in ambient temperature. Use of ferroelectrics in antenna structures, especially those subject to mechanical and thermal loads, requires knowledge of the phenomenological relationship between the ferroelectric properties of interest (especially dielectric permittivity) and the external physical variables, viz. electric field(s), mechanical strains and temperature. To this end, a phenomenological model of ferroelectric materials based on the Devonshire thermodynamic theory is presented. This model is then used to obtain a relationship expressing the dependence of the dielectric permittivity on the mechanical strain, applied electric field and ambient temperature. The relationship is compared with published experimental data and other models in literature. Subsequently, a relationship expressing the dependence of antenna performance on those physical quantities is described.